Publication

2026

1. Quantum Communication over Bandwidth-and-Time-Limited Channels

   Aditya Gandotra^* , Zhaoyou Wang^* , Aashish A. Clerk , and Liang Jiang

   Physical Review A, Mar 2026

   Standard communication systems have transmission spectra that characterize their ability to perform frequency multiplexing over a finite bandwidth. Realistic quantum signals in quantum communication systems like transducers are inherently limited in time due to intrinsic decoherence and finite latency, which hinders the direct implementation of frequency-multiplexed encoding. We investigate quantum channel capacities for bandwidth-and-time-limited channels to establish the optimal communication strategy in a realistic setting. For pure-loss bosonic channels, we derive analytical solutions of the optimal encoding and decoding modes for Lorentzian and box transmission spectra, along with numerical solutions for various other transmissions. Our findings reveal a general feature of sequential activation of quantum channels as the input signal duration increases, as well as the existence of optimal signal length for scenarios where only a limited number of channels are in use.

2. Passive Environment-Assisted Quantum Communication

   Evelyn Voss , Bikun Li , Zhaoyou Wang , and Liang Jiang

   arXiv, Feb 2026

   As quantum information systems mature, efficient and coherent transfer of quantum information through noisy channels becomes increasingly important. We examine how passive environment-assisted quantum communication enhances direct quantum information transfer efficiency. A bosonic pure-loss channel, modeled as transmission through a beam splitter with a vacuum input state at the dark port, has zero quantum capacity when transmissivity is below 50%. Quantum communication through the channel can be enhanced by passive environment assistance, achieved via the selection of an appropriate input state for the ancilla port. Although ideal Gottesman-Kitaev-Preskill (GKP) states enable perfect quantum information transmission at arbitrarily small transmissivity, they are challenging to realize experimentally. We therefore explore more experimentally accessible non-Gaussian ancilla states, such as Fock, cat, and squeezed cat states, and numerically determine the optimal encoding and decoding strategies. We also construct analytical schemes that yield high-fidelity transmission and good information rates.

2025

1. Pump Free Microwave-Optical Quantum Transduction

   Fangxin Li^* , Jaesung Heo^* , Zhaoyou Wang , Andrew P. Higginbotham , Alexander A. High , and Liang Jiang

   arXiv, Dec 2025

   Distributed quantum computing involves superconducting computation nodes operating at microwave frequencies, which are connected by long-distance transmission lines that transmit photons at optical frequencies. Quantum transduction, which coherently converts between microwave and optical (M-O) photons, is a critical component of such an architecture. Current approaches are hindered by the unavoidable problem of device heating due to the optical pump. In this work, we propose a pump-free scheme based on color centers that generates time-bin encoded M-O Bell pairs. Our scheme first creates spin-photon entanglement and then converts the spin state into a time-bin-encoded microwave photon using a strongly coupled Purcell-enhanced resonator. In our protocol, the microwave retrieval is heralded by detecting the microwave signal with a three-level transmon. We have analyzed the resulting Bell state fidelity and generation probability of this protocol. Our simulation shows that by combining a state-of-the-art spin-optical interface with our proposed strongly-coupled spin-microwave design, the pump-free scheme can generate M-O Bell pairs at a heralding rate exceeding one kilohertz with near-unity fidelity, which establishes the scheme as a promising source for M-O Bell pairs.

2. Optimality Condition for the Petz Map

   Bikun Li , Zhaoyou Wang , Guo Zheng , Yat Wong , and Liang Jiang

   Physical Review Letters, May 2025

   In quantum error correction, the Petz map serves as a perfect recovery map when the Knill-Laflamme conditions are satisfied. Notably, while perfect recovery is generally infeasible for most quantum channels of finite dimension, the Petz map remains a versatile tool with near-optimal performance in recovering quantum states. This work introduces and proves, for the first time, the necessary and sufficient conditions for the optimality of the Petz map in terms of entanglement fidelity. In some special cases, the violation of this condition can be easily characterized by a simple commutator that can be efficiently computed. We provide multiple examples that substantiate our new findings.

