Quantum computing

Entropy Computing: A Paradigm for Optimization in an Open Quantum System

Modern quantum technologies using matter are designed as closed quantum systems to isolate them from interactions with the environment. This design paradigm greatly constrains the scalability and limits practical implementation of such systems. Here, we introduce a novel computing paradigm, entropy computing, that works by conditioning a quantum reservoir thereby enabling the stabilization of a ground state. In this work, we experimentally demonstrate the feasibility of entropy computing by building a hybrid photonic-electronic computer that uses measurement-based feedback to solve non-convex optimization problems. The system functions by using temporal photonic modes to create qudits in order to encode probability amplitudes in the time-frequency degree of freedom of a photon. This scheme, when coupled with electronic interconnects, allows us to encode an arbitrary Hamiltonian into the system and solve non-convex continuous variables and combinatorial optimization problems. We show that the proposed entropy computing paradigm can act as a scalable and versatile platform for tackling a large range of NP-hard optimization problems.


Lac Nguyen, Mohammad-Ali Miri, R. Joseph Rupert, Wesley Dyk, Sam Wu, Nick Vrahoretis, Irwin Huang, Milan Begliarbekov, Nicholas Chancellor, Uchenna Chukwu, Pranav Mahamuni, Cesar Martinez-Delgado, David Haycraft, Carrie Spear, Mark Campanelli, Russell Huffman, Yong Meng Sua, Yuping Huang

Interaction-and measurement-free quantum Zeno gates for universal computation with single-atom and single-photon qubits

By extending the concept of interaction-free imaging to the few-atom level, we show that asymptotically on-demand interaction-and measurement-free quantum logic gates can be realized for both single-atom and single-photon qubits. The interaction-free feature suppresses the possibility of qubit decoherence via atomic spontaneous decay, while the elimination of measurements can significantly reduce errors arising from detector inefficiency. We present a general theory of universal quantum Zeno gates, and discuss physical implementations for quantum-information processing with individual atoms and photons. In addition, we propose a loss-tolerant protocol for long-distance quantum communication using quantum Zeno gates incorporated into a Mach-Zehnder interferometer. The efficiency of our Zeno gates is limited primarily by the imprecise control of atom-photon scattering and the finite number of feedback …


YP Huang, MG Moore

Experimental demonstration of interaction-free all-optical switching via the quantum Zeno effect

We experimentally demonstrate all-optical interaction-free switching using the quantum Zeno effect, achieving a high contrast of 35∶ 1. The experimental data match a zero-parameter theoretical model for several different regimes of operation, indicating a good understanding of the switch’s characteristics. We also discuss extensions of this work that will allow for significantly improved performance, and the integration of this technology onto chip-scale devices, which can lead to ultra-low-power all-optical switching, a long-standing goal with applications to both classical and quantum information processing.


KT McCusker, YP Huang, AS Kowligy, P Kumar

Interaction-free all-optical switching in χ(2)microdisks for quantum applications

We propose a quantum switch for telecom-band applications that is composed of a χ^(2) microdisk coupled to two fibers (or waveguides). The idea is to apply a pump pulse to shift the microdisk out of resonance, thereby switching the device between the cross and bar states in an interaction-free manner. As an example, a 2.5-μm-thick, 10μm radius GaAs microdisk with an intrinsic Q of ∼10^8 and a fiber-cavity-coupling Q of ∼10^4 can achieve low-loss (≲1%) switching for gigahertz-rate O-band quantum signals with milliwatt-peak-power pumps in the C band.


