CaltechAUTHORS: Combined
https://feeds.library.caltech.edu/people/Mirhosseini-M/combined.rss
A Caltech Library Repository Feedhttp://www.rssboard.org/rss-specificationpython-feedgenenFri, 13 Sep 2024 07:14:39 -0700Modal Analysis of Multilayer Conical Dielectric Waveguides for Azimuthal Invariant Modes
https://resolver.caltech.edu/CaltechAUTHORS:20190717-084218923
Year: 2010
DOI: 10.2528/pier09121602
By using field expansion in terms of the Legendre polynomials and Schelkunoff functions, Maxwell's equations in the spherical coordinate system are cast into a matrix form which lends itself to the analysis of a multilayer conical waveguide. The matrix formulation is then used to obtain an eigen-value problem whose eigen-values are the allowable wave-numbers for propagation in the radial direction. To verify the proposed numerical approach, it is used to evaluate the resonance frequency of a partially filled spherical resonator. The computed resonance frequencies are then compared with those obtained using commercial software based on the finite-element method. The computation time is enormously reduced using the semianalytical method of this work. Although results are shown for lossless isotropic dielectrics, the method is also applicable to conical waveguides made of lossy dielectrics even with negative permittivity.https://resolver.caltech.edu/CaltechAUTHORS:20190717-084218923Influence of atmospheric turbulence on the propagation of quantum states of light using plane-wave encoding
https://resolver.caltech.edu/CaltechAUTHORS:20190716-084537429
Year: 2011
DOI: 10.1364/oe.19.018310
We consider the possibility of performing quantum key distribution (QKD) by encoding information onto individual photons using plane-wave basis states. We compare the results of this calculation to those obtained by earlier workers, who considered encoding using OAM-carrying vortex modes of the field. We find theoretically that plane-wave encoding is less strongly influenced by atmospheric turbulence than is OAM encoding, with potentially important implications for free-space quantum key distribution.https://resolver.caltech.edu/CaltechAUTHORS:20190716-084537429Influence of Atmospheric Turbulence on the Performance of a High Dimensional Quantum Key Distribution System using Spatial Mode Encoding
https://resolver.caltech.edu/CaltechAUTHORS:20190717-091847143
Year: 2012
DOI: 10.1364/qim.2012.qw2a.3
The effects of atmospheric turbulence on a the channel capacity of a free-space quantum key distribution system with information encoded on the transverse modes of the photon are studied theoretically and experimentally.https://resolver.caltech.edu/CaltechAUTHORS:20190717-091847143Influence of thick atmospheric turbulence on the propagation of quantum states of light using spatial mode encoding
https://resolver.caltech.edu/CaltechAUTHORS:20190717-084844516
Year: 2012
DOI: 10.1364/cleo_at.2012.jtu2k.4
The effects of thick turbulence on transverse modes of light carrying orbital angular momentum are studied theoretically and experimentally. These results have potentially important implications for free-space quantum communications systems.https://resolver.caltech.edu/CaltechAUTHORS:20190717-084844516Influence of atmospheric turbulence on optical communications using orbital angular momentum for encoding
https://resolver.caltech.edu/CaltechAUTHORS:20190716-085135639
Year: 2012
DOI: 10.1364/oe.20.013195
We describe an experimental implementation of a free-space 11-dimensional communication system using orbital angular momentum (OAM) modes. This system has a maximum measured OAM channel capacity of 2.12 bits/photon. The effects of Kolmogorov thin-phase turbulence on the OAM channel capacity are quantified. We find that increasing the turbulence leads to a degradation of the channel capacity. We are able to mitigate the effects of turbulence by increasing the spacing between detected OAM modes. This study has implications for high-dimensional quantum key distribution (QKD) systems. We describe the sort of QKD system that could be built using our current technology.https://resolver.caltech.edu/CaltechAUTHORS:20190716-085135639New results in quantum nonlinear optics
https://resolver.caltech.edu/CaltechAUTHORS:20190716-094956207
Year: 2012
DOI: 10.1109/ipcon.2012.6358696
The methods of nonlinear optics lead to important capabilities within the field of quantum information science. Applications such as high-capacity quantum key distribution and enhanced measurement sensitivity are described.https://resolver.caltech.edu/CaltechAUTHORS:20190716-094956207Influence of atmospheric turbulence on states of light carrying orbital angular momentum
https://resolver.caltech.edu/CaltechAUTHORS:20190716-121440905
Year: 2012
DOI: 10.1364/ol.37.003735
We have experimentally studied the degradation of mode purity for light beams carrying orbital angular momentum (OAM) propagating through simulated atmospheric turbulence. The turbulence is modeled as a randomly varying phase aberration, which obeys statistics postulated by Kolmogorov turbulence theory. We introduce this simulated turbulence through the use of a phase-only spatial light modulator. Once the turbulence is introduced, the degradation in mode quality results in crosstalk between OAM modes. We study this crosstalk in OAM for 11 modes, showing that turbulence uniformly degrades the purity of all the modes within this range, irrespective of mode number.https://resolver.caltech.edu/CaltechAUTHORS:20190716-121440905Photon efficient wavefront sensing using an SLM for polarization-based weak measurements
https://resolver.caltech.edu/CaltechAUTHORS:20190716-094406367
Year: 2012
DOI: 10.1364/fio.2012.fw4a.3
A novel scheme is proposed for two dimensional direct measurement of wave functions using an SLM. This photon efficient method can be potentially useful for wavefront sensing of turbulence in adaptive optics systems used in free-space communication systems.https://resolver.caltech.edu/CaltechAUTHORS:20190716-094406367Direct Measurement of the Quantum Wavefunction using Weak Measurements in Orbital Angular Momentum
https://resolver.caltech.edu/CaltechAUTHORS:20190716-092901924
Year: 2012
DOI: 10.1364/fio.2012.fth4b.2
We propose a method that directly measures the photon wavefunction in the orbital angular momentum (OAM) basis by carrying out weak measurements in OAM and strong measurements in the conjugate basis of angular position.https://resolver.caltech.edu/CaltechAUTHORS:20190716-092901924Near-perfect sorting of orbital angular momentum and angular position states of light
https://resolver.caltech.edu/CaltechAUTHORS:20190716-093627981
Year: 2012
DOI: 10.1364/oe.20.024444
We present a novel method for efficient sorting of photons prepared in states of orbital angular momentum (OAM) and angular position (ANG). A log-polar optical transform is used in combination with a holographic beam-splitting method to achieve better mode discrimination and reduced cross-talk than reported previously. Simulating this method for 7 modes, we have calculated an improved mutual information of 2.43 bits/photon and 2.29 bits/photon for OAM and ANG modes respectively. In addition, we present preliminary results from an experimental implementation of this technique. This method is expected to have important applications for high-dimensional quantum key distribution systems.https://resolver.caltech.edu/CaltechAUTHORS:20190716-093627981Sensitive estimation of angular displacements using weak measurements
https://resolver.caltech.edu/CaltechAUTHORS:20190708-151341314
Year: 2013
DOI: 10.1364/cqo.2013.m6.45
We demonstrate an experimental method that allows for sensitive measurements of angular position of light using weak value amplification. This offers an alternative to previously established methods that use nonclassical light for angular displacement estimation.https://resolver.caltech.edu/CaltechAUTHORS:20190708-151341314Amplification of Optical Pulse Delays using Weak Measurements
https://resolver.caltech.edu/CaltechAUTHORS:20190708-151341375
Year: 2013
DOI: 10.1364/cqo.2013.m6.02
A novel scheme for super-sensitive measurement of optical pulse delays is proposed based on the concept of weak-value amplification. We discuss an experimental implementation of this technique utilizing a Mach-Zehnder interferometer.https://resolver.caltech.edu/CaltechAUTHORS:20190708-151341375Nonlinear Optics: The Enabling Technology for Quantum Information Science
https://resolver.caltech.edu/CaltechAUTHORS:20190708-151341456
Year: 2013
DOI: 10.1364/nlo.2013.nw1a.1
Nonlinear optical processes such as parametric down conversion and squeezed light generation are key elements of most quantum protocols, leading to crucial applications such as quantum imaging, sub-shot-noise metrology, and secure communication.https://resolver.caltech.edu/CaltechAUTHORS:20190708-151341456Visualizing Quantum State Rotations through Weak Measurements of Orbital Angular Momentum
https://resolver.caltech.edu/CaltechAUTHORS:20190708-151341699
Year: 2013
DOI: 10.1364/fio.2013.ftu1c.6
Using the technique of direct measurement, we observe the action of the angular momentum operator as the generator of rotations. Our method employs weak measurements of orbital angular momentum and strong measurements of angular position.https://resolver.caltech.edu/CaltechAUTHORS:20190708-151341699Recent Progress in Quantum Imaging and Ghost Imaging
https://resolver.caltech.edu/CaltechAUTHORS:20190628-110703214
Year: 2013
DOI: 10.1364/fio.2013.fw5d.1
We summarize recent work that demonstrates the utility of quantum effects for important technological applications in image science. We emphasize that what was considered to be "quantum weirdness" only a few years ago is today useful technology.https://resolver.caltech.edu/CaltechAUTHORS:20190628-110703214Near-perfect sorting of orbital angular momentum: A step towards high-dimensional quantum communications
https://resolver.caltech.edu/CaltechAUTHORS:20190708-151341620
Year: 2013
DOI: 10.1364/fio.2013.fw4d.5
A novel technique is introduced for separation of orbital-angular-momentum (OAM) states of light. Using this method, we demonstrate the realization of a free-space communication link with a channel capacity of more than 4 bits per photon.https://resolver.caltech.edu/CaltechAUTHORS:20190708-151341620Efficient separation of the orbital angular momentum eigenstates of light
https://resolver.caltech.edu/CaltechAUTHORS:20190628-110703341
Year: 2013
DOI: 10.1038/ncomms3781