3. Enhancing Microwave-Optical Bell Pairs Generation for Quantum Transduction Using Kerr Nonlinearity

   Fangxin Li , Ming Yuan , Zhaoyou Wang , Changchun Zhong , and Liang Jiang

   arXiv, May 2025

   Microwave-optical quantum transduction can be achieved via quantum teleportation using microwave-optical photon Bell pairs. The standard spontaneous parametric down-conversion (SPDC) has to trade off between generation fidelity and probability due to unwanted higher-excitation pairs in the output. In this work, we propose a pulsed SPDC scheme that employs strong Kerr nonlinearity in the microwave mode. This nonlinearity causes significant detuning of higher excitations due to the anharmonicity of energy levels, and the system can be pulse-driven to produce single-photon pairs in the output. Our pulsed nonlinear approach can generate high-fidelity Bell pairs with high probability, alleviating the trade-off between fidelity and probability inherent in traditional SPDC schemes. We optimize both the pulse width and driving strength, demonstrating that our protocol outperforms the SPDC scheme in a realistic setting of finite nonlinearity and intrinsic photon loss.

4. Resonance-Enhanced Floquet Cavity Electromagnonics

   Amin Pishehvar^* , Zixin Yan^* , Zhaoyou Wang , Yu Jiang , Yizhong Huang , Josep M. Jornet , Liang Jiang , and Xufeng Zhang

   Physical Review Applied, Jul 2025

   Floquet engineering has recently been recognized as an important tool for manipulating the coherent magnon-photon interaction in cavity electromagnonics systems at microwave frequencies. In spite of the novel hybrid magnonic functionalities that have been demonstrated, the effect of the Floquet drive has been relatively weak due to the limited driving efficiency, limiting its broader application. This work shows that, both experimentally and theoretically, the Floquet drive in our cavity electromagnonic device can be drastically enhanced by utilizing 𝐿⁢𝐶 resonances, giving rise to drastically boosted interaction between hybrid modes with fundamentally different spectral characteristics compared with previous demonstrations. In addition, the Floquet drives can also be obtained from gigahertz signals on such a system, allowing the demonstration of more advanced signal operations. Our resonance-enhanced Floquet cavity electromagnonics points to a promising direction to fully unleash the potential of Floquet hybrid magnonics.

5. On-Demand Magnon Resonance Isolation in Cavity Magnonics Editors' Suggestion

   Amin Pishehvar , Zhaoyou Wang , Yujie Zhu , Yu Jiang , Zixin Yan , Fangxin Li , Josep M. Jornet , Jia-Mian Hu , Liang Jiang , and Xufeng Zhang

   Physical Review Applied, Feb 2025

   Cavity magnonics is a promising field focusing on the interaction between spin waves (magnons) and other types of signal. In cavity magnonics, isolation of magnons from the cavity to allow signal storage and processing fully in the magnonic domain is highly desired, but its realization is often hindered by the lack of necessary tunability of the interaction. This work shows that by using the collective mode of two yttrium iron garnet spheres and applying Floquet engineering, magnonic signals can be switched on demand to a magnon dark mode that is protected from the environment, enabling a variety of manipulation over the magnon dynamics. Our demonstration can be scaled up to systems with an array of magnonic resonators, paving the way for large-scale programmable hybrid magnonic circuits.

6. Acoustic Phonon Phase Gates with Number-Resolving Phonon Detection

   Hong Qiao , Zhaoyou Wang , Gustav Andersson , Alexander Anferov , Christopher R. Conner , Yash J. Joshi , Shiheng Li , Jacob M. Miller , Xuntao Wu , Haoxiong Yan , Liang Jiang , and Andrew N. Cleland

   Nature Physics, Nov 2025

   Approaches to quantum computing that use itinerant photons are appealing because they have relatively few physical requirements. However, at present, many elements of photonic quantum computers are nondeterministic, presenting a challenge for large-scale devices. One alternative is to use similar schemes with itinerant phonons in solid-state devices, rather than photons, combined with superconducting transmon devices. Here we present an advancement in the ability to deterministically manipulate and measure acoustic phonon quantum states. First, we demonstrate the deterministic phase control of itinerant one- and two-phonon qubit states, which we measure using an acoustic Mach–Zehnder interferometer. We implement phonon phase control using the frequency-dependent scattering of phonon states from a superconducting transmon qubit. Additionally, we propose and implement a multiphonon detection scheme that enables coherent conversion between itinerant one- and two-phonon Fock states and transmon qutrit states, for example, transforming an entangled two-phonon output state into the entangled state of two transmons. The integration of quantum acoustics with superconducting circuits in our implementation promises further advances, including deterministic phonon quantum gates with direct applications to quantum computing.

