Showing 1–26 of 26 results for author: Qiu, C

Observation of Momentum-Band Topology in PT-Symmetric acoustic Floquet Lattices

Authors: Shuaishuai Tong, Qicheng Zhang, Gaohan Li, Kun Zhang, Chun Xie, Chunyin Qiu

Abstract: Momentum-band topology, which transcends conventional topological band theory, unlocks new topological phases that host fascinating temporal interface states. However, direct bulk experimental evidence of such emerging band topology is still lacking due to the great challenges in resolving eigenstates and topological invariants of time-varying systems. Here, we present a comprehensive study on the… ▽ More Momentum-band topology, which transcends conventional topological band theory, unlocks new topological phases that host fascinating temporal interface states. However, direct bulk experimental evidence of such emerging band topology is still lacking due to the great challenges in resolving eigenstates and topological invariants of time-varying systems. Here, we present a comprehensive study on the momentum-band topology in a PT-symmetric Floquet lattice, where the drive-induced momentum gap can be characterized by a quantized Berry phase in the energy Brillouin zone. Experimentally, we synthesize the Floquet lattice model using an acoustic cavity-tube structure coupled to custom-designed external circuits. By reconstructing the effective Hamiltonian, we extract the system's eigenstates and provide the first bulk evidence of momentum-band topology from the perspectives of band inversion and topological invariants. This is accompanied by an unambiguous observation of time-localized interface states in real physical time, thereby providing the boundary signature of the bulk topology. Our work paves the way for further experimental studies on the burgeoning momentum-gap physics. △ Less

Submitted 5 July, 2025; originally announced July 2025.

Comments: 7 pages, 5 figures

Observation of metastability in open quantum dynamics of a solid-state system

Authors: Jun-Xiang Zhang, Yuan-De Jin, Chu-Dan Qiu, Wen-Long Ma, Gang-Qin Liu

Abstract: Metastability is a ubiquitous phenomenon in non-equilibrium physics and classical stochastic dynamics.It arises when the system dynamics settles in long-lived states before eventually decaying to true equilibria. Remarkably, it has been predicted that quantum metastability can also occur in continuous-time and discrete-time open quantum dynamics. However, the direct experimental observation of met… ▽ More Metastability is a ubiquitous phenomenon in non-equilibrium physics and classical stochastic dynamics.It arises when the system dynamics settles in long-lived states before eventually decaying to true equilibria. Remarkably, it has been predicted that quantum metastability can also occur in continuous-time and discrete-time open quantum dynamics. However, the direct experimental observation of metastability in open quantum systems has remained elusive. Here, we experimentally observe metastability in the discrete-time evolution of a single nuclear spin in diamond, realized by sequential Ramsey interferometry measurements of a nearby nitrogen-vacancy electron spin. We demonstrate that the metastable polarization of the nuclear spin emerges at around 60,000-250,000 sequential measurements, enabling high-fidelity single-shot readout of the nuclear spin under a small magnetic field of 108.4 gauss. An ultra-long spin relaxation time of more than 10 s has been observed at room temperature. By further increasing the measurement number, the nuclear spin eventually relaxes into the maximally mixed state. Our results represent a concrete step towards uncovering non-equilibrium physics in open quantum dynamics, which is practically relevant for the utilization of metastable information in various quantum information processing tasks, such as accurate quantum operations, quantum channel discrimination and quantum error correction. △ Less

Submitted 30 December, 2024; originally announced December 2024.

Diverse methods and practical aspects in controlling single semiconductor qubits: a review

Authors: Jia-Ao Peng, Chu-Dan Qiu, Wen-Long Ma, Jun-Wei Luo

Abstract: Quantum control allows a wide range of quantum operations employed in molecular physics, nuclear magnetic resonance and quantum information processing. Thanks to the existing microelectronics industry, semiconducting qubits, where quantum information is encoded in spin or charge degree freedom of electrons or nuclei in semiconductor quantum dots, constitute a highly competitive candidate for scala… ▽ More Quantum control allows a wide range of quantum operations employed in molecular physics, nuclear magnetic resonance and quantum information processing. Thanks to the existing microelectronics industry, semiconducting qubits, where quantum information is encoded in spin or charge degree freedom of electrons or nuclei in semiconductor quantum dots, constitute a highly competitive candidate for scalable solid-state quantum technologies. In quantum information processing, advanced control techniques are needed to realize quantum manipulations with both high precision and noise resilience. In this review, we first introduce the basics of various widely-used control methods, including resonant excitation, adabatic passage, shortcuts to adiabaticity, composite pulses, and quantum optimal control. Then we review the practical aspects in applying these methods to realize accurate and robust quantum gates for single semiconductor qubits, such as Loss-DiVincenzo spin qubit, spinglet-triplet qubit, exchange-only qubit and charge qubit. △ Less

Submitted 4 December, 2024; originally announced December 2024.