Orbital angular momentum (OAM) of light is an attractive degree of freedom for fundamental studies in quantum mechanics. In addition, the discrete unbounded state-space of OAM has been used to enhance classical and quantum communications. Unambiguous measurement of OAM is a key part of all such experiments. However, state-of-the-art methods for separating single photons carrying a large number of different OAM values are limited to a theoretical separation efficiency of about 77%. Here we demonstrate a method which uses a series of unitary optical transformations to enable the measurement of light's OAM with an experimental separation efficiency of >92%. Furthermore, we demonstrate the separation of modes in the angular position basis, which is mutually unbiased with respect to the OAM basis. The high degree of certainty achieved by our method makes it particularly attractive for enhancing the information capacity of multi-level quantum cryptography systems.https://resolver.caltech.edu/CaltechAUTHORS:20190628-110703341Rapid generation of light beams carrying orbital angular momentum
https://resolver.caltech.edu/CaltechAUTHORS:20190628-110703432
Year: 2013
DOI: 10.1364/oe.21.030196
We report a technique for encoding both amplitude and phase variations onto a laser beam using a single digital micro-mirror device (DMD). Using this technique, we generate Laguerre-Gaussian and vortex orbital-angular-momentum (OAM) modes, along with modes in a set that is mutually unbiased with respect to the OAM basis. Additionally, we have demonstrated rapid switching among the generated modes at a speed of 4 kHz, which is much faster than the speed regularly achieved by phase-only spatial light modulators (SLMs). The dynamic control of both phase and amplitude of a laser beam is an enabling technology for classical communication and quantum key distribution (QKD) systems that employ spatial mode encoding.https://resolver.caltech.edu/CaltechAUTHORS:20190628-110703432Free-space communication through turbulence: a comparison of plane-wave and orbital-angular-momentum encodings
https://resolver.caltech.edu/CaltechAUTHORS:20190708-151341518
Year: 2014
DOI: 10.1080/09500340.2013.834084
Free-space communication allows one to use spatial mode encoding, which is susceptible to the effects of diffraction and turbulence. Here, we discuss the optimum communication modes of a system while taking such effects into account. We construct a free-space communication system that encodes information onto the plane-wave (PW) modes of light. We study the performance of this system in the presence of atmospheric turbulence, and compare it with previous results for a system employing orbital-angular-momentum (OAM) encoding. We are able to show that the PW basis is the preferred basis set for communication through atmospheric turbulence for a system with a large Fresnel number product. This study has important implications for high-dimensional quantum key distribution systems.https://resolver.caltech.edu/CaltechAUTHORS:20190708-151341518Direct measurement of a 27-dimensional orbital-angular-momentum state vector
https://resolver.caltech.edu/CaltechAUTHORS:20190628-110703716
Year: 2014
DOI: 10.1038/ncomms4115
The measurement of a quantum state poses a unique challenge for experimentalists. Recently, the technique of 'direct measurement' was proposed for characterizing a quantum state in situ through sequential weak and strong measurements. While this method has been used for measuring polarization states, its real potential lies in the measurement of states with a large dimensionality. Here we show the practical direct measurement of a high-dimensional state vector in the discrete basis of orbital angular momentum. Through weak measurements of orbital angular momentum and strong measurements of angular position, we measure the complex probability amplitudes of a pure state with a dimensionality, d=27. Further, we use our method to directly observe the relationship between rotations of a state vector and the relative phase between its orbital-angular-momentum components. Our technique has important applications in high-dimensional classical and quantum information systems and can be extended to characterize other types of large quantum states.https://resolver.caltech.edu/CaltechAUTHORS:20190628-110703716Towards Quantum Communication with more than 4 bits/photon: Near-Perfect Sorting of the Orbital Angular Momentum Modes of Light
https://resolver.caltech.edu/CaltechAUTHORS:20190628-110703857
Year: 2014
DOI: 10.1364/qim.2014.qw3a.6
We demonstrate a method that uses a series of optical transformations to sort the orbital angular momentum and the mutually-unbiased angular position modes of light with a separation efficiency of more than 92%.https://resolver.caltech.edu/CaltechAUTHORS:20190628-110703857Simulating thick atmospheric turbulence in the lab with application to orbital angular momentum communication
https://resolver.caltech.edu/CaltechAUTHORS:20190708-151341121
Year: 2014
DOI: 10.1088/1367-2630/16/3/033020
We describe a procedure by which a long (≳1 km)optical path through atmospheric turbulence can be experimentally simulated in a controlled fashion and scaled down to distances easily accessible in a laboratory setting. This procedure is then used to simulate a 1 km long free-space communication link in which information is encoded in orbital angular momentum spatial modes. We also demonstrate that standard adaptive optics methods can be used to mitigate many of the effects of thick atmospheric turbulence.https://resolver.caltech.edu/CaltechAUTHORS:20190708-151341121Amplification of Angular Rotations Using Weak Measurements
https://resolver.caltech.edu/CaltechAUTHORS:20190628-110703526
Year: 2014
DOI: 10.1103/physrevlett.112.200401
We present a weak measurement protocol that permits a sensitive estimation of angular rotations based on the concept of weak-value amplification. The shift in the state of a pointer, in both angular position and the conjugate orbital angular momentum bases, is used to estimate angular rotations. This is done by an amplification of both the real and imaginary parts of the weak-value of a polarization operator that has been coupled to the pointer, which is a spatial mode, via a spin-orbit coupling. Our experiment demonstrates the first realization of weak-value amplification in the azimuthal degree of freedom. We have achieved effective amplification factors as large as 100, providing a sensitivity that is on par with more complicated methods that employ quantum states of light or extremely large values of orbital angular momentum.https://resolver.caltech.edu/CaltechAUTHORS:20190628-110703526Experimental generation of an optical field with arbitrary spatial coherence properties
https://resolver.caltech.edu/CaltechAUTHORS:20190628-110703620
Year: 2014
DOI: 10.1364/josab.31.000a51
We describe an experimental technique for generating a quasi-monochromatic field with any arbitrary spatial coherence properties that can be described by the cross-spectral density function, W(r_1,r_2). This is done by using a dynamic binary amplitude grating generated by a digital micromirror device to rapidly alternate between a set of coherent fields, creating an incoherent mix of modes that represent the coherent mode decomposition of the desired W(r_1,r_2). This method was then demonstrated experimentally by interfering two plane waves and then spatially varying the coherence between them. It is then shown that this creates an interference pattern between the two beams whose fringe visibility varies spatially in an arbitrary and prescribed way.https://resolver.caltech.edu/CaltechAUTHORS:20190628-110703620Compressive Direct Measurement of the Quantum Wave Function
https://resolver.caltech.edu/CaltechAUTHORS:20190628-110703950
Year: 2014
DOI: 10.1103/physrevlett.113.090402
The direct measurement of a complex wave function has been recently realized by using weak values. In this Letter, we introduce a method that exploits sparsity for the compressive measurement of the transverse spatial wave function of photons. The procedure involves weak measurements of random projection operators in the spatial domain followed by postselection in the momentum basis. Using this method, we experimentally measure a 192-dimensional state with a fidelity of 90% using only 25 percent of the total required measurements. Furthermore, we demonstrate the measurement of a 19 200-dimensional state, a task that would require an unfeasibly large acquiring time with the standard direct measurement technique.https://resolver.caltech.edu/CaltechAUTHORS:20190628-110703950High-dimensional Quantum Key Distribution with Photonic Orbital Angular Momentum
https://resolver.caltech.edu/CaltechAUTHORS:20190628-110704267
Year: 2014
DOI: 10.1364/fio.2014.fm4e.4
We experimentally demonstrate a quantum cryptography system based on photonic orbital angular momentum. The system achieves a channel capacity of 2.1 bits per sifted photon through the use of a 7-dimensional alphabet for encoding information.https://resolver.caltech.edu/CaltechAUTHORS:20190628-110704267Compressive Direct Measurement of the Transverse Photonic Wavefunction
https://resolver.caltech.edu/CaltechAUTHORS:20190628-110704136
Year: 2014
DOI: 10.1364/fio.2014.fm4e.5
We generalize the method of direct measurement and combine it with compressive sensing. Using our method, we measure a 19200-dimensional state using only 20% of the total required measurements.https://resolver.caltech.edu/CaltechAUTHORS:20190628-110704136Measurement of the Second Order Coherence of Pseudo-Thermal Light in the Azimuthal Degree of Freedom
https://resolver.caltech.edu/CaltechAUTHORS:20190628-110704048
Year: 2014
DOI: 10.1364/fio.2014.ftu1g.6
Using an angular version of the Hanbury Brown Twiss interferometer, we show for the first time second-order interference in the azimuthal degree of freedom, which exhibits higher resolution fringes than if coherent light were used.https://resolver.caltech.edu/CaltechAUTHORS:20190628-110704048Achromatic orbital angular momentum generator
https://resolver.caltech.edu/CaltechAUTHORS:20190628-110704360
Year: 2014
DOI: 10.1088/1367-2630/16/12/123006