7. Passive Environment-Assisted Quantum Communication with GKP States

   Zhaoyou Wang and Liang Jiang

   Physical Review X, Apr 2025

   Bosonic pure-loss channel, which represents the process of photons decaying into a vacuum environment, has zero quantum capacity when the channel’s transmissivity is less than 50%. Modeled as a beam splitter interaction between the system and its environment, the performance of bosonic pure-loss channel can be enhanced by controlling the environment state. We show that by choosing the ideal Gottesman-Kitaev-Preskill (GKP) states for the system and its environment, perfect transmission of quantum information through a beam splitter is achievable at arbitrarily low transmissivities. Our explicit constructions allow for experimental demonstration of the improved performance of a quantum channel through passive environment assistance, which is potentially useful for quantum transduction where the environment state can be naturally controlled. In practice, it is crucial to consider finite-energy constraints, and high-fidelity quantum communication through a beam splitter remains achievable with GKP states at the few-photon level.

8. Quantum Random Access Memory with Transmon-Controlled Phonon Routing

   Zhaoyou Wang^* , Hong Qiao^* , Andrew N. Cleland , and Liang Jiang

   Physical Review Letters, May 2025

   Quantum random access memory (QRAM) promises simultaneous data queries at multiple memory locations, with data retrieved in coherent superpositions, essential for achieving quantum speedup in many quantum algorithms. We introduce a transmon-controlled phonon router and propose a QRAM implementation by connecting these routers in a treelike architecture. The router controls the motion of itinerant surface acoustic wave phonons based on the state of the control transmon, implementing the core functionality of conditional routing for QRAM. Our QRAM design is compact, supports fast routing operations, and avoids frequency crowding. Additionally, we propose a hybrid dual-rail encoding method to detect dominant loss errors without additional hardware, a versatile approach applicable to other QRAM platforms. Our estimates indicate that the proposed QRAM platform can achieve high heralding rates using current device parameters, with heralding fidelity primarily limited by transmon dephasing.

2024

1. Quantum Control and Noise Protection of a Floquet 0-π Qubit Editors' Suggestion

   Zhaoyou Wang and Amir H. Safavi-Naeini

   Physical Review A, Apr 2024

   Time-periodic systems allow engineering new effective Hamiltonians from limited physical interactions. For example, the inverted position of the Kapitza pendulum emerges as a stable equilibrium with rapid drive of its pivot point. In this work we propose the Kapitzonium: a Floquet qubit that is the superconducting circuit analog of a mechanical Kapitza pendulum. Under periodic driving, the bit- and phase-flip rates of the emerging qubit states are exponentially suppressed with respect to the ratio of the effective Josephson energy to charging energy. However, we find that dissipation causes leakage out of the Floquet qubit subspace. We engineer a passive cooling scheme to stabilize the qubit subspace, which is crucial for high-fidelity quantum control under dissipation. Furthermore, we introduce a hardware-efficient fluorescence-based method for qubit measurement and discuss the experimental implementation of the Floquet qubit. Our work provides the fundamental steps to develop more complex Floquet quantum systems from the ground up to realize large-scale protected engineered dynamics.

2023

1. Strong Dispersive Coupling Between a Mechanical Resonator and a Fluxonium Superconducting Qubit

   Nathan R.A. Lee , Yudan Guo , Agnetta Y. Cleland , E. Alex Wollack , Rachel G. Gruenke , Takuma Makihara , Zhaoyou Wang , Taha Rajabzadeh , Wentao Jiang , Felix M. Mayor , Patricio Arrangoiz-Arriola , Christopher J. Sarabalis , and Amir H. Safavi-Naeini

   PRX Quantum, Dec 2023

   We demonstrate strong dispersive coupling between a fluxonium superconducting qubit and a 690 megahertz mechanical oscillator, extending the reach of circuit quantum acousto-dynamics (cQAD) experiments into a new range of frequencies. We have engineered a qubit-phonon coupling rate of 𝑔 ≈2⁢𝜋 ×14 MHz, and achieved a dispersive interaction that exceeds the decoherence rates of both systems while the qubit and mechanics are highly nonresonant (Δ/𝑔 ≳10). Leveraging this strong coupling, we perform phonon-number-resolved measurements of the mechanical resonator and investigate its dissipation and dephasing properties. Our results demonstrate the potential for fluxonium-based hybrid quantum systems, and a path for developing new quantum sensing and information processing schemes with phonons at frequencies below 700 MHz to significantly expand the toolbox of cQAD.

