Showing 1–50 of 76 results for author: He, G

Anomalous nonlocality of information masked in quantum correlations

Authors: Guang Ping He

Abstract: Although information, strictly speaking, is not a physical entity, it generally requires physical entities as its carriers, e.g., writing it down on paper, encoding it with quantum particles, or transmitting it using electro-magnetic fields. And it seems natural that these carriers cannot travel faster than light. Here we reveal that if we use quantum correlations as the carrier of information (ei… ▽ More Although information, strictly speaking, is not a physical entity, it generally requires physical entities as its carriers, e.g., writing it down on paper, encoding it with quantum particles, or transmitting it using electro-magnetic fields. And it seems natural that these carriers cannot travel faster than light. Here we reveal that if we use quantum correlations as the carrier of information (either quantum or classical), then it can display a kind of nonlocality, which bears both similarities to and distinctions from the nonlocality of physical particles. Notably, though superluminal signaling is still not allowed so that the special relativity is not violated, it is possible to select at our will whether to decode the information at one location, or to dispatch it to another location far away (i.e., to give up the chance of decoding the information and let it be decodable in somewhere else only) without needing the assistance of classical information, so that it occurs instantaneously without being limited by the speed of light. This phenomenon differs sharply from the nonlocality of physical particles that we once knew, where whether a particle can be detected in one location or another is governed by quantum uncertainty, which cannot be chosen freely. △ Less

Submitted 18 April, 2026; originally announced April 2026.

Comments: 4 pages, 1 figure

Efficient Quantum Algorithm for Robust Training

Authors: Yue Wang, Guangyi He, Liepeng Zhang, Lukas Gonon, Qi Zhao

Abstract: Adversarial training is a standard defense against malicious input perturbations in security-critical machine-learning systems. Its main burden is structural: before every parameter update, the current model must first be attacked to find a new adversarial perturbation, making training increasingly expensive and hard to sustain at large-model scale. Here we give an end-to-end quantum procedure for… ▽ More Adversarial training is a standard defense against malicious input perturbations in security-critical machine-learning systems. Its main burden is structural: before every parameter update, the current model must first be attacked to find a new adversarial perturbation, making training increasingly expensive and hard to sustain at large-model scale. Here we give an end-to-end quantum procedure for projected-gradient robust training under local stability and sparsity assumptions. The key step is to reformulate the coupled attacker--learner dynamics as a high-dimensional sparse linear system whose terminal block yields the final network-parameter state. In this formulation, the dominant query cost scales linearly with training time steps, up to logarithmic factors, and polylogarithmically with model size, while the full gate complexity records separate input-preparation and sparse-access overheads. This places core computational tasks for AI security on a concrete quantum footing and identifies a regime in which robust-training overhead can be reduced. △ Less

Submitted 30 March, 2026; originally announced March 2026.

Comments: 33 pages, 3 figures, comments are welcome

Spin Relaxometry with Solid-State Defects: Theory, Platforms, and Applications

Authors: Ruotian Gong, Alex L. Melendez, Guanghui He, Zhongyuan Liu, Chong Zu, Huan Zhao

Abstract: Spin relaxometry using solid-state spin defects, such as the diamond nitrogen-vacancy (NV) center, probes dynamical processes by measuring how environmental fluctuations enhance the spin relaxation rate. In the weak-coupling limit, relaxation rates sample the transverse magnetic-noise power spectral density through a sensor-specific filter function, turning the defect into a local, frequency-selec… ▽ More Spin relaxometry using solid-state spin defects, such as the diamond nitrogen-vacancy (NV) center, probes dynamical processes by measuring how environmental fluctuations enhance the spin relaxation rate. In the weak-coupling limit, relaxation rates sample the transverse magnetic-noise power spectral density through a sensor-specific filter function, turning the defect into a local, frequency-selective noise spectrometer. This review bridges theory and experiment, clarifying how measured relaxation rates map onto noise spectra and how near-field geometry shapes the response. We highlight representative applications across condensed-matter physics, chemical and biological sensing, and relaxometry-based magnetic-resonance spectroscopy. We conclude with emerging opportunities and key challenges. △ Less

Submitted 10 July, 2026; v1 submitted 1 February, 2026; originally announced February 2026.