We describe a novel approach for generating light beams that carry orbital angular momentum (OAM) by means of total internal reflection in an isotropic medium. A continuous space-varying cylindrically symmetric reflector, in the form of two glued hollow axicons, is used to introduce a nonuniform rotation of polarization into a linearly polarized input beam. This device acts as a full spin-to-orbital angular momentum convertor. It functions by switching the helicity of the incoming beamʼs polarization, and by conservation of total angular momentum thereby generates a well-defined value of OAM. Our device is broadband, since the phase shift due to total internal reflection is nearly independent of wavelength. We verify the broad-band behaviour by measuring the conversion efficiency of the device for three different wavelengths corresponding to the RGB colours, red, green and blue. An average conversion efficiency of 95% for these three different wavelengths is observed. This device may find applications in imaging from micro- to astronomical systems where a white vortex beam is needed.https://resolver.caltech.edu/CaltechAUTHORS:20190628-110704360High-dimensional quantum cryptography with twisted light
https://resolver.caltech.edu/CaltechAUTHORS:20190628-110704546
Year: 2015
DOI: 10.1088/1367-2630/17/3/033033
Quantum key distribution (QKD) systems often rely on polarization of light for encoding, thus limiting the amount of information that can be sent per photon and placing tight bounds on the error rates that such a system can tolerate. Here we describe a proof-of-principle experiment that indicates the feasibility of high-dimensional QKD based on the transverse structure of the light field allowing for the transfer of more than 1 bit per photon. Our implementation uses the orbital angular momentum (OAM) of photons and the corresponding mutually unbiased basis of angular position (ANG). Our experiment uses a digital micro-mirror device for the rapid generation of OAM and ANG modes at 4 kHz, and a mode sorter capable of sorting single photons based on their OAM and ANG content with a separation efficiency of 93%. Through the use of a seven-dimensional alphabet encoded in the OAM and ANG bases, we achieve a channel capacity of 2.05 bits per sifted photon. Our experiment demonstrates that, in addition to having an increased information capacity, multilevel QKD systems based on spatial-mode encoding can be more resilient against intercept-resend eavesdropping attacks.https://resolver.caltech.edu/CaltechAUTHORS:20190628-110704546Q-plates as higher order polarization controllers for orbital angular momentum modes of fiber
https://resolver.caltech.edu/CaltechAUTHORS:20190628-110704658
Year: 2015
DOI: 10.1364/ol.40.001729
We demonstrate that a |q|=1/2 plate, in conjunction with appropriate polarization optics, can selectively and switchably excite all linear combinations of the first radial mode order |l|=1 orbital angular momentum (OAM) fiber modes. This enables full mapping of free-space polarization states onto fiber vector modes, including the radially (TM) and azimuthally polarized (TE) modes. The setup requires few optical components and can yield mode purities as high as ∼30 dB. Additionally, just as a conventional fiber polarization controller creates arbitrary elliptical polarization states to counteract fiber birefringence and yield desired polarizations at the output of a single-mode fiber, q-plates disentangle degenerate state mixing effects between fiber OAM states to yield pure states, even after long-length fiber propagation. We thus demonstrate the ability to switch dynamically, potentially at ∼GHz rates, between OAM modes, or create desired linear combinations of them. We envision applications in fiber-based lasers employing vector or OAM mode outputs, as well as communications networking schemes exploiting spatial modes for higher dimensional encoding.https://resolver.caltech.edu/CaltechAUTHORS:20190628-110704658Scan-free direct measurement of an extremely high-dimensional photonic state
https://resolver.caltech.edu/CaltechAUTHORS:20190628-110704771
Year: 2015
DOI: 10.1364/optica.2.000388
Retrieving the vast amount of information carried by a photon is an enduring challenge in quantum metrology science and quantum photonics research. The transverse spatial state of a photon is a convenient high-dimensional quantum system for study, as it has a well-understood classical analog as the transverse complex field profile of an optical beam. One severe drawback of all currently available quantum metrology techniques is the need for a time-consuming characterization process, which scales very unfavorably with the dimensionality of the quantum system. Here we demonstrate a technique that directly measures a million-dimensional photonic spatial state with a single setting of the measurement apparatus. Through the arrangement of a weak measurement of momentum and parallel strong measurements of position, the complex values of the entire photon state vector become measurable directly. The dimension of our measured state is approximately four orders of magnitude larger than previously measured. Our work opens up a practical route for characterizing high-dimensional quantum systems in real time. Furthermore, our demonstration also serves as a high-speed, extremely high-resolution unambiguous complex field measurement technique for diverse classical applications.https://resolver.caltech.edu/CaltechAUTHORS:20190628-110704771Direct measurement of the quantum density matrix in the basis of azimuthal angle
https://resolver.caltech.edu/CaltechAUTHORS:20190628-110704960
Year: 2015
DOI: 10.1364/cleo_qels.2015.ftu4a.2
We theoretically propose and experimentally demonstrate a method for directly measuring the density matrix of an unknown quantum system in the basis of azimuthal angle. We apply our method for characterizing 7-dimensional pure and mixed superpositions of orbital-angular-momentum modes.https://resolver.caltech.edu/CaltechAUTHORS:20190628-110704960Q-plates for Switchable Excitation of Fiber OAM Modes
https://resolver.caltech.edu/CaltechAUTHORS:20190628-110704866
Year: 2015
DOI: 10.1364/cleo_si.2015.sw4m.3
We demonstrate that a |q|=1/2 plate plus polarization optics can tunably excite all linear combinations of |l|=1 fiber OAM modes with up to ~30 dB purity, enabling switch fabrics in fiber-OAM networks and disentangling of degenerate mode mixing effects in long fibers.https://resolver.caltech.edu/CaltechAUTHORS:20190628-110704866State transfer based on classical nonseparability
https://resolver.caltech.edu/CaltechAUTHORS:20190628-110704451
Year: 2015
DOI: 10.1103/physreva.92.023827
We present a state-transfer protocol that is mathematically equivalent to quantum teleportation but uses classical nonseparability instead of quantum entanglement. In our implementation we take advantage of nonseparability among three parties: orbital angular momentum (OAM), polarization, and the radial degrees of freedom of a beam of light. We demonstrate the transfer of arbitrary OAM states, in the subspace spanned by any two OAM states, to the polarization of the same beam.https://resolver.caltech.edu/CaltechAUTHORS:20190628-110704451Scan-free direct measurement of an one-million-dimensional photonic state
https://resolver.caltech.edu/CaltechAUTHORS:20190628-110705149
Year: 2015
DOI: 10.1364/fio.2015.fw4d.6
We describe a technique that directly measures a pure quantum state of arbitrary dimensions with a single setting of the measurement apparatus. We demonstrate our method by measuring a million-dimensional photonic spatial state.https://resolver.caltech.edu/CaltechAUTHORS:20190628-110705149Quantum Hilbert Hotel
https://resolver.caltech.edu/CaltechAUTHORS:20190628-110705053
Year: 2015
DOI: 10.1103/physrevlett.115.160505
In 1924 David Hilbert conceived a paradoxical tale involving a hotel with an infinite number of rooms to illustrate some aspects of the mathematical notion of "infinity." In continuous-variable quantum mechanics we routinely make use of infinite state spaces: here we show that such a theoretical apparatus can accommodate an analog of Hilbert's hotel paradox. We devise a protocol that, mimicking what happens to the guests of the hotel, maps the amplitudes of an infinite eigenbasis to twice their original quantum number in a coherent and deterministic manner, producing infinitely many unoccupied levels in the process. We demonstrate the feasibility of the protocol by experimentally realizing it on the orbital angular momentum of a paraxial field. This new non-Gaussian operation may be exploited, for example, for enhancing the sensitivity of NOON states, for increasing the capacity of a channel, or for multiplexing multiple channels into a single one.https://resolver.caltech.edu/CaltechAUTHORS:20190628-110705053Experimental demonstration of 20 Gbit/s data encoding and 2 ns channel hopping using orbital angular momentum modes
https://resolver.caltech.edu/CaltechAUTHORS:20190628-110705247
Year: 2015
DOI: 10.1364/ol.40.005810
We explore the use of the spatial domain as a degree of freedom for data encoding and channel hopping. We experimentally demonstrate data encoding at 20 Gbit/s using four possible orbital angular momentum (OAM) modes. The influence of mode spacing and time misalignment between modal channels on the switching crosstalk and bit-error rates is investigated. We find that the use of adjacent modes with a mode spacing of one introduces an extra power penalty of 3.2 dB compared with a larger mode spacing. Moreover, we demonstrate reconfigurable hopping of a 100 Gbit/s quadrature-phase-shift-keying (QPSK) data channel between four OAM modes with a 2 ns switching guard time. The results show that the power penalties for different hopping rates and mode spacings are less than 5.3 dB.https://resolver.caltech.edu/CaltechAUTHORS:20190628-110705247Recent progress in weak value amplification and direct measurement
https://resolver.caltech.edu/CaltechAUTHORS:20190716-080008044
Year: 2016
DOI: 10.3254/978-1-61499-647-7-77
The ability to manipulate light has allowed scientists to verify fundamental theories of physics and to develop a new generation of technologies that use photons as a primary resource. Recent developments in quantum measurement theory have offered new alternatives to approach some of the most remarkable problems in quantum physics. Consequently, the principles of quantum mechanics have been exploited in the development of quantum technologies such as optical metrology, quantum communication, and quantum information. In recent years, weak measurements and two of its most remarkable variants: weak value amplification and direct measurement, have been developed and are considered important resources for quantum applications. In this paper, we discuss weak measurements and some significant applications of weak values. We elaborate on how distinct forms of weak values are used to observe and amplify small effects or to directly measure the quantum wave function of photons, a crucial task for schemes for quantum communication and quantum information. We also review some of the most recent methods for weak value amplification and direct measurement that our group has developed.https://resolver.caltech.edu/CaltechAUTHORS:20190716-080008044Light-Drag Enhancement by a Highly Dispersive Rubidium Vapor