2. Analysis of Arbitrary Superconducting Quantum Circuits Accompanied by a Python Package: SQcircuit

   Taha Rajabzadeh , Zhaoyou Wang , Nathan Lee , Takuma Makihara , Yudan Guo , and Amir H. Safavi-Naeini

   Quantum, Sep 2023

   Taha Rajabzadeh, Zhaoyou Wang, Nathan Lee, Takuma Makihara, Yudan Guo, and Amir H. Safavi-Naeini, Quantum 7, 1118 (2023). Superconducting quantum circuits are a promising hardware platform for realizing a fault-tolerant quantum computer. Accelerating progress in this field of research demands general approaches…

3. Optimized Protocols for Duplex Quantum Transduction

   Zhaoyou Wang , Mengzhen Zhang , Yat Wong , Changchun Zhong , and Liang Jiang

   Physical Review Letters, Nov 2023

   Quantum transducers convert quantum signals through hybrid interfaces of physical platforms in quantum networks. Modeled as quantum communication channels, performance of unidirectional quantum transduction can be measured by the quantum channel capacity. However, characterizing performance of quantum transducers used for duplex quantum transduction where signals are converted bidirectionally remains an open question. Here, we propose rate regions to characterize the performance of duplex quantum transduction. Using this tool, we find that quantum transducers optimized for simultaneous duplex transduction can outperform strategies based on the standard protocol of time-shared unidirectional transduction. Integrated over the frequency domain, we demonstrate that the rate region can also characterize quantum transducers with finite bandwidth.

2022

1. Skopi: A Simulation Package for Diffractive Imaging of Noncrystalline Biomolecules

   A. Peck^* , H.-Y. Chang^* , A. Dujardin , D. Ramalingam , M. Uervirojnangkoorn , Z. Wang , A. Mancuso , F. Poitevin , and C. H. Yoon

   Journal of Applied Crystallography, Aug 2022

   X-ray free-electron lasers (XFELs) have the ability to produce ultra-bright femtosecond X-ray pulses for coherent diffraction imaging of biomolecules. While the development of methods and algorithms for macromolecular crystallography is now mature, XFEL experiments involving aerosolized or solvated biomolecular samples offer new challenges in terms of both experimental design and data processing. Skopi is a simulation package that can generate single-hit diffraction images for reconstruction algorithms, multi-hit diffraction images of aggregated particles for training machine learning classifiers using labeled data, diffraction images of randomly distributed particles for fluctuation X-ray scattering algorithms, and diffraction images of reference and target particles for holographic reconstruction algorithms. Skopi is a resource to aid feasibility studies and advance the development of algorithms for noncrystalline experiments at XFEL facilities.

2. Automated Discovery of Autonomous Quantum Error Correction Schemes

   Zhaoyou Wang , Taha Rajabzadeh , Nathan Lee , and Amir H. Safavi-Naeini

   PRX Quantum, Apr 2022

   We can encode a qubit in the energy levels of a quantum system. Relaxation and other dissipation processes lead to decay of the fidelity of this stored information. Is it possible to preserve the quantum information for a longer time by introducing additional drives and dissipation? The existence of autonomous quantum error correcting codes answers this question in the positive. Nonetheless, discovering these codes for a real physical system, i.e., finding the encoding and the associated driving fields and bath couplings, remains a challenge that has required intuition and inspiration to overcome. In this work, we develop and demonstrate a computational approach based on adjoint optimization for discovering autonomous quantum error correcting codes given a Hamiltonian description of a physical system. We implement an optimizer that searches for a logical subspace and control parameters to better preserve quantum information. We demonstrate our method on a system of a harmonic oscillator coupled to a lossy qubit, and find that varying the Hamiltonian distance in Fock space—a proxy for the control hardware complexity—leads to discovery of different and new error correcting schemes. We discover what we call the √3 code, realizable with a Hamiltonian distance d=2, and propose a hardware-efficient implementation based on superconducting circuits.