Dielectric Fano Nanoantennas for Enabling Sub-Nanosecond Lifetimes in NV-based Single Photon Emitters

Authors: Shu An, Dmitry Kalashnikov, Wenqiao Shi, Zackaria Mahfoud, Ah Bian Chew, Yan Liu, Jing Wu, Di Zhu, Weibo Gao, Cheng-Wei Qiu, Victor Leong, Zhaogang Dong

Abstract: Solid-state quantum emitters are essential sources of single photons, and enhancing their emission rates is of paramount importance for applications in quantum communications, computing, and metrology. One approach is to couple quantum emitters with resonant photonic nanostructures, where the emission rate is enhanced due to the Purcell effect. Dielectric nanoantennas are promising as they provide… ▽ More Solid-state quantum emitters are essential sources of single photons, and enhancing their emission rates is of paramount importance for applications in quantum communications, computing, and metrology. One approach is to couple quantum emitters with resonant photonic nanostructures, where the emission rate is enhanced due to the Purcell effect. Dielectric nanoantennas are promising as they provide strong emission enhancement compared to plasmonic ones, which suffer from high Ohmic loss. Here, we designed and fabricated a dielectric Fano resonator based on a pair of silicon (Si) ellipses and a disk, which supports the mode hybridization between quasi-bound-states-in-the-continuum (quasi-BIC) and Mie resonance. We demonstrated the performance of the developed resonant system by interfacing it with single photon emitters (SPEs) based on nitrogen-vacancy (NV-) centers in nanodiamonds (NDs). We observed that the interfaced emitters have a Purcell enhancement factor of ~10, with sub-ns emission lifetime and a polarization contrast of 9. Our results indicate a promising method for developing efficient and compact single-photon sources for integrated quantum photonics applications. △ Less

Submitted 3 July, 2024; originally announced July 2024.

Comments: 20 pages, 4 figures

How coherence measurements of a qubit steer its quantum environment

Authors: Chu-Dan Qiu, Yuan-De Jin, Jun-Xiang Zhang, Gang-Qin Liu, Wen-Long Ma

Abstract: Repetitive Ramsey interferometry measurements (RIMs) are often used to measure qubit coherence, assuming that the environment remains unaffected after each measurement and the outcomes of all measurements are independent and identically distributed (i.i.d.). While this assumption is valid for a classical environment, it may not hold for a quantum environment due to the non-negligible backaction fr… ▽ More Repetitive Ramsey interferometry measurements (RIMs) are often used to measure qubit coherence, assuming that the environment remains unaffected after each measurement and the outcomes of all measurements are independent and identically distributed (i.i.d.). While this assumption is valid for a classical environment, it may not hold for a quantum environment due to the non-negligible backaction from qubit to environment. Here we present a general theoretical framework to incorporate the measurement backaction from qubit to environment in sequential RIMs. We show that a RIM of a qubit induces a quantum channel on the quantum environment, and sequential RIMs gradually steer the quantum environment to the fixed points of the channel. We reveal three distinct environment steering effects -- polarization, depolarization and metastable polarization, depending on the commutativity of the noise operator $B$ and the free environment Hamiltonian $H_e$: (1) if $B$ commutes with $H_e$, i.e., $[B,H_e]=0$, the quantum environment is gradually polarized to different eigenstates of $B$ as the number $m$ of repetitive RIMs increases; (2) When $[B,H_e]\neq 0$, the quantum environment is gradually depolarized to a maximally mixed state of its whole Hilbert space or a Hilbert subspace; (3) When $[B,H_e]\neq 0$ but one of $H_e$ and $B$ is a small perturbation on the other, metastable polarization can happen, such that the quantum environment is first polarized for a finite range of $m$ but becomes gradually depolarized as $m$ increases further. The environment steering also makes the measurement statistics of sequential RIMs develop non-i.i.d. features, such that the measurement result distribution can display multiple peaks for a small quantum environment, corresponding to different fixed points of the quantum channel. △ Less

Submitted 26 June, 2024; v1 submitted 9 April, 2024; originally announced April 2024.

Quantum Advantage of One-Way Squeezing in Enhancing Weak-Force Sensing

Authors: Jie Wang, Qian Zhang, Ya-Feng Jiao, Sheng-Dian Zhang, Tian-Xiang Lu, Zhipeng Li, Cheng-Wei Qiu, Hui Jing

Abstract: Cavity optomechanical (COM) sensors, featuring efficient light-motion couplings, have been widely used for ultra sensitive measurements of various physical quantities ranging from displacements to accelerations or weak forces. Previous works, however, have mainly focused on reciprocal COM systems. Here, we propose how to further improve the performance of quantum COM sensors by breaking reciprocal… ▽ More Cavity optomechanical (COM) sensors, featuring efficient light-motion couplings, have been widely used for ultra sensitive measurements of various physical quantities ranging from displacements to accelerations or weak forces. Previous works, however, have mainly focused on reciprocal COM systems. Here, we propose how to further improve the performance of quantum COM sensors by breaking reciprocal symmetry in purely quantum regime. Specifically, we consider a spinning COM resonator and show that by selectively driving it in opposite directions, highly nonreciprocal optical squeezing can emerge, which in turn provides an efficient way to surpass the standard quantum limit that otherwise exists in conventional reciprocal devices. Our work confirms that breaking reciprocal symmetry, already achieved in diverse systems well beyond spinning systems, can serve as a new strategy to further enhance the abilities of advanced quantum sensors, for applications ranging from testing fundamental physical laws to practical quantum metrology. △ Less

Submitted 14 March, 2024; originally announced March 2024.