https://resolver.caltech.edu/CaltechAUTHORS:20190628-110705352
Year: 2016
DOI: 10.1103/physrevlett.116.013601
The change in the speed of light as it propagates through a moving material has been a subject of study for almost two centuries. This phenomenon, known as the Fresnel light-drag effect, is quite small and usually requires a large interaction path length and/or a large velocity of the moving medium to be observed. Here, we show experimentally that the observed drag effect can be enhanced by over 2 orders of magnitude when the light beam propagates through a moving slow-light medium. Our results are in good agreement with the theoretical prediction, which indicates that, in the limit of large group indices, the strength of the light-drag effect is proportional to the group index of the moving medium.https://resolver.caltech.edu/CaltechAUTHORS:20190628-110705352Hanbury Brown and Twiss interferometry with twisted light
https://resolver.caltech.edu/CaltechAUTHORS:20190628-110705665
Year: 2016
DOI: 10.1126/sciadv.1501143
PMCID: PMC4846462
The rich physics exhibited by random optical wave fields permitted Hanbury Brown and Twiss to unveil fundamental aspects of light. Furthermore, it has been recognized that optical vortices are ubiquitous in random light and that the phase distribution around these optical singularities imprints a spectrum of orbital angular momentum onto a light field. We demonstrate that random fluctuations of intensity give rise to the formation of correlations in the orbital angular momentum components and angular positions of pseudothermal light. The presence of these correlations is manifested through distinct interference structures in the orbital angular momentum–mode distribution of random light. These novel forms of interference correspond to the azimuthal analog of the Hanbury Brown and Twiss effect. This family of effects can be of fundamental importance in applications where entanglement is not required and where correlations in angular position and orbital angular momentum suffice. We also suggest that the azimuthal Hanbury Brown and Twiss effect can be useful in the exploration of novel phenomena in other branches of physics and astrophysics.https://resolver.caltech.edu/CaltechAUTHORS:20190628-110705665Wigner Distribution of Twisted Photons
https://resolver.caltech.edu/CaltechAUTHORS:20190628-110705451
Year: 2016
DOI: 10.1103/physrevlett.116.130402
We present the first experimental characterization of the azimuthal Wigner distribution of a photon. Our protocol fully characterizes the transverse structure of a photon in conjugate bases of orbital angular momentum (OAM) and azimuthal angle. We provide a test of our protocol by characterizing pure superpositions and incoherent mixtures of OAM modes in a seven-dimensional space. The time required for performing measurements in our scheme scales only linearly with the dimension size of the state under investigation. This time scaling makes our technique suitable for quantum information applications involving a large number of OAM states.https://resolver.caltech.edu/CaltechAUTHORS:20190628-110705451Multiplexing free-space channels using twisted light
https://resolver.caltech.edu/CaltechAUTHORS:20190628-110705553
Year: 2016
DOI: 10.1088/2040-8978/18/5/054015
We experimentally demonstrate an interferometric protocol for multiplexing optical states of light in a lossless manner, with potential to become a standard element in free-space communication schemes that utilize light endowed with orbital angular momentum (OAM). We demonstrate multiplexing for odd and even OAM superpositions generated using different sources. In addition, our technique permits one to prepare either coherent superpositions or statistical mixtures of OAM states. We employ state tomography to study the performance of this protocol, and we demonstrate fidelities greater than 0.98.https://resolver.caltech.edu/CaltechAUTHORS:20190628-110705553Weak-value amplification of the fast-light effect in rubidium vapor
https://resolver.caltech.edu/CaltechAUTHORS:20190708-151341796
Year: 2016
DOI: 10.1103/physreva.93.053836
We use weak-value amplification to enhance the polarization-sensitive fast-light effect from induced Raman absorption in hot rubidium vapor. We experimentally demonstrate that projecting the output signal into an appropriate polarization state enables a pulse advancement of 4.2 μs, which is more than 15 times larger than that naturally caused by dispersion. More significantly, we show that combining weak-value amplification with the dispersive response of an atomic system provides a clear advantage in terms of the maximum pulse advance achievable for a given value of loss. This technique has potential applications for designing novel quantum-information-processing gates and optical buffers for telecommunication systems.https://resolver.caltech.edu/CaltechAUTHORS:20190708-151341796Finite-key security analysis for multilevel quantum key distribution
https://resolver.caltech.edu/CaltechAUTHORS:20190708-151342075
Year: 2016
DOI: 10.1088/1367-2630/18/7/073030
We present a detailed security analysis of a d-dimensional quantum key distribution protocol based on two and three mutually unbiased bases (MUBs) both in an asymptotic and finite-key-length scenario. The finite secret key rates (in bits per detected photon) are calculated as a function of the length of the sifted key by (i) generalizing the uncertainly relation-based insight from BB84 to any d-level 2-MUB QKD protocol and (ii) by adopting recent advances in the second-order asymptotics for finite block length quantum coding (for both d-level 2- and 3-MUB QKD protocols). Since the finite and asymptotic secret key rates increase with d and the number of MUBs (together with the tolerable threshold) such QKD schemes could in principle offer an important advantage over BB84. We discuss the possibility of an experimental realization of the 3-MUB QKD protocol with the orbital angular momentum degrees of freedom of photons.https://resolver.caltech.edu/CaltechAUTHORS:20190708-151342075Direct measurement of an one-million-dimensional photonic state
https://resolver.caltech.edu/CaltechAUTHORS:20190717-080451530
Year: 2016
DOI: 10.1109/piers.2016.7734289
The state vector of a pure quantum system is a set of complex probability amplitudes used for describing the system in each state of a given Hilbert space. Characterizing the state of a quantum system is crucial for fundamental studies in quantum mechanics as well as for manipulating and utilizing quantum systems for practical applications. Here we describe a scan-free direct measurement approach [1] that is capable of simultaneously measuring the entire state vector of a pure quantum system, consequently eliminating the need for scanning through each basis state. Our method involves a proper arrangement of weak [2, 3] and strong measurements. Specifically, to measure the state vector of a quantum system in one
Hilbert space A, one first applies a weak measurement to the quantum system in one fixed state |b_0〉. of its complementary basis B, and then performs the strong measurement directly in A. As an example, we have designed a procedure of measuring the transverse spatial state of a photon, which is a convenient high-dimensional quantum system for study, and which has a well- understood classical analogue as the transverse complex field profile of an optical beam. In order to measure the complex probability amplitude of a photon at a position state x, one first performs a weak projection measurement of the zero momentum state p_0 = 0, followed by a strong measurement of the position state. Through such a procedure, the measured weak values are inversely proportional to the state vector of the quantum system. To demonstrate our method, we characterize photons carrying different spatial modes, such as uniform amplitude and Zernike phase profiles, circular mode carrying orbital angular momentum (OAM) [4, 5], etc. Since one can have independent control of the complex probability amplitude of the photons at each pixel of the transverse space, the dimensionality of our measured state is approximately 1.2 million, which is determined by the spatial extent of the photons (approximately 7mm in diameter) and the discrete nature of our detector array (with pixel size of 5.4 µm^2). The fidelity of the photon state in the spatial Hilbert space is calculated to be approximately 0.93. Such a high fidelity of our result demonstrates that our direct measurement technique is indeed capable of measuring the complex-value quantum state vector with very high accuracy. Our scan-free direct measurement approach opens up the possibility to characterize high dimensional quantum systems in real time for which a state-by-state scanning process would become impractically time-consuming or even infeasible. Moreover, our specific demonstration of measuring photons' transverse spatial state is also a promising new technology for classical wavefront sensing applications in fields as diverse as observational astronomy, free-space optical communication, and biomedical imaging.https://resolver.caltech.edu/CaltechAUTHORS:20190717-080451530Quantum Information with Structured Light
https://resolver.caltech.edu/CaltechAUTHORS:20190708-151342166
Year: 2016
DOI: 10.1364/ls.2016.ltu1e.3
We investigate structured photons as carriers of quantum information. We describe our implementation of quantum cryptography with orbital angular momentum, and present our results on efficient implementation of quantum state tomography for structured light fields.https://resolver.caltech.edu/CaltechAUTHORS:20190708-151342166Measuring Exotic Looped Trajectories of Light
https://resolver.caltech.edu/CaltechAUTHORS:20190708-151342343
Year: 2016
DOI: 10.1364/fio.2016.fw2e.5
The probability of a photon to follow looped trajectories in a three-slit interferometer is extremely small and difficult to measure. We unveil the underlying physics and implications behind these trajectories and present their first observation.https://resolver.caltech.edu/CaltechAUTHORS:20190708-151342343Non-local angular double-slit ghost diffraction with thermal light