3. Quantum State Preparation and Tomography of Entangled Mechanical Resonators

   E. Alex Wollack^* , Agnetta Y. Cleland^* , Rachel G. Gruenke , Zhaoyou Wang , Patricio Arrangoiz-Arriola , and Amir H. Safavi-Naeini

   Nature, Apr 2022

   Precisely engineered mechanical oscillators keep time, filter signals and sense motion, making them an indispensable part of the technological landscape of today. These unique capabilities motivate bringing mechanical devices into the quantum domain by interfacing them with engineered quantum circuits. Proposals to combine microwave-frequency mechanical resonators with superconducting devices suggest the possibility of powerful quantum acoustic processors1–3. Meanwhile, experiments in several mechanical systems have demonstrated quantum state control and readout4,5, phonon number resolution6,7 and phonon-mediated qubit–qubit interactions8,9. At present, these acoustic platforms lack processors capable of controlling the quantum states of several mechanical oscillators with a single qubit and the rapid quantum non-demolition measurements of mechanical states needed for error correction. Here we use a superconducting qubit to control and read out the quantum state of a pair of nanomechanical resonators. Our device is capable of fast qubit–mechanics swap operations, which we use to deterministically manipulate the mechanical states. By placing the qubit into the strong dispersive regime with both mechanical resonators simultaneously, we determine the phonon number distributions of the resonators by means of Ramsey measurements. Finally, we present quantum tomography of the prepared nonclassical and entangled mechanical states. Our result represents a concrete step towards feedback-based operation of a quantum acoustic processor.

2021

1. Room-Temperature Mechanical Resonator with a Single Added or Subtracted Phonon

   Rishi N. Patel , Timothy P. McKenna , Zhaoyou Wang , Jeremy D. Witmer , Wentao Jiang , Raphaël Van Laer , Christopher J. Sarabalis , and Amir H. Safavi-Naeini

   Physical Review Letters, Sep 2021

   A room-temperature mechanical oscillator undergoes thermal Brownian motion with an amplitude much larger than the amplitude associated with a single phonon of excitation. This motion can be read out and manipulated using laser light using a cavity-optomechanical approach. By performing a strong quantum measurement (i.e., counting single photons in the sidebands imparted on a laser), we herald the addition and subtraction of single phonons on the 300 K thermal motional state of a 4 GHz mechanical oscillator. To understand the resulting mechanical state, we implement a tomography scheme and observe highly non-Gaussian phase-space distributions. Using a maximum likelihood method, we infer the density matrix of the oscillator, and we confirm the counterintuitive doubling of the mean phonon number resulting from phonon addition and subtraction.

2020

1. Propagation of Microwave Photons along a Synthetic Dimension

   Nathan R. A. Lee , Marek Pechal , E. Alex Wollack , Patricio Arrangoiz-Arriola , Zhaoyou Wang , and Amir H. Safavi-Naeni

   Physical Review A, May 2020

   The evenly spaced modes of an electromagnetic resonator are coupled to each other by appropriate time modulation, leading to dynamics analogous to those of particles hopping between different sites of a lattice. This substitution of a real spatial dimension of a lattice with a “synthetic” dimension in frequency space greatly reduces the hardware complexity of an analog quantum simulator. Complex control and readout of a highly multimoded structure can thus be accomplished with very few physical control lines. We demonstrate this concept with microwave photons in a superconducting transmission line resonator by modulating the system parameters at frequencies near the resonator’s free spectral range and observing propagation of photon wave packets in time domain. The linear propagation dynamics are equivalent to a tight-binding model, which we probe by measuring scattering parameters between frequency sites. We extract an approximate tight-binding dispersion relation for the synthetic lattice and initialize photon wave packets with well-defined quasimomenta and group velocities. As an example application of this platform in simulating a physical system, we demonstrate Bloch oscillations associated with a particle in a periodic potential and subject to a constant external field. The simulated field strongly affects the photon dynamics despite photons having zero charge. Our observation of photon dynamics along a synthetic frequency dimension generalizes immediately to topological photonics and single-photon power levels, and expands the range of physical systems addressable by quantum simulation.