YP Huang, P Kumar

Large-scale Ising emulation with four body interaction and all-to-all connections

Optical Ising machines with two-body interactions have shown potential in solving combinatorial optimization problems which are extremely hard to solve with digital computers. Yet, some physical systems cannot be properly described by only two-body interactions. Here, we propose and demonstrate a nonlinear optics approach to emulate Ising machines containing many spins (up to a million in the absence of optical imperfections) and with tailored all-to-all two and four-body interactions. Our approach employs a spatial light modulator to encode and control the spins in the form of the binary-phase values, and emulates the high-order interaction with frequency conversion in a nonlinear crystal. By implementing adaptive feedback, the system can be evolved into effective spin configurations that well-approximate the ground-states of Ising Hamiltonians with all-to-all connected many-body interactions. Our technique …


S Kumar, H Zhang, YP Huang

Photonic nonlinearities via quantum zeno blockade

Realizing optical-nonlinear effects at a single-photon level is a highly desirable but also extremely challenging task, because of both fundamental and practical difficulties. We present an avenue to surmounting these difficulties by exploiting quantum Zeno blockade in nonlinear optical systems. Considering specifically a lithium-niobate microresonator, we find that a deterministic phase gate can be realized between single photons with near-unity fidelity. Supported by established techniques for fabricating and operating such devices, our approach can provide an enabling tool for all-optical applications in both classical and quantum domains.


YZ Sun, YP Huang, P Kumar

Antibunched emission of photon pairs via quantum zeno blockade

We propose a new methodology, namely, the “quantum Zeno blockade,” for managing light scattering at a few-photon level in general nonlinear-optical media, such as crystals, fibers, silicon microrings, and atomic vapors. Using this tool, antibunched emission of photon pairs can be achieved, leading to potent quantum-optics applications such as deterministic entanglement generation without the need for heralding. In a practical implementation using an on-chip toroidal microcavity immersed in rubidium vapor, we estimate that high-fidelity entangled photons can be produced on-demand at MHz rates or higher, corresponding to an improvement of≳ 10 7 times from the state-of-the-art.


YP Huang, P Kumar

Interaction-Free Quantum Optical Fredkin Gates in Microdisks

We present novel “interaction-free” realizations of quantum optical Fredkin gates that do not rely on direct physical coupling between the target light (signal) and the control light (pump). The interaction-free feature of such gates allow to overcome the fundamental limits of photon loss and quantum-state decoherence imposed by the signal-pump coupling. This advantage, together with the low inherent quantum-noise level in χ (2) microdisks, gives rise to substantially improved performance over the existing Fredkin-gate designs. Explicitly using lithium-niobate mircrodisks, we present two kinds of interaction-free Fredkin gates, a phase gate and an optical-path gate, both of which are designed with telecom-band applications in mind. For both gates, the threshold pump peak power to achieve a gate contrast >;100 and a signal loss <;10% is hundreds of microwatts for practical parameters of the devices.


YP Huang, P Kumar

Interaction-free all-optical switching via the quantum Zeno effect

We propose an interaction-free scheme for all-optical switching which does not rely on the physical coupling between signal and control waves. The interaction-free nature of the scheme allows it to overcome the fundamental photon-loss limit imposed by the signal-pump coupling. The same phenomenon protects photonic-signal states from decoherence, making devices based on this scheme suitable for quantum applications. Focusing on χ (2) waveguides, we provide device designs for traveling-wave and Fabry-Perot switches. In both designs, the performance is optimal when the signal switching is induced by coherent dynamical evolution. In contrast, when the switching is induced by a rapid dissipation channel, it is less efficient.


YP Huang, JB Altepeter, P Kumar

Two-qubit conditional phase gate in laser-excited semiconductor quantum dots using the quantum Zeno effect

We propose a scheme for a two-qubit conditional quantum Zeno phase gate for semiconductor quantum dots. The proposed system consists of two charged dots and one ancillary neutral dot driven by a laser pulse tuned to the exciton resonance. The primary decoherence mechanism is phonon-assisted exciton relaxation, which can be viewed as continuous monitoring by the environment. Because of the Zeno effect, a strong possibility of emission is sufficient to strongly modify the coherent dynamics, with negligible probability of actual emission. We solve analytically the master equation and simulate the dynamics of the system using a realistic set of parameters. In contrast to standard schemes, larger phonon relaxation rates increase the fidelity of the operations.