https://resolver.caltech.edu/CaltechAUTHORS:20190708-151342257
Year: 2016
DOI: 10.1364/fio.2016.jth2a.14
We report an experimental observation of ghost diffraction with non-local angular double-slit by making use of thermal light and orbital angular momentum (OAM) correlation measurement. A correlated angular interference pattern of the distributed angular double-slit is measured.https://resolver.caltech.edu/CaltechAUTHORS:20190708-151342257Exotic looped trajectories of photons in three-slit interference
https://resolver.caltech.edu/CaltechAUTHORS:20190708-151342444
Year: 2016
DOI: 10.1038/ncomms13987
PMCID: PMC5196392
The validity of the superposition principle and of Born's rule are well-accepted tenants of quantum mechanics. Surprisingly, it has been predicted that the intensity pattern formed in a three-slit experiment is seemingly in contradiction with the most conventional form of the superposition principle when exotic looped trajectories are taken into account. However, the probability of observing such paths is typically very small, thus rendering them extremely difficult to measure. Here we confirm the validity of Born's rule and present the first experimental observation of exotic trajectories as additional paths for the light by directly measuring their contribution to the formation of optical interference fringes. We accomplish this by enhancing the electromagnetic near-fields in the vicinity of the slits through the excitation of surface plasmons. This process increases the probability of occurrence of these exotic trajectories, demonstrating that they are related to the near-field component of the photon's wavefunction.https://resolver.caltech.edu/CaltechAUTHORS:20190708-151342444Distributed angular double-slit interference with pseudo-thermal light
https://resolver.caltech.edu/CaltechAUTHORS:20190708-151342553
Year: 2017
DOI: 10.1063/1.4976575
We propose and perform an interference experiment involving a distributed angular double-slit and the orbital angular momentum (OAM) correlations of thermal light. In the experiment, two spatially separated angular apertures are placed in two correlated light beams generated by splitting the thermal light beam via a beam splitter. The superposition of the two spatially separated slits constitutes an angular double-slit in two-photon measurements. The angular interference pattern of the distributed double-slit is measured even though each beam interacts with a different part of the object. This scheme allows us to discriminate among different angular amplitude objects using a classical incoherent light source. This procedure has potential applications in remote sensing or optical metrology in the OAM domain.https://resolver.caltech.edu/CaltechAUTHORS:20190708-151342553Quantum-enhanced interferometry with weak thermal light
https://resolver.caltech.edu/CaltechAUTHORS:20190716-083419604
Year: 2017
DOI: 10.1364/optica.4.000487
We propose and implement a procedure for enhancing the sensitivity with which one can determine the phase shift experienced by a thermal light beam possessing on average fewer than four photons in passing through an interferometer. Our procedure entails subtracting exactly one (which can be generalized to m) photon from the light field exiting an interferometer containing a phase-shifting element in one of its arms. As a consequence of the process of photon subtraction, the mean photon number and signal-to-noise ratio (SNR) of the resulting light field are increased, leading to an enhancement of the SNR of the interferometric signal for that fraction of the incoming data that leads to photon subtraction.https://resolver.caltech.edu/CaltechAUTHORS:20190716-083419604Digital spiral object identification using random light
https://resolver.caltech.edu/CaltechAUTHORS:20190708-151342661
Year: 2017
DOI: 10.1038/lsa.2017.13
PMCID: PMC6062229
Photons that are entangled or correlated in orbital angular momentum have been extensively used for remote sensing, object identification and imaging. It has recently been demonstrated that intensity fluctuations give rise to the formation of correlations in the orbital angular momentum components and angular positions of random light. Here we demonstrate that the spatial signatures and phase information of an object with rotational symmetries can be identified using classical orbital angular momentum correlations in random light. The Fourier components imprinted in the digital spiral spectrum of the object, as measured through intensity correlations, unveil its spatial and phase information. Sharing similarities with conventional compressive sensing protocols that exploit sparsity to reduce the number of measurements required to reconstruct a signal, our technique allows sensing of an object with fewer measurements than other schemes that use pixel-by-pixel imaging. One remarkable advantage of our technique is that it does not require the preparation of fragile quantum states of light and operates at both low- and high-light levels. In addition, our technique is robust against environmental noise, a fundamental feature of any realistic scheme for remote sensing.https://resolver.caltech.edu/CaltechAUTHORS:20190708-151342661Sorting Photons by Radial Quantum Number
https://resolver.caltech.edu/CaltechAUTHORS:20180117-165148565
Year: 2017
DOI: 10.1103/PhysRevLett.119.263602
The Laguerre-Gaussian (LG) modes constitute a complete basis set for representing the transverse structure of a paraxial photon field in free space. Earlier workers have shown how to construct a device for sorting a photon according to its azimuthal LG mode index, which describes the orbital angular momentum (OAM) carried by the field. In this paper we propose and demonstrate a mode sorter based on the fractional Fourier transform to efficiently decompose the optical field according to its radial profile. We experimentally characterize the performance of our implementation by separating individual radial modes as well as superposition states. The reported scheme can, in principle, achieve unit efficiency and thus can be suitable for applications that involve quantum states of light. This approach can be readily combined with existing OAM mode sorters to provide a complete characterization of the transverse profile of the optical field.https://resolver.caltech.edu/CaltechAUTHORS:20180117-165148565Sorting Laguerre-Gaussian modes by radial quantum number
https://resolver.caltech.edu/CaltechAUTHORS:20190708-151342758
Year: 2018
DOI: 10.1364/cleo_at.2018.jth2a.4
An efficient sorter based on the fractional Fourier transform is realized to detect the radial quantum number of the Laguerre-Gaussian modes. The reported scheme can, in principle, have unit efficiency and no cross-talk.https://resolver.caltech.edu/CaltechAUTHORS:20190708-151342758Performance analysis of d-dimensional quantum cryptography with mode-dependent diffraction
https://resolver.caltech.edu/CaltechAUTHORS:20190716-090724755
Year: 2018
DOI: 10.1364/cleo_at.2018.jth2a.19
We analyze the degraded performance of QKD that results from mode-dependent diffraction in spatial-mode-encoded QKD systems. A pre-compensation method is proposed to solve this problem without sacrificing the security.https://resolver.caltech.edu/CaltechAUTHORS:20190716-090724755Superconducting metamaterials for waveguide quantum electrodynamics
https://resolver.caltech.edu/CaltechAUTHORS:20180313-154248544
Year: 2018
DOI: 10.1038/s41467-018-06142-z
PMCID: PMC6135821
Embedding tunable quantum emitters in a photonic bandgap structure enables control of dissipative and dispersive interactions between emitters and their photonic bath. Operation in the transmission band, outside the gap, allows for studying waveguide quantum electrodynamics in the slow-light regime. Alternatively, tuning the emitter into the bandgap results in finite-range emitter–emitter interactions via bound photonic states. Here, we couple a transmon qubit to a superconducting metamaterial with a deep sub-wavelength lattice constant (λ/60). The metamaterial is formed by periodically loading a transmission line with compact, low-loss, low-disorder lumped-element microwave resonators. Tuning the qubit frequency in the vicinity of a band-edge with a group index of n_g = 450, we observe an anomalous Lamb shift of −28 MHz accompanied by a 24-fold enhancement in the qubit lifetime. In addition, we demonstrate selective enhancement and inhibition of spontaneous emission of different transmon transitions, which provide simultaneous access to short-lived radiatively damped and long-lived metastable qubit states.https://resolver.caltech.edu/CaltechAUTHORS:20180313-154248544Hermite–Gaussian mode sorter
https://resolver.caltech.edu/CaltechAUTHORS:20181114-153202275
Year: 2018
DOI: 10.1364/ol.43.005263
The Hermite–Gaussian (HG) modes, sometimes referred to as transverse electromagnetic modes in free space, form a complete and orthonormal basis that have been extensively used to describe optical fields. In addition, these modes have been shown to be helpful in enhancing information capacity of optical communications as well as achieving super-resolution imaging in microscopy. Here we propose and present the realization of an efficient, robust mode sorter that can sort a large number of HG modes based on the relation between HG modes and Laguerre–Gaussian (LG) modes. We experimentally demonstrate the sorting of 16 HG modes, and our method can be readily extended to a higher-dimensional state space in a straightforward manner. We expect that our demonstration will have direct applications in a variety of fields including fiber optics, classical and quantum communications, as well as super-resolution imaging.https://resolver.caltech.edu/CaltechAUTHORS:20181114-153202275Realization of a scalable Laguerre–Gaussian mode sorter based on a robust radial mode sorter
https://resolver.caltech.edu/CaltechAUTHORS:20190708-151342989
Year: 2018
DOI: 10.1364/oe.26.033057