2. Calculating Rényi Entropies with Neural Autoregressive Quantum States

   Zhaoyou Wang^* and Emily J. Davis^*

   Physical Review A, Dec 2020

   Entanglement entropy is an essential metric for characterizing quantum many-body systems, but its numerical evaluation for neural network representations of quantum states has so far been inefficient and demonstrated only for the restricted Boltzmann machine architecture. Here we estimate generalized Rényi entropies of autoregressive neural quantum states with up to 𝑁=256 spins using quantum Monte Carlo methods. A naive “direct sampling” approach performs well for low-order Rényi entropies but fails for larger orders when benchmarked on a one-dimensional Heisenberg model. We therefore propose an improved “conditional sampling” method exploiting the autoregressive structure of the network ansatz, which outperforms direct sampling and facilitates calculations of higher-order Rényi entropies in both one- and two-dimensional Heisenberg models. Access to higher-order Rényi entropies allows for an approximation of the von Neumann entropy as well as extraction of the single-copy entanglement. Both methods elucidate the potential of neural network quantum states in quantum Monte Carlo studies of entanglement entropy for many-body systems.

2019

1. Resolving the Energy Levels of a Nanomechanical Oscillator

   Patricio Arrangoiz-Arriola^* , E. Alex Wollack^* , Zhaoyou Wang , Marek Pechal , Wentao Jiang , Timothy P. McKenna , Jeremy D. Witmer , Raphaël Van Laer , and Amir H. Safavi-Naeini

   Nature, Jul 2019

   The quantum nature of an oscillating mechanical object is anything but apparent. The coherent states that describe the classical motion of a mechanical oscillator do not have a well defined energy, but are quantum superpositions of equally spaced energy eigenstates. Revealing this quantized structure is only possible with an apparatus that measures energy with a precision greater than the energy of a single phonon. One way to achieve this sensitivity is by engineering a strong but nonresonant interaction between the oscillator and an atom. In a system with sufficient quantum coherence, this interaction allows one to distinguish different energy eigenstates using resolvable differences in the atom’s transition frequency. For photons, such dispersive measurements have been performed in cavity1,2 and circuit quantum electrodynamics3. Here we report an experiment in which an artificial atom senses the motional energy of a driven nanomechanical oscillator with sufficient sensitivity to resolve the quantization of its energy. To realize this, we build a hybrid platform that integrates nanomechanical piezoelectric resonators with a microwave superconducting qubit on the same chip. We excite phonons with resonant pulses and probe the resulting excitation spectrum of the qubit to observe phonon-number-dependent frequency shifts that are about five times larger than the qubit linewidth. Our result demonstrates a fully integrated platform for quantum acoustics that combines large couplings, considerable coherence times and excellent control over the mechanical mode structure. With modest experimental improvements, we expect that our approach will enable quantum nondemolition measurements of phonons4 and will lead to quantum sensors and information-processing approaches5 that use chip-scale nanomechanical devices.

2. Quantum Dynamics of a Few-Photon Parametric Oscillator

   Zhaoyou Wang^* , Marek Pechal^* , E. Alex Wollack , Patricio Arrangoiz-Arriola , Maodong Gao , Nathan R. Lee , and Amir H. Safavi-Naeini

   Physical Review X, Jun 2019

   Modulating the frequency of a harmonic oscillator at nearly twice its natural frequency leads to amplification and self-oscillation. Above the oscillation threshold and in the presence of a nonlinearity, the field settles into a coherent oscillating state with a well-defined phase of either 0 or 𝜋. We demonstrate a quantum parametric oscillator operating at microwave frequencies and drive it into oscillating states containing only a few photons. The small number of photons present in the system and the coherent nature of the nonlinearity prevent the environment from learning the randomly chosen phase of the oscillator. This result allows the system to oscillate briefly in a quantum superposition of both phases at once, effectively generating a nonclassical Schrödinger’s cat state. We characterize the dynamics and states of the system by analyzing the output field emitted by the oscillator and implementing quantum state tomography suited for nonlinear resonators. By demonstrating a quantum parametric oscillator and the requisite techniques for characterizing its quantum state, we set the groundwork for new schemes of quantum and classical information processing and extend the reach of these ubiquitous devices deep into the quantum regime.

2018

1. Painting Nonclassical States of Spin or Motion with Shaped Single Photons

   Emily J. Davis^* , Zhaoyou Wang^* , Amir H. Safavi-Naeini , and Monika H. Schleier-Smith

   Physical Review Letters, Sep 2018

   We propose a robust scheme for generating macroscopic superposition states of spin or motion with the aid of a single photon. Shaping the wave packet of the photon enables high-fidelity preparation of nonclassical states of matter even in the presence of photon loss. Success is heralded by photodetection, enabling the scheme to be implemented with a weak coherent field. We analyze applications to preparing Schrödinger cat states of a collective atomic spin or of a mechanical oscillator coupled to an optical resonator. The method generalizes to preparing arbitrary superpositions of coherent states, enabling full quantum control. We illustrate this versatility by showing how to prepare Dicke or Fock states, as well as superpositions in the Dicke or Fock basis.