Comments: 7 pages,3 figures

Recursive expansion of Tanner graph: a method to construct stabilizer codes with high coding rate

Authors: Zhengzhong Yi, Zhipeng Liang, Zicheng Wang, Jiahan Chen, Chen Qiu, Yulin Wu, Xuan Wang

Abstract: Quantum stabilizer codes face the problem of low coding rate. In this article, following the idea of recursively expanding Tanner graph proposed in our previous work, we try to construct new stabilizer codes with high coding rate, and propose XZ-type Tanner-graph-recursive-expansion (XZ-TGRE) code and Tanner-graph-recursive-expansion hypergraph product (TGRE-HP) code. XZ-TGRE code have zero asympt… ▽ More Quantum stabilizer codes face the problem of low coding rate. In this article, following the idea of recursively expanding Tanner graph proposed in our previous work, we try to construct new stabilizer codes with high coding rate, and propose XZ-type Tanner-graph-recursive-expansion (XZ-TGRE) code and Tanner-graph-recursive-expansion hypergraph product (TGRE-HP) code. XZ-TGRE code have zero asymptotic coding rate, but its coding rate tends to zero extremely slowly with the growth of code length. Under the same code length, its coding rate is much higher than that of surface code. The coding rate of TGRE-HP is the constant 0.2, which is the highest constant coding rate of stabilizer codes to our best knowledge. We prove that the code distance of XZ-TGRE code scales as $O(log(N))$, and that of TGRE-HP code scales as $O(\log \sqrt{N})$, where $N$ is the code length. Moreover, the code capacity noise threshold of XZ-TGRE code is around 0.078, and that of TGRE-HP code is around 0.096. This articles shows that the idea of recursively expanding Tanner graph might have potential to construct quantum codes with good performance. △ Less

Submitted 11 April, 2024; v1 submitted 12 February, 2024; originally announced February 2024.

Determining the upper bound of code distance of quantum stabilizer codes through Monte Carlo method based on fully decoupled belief propagation

Authors: Zhipeng Liang, Zicheng Wang, Zhengzhong Yi, Yulin Wu, Chen Qiu, Xuan Wang

Abstract: Code distance is an important parameter for quantum stabilizer codes (QSCs). Directly precisely computing it is an NP-complete problem. However, the upper bound of code distance can be computed by some efficient methods. In this paper, employing the idea of Monte Carlo method, we propose the algorithm of determining the upper bound of code distance of QSCs based on fully decoupled belief propagati… ▽ More Code distance is an important parameter for quantum stabilizer codes (QSCs). Directly precisely computing it is an NP-complete problem. However, the upper bound of code distance can be computed by some efficient methods. In this paper, employing the idea of Monte Carlo method, we propose the algorithm of determining the upper bound of code distance of QSCs based on fully decoupled belief propagation. Our algorithm shows high precision - the upper bound of code distance determined by the algorithm of a variety of QSCs whose code distance is known is consistent with actual code distance. Besides, we explore the upper bound of logical X operators of Z-type Tanner-graph-recursive-expansion (Z-TGRE) code and Chamon code, which is a kind of XYZ product code constructed by three repetition codes. The former is consistent with the theoretical analysis, and the latter implies the code distance of XYZ product codes can very likely achieve $O(N^{2/3})$, which supports the conjecture of Leverrier et al.. △ Less

Submitted 9 February, 2024; originally announced February 2024.

Observation of quantum strong Mpemba effect

Authors: Jie Zhang, Gang Xia, Chun-Wang Wu, Ting Chen, Qian Zhang, Yi Xie, Wen-Bo Su, Wei Wu, Cheng-Wei Qiu, Ping-xing Chen, Weibin Li, Hui Jing, Yan-Li Zhou

Abstract: An ancient and counterintuitive phenomenon know as the Mpemba effect (water can cool faster when initially heated up) showcases the critical role of initial conditions in relaxation processes. How to realize and utilize this effect for speeding up relaxation is an important but challenging task in purely quantum system till now. Here, we report the first experiment, as far as we know,about the str… ▽ More An ancient and counterintuitive phenomenon know as the Mpemba effect (water can cool faster when initially heated up) showcases the critical role of initial conditions in relaxation processes. How to realize and utilize this effect for speeding up relaxation is an important but challenging task in purely quantum system till now. Here, we report the first experiment, as far as we know,about the strong Mpemba effect in a single trapped ion system in which an exponentially expedited relaxation in time is observed by preparing an optimal initial state with no excitation of the slowest decaying mode. Also, we find that the condition of realizing such effect coincides with the Liouvillian exceptional point, featuring the coalescence of both the eigenvalues and the eigenmodes of the system. Our work provides an efficient strategy to exponentially accelerate relaxations of quantum system to their stationary state, and suggests a link unexplored yet between the Mpemba effect and the non-Hermitian physics. It could open up the door to engineer a wide range of dissipative quantum systems by utilizing the anomalous Mpemba effect, for applications in quantum simulation and quantum information processing. △ Less

Submitted 13 November, 2024; v1 submitted 29 January, 2024; originally announced January 2024.

Comments: Accepted by Nature Communications

Journal ref: Nat Commun 16, 301 (2025)

Theory of Metastability in Discrete-Time Open Quantum Dynamics

Authors: Yuan-De Jin, Chu-Dan Qiu, Wen-Long Ma

Abstract: Metastability in open system dynamics describes the phenomena of initial relaxation to longlived metastable states before decaying to the asymptotic stable states. It has been predicted in continuous-time stochastic dynamics of both classical and quantum systems. Here we present a general theory of metastability in discrete-time open quantum dynamics, described by sequential quantum channels. We f… ▽ More Metastability in open system dynamics describes the phenomena of initial relaxation to longlived metastable states before decaying to the asymptotic stable states. It has been predicted in continuous-time stochastic dynamics of both classical and quantum systems. Here we present a general theory of metastability in discrete-time open quantum dynamics, described by sequential quantum channels. We focus on a general class of quantum channels on a target system, induced by an ancilla system with a pure-dephasing coupling to the target system and under Ramsey sequences. Interesting metastable behaviors are predicted and numerically demonstrated by decomposing the average dynamics into stochastic trajectories. Examples and applications are also discussed. △ Less

Submitted 4 January, 2024; v1 submitted 30 December, 2023; originally announced January 2024.