Comments: 27 pages, 6 figures

Toward end-to-end quantum simulation of rapidly distorted turbulence

Authors: Zhaoyuan Meng, Leyu Chen, Jin-Peng Liu, Guowei He

Abstract: We propose an end-to-end quantum algorithm to simulate rapidly distorted turbulence via linear combination of Hamiltonian (LCHS). The algorithm comprises three primary stages: the efficient preparation of an initial turbulent state with a prescribed energy spectrum, its subsequent time evolution via LCHS, and the direct measurement of key turbulence statistics. Our analysis indicates that the algo… ▽ More We propose an end-to-end quantum algorithm to simulate rapidly distorted turbulence via linear combination of Hamiltonian (LCHS). The algorithm comprises three primary stages: the efficient preparation of an initial turbulent state with a prescribed energy spectrum, its subsequent time evolution via LCHS, and the direct measurement of key turbulence statistics. Our analysis indicates that the algorithm can offer a practical quantum speedup over the classical simulation methods for a sufficiently large computational grid. We evaluate the quantum resource requirements for simulating a minimal instance of non-trivial turbulence with classical validation. The numerical results show excellent agreement with ground-truth solutions, capturing both the qualitative evolution of turbulent fields and the quantitative behavior of statistics, including the Reynolds stresses and the fluctuating velocity spectrum. Despite its linearity, rapidly distorted turbulence captures essential turbulence mechanisms and may inform the development of quantum algorithms for the Navier-Stokes equations. Our work establishes a foundation for addressing more complex turbulent phenomena on future fault-tolerant quantum computers. △ Less

Submitted 24 November, 2025; originally announced November 2025.

Modulation Instability-Induced Multimode Squeezing in Quadratic Frequency Combs

Authors: Haodong Xu, Nianqin Li, Zijun Shu, Yang Shen, Bo Ji, Aiping Xie, Feng Yang, Dengcai Yang, Jing Peng, Hang Gong, Guoxiang Huang, Chunbo Zhao, Wei Li, Tengfei Wu, Guangqiang He

Abstract: Lithium niobate (LN) microring resonators, characterized by an exceptionally high second-order nonlinear coefficient and superior electro-optic tunability, serve as an outstanding platform for the precise control of integrated quantum frequency combs (QFCs). In this study, we introduce a bipartite entanglement criterion to investigate the pairwise entanglement characteristics of QFCs generated via… ▽ More Lithium niobate (LN) microring resonators, characterized by an exceptionally high second-order nonlinear coefficient and superior electro-optic tunability, serve as an outstanding platform for the precise control of integrated quantum frequency combs (QFCs). In this study, we introduce a bipartite entanglement criterion to investigate the pairwise entanglement characteristics of QFCs generated via the spontaneous parametric down-conversion (SPDC) process in lithium niobate microring resonators operating below threshold. Furthermore, we propose a universal framework for analyzing multimode squeezing in quadratic frequency combs, enabling the realization of ultrabroadband and high-degree multimode squeezing. We further reveal the underlying physical mechanism: modulation instability (MI), regulated by temporal walk-off control, not only enables the formation of frequency combs but also induces multimode squeezing in the corresponding resonant modes. This study uncovers the previously unexplored role of on-chip multimode squeezing in quadratic frequency combs while facilitating collective noise suppression across multiple modes, thus holding substantial potential for advancing quantum precision measurement and quantum information processing. △ Less

Submitted 28 August, 2025; originally announced August 2025.

Jenga-Krotov algorithm: Efficient compilation of multi-qubit gates for exchange-only qubits