2. Single-Mode Phononic Wire

   Rishi N. Patel , Zhaoyou Wang , Wentao Jiang , Christopher J. Sarabalis , Jeff T. Hill , and Amir H. Safavi-Naeini

   Physical Review Letters, Jul 2018

   Photons and electrons transmit information to form complex systems and networks. Phonons on the other hand, the quanta of mechanical motion, are often considered only as carriers of thermal energy. Nonetheless, their flow can also be molded in fabricated nanoscale circuits. We design and experimentally demonstrate wires for phonons by patterning the surface of a silicon chip. Our device eliminates all but one channel of phonon conduction, allowing coherent phonon transport over millimeter length scales. We characterize the phononic wire optically, by coupling it strongly to an optomechanical transducer. The phononic wire enables new ways to manipulate information and energy on a chip. In particular, our result is an important step towards realizing on-chip phonon networks, in which quantum information is transmitted between nodes via phonons.Physics Subject Headings (PhySH)Acoustic wave phenomenaHybrid quantum systemsNanophotonicsOptomechanicsPhononsQuantum channelsQuantum networksNanomechanical devicesNanostructuresQuantum wiresCavity resonatorsCryogenicsLithographyPlasma etchingwindow.articlePhySH = {"concepts":{"c9118388-9237-4f60-a4f7-29316d3d1af7":{"id":"c9118388-9237-4f60-a4f7-29316d3d1af7","label":"Nanomechanical devices","paths":[[{"id":"f45b3c40-959c-4e90-ba0e-38232980802a","label":"Physical Systems","uri":"https://doi.org/10.29172/f45b3c40-959c-4e90-ba0e-38232980802a","exclude_from_indexing":true,"type":"facet"},{"id":"2360e96e-a12b-4d21-9b65-36ed1177c0e6","label":"Devices","uri":"https://doi.org/10.29172/2360e96e-a12b-4d21-9b65-36ed1177c0e6","type":"concept"},{"id":"c9118388-9237-4f60-a4f7-29316d3d1af7","label":"Nanomechanical 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2017

1. Enhancing a Slow and Weak Optomechanical Nonlinearity with Delayed Quantum Feedback

   Zhaoyou Wang and Amir H. Safavi-Naeini

   Nature Communications, Jul 2017

   A central goal of quantum optics is to generate large interactions between single photons so that one photon can strongly modify the state of another one. In cavity optomechanics, photons interact with the motional degrees of freedom of an optical resonator, for example, by imparting radiation pressure forces on a movable mirror or sensing minute fluctuations in the position of the mirror. Here, we show that the optical nonlinearity arising from these effects, typically too small to operate on single photons, can be sufficiently enhanced with feedback to generate large interactions between single photons. We propose a protocol that allows photons propagating in a waveguide to interact with each other through multiple bounces off an optomechanical system. The protocol is analysed by evolving the full many-body quantum state of the waveguide-coupled system, illustrating that large photon–photon interactions mediated by mechanical motion may be within experimental reach.

2015

1. Time-Reversal Symmetry Protected Chiral Interface States between Quantum Spin and Quantum Anomalous Hall Insulators

   Huaqing Huang , Zhaoyou Wang , Nannan Luo , Zhirong Liu , Rong Lü , Jian Wu , and Wenhui Duan

   Physical Review B, Aug 2015

   We theoretically investigate the electronic properties of the interface between quantum spin Hall (QSH) and quantum anomalous Hall (QAH) insulators. A robust chiral gapless state, which substantially differs from edge states of QSH or QAH insulators, is predicted at the QSH/QAH interface using an effective Hamiltonian model. We systematically reveal distinctive properties of interface states between QSH and single-valley QAH, multivalley high-Chern-number QAH and valley-polarized QAH insulators based on tight-binding models using the interface Green’s function method. As an example, first-principles calculations are conducted for the interface states between fully and semihydrogenated bismuth (111) thin films, verifying the existence of interface states in realistic material systems. Due to the physically protected junction structure, the interface state is expected to be more stable and insensitive than topological boundary states against edge defects and chemical decoration. Hence our results of the interface states provide a promising route towards enhancing the performance and stability of low-dissipation electronics in real environment.