Comments: 7 pages, 2 figures (+9 pages, 5 figures supplement)

Super-resolved snapshot hyperspectral imaging of solid-state quantum emitters for high-throughput integrated quantum technologies

Authors: Shunfa Liu, Xueshi Li, Hanqing Liu, Guixin Qiu, Jiantao Ma, Liang Nie, Haiqiao Ni, Zhichuan Niu, Cheng-Wei Qiu, Xuehua Wang, Jin Liu

Abstract: Solid-state quantum emitters coupled to integrated photonic nanostructures are quintessential for exploring fundamental phenomena in cavity quantum electrodynamics and widely employed in photonic quantum technologies such as non-classical light sources, quantum repeaters, and quantum transducers, etc. One of the most exciting promises from integrated quantum photonics is the potential of scalabili… ▽ More Solid-state quantum emitters coupled to integrated photonic nanostructures are quintessential for exploring fundamental phenomena in cavity quantum electrodynamics and widely employed in photonic quantum technologies such as non-classical light sources, quantum repeaters, and quantum transducers, etc. One of the most exciting promises from integrated quantum photonics is the potential of scalability that enables massive productions of miniaturized devices on a single chip. In reality, the yield of efficient and reproducible light-matter couplings is greatly hindered by the spectral and spatial mismatches between the single solid-state quantum emitters and confined or propagating optical modes supported by the photonic nanostructures, preventing the high-throughput realization of large-scale integrated quantum photonic circuits for more advanced quantum information processing tasks. In this work, we introduce the concept of hyperspectral imaging in quantum optics, for the first time, to address such a long-standing issue. By exploiting the extended mode with a unique dispersion in a 1D planar cavity, the spectral and spatial information of each individual quantum dot in an ensemble can be accurately and reliably extracted from a single wide-field photoluminescence image with super-resolutions. With the extracted quantum dot positions and emission wavelengths, surface-emitting quantum light sources and in-plane photonic circuits can be deterministically fabricated with a high-throughput by etching the 1D confined planar cavity into 3D confined micropillars and 2D confined waveguides. Further extension of this technique by employing an open planar cavity could be exploited for pursuing a variety of compact quantum photonic devices with expanded functionalities for large-scale integration. Our work is expected to change the landscape of integrated quantum photonic technology. △ Less

Submitted 5 November, 2023; originally announced November 2023.

Comments: 5 pages, 8 figures,comments are welcome

Noisy intermediate-scale quantum computers

Authors: Bin Cheng, Xiu-Hao Deng, Xiu Gu, Yu He, Guangchong Hu, Peihao Huang, Jun Li, Ben-Chuan Lin, Dawei Lu, Yao Lu, Chudan Qiu, Hui Wang, Tao Xin, Shi Yu, Man-Hong Yung, Junkai Zeng, Song Zhang, Youpeng Zhong, Xinhua Peng, Franco Nori, Dapeng Yu

Abstract: Quantum computers have made extraordinary progress over the past decade, and significant milestones have been achieved along the path of pursuing universal fault-tolerant quantum computers. Quantum advantage, the tipping point heralding the quantum era, has been accomplished along with several waves of breakthroughs. Quantum hardware has become more integrated and architectural compared to its tod… ▽ More Quantum computers have made extraordinary progress over the past decade, and significant milestones have been achieved along the path of pursuing universal fault-tolerant quantum computers. Quantum advantage, the tipping point heralding the quantum era, has been accomplished along with several waves of breakthroughs. Quantum hardware has become more integrated and architectural compared to its toddler days. The controlling precision of various physical systems is pushed beyond the fault-tolerant threshold. Meanwhile, quantum computation research has established a new norm by embracing industrialization and commercialization. The joint power of governments, private investors, and tech companies has significantly shaped a new vibrant environment that accelerates the development of this field, now at the beginning of the noisy intermediate-scale quantum era. Here, we first discuss the progress achieved in the field of quantum computation by reviewing the most important algorithms and advances in the most promising technical routes, and then summarizing the next-stage challenges. Furthermore, we illustrate our confidence that solid foundations have been built for the fault-tolerant quantum computer and our optimism that the emergence of quantum killer applications essential for human society shall happen in the future. △ Less

Submitted 7 March, 2023; originally announced March 2023.

Journal ref: Front. Phys. 18, 21308 (2023)

Preserving Entanglement in a Solid-Spin System Using Quantum Autoencoders

Authors: Feifei Zhou, Yu Tian, Yumeng Song, Chudan Qiu, Xiangyu Wang, Mingti Zhou, Bing Chen, Nanyang Xu, Dawei Lu

Abstract: Entanglement, as a key resource for modern quantum technologies, is extremely fragile due to the decoherence. Here, we show that a quantum autoencoder, which is trained to compress a particular set of quantum entangled states into a subspace that is robust to decoherence, can be employed to preserve entanglement. The training process is based on a hybrid quantum-classical approach to improve the e… ▽ More Entanglement, as a key resource for modern quantum technologies, is extremely fragile due to the decoherence. Here, we show that a quantum autoencoder, which is trained to compress a particular set of quantum entangled states into a subspace that is robust to decoherence, can be employed to preserve entanglement. The training process is based on a hybrid quantum-classical approach to improve the efficiency in building the autoencoder and reduce the experimental errors during the optimization. Using nitrogen-vacancy centers in diamond, we demonstrate that the entangled states between the electron and nuclear spins can be encoded into the nucleus subspace which has much longer coherence time. As a result, lifetime of the Bell states in this solid-spin system is extended from 2.22 {\pm} 0.43 μs to 3.03 {\pm} 0.56 ms, yielding a three orders of magnitude improvement. The quantum autoencoder approach is universal, paving the way of utilizing long lifetime nuclear spins as immediate-access quantum memories in quantum information tasks. △ Less

Submitted 15 June, 2022; originally announced June 2022.