The transverse structure of light is recognized as a resource that can be used to encode information onto photons and has been shown to be useful to enhance communication capacity as well as resolve point sources in superresolution imaging. The Laguerre–Gaussian (LG) modes form a complete and orthonormal basis set and are described by a radial index p and an orbital angular momentum (OAM) index ℓ. Earlier works have shown how to build a sorter for the radial index p or/and the OAM index ℓ of LG modes, but a scalable and dedicated LG mode sorter which simultaneous determinate p and ℓ is immature. Here we propose and experimentally demonstrate a scheme to accomplish complete LG mode sorting, which consists of a novel, robust radial mode sorter that can be used to couple radial modes to polarizations, an ℓ-dependent phase shifter and an OAM mode sorter. Our scheme is in principle efficient, scalable, and crosstalk-free, and therefore has potential for applications in optical communications, quantum information technology, superresolution imaging, and fiber optics.https://resolver.caltech.edu/CaltechAUTHORS:20190708-151342989Measurement of the radial mode spectrum of photons through a phase-retrieval method
https://resolver.caltech.edu/CaltechAUTHORS:20190102-155139431
Year: 2018
DOI: 10.1364/ol.43.006101
We propose and demonstrate a simple and easy-to-implement projective-measurement protocol to determine the radial index p of a Laguerre–Gaussian (LG_p^l ) mode. Our method entails converting any specified high-order LG_p^0 mode into a near-Gaussian distribution that matches the fundamental mode of a single-mode fiber (SMF) through the use of two phase screens (unitary transforms) obtained by applying a phase-retrieval algorithm. The unitary transforms preserve the orthogonality of modes before the SMF and guarantee that our protocol can, in principle, be free of crosstalk. We measure the coupling efficiency of the transformed radial modes to the SMF for different pairs of phase screens. Because of the universality of phase-retrieval methods, we believe that our protocol provides an efficient way of fully characterizing the radial spatial profile of an optical field.https://resolver.caltech.edu/CaltechAUTHORS:20190102-155139431Waveguide-mediated interaction of artificial atoms in the strong coupling regime
https://resolver.caltech.edu/CaltechAUTHORS:20190108-091005866
Year: 2019
DOI: 10.48550/arXiv.1809.09752
Waveguide quantum electrodynamics studies photon-mediated interactions of quantum emitters in a one-dimensional radiation channel. Although signatures of such interactions have been observed previously in a variety of physical systems, observation of coherent cooperative dynamics has been obscured by radiative decay of atoms into the waveguide. Employing transmon qubits as artificial atoms coupled to a microwave coplanar waveguide, here we observe dynamical oscillations in an open system where a designated probe qubit interacts with an entangled dark state of an array of qubits which effectively traps radiation as an atomic cavity. The qubit-cavity system is shown to achieve a large cooperativity of C=172 due to collective enhancement of photon-mediated interactions, entering the strong coupling regime. The quantum coherence of the dark state cavity is also explored through its nonlinear response at the single-excitation level. With realistic refinements, this system is suitable for studying the many-body dynamics of large (N>10) quantum spin chains, synthesizing highly non-classical radiation fields on demand, and implementing universal quantum logic operations with high fidelity on information encoded within decoherence-free subspaces.https://resolver.caltech.edu/CaltechAUTHORS:20190108-091005866Direct Measurement of the Photon's Spatial Wave Function
https://resolver.caltech.edu/CaltechAUTHORS:20190716-081016277
Year: 2019
DOI: 10.1007/978-3-319-98402-5_2
We overview recent progress in the tomography of structured light fields, with an emphasis on the method of direct measurement. Direct measurement provides a scalable and easy- to-implement approach for characterizing the transverse structure of single photons. This protocol is particularly attractive in light of the emerging role of high-dimensional optical states as a resource for encoding quantum information. We present a summary of various implementations of this technique that aim to characterize the spatial degree of freedom of the optical field.https://resolver.caltech.edu/CaltechAUTHORS:20190716-081016277Quantum electromechanics of a hypersonic crystal
https://resolver.caltech.edu/CaltechAUTHORS:20190107-154636309
Year: 2019
DOI: 10.1038/s41565-019-0377-2
Recent technical developments in the fields of quantum electromechanics and optomechanics have spawned nanoscale mechanical transducers with the sensitivity to measure mechanical displacements at the femtometre scale and the ability to convert electromagnetic signals at the single photon level. A key challenge in this field is obtaining strong coupling between motion and electromagnetic fields without adding additional decoherence. Here we present an electromechanical transducer that integrates a high-frequency (0.42 GHz) hypersonic phononic crystal with a superconducting microwave circuit. The use of a phononic bandgap crystal enables quantum-level transduction of hypersonic mechanical motion and concurrently eliminates decoherence caused by acoustic radiation. Devices with hypersonic mechanical frequencies provide a natural pathway for integration with Josephson junction quantum circuits, a leading quantum computing technology, and nanophotonic systems capable of optical networking and distributing quantum information.https://resolver.caltech.edu/CaltechAUTHORS:20190107-154636309Using all transverse degrees of freedom in quantum communications based on a generic mode sorter
https://resolver.caltech.edu/CaltechAUTHORS:20190523-101902938
Year: 2019
DOI: 10.1364/oe.27.010383
The dimension of the state space for information encoding offered by the transverse structure of light is usually limited by the finite size of apertures. The widely used orbital angular momentum (OAM) number of Laguerre-Gaussian (LG) modes in free-space communications cannot achieve the theoretical maximum transmission capacity unless the radial degree of freedom is multiplexed into the protocol. While the methodology to sort the radial quantum number has been developed, the application of radial modes in quantum communications requires an additional ability to efficiently measure the superposition of LG modes in the mutually unbiased basis. Here we develop and implement a generic mode sorter that is capable of sorting the superposition of LG modes through the use of a mode converter. As a consequence, we demonstrate an 8-dimensional quantum key distribution experiment involving all three transverse degrees of freedom: spin, azimuthal, and radial quantum numbers of photons. Our protocol presents an important step towards the goal of reaching the capacity limit of a free-space link and can be useful to other applications that involve spatial modes of photons.https://resolver.caltech.edu/CaltechAUTHORS:20190523-101902938Quantum-limited estimation of the axial separation of two incoherent point sources
https://resolver.caltech.edu/CaltechAUTHORS:20190606-081531090
Year: 2019
DOI: 10.1364/optica.6.000534
Improving axial resolution is crucial for three-dimensional optical imaging systems. Here we present a scheme of axial superresolution for two incoherent point sources based on spatial mode demultiplexing. A radial mode sorter is used to losslessly decompose the optical fields into a radial mode basis set to extract the phase information associated with the axial positions of the point sources. We show theoretically and experimentally that, in the limit of a zero axial separation, our scheme allows for reaching the quantum Cramér–Rao lower bound and thus can be considered as one of the optimal measurement methods. Unlike other superresolution schemes, this scheme does not require either activation of fluorophores or sophisticated stabilization control. Moreover, it is applicable to the localization of a single point source in the axial direction. Our demonstration can be useful for a variety of applications such as far-field fluorescence microscopy.https://resolver.caltech.edu/CaltechAUTHORS:20190606-081531090Cavity quantum electrodynamics with atom-like mirrors
https://resolver.caltech.edu/CaltechAUTHORS:20190225-095611254
Year: 2019
DOI: 10.1038/s41586-019-1196-1
It has long been recognized that atomic emission of radiation is not an immutable property of an atom, but is instead dependent on the electromagnetic environment and, in the case of ensembles, also on the collective interactions between the atoms. In an open radiative environment, the hallmark of collective interactions is enhanced spontaneous emission—super-radiance—with non-dissipative dynamics largely obscured by rapid atomic decay. Here we observe the dynamical exchange of excitations between a single artificial atom and an entangled collective state of an atomic array through the precise positioning of artificial atoms realized as superconducting qubits along a one-dimensional waveguide. This collective state is dark, trapping radiation and creating a cavity-like system with artificial atoms acting as resonant mirrors in the otherwise open waveguide. The emergent atom–cavity system is shown to have a large interaction-to-dissipation ratio (cooperativity exceeding 100), reaching the regime of strong coupling, in which coherent interactions dominate dissipative and decoherence effects. Achieving strong coupling with interacting qubits in an open waveguide provides a means of synthesizing multi-photon dark states with high efficiency and paves the way for exploiting correlated dissipation and decoherence-free subspaces of quantum emitter arrays at the many-body level.https://resolver.caltech.edu/CaltechAUTHORS:20190225-095611254Switchable detector array scheme to reduce the effect of single-photon detector's deadtime in a multi-bit/photon quantum link
https://resolver.caltech.edu/CaltechAUTHORS:20190716-075301026
Year: 2019
DOI: 10.1016/j.optcom.2019.01.081
We explore the use of a switchable single-photon detector (SPD) array scheme to reduce the effect of a detector's deadtime for a multi-bit/photon quantum link. The case of data encoding using M possible orbital-angular-momentum (OAM) states is specifically studied in this paper. Our method uses N SPDs with a controllable M×N optical switch and we use a Monte Carlo-based method to simulate the quantum detection process. The simulation results show that with the use of the switchable SPD array, the detection system can allow a higher incident photon rate than what might otherwise be limited by detectors' deadtime. For the case of M=4, N=20, a 50-ns deadtime for the individual SPDs, an average photon number per pulse of 0.1, and under the limit that at most 10 % of the photon-containing pulses are missed, the switchable SPD array will allow an incident photon rate of 2250 million counts/s (Mcts/s). This is 25 times the 90 Mcts/s incident photon rate that a non-switchable, 4-SPD array will allow. The increase in incident photon rate is more than the 5 times increase, which is the simple increase in the number of SPDs and the number of OAM encoding states (e.g., N/M = 20/4).https://resolver.caltech.edu/CaltechAUTHORS:20190716-075301026Enhanced Thermal Object Imaging by Photon Addition or Subtraction