KJ Xu, YP Huang, MG Moore, C Piermarocchi

Self-stabilized quantum optical Fredkin gate

The quantum optical Fredkin gate is an indispensable resource for networkable quantum applications. Its performance in practical implementations, however, is limited fundamentally by the inherent quantum fluctuations of the pump waves. We demonstrate a method to overcome this drawback by exploiting stimulated Raman scattering in fiber-based implementations. Using a Sagnac fiber-loop switch as a specific example, we show that high switching contrast can be maintained even in the presence of significant pump fluctuations. This unique feature of self-stabilization, together with high-speed and low-loss performance of such devices, point to a viable technology for practical quantum communications.


J Hu, YP Huang, P Kumar

Observation of quantum zeno blockade on chip

Overlapping in an optical medium with nonlinear susceptibilities, lightwaves can interact, changing each other’s phase, wavelength, waveform shape, or other properties. Such nonlinear optical phenomena, discovered over a half-century ago, have led to a breadth of important applications. Applied to quantum-mechanical signals, however, these phenomena face fundamental challenges that arise from the multimodal nature of the interaction between the electromagnetic fields, such as phase noises and spontaneous Raman scattering. The quantum Zeno blockade allows strong interaction between lightwaves without physical overlap between them, thus offering a viable solution for the aforementioned challenges, as indicated in recent bulk-optics experiments. Here, we report on the observation of quantum Zeno blockade on chip, where a lightwave is modulated by another in a distinct “interaction-free” manner. For …


JY Chen, YM Sua, ZT Zhao, M Li, YP Huang

Fredkin gates in χ (2) microdisks via quantum zeno blockade

Using the quantum Zeno effect, we present a quantum optical Fredkin gate in LiNbO 3 microdisks for telecom applications. Such gates can operate with sub-femtojoule pumps and, in the ideal limit, without any energy dissipation.


YP Huang, P Kumar

Programmable Spatiotemporal Quantum Parametric Mode Sorter

We experimentally demonstrate a programmable parametric mode sorter of high-dimensional signals in a composite spatiotemporal Hilbert space through mode-selective quantum frequency up-conversion. As a concrete example and with quantum communication applications in mind, we consider the Laguerre-Gaussian and Hermite-Gaussian modes as the spatial and temporal state basis for the signals, respectively. By modulating the spatiotemporal profiles of the up-conversion pump, we demonstrate the faithful selection of signal photons in those modes and their superposition modes. Our results show an improvement in the quantum mode-sorting performance by coupling the up-converted light into a single-mode fiber and/or operating the up-conversion at the edge of phase matching. Optimizing pump temporal profiles allows us to achieve more than 12-dB extinction for mutually unbiased basis (MUB) sets of …


M Garikapati, S Kumar, H Zhang, YM Sua, YP Huang

Observation of distinct phase transitions in a nonlinear optical Ising machine

Optical Ising machines promise to solve complex optimization problems with an optical hardware acceleration advantage. Here we study the ground state properties of a nonlinear optical Ising machine realized by spatial light modulator, Fourier optics, and second-harmonic generation in a nonlinear crystal. By tuning the ratio of the light intensities at the fundamental and second-harmonic frequencies, we experimentally observe two distinct ferromagnetic-to-paramagnetic phase transitions: a second-order phase transition where the magnetization changes to zero continuously and a first-order phase transition where the magnetization drops to zero abruptly as the effective temperature increases. Our experimental results are corroborated by a numerical simulation based on the Monte Carlo Metropolis-Hastings algorithm, and the physical mechanism for the distinct phase transitions can be understood with a mean …


S Kumar, Z Li, T Bu, C Qu, Y Huang

Counteracting quantum decoherence with optimized disorder in discrete-time quantum walks

Decoherence and disorder are two major difficulties limiting the performance of quantum systems in practical settings. Yet they can potentially counteract each other to partially restore the systems' quantum signatures. We adopt the particle swarm optimization method to find the optimal disorder for mitigating the effects of decoherence in one- and two-dimensional quantum random walks, achieving substantial increase in the mean walking distance for a wide range of decoherence strength. This result suggests a viable approach to constructing practical quantum systems robust against decoherence and disorder.