Squeezing-enhanced quantum sensing with quadratic optomechanics

Authors: Sheng-Dian Zhang, Jie Wang, Qian Zhang, Ya-Feng Jiao, Yun-Lan Zuo, Şahin K. Özdemir, Cheng-Wei Qiu, Franco Nori, Hui Jing

Abstract: Cavity optomechanical (COM) sensors, enhanced by quantum squeezing or entanglement, have become powerful tools for measuring ultra-weak forces with high precision and sensitivity. However, these sensors usually rely on linear COM couplings, a fundamental limitation when measurements of the mechanical energy are desired. Very recently, a giant enhancement of the signal-to-noise ratio was predicted… ▽ More Cavity optomechanical (COM) sensors, enhanced by quantum squeezing or entanglement, have become powerful tools for measuring ultra-weak forces with high precision and sensitivity. However, these sensors usually rely on linear COM couplings, a fundamental limitation when measurements of the mechanical energy are desired. Very recently, a giant enhancement of the signal-to-noise ratio was predicted in a quadratic COM system. Here we show that the performance of such a system can be further improved surpassing the standard quantum limit by using quantum squeezed light. Our approach is compatible with available engineering techniques of advanced COM sensors and provides new opportunities for using COM sensors in tests of fundamental laws of physics and quantum metrology applications. △ Less

Submitted 3 August, 2024; v1 submitted 17 February, 2022; originally announced February 2022.

Comments: 7+7 pages, 4+2 figures

Journal ref: Optica Quantum 2, 222-229 (2024)

Arbitrary cylindrical vector beam generation enabled by polarization-selective Gouy phase shifter

Authors: J. Jia, K. Zhang, G. Hu, M. Hu, T. Tong, Q. Mu, H. Gao, F. Li, C. Qiu, P. Zhang

Abstract: Cylindrical vector beams (CVBs), which possesses polarization distribution of rotational symmetry on the transverse plane, can be developed in many optical technologies. Conventional methods to generate CVBs contain redundant interferometers or need to switch among diverse elements, thus being inconvenient in applications containing multiple CVBs. Here we provide a passive polarization-selective d… ▽ More Cylindrical vector beams (CVBs), which possesses polarization distribution of rotational symmetry on the transverse plane, can be developed in many optical technologies. Conventional methods to generate CVBs contain redundant interferometers or need to switch among diverse elements, thus being inconvenient in applications containing multiple CVBs. Here we provide a passive polarization-selective device to substitute interferometers and simplify generation setup. It is accomplished by reversing topological charges of orbital angular momentum based on polarization-selective Gouy phase. In the process, tunable input light is the only condition to generate CVB with arbitrary topological charges. To cover both azimuthal and radial parameters of CVBs, we express the mapping between scalar Laguerre-Gaussian light on basic Poincaré sphere and CVB on high-order Poincaré sphere. The proposed device simplifies the generation of CVBs enormously, and thus has potentials in integrated devices for both quantum and classic optical experiments. △ Less

Submitted 11 January, 2021; originally announced January 2021.

Comments: 9 pages, 4 figures

Journal ref: Photonics Research 9.6 (2021): 1048-1054

Experimental Realization of a Quantum Refrigerator Driven by Indefinite Causal Orders

Authors: Xinfang Nie, Xuanran Zhu, Keyi Huang, Kai Tang, Xinyue Long, Zidong Lin, Yu Tian, Chudan Qiu, Cheng Xi, Xiaodong Yang, Jun Li, Ying Dong, Tao Xin, Dawei Lu

Abstract: Indefinite causal order (ICO) is playing a key role in recent quantum technologies. Here, we experimentally study quantum thermodynamics driven by ICO on nuclear spins using the nuclear magnetic resonance system. We realize the ICO of two thermalizing channels to exhibit how the mechanism works, and show that the working substance can be cooled or heated albeit it undergoes thermal contacts with r… ▽ More Indefinite causal order (ICO) is playing a key role in recent quantum technologies. Here, we experimentally study quantum thermodynamics driven by ICO on nuclear spins using the nuclear magnetic resonance system. We realize the ICO of two thermalizing channels to exhibit how the mechanism works, and show that the working substance can be cooled or heated albeit it undergoes thermal contacts with reservoirs of the same temperature. Moreover, we construct a single cycle of the ICO refrigerator based on the Maxwell's demon mechanism, and evaluate its performance by measuring the work consumption and the heat energy extracted from the low-temperature reservoir. Unlike classical refrigerators in which the coefficient of performance (COP) is perversely higher the closer the temperature of the high-temperature and low-temperature reservoirs are to each other, the ICO refrigerator's COP is always bounded to small values due to the non-unit success probability in projecting the ancillary qubit to the preferable subspace. To enhance the COP, we propose and experimentally demonstrate a general framework based on the density matrix exponentiation (DME) approach, as an extension to the ICO refrigeration. The COP is observed to be enhanced by more than three times with the DME approach. Our work demonstrates a new way for non-classical heat exchange, and paves the way towards construction of quantum refrigerators on a quantum system. △ Less

Submitted 7 September, 2022; v1 submitted 25 November, 2020; originally announced November 2020.