https://resolver.caltech.edu/CaltechAUTHORS:20190717-082422658
Year: 2019
DOI: 10.48550/arXiv.1609.02780
Long-baseline interferometry (LBI) is used to reconstruct the image of faint thermal objects. The image quality, for a given exposure time, is in general limited by a low signal-to-noise ratio (SNR). We show theoretically that a significant increase of the SNR, in a LBI, is possible by adding or subtracting photons to the thermal beam. At low photon counts, photon addition-subtraction technology strongly enhances the image quality. We have experimentally realized a nondeterministic physical protocol for photon subtraction. Our theoretical predictions are supported by experimental results.https://resolver.caltech.edu/CaltechAUTHORS:20190717-082422658Photon Added Coherent States: Nondeterministic, Noiseless Amplification in Quantum Metrology
https://resolver.caltech.edu/CaltechAUTHORS:20190717-083003422
Year: 2019
DOI: 10.48550/arXiv.1606.09598
Probabilistic amplification through photon addition, at the output of an Mach-Zehnder interferometer is discussed for a coherent input state. When a metric of signal to noise ratio is considered, nondeterministic, noiseless amplification of a coherent state shows improvement over a standard coherent state, for the general addition of m photons. The efficiency of realizable implementation of photon addition is also considered and shows how the collected statistics of a post selected state, depend on this efficiency. We also consider the effects of photon loss and inefficient detectors.https://resolver.caltech.edu/CaltechAUTHORS:20190717-083003422Performance analysis of d-dimensional quantum cryptography under state-dependent diffraction
https://resolver.caltech.edu/CaltechAUTHORS:20190716-085941770
Year: 2019
DOI: 10.1103/PhysRevA.100.032319
Standard protocols for quantum key distribution (QKD) require that the sender be able to transmit in two or more mutually unbiased bases. Here, we analyze the extent to which the performance of QKD is degraded by diffraction effects that become relevant for long propagation distances and limited sizes of apertures. In such a scenario, different states experience different amounts of diffraction, leading to state-dependent loss and phase acquisition, causing an increased error rate and security loophole at the receiver. To solve this problem, we propose a precompensation protocol based on preshaping the transverse structure of quantum states. We demonstrate, both theoretically and experimentally, that when performing QKD over a link with known, state-dependent loss and phase shift, the performance of QKD will be better if we intentionally increase the loss of certain states to make the loss and phase shift of all states equal. Our results show that the precompensated protocol can significantly reduce the error rate induced by state-dependent diffraction and thereby improve the secure key rate of QKD systems without sacrificing the security.https://resolver.caltech.edu/CaltechAUTHORS:20190716-085941770High-dimensional quantum key distribution based on mutually partially unbiased bases
https://resolver.caltech.edu/CaltechAUTHORS:20200323-120745266
Year: 2020
DOI: 10.1103/physreva.101.032340
We propose a practical high-dimensional quantum key distribution protocol based on mutually partially unbiased bases utilizing transverse modes of light. In contrast to conventional protocols using mutually unbiased bases, our protocol uses Laguerre-Gaussian and Hermite-Gaussian modes of the same mode order as two mutually partially unbiased bases for encoding, which leads to a scheme free from mode-dependent diffraction in long-distance channels. Since only linear and passive optical elements are needed, our experimental implementation significantly simplifies qudit generation and state measurement. Since this protocol differs from conventional protocols using mutually unbiased bases, we provide a security analysis of our protocol.https://resolver.caltech.edu/CaltechAUTHORS:20200323-120745266Two-dimensional optomechanical crystal cavity with high quantum cooperativity
https://resolver.caltech.edu/CaltechAUTHORS:20200330-152420978
Year: 2020
DOI: 10.1038/s41467-020-17182-9
PMCID: PMC7338352
Optomechanical systems offer new opportunities in quantum information processing and quantum sensing. Many solid-state quantum devices operate at millikelvin temperatures—however, it has proven challenging to operate nanoscale optomechanical devices at these ultralow temperatures due to their limited thermal conductance and parasitic optical absorption. Here, we present a two-dimensional optomechanical crystal resonator capable of achieving large cooperativity C and small effective bath occupancy n_b, resulting in a quantum cooperativity C_(eff) ≡ C/n_b > 1 under continuous-wave optical driving. This is realized using a two-dimensional phononic bandgap structure to host the optomechanical cavity, simultaneously isolating the acoustic mode of interest in the bandgap while allowing heat to be removed by phonon modes outside of the bandgap. This achievement paves the way for a variety of applications requiring quantum-coherent optomechanical interactions, such as transducers capable of bi-directional conversion of quantum states between microwave frequency superconducting quantum circuits and optical photons in a fiber optic network.https://resolver.caltech.edu/CaltechAUTHORS:20200330-152420978Nano-acoustic resonator with ultralong phonon lifetime
https://resolver.caltech.edu/CaltechAUTHORS:20190115-155728077
Year: 2020
DOI: 10.1126/science.abc7312
The energy damping time in a mechanical resonator is critical to many precision metrology applications, such as timekeeping and force measurements. We present measurements of the phonon lifetime of a microwave-frequency, nanoscale silicon acoustic cavity incorporating a phononic bandgap acoustic shield. Using pulsed laser light to excite a colocalized optical mode of the cavity, we measured the internal acoustic modes with single-phonon sensitivity down to millikelvin temperatures, yielding a phonon lifetime of up to τ_(ph,0) ≈ 1.5 seconds (quality factor Q = 5 × 10¹⁰) and a coherence time of τ_(coh,0) ≈ 130 microseconds for bandgap-shielded cavities. These acoustically engineered nanoscale structures provide a window into the material origins of quantum noise and have potential applications ranging from tests of various collapse models of quantum mechanics to miniature quantum memory elements in hybrid superconducting quantum circuits.https://resolver.caltech.edu/CaltechAUTHORS:20190115-155728077Superconducting qubit to optical photon transduction
https://resolver.caltech.edu/CaltechAUTHORS:20200416-091933770
Year: 2020
DOI: 10.1038/s41586-020-3038-6
Conversion of electrical and optical signals lies at the foundation of the global internet. Such converters are used to extend the reach of long-haul fibre-optic communication systems and within data centres for high-speed optical networking of computers. Likewise, coherent microwave-to-optical conversion of single photons would enable the exchange of quantum states between remotely connected superconducting quantum processors1. Despite the prospects of quantum networking, maintaining the fragile quantum state in such a conversion process with superconducting qubits has not yet been achieved. Here we demonstrate the conversion of a microwave-frequency excitation of a transmon—a type of superconducting qubit—into an optical photon. We achieve this by using an intermediary nanomechanical resonator that converts the electrical excitation of the qubit into a single phonon by means of a piezoelectric interaction and subsequently converts the phonon to an optical photon by means of radiation pressure. We demonstrate optical photon generation from the qubit by recording quantum Rabi oscillations of the qubit through single-photon detection of the emitted light over an optical fibre. With proposed improvements in the device and external measurement set-up, such quantum transducers might be used to realize new hybrid quantum networks and, ultimately, distributed quantum computers.https://resolver.caltech.edu/CaltechAUTHORS:20200416-091933770Quantum Electrodynamics in a Topological Waveguide
https://resolver.caltech.edu/CaltechAUTHORS:20201028-082500909
Year: 2021
DOI: 10.1103/PhysRevX.11.011015
While designing the energy-momentum relation of photons is key to many linear, nonlinear, and quantum optical phenomena, a new set of light-matter properties may be realized by employing the topology of the photonic bath itself. In this work we experimentally investigate the properties of superconducting qubits coupled to a metamaterial waveguide based on a photonic analog of the Su-Schrieffer-Heeger model. We explore topologically induced properties of qubits coupled to such a waveguide, ranging from the formation of directional qubit-photon bound states to topology-dependent cooperative radiation effects. Addition of qubits to this waveguide system also enables direct quantum control over topological edge states that form in finite waveguide systems, useful for instance in constructing a topologically protected quantum communication channel. More broadly, our work demonstrates the opportunity that topological waveguide-QED systems offer in the synthesis and study of many-body states with exotic long-range quantum correlations.https://resolver.caltech.edu/CaltechAUTHORS:20201028-082500909Initial Design of a W-Band Superconducting Kinetic Inductance Qubit
https://resolver.caltech.edu/CaltechAUTHORS:20210420-101341415
Year: 2021
DOI: 10.1109/TASC.2021.3065304