I Huang, YP Huang

Self-stabilized quantum optical Fredkin gate enabled by the Raman effect

We demonstrate a quantum optical Fredkin gate in an all-fiber setup, which is self-stabilizing against pump fluctuations owing to stimulated Raman scattering occurring naturally in such a system.


J Hu, YP Huang, P Kumar

CLEO: 2013, 1-2 1 2013

Observation of Quantum Zeno Blockade in χ (2) Microresonators

We report observing all-optical modulation with a contrast of 80% via quantum Zeno blockade in a Lithium Niobate whispering-gallery-mode resonator at a pump peak power of 100µW.


DV Strekalov, A Kowligy, YP Huang, P Kumar

CLEO: QELS_Fundamental Science, QTu3C. 4 1 2013

Devices and methods for giant single-photon nonlinearities

A periodically poled microring resonator structure, a method for fabrication of the periodically poled microring resonator structure, and a method to achieve giant single-photon nonlinearity are disclosed. The strong single-photon nonlinearity in the microring resonator structure is achieved through its optimized design and fabrication procedures.


Y Huang, J Chen

US Patent 11,754,908 2023

Super ising emulator with multi-body interactions and all-to-all connections

An optical computation system includes a light source configured to produce a pump beam, an optical modulator configured to modulate the pump beam based on the modulation mask to generate a modulated beam, a non-linear medium configured to convert a portion of the modulated beam to a second harmonic (SH) beam and to produce an output including the SH beam and an unconverted portion of the pump beam, and a dichroic mirror configured to receive the output of the non-linear medium and to decouple the SH beam and the unconverted portion of the pump beam, a detector configured to detect a first optical power of the unconverted portion of the pump beam and to detect a second optical power of the SH beam, and a controller configured to generate an updated modulation mask based on the first and second optical powers for transmission to the optical modulator.


S Kumar, H Zhang, Y Huang, BU Ting

US Patent App. 17/924,638 2023

Phase transitions in nonlinear optical Ising machine

We experimentally measured the magnetization of a nonlinear optical Ising machine and observed two types of phase transitions. Our results may have important potential application in solving combinatorial optimization problems.


S Kumar, Z Li, T Bu, C Qu, Y Huang

Laser Science, JW5B. 27 2022

Devices and methods for giant single-photon nonlinearities

A periodically poled microring resonator structure, a method for fabrication of the periodically poled microring resonator structure, and a method to achieve giant single-photon nonlinearity are disclosed. The strong single-photon nonlinearity in the microring resonator structure is achieved through its optimized design and fabrication procedures.


Y Huang, J Chen

US Patent App. 17/468,182 2022

Large-scale Ising Emulator with All-to-All Connected Four-Body Interactions

We propose a nonlinear-optics approach to emulate Ising machine containing a million spins with weighted all-to-all four-body interactions. Using adaptive feedback control, this machine can be evolved to find the optimum solution of Ising problem.


H Zhang, S Kumar, YP Huang

Frontiers in Optics, JM6A. 26 2020

A Super Ising Machine with All-to-All Two-body and Four-body Interactions

S Kumar, H Zhang, YP Huang

CLEO: Applications and Technology, JM4G. 3 2020

Interaction-free All-optical Switches for Quantum Applications

We present a realization of all-optical switching in whispering-gallery-mode microcavities. Operating without the control and probe light beams overlapping in the cavity (in the asymptotic limit), such switches are ideal for use with quantum signals.


YP Huang, AS Kowligy, YZ Sun, DV Strekalov, P Kumar

Frontiers in Optics, FM4B. 2 2014

Experimental Demonstration of All-Optical Switching Using the Quantum Zeno Effect

We experimentally demonstrate interaction-free all-optical switching via the quantum Zeno effect. The switch contrast is 35: 1, and the experimental data matches a parameter-free fit. We discuss possible applications and future extensions.


KT McCusker, YP Huang, AS Kowligy, P Kumar

Quantum Information and Measurement, Th4A. 2 2013

All-optical quantum switching

We will present progress in ultrafast all-optical quantum switching. c (3)-based devices can route entangled photons without disturbing their quantum state, whereas c (2)-based devices can, in principle, lead to dissipation-free quantum-optical Fredkin gates.