Comments: 5 pages, 4 figures

Reconfigurable photon sources based on quantum plexcitonic systems

Authors: Jia-Bin You, Xiao Xiong, Ping Bai, Zhang-Kai Zhou, Ren-Min Ma, Wan-Li Yang, Yu-Kun Lu, Yun-Feng Xiao, Ching Eng Png, Francisco J. Garcia-Vidal, Cheng-Wei Qiu, Lin Wu

Abstract: A single photon in a strongly nonlinear cavity is able to block the transmission of the second photon, thereby converting incident coherent light into anti-bunched light, which is known as photon blockade effect. On the other hand, photon anti-pairing, where only the entry of two photons is blocked and the emission of bunches of three or more photons is allowed, is based on an unconventional photo… ▽ More A single photon in a strongly nonlinear cavity is able to block the transmission of the second photon, thereby converting incident coherent light into anti-bunched light, which is known as photon blockade effect. On the other hand, photon anti-pairing, where only the entry of two photons is blocked and the emission of bunches of three or more photons is allowed, is based on an unconventional photon blockade mechanism due to destructive interference of two distinct excitation pathways. We propose quantum plexcitonic systems with moderate nonlinearity to generate both anti-bunched and anti-paired photons. The proposed plexitonic systems benefit from subwavelength field localizations that make quantum emitters spatially distinguishable, thus enabling a reconfigurable photon source between anti-bunched and anti-paired states via tailoring the energy bands. For a realistic nanoprism plexitonic system, two schemes of reconfiguration are suggested: (i) the chemical means by partially changing the type of the emitters; or (ii) the optical approach by rotating the polarization angle of the incident light to tune the coupling rate of the emitters. These results pave the way to realize reconfigurable nonclassical photon sources in a simple quantum plexcitonic platform with readily accessible experimental conditions. △ Less

Submitted 4 May, 2020; originally announced May 2020.

Dynamical-Invariant-based Holonomic Quantum Gates: Theory and Experiment

Authors: Yingcheng Li, Tao Xin, Chudan Qiu, Keren Li, Gangqin Liu, Jun Li, Yidun Wan, Dawei Lu

Abstract: Among existing approaches to holonomic quantum computing, the adiabatic holonomic quantum gates (HQGs) suffer errors due to decoherence, while the non-adiabatic HQGs either require additional Hilbert spaces or are difficult to scale. Here, we report a systematic, scalable approach based on dynamical invariants to realize HQGs without using additional Hilbert spaces. While presenting the theoretica… ▽ More Among existing approaches to holonomic quantum computing, the adiabatic holonomic quantum gates (HQGs) suffer errors due to decoherence, while the non-adiabatic HQGs either require additional Hilbert spaces or are difficult to scale. Here, we report a systematic, scalable approach based on dynamical invariants to realize HQGs without using additional Hilbert spaces. While presenting the theoretical framework of our approach, we design and experimentally evaluate single-qubit and two-qubits HQGs for the nuclear magnetic resonance system. The single-qubit gates acquire average fidelity 0.9972 by randomized benchmarking, and the controlled-NOT gate acquires fidelity 0.9782 by quantum process tomography. Our approach is also platform-independent, and thus may open a way to large-scale holonomic quantum computation. △ Less

Submitted 14 April, 2020; v1 submitted 22 March, 2020; originally announced March 2020.

Comments: 9 pages, 3 figures

Breaking Anti-$\mathcal{PT}$ Symmetry by Spinning a Resonator

Authors: Huilai Zhang, Ran Huang, Sheng-Dian Zhang, Ying Li, Cheng-Wei Qiu, Franco Nori, Hui Jing

Abstract: Non-Hermitian systems, with symmetric or antisymmetric Hamiltonians under the parity-time ($\mathcal{PT}$) operations, can have entirely real eigenvalues. This fact has led to surprising discoveries such as loss-induced lasing and topological energy transfer. A merit of anti-$\mathcal{PT}$ systems is free of gain, but in recent efforts on making anti-$\mathcal{PT}$ devices, nonlinearity is still r… ▽ More Non-Hermitian systems, with symmetric or antisymmetric Hamiltonians under the parity-time ($\mathcal{PT}$) operations, can have entirely real eigenvalues. This fact has led to surprising discoveries such as loss-induced lasing and topological energy transfer. A merit of anti-$\mathcal{PT}$ systems is free of gain, but in recent efforts on making anti-$\mathcal{PT}$ devices, nonlinearity is still required. Here, counterintuitively, we show how to achieve anti-$\mathcal{PT}$ symmetry and its spontaneous breaking in a linear device by spinning a lossy resonator. Compared with a Hermitian spinning device, significantly enhanced optical isolation and ultrasensitive nanoparticle sensing are achievable in the anti-$\mathcal{PT}$-broken phase. In a broader view, our work provides a new tool to study anti-$\mathcal{PT}$ physics, with such a wide range of applications as anti-$\mathcal{PT}$ lasers, anti-$\mathcal{PT}$ gyroscopes, and anti-$\mathcal{PT}$ topological photonics or optomechanics. △ Less

Submitted 13 September, 2020; v1 submitted 9 March, 2020; originally announced March 2020.