Superconducting qubits are widely used in quantum computing research and industry. We describe a superconducting kinetic inductance qubit (and introduce the term Kineticon to describe it) operating at W-band frequencies with a nonlinear nanowire section that provides the anharmonicity required for two distinct quantum energy states. Operating the qubits at higher frequencies may relax the dilution refrigerator temperature requirements for these devices and paves the path for multiplexing a large number of qubits. Millimeter-wave operation requires superconductors with relatively high T_c, which implies high gap frequency, 2 Δ/h , beyond which photons break Cooper pairs. For example, NbTiN with T_c = 15K has a gap frequency near 1.4 THz, which is much higher than that of aluminum (90 GHz), allowing for operation throughout the millimeter-wave band. Here we describe a design and simulation of a W-band Kineticon qubit embedded in a 3-D cavity. We perform classical electromagnetic calculations of the resulting field distributions.https://resolver.caltech.edu/CaltechAUTHORS:20210420-101341415Collapse and Revival of an Artificial Atom Coupled to a Structured Photonic Reservoir
https://resolver.caltech.edu/CaltechAUTHORS:20200409-164102679
Year: 2021
DOI: 10.1103/PhysRevX.11.041043
A structured electromagnetic reservoir can result in novel dynamics of quantum emitters. In particular, the reservoir can be tailored to have a memory of past interactions with emitters, in contrast to memory-less Markovian dynamics of typical open systems. In this Article, we investigate the non-Markovian dynamics of a superconducting qubit strongly coupled to a superconducting slow-light waveguide reservoir. Tuning the qubit into the spectral vicinity of the passband of this waveguide, we find non-exponential energy relaxation as well as substantial changes to the qubit emission rate. Further, upon addition of a reflective boundary to one end of the waveguide, we observe revivals in the qubit population on a timescale 30 times longer than the inverse of the qubit's emission rate, corresponding to the round-trip travel time of an emitted photon. By tuning of the qubit-waveguide interaction strength, we probe a crossover between Markovian and non-Markovian qubit emission dynamics. These attributes allow for future studies of multi-qubit circuits coupled to structured reservoirs, in addition to constituting the necessary resources for generation of multiphoton highly entangled states.https://resolver.caltech.edu/CaltechAUTHORS:20200409-164102679Deep sub-wavelength localization of light and sound in dielectric resonators
https://resolver.caltech.edu/CaltechAUTHORS:20220223-214609456
Year: 2022
DOI: 10.1364/OE.455248
Optomechanical crystals provide coupling between phonons and photons by confining them to commensurate wavelength-scale dimensions. We present a new concept for designing optomechanical crystals capable of achieving unprecedented coupling rates by confining optical and mechanical waves to deep sub-wavelength dimensions. Our design is based on a dielectric bowtie unit cell with an effective optical/mechanical mode volume of 7.6 × 10⁻³ (λ/n_(Si))³/1.2 × 10⁻³ λ_(mech)³. We present results from numerical modeling, indicating a single-photon optomechanical coupling of 2.2 MHz with experimentally viable parameters. Monte Carlo simulations are used to demonstrate the design's robustness against fabrication disorder.https://resolver.caltech.edu/CaltechAUTHORS:20220223-214609456Electro-optic transduction in silicon via GHz-frequency nanomechanics
https://resolver.caltech.edu/CaltechAUTHORS:20230512-186474000.2
Year: 2022
Interfacing electronics with optical fiber networks is key to the long-distance transfer of classical and quantum information. Piezo-optomechanical transducers enable such interfaces by using GHz-frequency acoustic vibrations as mediators for converting microwave photons to optical photons via the combination of optomechanical and piezoelectric interactions. However, despite successful demonstrations, efficient piezo-optomechanical transduction remains out of reach due to the challenges associated with hybrid material integration and increased loss from piezoelectric materials when operating in the quantum regime. Here, we demonstrate an alternative approach in which we actuate 5-GHz phonons in a conventional silicon-on-insulator platform. In our experiment, microwave photons resonantly drive a phononic crystal oscillator via the electrostatic force realized in a charge-biased narrow-gap capacitor. The mechanical vibrations are subsequently transferred via a phonon waveguide to an optomechanical cavity, where they transform into optical photons in the sideband of a pump laser field. Operating at room temperature and atmospheric pressure, we measure a microwave-to-optical photon conversion efficiency of 1.8 × 10⁻⁷ in a 3.3 MHz bandwidth, and demonstrate efficient phase modulation with a half-wave voltage of V_π = 750 mV. Our results mark a stepping stone towards quantum transduction with integrated devices made from crystalline silicon, which promise efficient high-bandwidth operation, and integration with superconducting qubits. Additionally, the lack of need for piezoelectricity or other intrinsic nonlinearities makes our approach adaptable to a wide range of materials for potential applications beyond quantum technologies.https://resolver.caltech.edu/CaltechAUTHORS:20230512-186474000.2Resonance Fluorescence of a Chiral Artificial Atom
https://authors.library.caltech.edu/records/5wdz9-s1f96
Year: 2023
DOI: 10.1103/PhysRevX.13.021039
<p>We demonstrate a superconducting artificial atom with strong unidirectional coupling to a microwave photonic waveguide. Our artificial atom is realized by coupling a transmon qubit to the waveguide at two spatially separated points with time-modulated interactions. Direction-sensitive interference arising from the parametric couplings in our scheme results in a nonreciprocal response, where we measure a forward/backward ratio of spontaneous emission exceeding 100. We verify the quantum nonlinear behavior of this artificial chiral atom by measuring the resonance fluorescence spectrum under a strong resonant drive and observing well-resolved Mollow triplets. Further, we demonstrate chirality for the second transition energy of the artificial atom and control it with a pulse sequence to realize a qubit-state-dependent nonreciprocal phase on itinerant photons. Our demonstration puts forth a superconducting hardware platform for the scalable realization of several key functionalities pursued within the paradigm of chiral quantum optics, including quantum networks with all-to-all connectivity, driven-dissipative stabilization of many-body entanglement, and the generation of complex nonclassical states of light.</p>https://authors.library.caltech.edu/records/5wdz9-s1f96A quantum electromechanical interface for long-lived phonons
https://resolver.caltech.edu/CaltechAUTHORS:20230510-141132000.2
Year: 2023
Controlling long-lived mechanical oscillators in the quantum regime holds promises for quantum information processing. Here, we present an electromechanical system capable of operating in the GHz-frequency band in a silicon-on-insulator platform. Relying on a novel driving scheme based on an electrostatic field and high-impedance microwave cavities based on TiN superinductors, we are able to demonstrate a parametrically-enhanced electromechanical coupling of g/2π = 1.1 MHz, sufficient to enter the strong-coupling regime with a cooperativity of C = 1200. The absence of piezoelectric materials in our platform leads to long mechanical lifetimes, finding intrinsic values up to τ_d = 265 μs (Q = 8.4 × 10⁶ at ωₘ/2π= 5 GHz) measured at low-phonon numbers and millikelvin temperatures. Despite the strong parametric drives, we find the cavity-mechanics system in the quantum ground state by performing sideband thermometry measurements. Simultaneously achieving ground-state operation, long mechanical lifetimes, and strong coupling sets the stage for employing silicon electromechanical resonators as memory elements and transducers in hybrid quantum systems, and as a tool for probing the origins of acoustic loss in the quantum regime.https://resolver.caltech.edu/CaltechAUTHORS:20230510-141132000.2Strong kinetic-inductance Kerr nonlinearity with titanium nitride nanowires
https://resolver.caltech.edu/CaltechAUTHORS:20230512-186482000.3
Year: 2023
Thin films of disordered superconductors such as titanium nitride (TiN) exhibit large kinetic inductance (KI), high critical temperature, and large quality factors at the single-photon level. KI nonlinearity can be exploited as an alternative to Josephson junctions for creating novel nonlinear quantum devices with the potential to operate at higher frequencies and at elevated temperatures. We study a means of magnifying KI nonlinearity by confining the current density of resonant electromagnetic modes in nanowires with a small volume V ≃ 10⁻⁴ um³. Using this concept, we realize microwave-frequency Kerr cavities with a maximum Kerr-shift per photon of K/2π = 123.5 ± 3 kHz and report a nonlinearity-to-linewidth ratio K/γ = 21%. With improved design, our devices are expected to approach the regime of strong quantum nonlinearity in the millimeter-wave spectrum.https://resolver.caltech.edu/CaltechAUTHORS:20230512-186482000.3A quantum electromechanical interface for long-lived phonons
https://resolver.caltech.edu/CaltechAUTHORS:20230628-295397000.6
Year: 2023
DOI: 10.1038/s41567-023-02080-w
In single crystals, the suppression of intrinsic loss channels at low temperatures leads to exceptionally long mechanical lifetimes. Quantum electrical control of such long-lived mechanical oscillators would enable the development of phononic memory elements, sensors and transducers. The integration of piezoelectric materials is one approach to introducing electrical control, but the challenges of combining heterogeneous materials lead to severely limited phonon lifetimes. Here we present a non-piezoelectric silicon electromechanical system capable of operating in the gigahertz frequency band. Relying on a driving scheme based on electrostatic fields and the kinetic inductance effect in disordered superconductors, we demonstrate a parametrically enhanced electromechanical coupling of g/2π = 1.1 MHz, sufficient to enter the strong-coupling regime with a cooperativity of C = 1,200. In our best devices, we measure mechanical quality factors approaching Q ≈ 10⁷, measured at low-phonon numbers and millikelvin temperatures. Despite using strong electrostatic fields, we find the cavity mechanics system in the quantum ground state, verified by thermometry measurements. Simultaneously achieving ground-state operation, long mechanical lifetimes and strong coupling sets the stage for employing silicon electromechanical devices in hybrid quantum systems and as a tool for studying the origins of acoustic loss in the quantum regime.https://resolver.caltech.edu/CaltechAUTHORS:20230628-295397000.6