P Kumar, YP Huang

International Conference on Fibre Optics and Photonics, W1C. 1 2012

Ultrafast switching of photonic entanglement

We present our recent development of fiber-optic technology for all-optical switching and routing of entangled photons at high speeds, with minimal loss and added in-band noise, and-most importantly-without disturbing the photons' quantum state.


NN Oza, YP Huang, P Kumar

IEEE Photonics Conference 2012, 413-414 2012

Quantum information processing in the telecom waveband

We present recent progress in all-optical routing of entangled single photons at high speeds, with minimal loss and added in-band noise, and-most importantly-without disturbing the photons' quantum state.


P Kumar, YP Huang, JB Altepeter, M Patel, NN Oza, MA Hall

OFC/NFOEC, 1-3 2012

Interaction-Free All-Optical Switching via Quantum Zeno Blockade

Embedding a χ (2) crystal in a Fabry-Perot cavity, we propose and demonstrate an all-optical switch via quantum Zeno blockade that is implemented without any physical coupling between the signal and pump waves.


YP Huang, AS Kowligy, JB Altepeter, P Kumar

Frontiers in Optics, FThS2 2011

Mixing light and matter waves: Principles and applications

The work of this dissertation is committed to theoretically explore rich physics involving quantum-mechanical mixing of light and matter waves, while specifically seeking applications in the fields of quantum interferometry, quantum information processing, and testing fundamental quantum mechanics. Towards this goal, the present research is guided by two lines. The first line is to study and manipulate collective behaviors of multi-atom systems at quantum-degenerate temperature, where the wave nature of atoms is maximized. Specifically, a variety of phase-coherent mixing processes of two macroscopic matter-waves, in the form of gaseous Bose-Einstein condensate (BEC), are investigated and engineered via (i) tuning atomic collisional interaction and/or inter-wave tunneling rate;(ii) mixing with optical waves of phase-locked lasers. By these means, a series of novel applications are proposed for generating highly …


Y Huang

Michigan State University 2009

Interaction-and measurement-free quantum information processing with single-atom and/or single-photon qubits

Interaction-free measurement (IFM) uses quantum interference to allow a single photon to detect a perfectly absorbing object without the photon interacting with the object directly. In high-efficiency IFM, the Quantum Zeno Effect is employed to increase the success probability from the original 50% to (Na)/N, where N is the number of cycles the photon makes through the device and a 1. In principle IFM protocols allow the hyperfine state of a single atom to become entangled with the polarization of a single photon. To date, attempts to employ this entanglement to create universal atom-atom quantum logic gates, such as CNOT gates, have not succeeded in achieving (Na)/N efficiency. In addition, they also require the detection of ancillary photons. At present, single-photon detection cannot be implemented experimentally with high efficiency. By making several key modications, we have developed a pair of …


M Moore, Y Huang

APS Division of Atomic, Molecular and Optical Physics Meeting Abstracts 38 … 2007

Measuring an unknown phase with quantum-limited precision using nonlinear beamsplitters

High precision phase measurement is currently a central goal of quantum interferometry. In general, the precision is described by the phase estimation uncertainty δθ, which is characterized by two scaling behaviors, shot-noise limited with δθ∼ 1/√ N and Heisenberg limited with δθ∼ 1/N (N the total particle number). According to Bayesian analysis, Heisenberg limited preciosion for θ= 0 can be achieved in a Mach-Zehnder interferometer with (| N-1, N+ 1>+| N+ 1, N-1>)/√ 2 as input state based and a single measurement or| N, N> input based on multiple measurements. As θ deviates from zero, both schemes degrade rapidly to worse than shot-noise-limited precision. In contrast, a Quantum Fourier Transform (QFT) based interferometer can measure an arbitrary θ at Heisenberg limited precision, but requires a quantum computer. To extend the range of precisely measurable θ without a quantum computer, we …


Y Huang, M Moore

APS Division of Atomic, Molecular and Optical Physics Meeting Abstracts 38 … 2007