Comments: 10+14 pages, 3+6 figures, 2 tables, to be published in Nano Letters

Experimental Observation of Equilibrium and Dynamical Quantum Phase Transitions via Out-of-Time-Ordered Correlators

Authors: Xinfang Nie, Bo-Bo Wei, Xi Chen, Ze Zhang, Xiuzhu Zhao, Chudan Qiu, Yu Tian, Yunlan Ji, Tao Xin, Dawei Lu, Jun Li

Abstract: The out-of-time-ordered correlators (OTOC) have been established as a fundamental concept for quantifying quantum information scrambling and diagnosing quantum chaotic behavior. Recently, it was theoretically proposed that the OTOC can be used as an order parameter to dynamically detect both equilibrium quantum phase transitions (EQPTs) and dynamical quantum phase transitions (DQPTs) in one-dimens… ▽ More The out-of-time-ordered correlators (OTOC) have been established as a fundamental concept for quantifying quantum information scrambling and diagnosing quantum chaotic behavior. Recently, it was theoretically proposed that the OTOC can be used as an order parameter to dynamically detect both equilibrium quantum phase transitions (EQPTs) and dynamical quantum phase transitions (DQPTs) in one-dimensional many-body systems. Here we report the first experimental observation of EQPTs and DQPTs in a quantum spin chain via quench dynamics of OTOC on a nuclear magnetic resonance quantum simulator. We observe that the quench dynamics of both the order parameter and the two-body correlation function cannot detect the DQPTs, but the OTOC can unambiguously detect the DQPTs. Moreover, we demonstrate that the long-time average value of the OTOC in quantum quench signals the equilibrium quantum critical point and ordered quantum phases, thus one can measure the EQPTs from the non-equilibrium quantum quench dynamics. Our experiment paves a way for experimentally investigating DQPTs through OTOCs and for studying the EQPTs through the non-equilibrium quantum quench dynamics with quantum simulators. △ Less

Submitted 27 December, 2019; originally announced December 2019.

Comments: 5 pages and 3 figures. Supplementary Materials contain 4 pages and 5 figures

Journal ref: Phys. Rev. Lett. 124, 250601 (2020)

Synchronization and temporal nonreciprocity of optical microresonators via spontaneous symmetry breaking

Authors: Da Xu, Zi-Zhao Han, Yu-Kun Lu, Qihuang Gong, Cheng-Wei Qiu, Gang Chen, Yun-Feng Xiao

Abstract: Synchronization is of importance in both fundamental and applied physics, but their demonstration at the micro/nanoscale is mainly limited to low-frequency oscillations like mechanical resonators. Here, we report the synchronization of two coupled optical microresonators, in which the high-frequency resonances in optical domain are aligned with reduced noise. It is found that two types of synchron… ▽ More Synchronization is of importance in both fundamental and applied physics, but their demonstration at the micro/nanoscale is mainly limited to low-frequency oscillations like mechanical resonators. Here, we report the synchronization of two coupled optical microresonators, in which the high-frequency resonances in optical domain are aligned with reduced noise. It is found that two types of synchronization emerge with either the first- or second-order transition, both presenting a process of spontaneous symmetry breaking. In the second-order regime, the synchronization happens with an invariant topological character number and a larger detuning than that of the first-order case. Furthermore, an unconventional hysteresis behavior is revealed for a time-dependent coupling strength, breaking the static limitation and the temporal reciprocity. The synchronization of optical microresonators offers great potential in reconfigurable simulations of many-body physics and scalable photonic devices on a chip. △ Less

Submitted 7 July, 2019; originally announced July 2019.

High Efficiency Raman Memory by Suppressing Radiation Trapping

Authors: S. E. Thomas, J. H. D. Munns, K. T. Kaczmarek, C. Qiu, B. Brecht, A. Feizpour, P. M. Ledingham, I. A. Walmsley, J. Nunn, D. J. Saunders

Abstract: Raman interactions in alkali vapours are used in applications such as atomic clocks, optical signal processing, generation of squeezed light and Raman quantum memories for temporal multiplexing. To achieve a strong interaction the alkali ensemble needs both a large optical depth and a high level of spin-polarisation. We implement a technique known as quenching using a molecular buffer gas which al… ▽ More Raman interactions in alkali vapours are used in applications such as atomic clocks, optical signal processing, generation of squeezed light and Raman quantum memories for temporal multiplexing. To achieve a strong interaction the alkali ensemble needs both a large optical depth and a high level of spin-polarisation. We implement a technique known as quenching using a molecular buffer gas which allows near-perfect spin-polarisation of over $99.5\%$ in caesium vapour at high optical depths of up to $\sim 2 \times 10^5$; a factor of 4 higher than can be achieved without quenching. We use this system to explore efficient light storage with high gain in a GHz bandwidth Raman memory. △ Less

Submitted 1 February, 2017; v1 submitted 12 October, 2016; originally announced October 2016.

Comments: 11 pages, 6 figures

Atom-light superposition oscillation and Ramsey-like atom-light interferometer

Authors: Cheng Qiu, Shuying Chen, L. Q. Chen, Bing Chen, Jinxian Guo, Z. Y. Ou, Weiping Zhang

Abstract: Coherent wave splitting is crucial in interferometers. Normally, the waves after this splitting are of the same type. But recent progress in interaction between atom and light has led to the coherent conversion of photon to atomic excitation. This makes it possible to split an incoming light wave into a coherent superposition state of atom and light and paves the way for an interferometer made of… ▽ More Coherent wave splitting is crucial in interferometers. Normally, the waves after this splitting are of the same type. But recent progress in interaction between atom and light has led to the coherent conversion of photon to atomic excitation. This makes it possible to split an incoming light wave into a coherent superposition state of atom and light and paves the way for an interferometer made of different types of waves. Here we report on a Rabi-like coherent-superposition oscillation observed between atom and light and a coherent mixing of light wave with excited atomic spin wave in a Raman process. We construct a new kind of hybrid interferometer based on the atom-light coherent superposition state. Interference fringes are observed in both optical output intensity and atomic output in terms of the atomic spin wave strength when we scan either or both of the optical and atomic phases. Such a hybrid interferometer can be used to interrogate atomic states by optical detection and will find its applications in precision measurement and quantum control of atoms and light. △ Less

Submitted 18 February, 2016; originally announced February 2016.

Journal ref: Optica 3, 775-780 (2016)

Theory of noise suppression in Λ-type quantum memories by means of a cavity

Authors: J. Nunn, S. Thomas, J. H. D. Munns, K. T. Kaczmarek, C. Qiu, A. Feizpour, E. Poem, B. Brecht, D. J. Saunders, P. M. Ledingham, Dileep V. Reddy, M. G. Raymer, I. A. Walmsley

Abstract: Quantum memories, capable of storing single photons or other quantum states of light, to be retrieved on-demand, offer a route to large-scale quantum information processing with light. A promising class of memories is based on far-off-resonant Raman absorption in ensembles of $Λ$-type atoms. However at room temperature these systems exhibit unwanted four-wave mixing, which is prohibitive for appli… ▽ More Quantum memories, capable of storing single photons or other quantum states of light, to be retrieved on-demand, offer a route to large-scale quantum information processing with light. A promising class of memories is based on far-off-resonant Raman absorption in ensembles of $Λ$-type atoms. However at room temperature these systems exhibit unwanted four-wave mixing, which is prohibitive for applications at the single-photon level. Here we show how this noise can be suppressed by placing the storage medium inside a moderate-finesse optical cavity, thereby removing the main roadblock hindering this approach to quantum memory. △ Less

Submitted 2 January, 2016; originally announced January 2016.

Comments: 10 pages, 3 figures. This paper provides the theoretical background to our recent experimental demonstration of noise suppression in a cavity-enhanced Raman-type memory ( arXiv:1510.04625 ). See also the related paper arXiv:1511.05448, which describes numerical modelling of an atom-filled cavity. Comments welcome

Journal ref: Phys. Rev. A 96, 012338 (2017)

A Cavity-Enhanced Room-Temperature Broadband Raman Memory

Authors: D. J. Saunders, J. H. D. Munns, T. F. M. Champion, C. Qiu, K. T. Kaczmarek, E. Poem, P. M. Ledingham, I. A. Walmsley, J. Nunn

Abstract: Broadband quantum memories hold great promise as multiplexing elements in future photonic quantum information protocols. Alkali vapour Raman memories combine high-bandwidth storage, on-demand read-out, and operation at room temperature without collisional fluorescence noise. However, previous implementations have required large control pulse energies and suffered from four-wave mixing noise. Here… ▽ More Broadband quantum memories hold great promise as multiplexing elements in future photonic quantum information protocols. Alkali vapour Raman memories combine high-bandwidth storage, on-demand read-out, and operation at room temperature without collisional fluorescence noise. However, previous implementations have required large control pulse energies and suffered from four-wave mixing noise. Here we present a Raman memory where the storage interaction is enhanced by a low-finesse birefringent cavity tuned into simultaneous resonance with the signal and control fields, dramatically reducing the energy required to drive the memory. By engineering anti-resonance for the anti-Stokes field, we also suppress the four-wave mixing noise and report the lowest unconditional noise floor yet achieved in a Raman-type warm vapour memory, $(15\pm2)\times10^{-3}$ photons per pulse, with a total efficiency of $(9.5\pm0.5)$%. △ Less

Submitted 15 October, 2015; originally announced October 2015.

Journal ref: Phys. Rev. Lett. 116, 090501 (2016)

Efficient Raman Frequency Conversion by Feedbacks of Pump and Stokes Fields

Authors: Bing Chen, Kai Zhang, Chun-Hua Yuan, Chengling Bian, Cheng Qiu, L. Q. Chen, Z. Y. Ou, Weiping Zhang

Abstract: We experimentally demonstrate efficient Raman conversion to respective Stokes and anti-Stokes fields in both pulsed and continuous modes with a Rb-87 atomic vapor cell. The conversion efficiency is about 40-50% for the Stokes field and 20-30% for the anti-Stokes field, respectively. This conversion process is realized with feedback of both the Raman pump and the frequency-converted fields (Stokes… ▽ More We experimentally demonstrate efficient Raman conversion to respective Stokes and anti-Stokes fields in both pulsed and continuous modes with a Rb-87 atomic vapor cell. The conversion efficiency is about 40-50% for the Stokes field and 20-30% for the anti-Stokes field, respectively. This conversion process is realized with feedback of both the Raman pump and the frequency-converted fields (Stokes or anti-Stokes). The experimental setup is very simple and can be applied easily to produce the light source with larger frequency difference using other Raman media. They may have wide applications in nonlinear optics, atomic physics, quantum optics and precise measurement. △ Less

Submitted 18 October, 2012; originally announced October 2012.

Comments: 4 pages, 5 figure