Authors: Jiahao Wu, Guanjie He, Wenyuan Zhuo, Quan Fu, Xin Wang

Abstract: Exchange-only (EO) qubits, implemented in triple-quantum-dot systems, offer a compelling platform for scalable semiconductor-based quantum computing by enabling universal control through purely exchange interactions. While high-fidelity single- and two-qubit gates have been demonstrated, the synthesis of efficient multi-qubit operations-such as the Toffoli gate-remains a key bottleneck. Convention… ▽ More Exchange-only (EO) qubits, implemented in triple-quantum-dot systems, offer a compelling platform for scalable semiconductor-based quantum computing by enabling universal control through purely exchange interactions. While high-fidelity single- and two-qubit gates have been demonstrated, the synthesis of efficient multi-qubit operations-such as the Toffoli gate-remains a key bottleneck. Conventional gate decompositions into elementary operations lead to prohibitively long and error-prone pulse sequences, limiting practical deployment. In this work, we introduce a gradient-based optimization algorithm, Jenga-Krotov (JK), tailored to discover compact, high-fidelity EO gate sequences. Applying JK to the Toffoli gate, we reduce the number of required exchange unitaries from 216 (in direct decomposition) to 92, and compress the time steps required from 162 to 50, all while maintaining target fidelity. Under realistic noise, the accumulated gate error from our optimized sequence is an order of magnitude lower than that of conventional approaches. We have also applied the JK algorithm to other multi-qubit gates and algorithm. For the Fredkin gate, it reduces the number of time steps from 200 to 104 and the number of exchange unitaries from 276 to 172. For the quantum Fourier transform, it compresses the sequence from 180 to 80 time steps and from 237 to 202 exchange unitaries. These results demonstrate that the JK algorithm is a general and scalable strategy for multi-qubit gate synthesis in EO architectures, potentially facilitating realization of multi-qubit algorithms on semiconductor platforms. △ Less

Submitted 15 October, 2025; v1 submitted 16 July, 2025; originally announced July 2025.

Comments: 16+12 pages, 11+2 figures

Journal ref: Phys. Rev. Research 7, 043161 (2025)

Realizing Bloch Dynamics in a Low-Cost Electrically Driven Acoustic Two-Level System

Authors: Xiao-Meng Zhang, Guang-Chen He, Zhao-Xian Chen, Ze-Guo Chen, Ming-Hui Lu, Yan-Feng Chen

Abstract: Unlike classical bits that can only occupy one of two discrete states, quantum bits (qubits) can exist in arbitrary coherent superpositions of the ground and excited states. This fundamental distinction grants qubits enhanced capabilities for information storage and processing. The Bloch sphere provides an intuitive and powerful geometric framework for visualizing, characterizing, and controlling… ▽ More Unlike classical bits that can only occupy one of two discrete states, quantum bits (qubits) can exist in arbitrary coherent superpositions of the ground and excited states. This fundamental distinction grants qubits enhanced capabilities for information storage and processing. The Bloch sphere provides an intuitive and powerful geometric framework for visualizing, characterizing, and controlling the dynamical evolution of a qubit under external driving fields. By mapping the state evolution onto the Bloch sphere, processes such as spin flips and phase accumulation can be vividly represented as trajectories, enabling direct insight into coherent control mechanisms. Here, we implement Bloch dynamics in a classical platform by constructing a tunable acoustic two-level system based on high-quality-factor electro-acoustic coupled cavities. Using programmable spatiotemporal external field modulation, we demonstrate full Bloch sphere control through classical analogs of quantum phenomena, including Rabi oscillations, Floquet dynamics, Ramsey interference, and spin echo sequences. Our results bridge coherent Bloch dynamics with classical wave control, revealing a versatile experimental platform for exploring quantum-inspired physics. Furthermore, the system exhibits exceptional capabilities for precision transient acoustic field shaping, enabled by high-fidelity pulse-driven modulation. △ Less

Submitted 27 May, 2025; originally announced May 2025.

Comments: 18 pages, 4 figures

Direct Measurement of Zak Phase and Higher Winding Numbers in an Electroacoustic Cavity System

Authors: Guang-Chen He, Zhao-Xian Chen, Xiao-Meng Zhang, Ze-Guo Chen, Ming-Hui Lu

Abstract: Topological phases are states of matter defined by global topological invariants that remain invariant under adiabatic parameter variations, provided no topological phase transition occurs. This endows them with intrinsic robustness against local perturbations. Experimentally, these phases are often identified indirectly by observing robust boundary states, protected by the bulk-boundary correspon… ▽ More Topological phases are states of matter defined by global topological invariants that remain invariant under adiabatic parameter variations, provided no topological phase transition occurs. This endows them with intrinsic robustness against local perturbations. Experimentally, these phases are often identified indirectly by observing robust boundary states, protected by the bulk-boundary correspondence. Here, we propose an experimental method for the direct measurement of topological invariants via adiabatic state evolution in electroacoustic coupled resonators, where time-dependent cavity modes effectively emulate the bulk wavefunction of a periodic system. Under varying external driving fields, specially prepared initial states evolve along distinct parameter-space paths. By tracking the relative phase differences among states along these trajectories, we successfully observe the quantized Zak phase in both the conventional Su-Schrieffer-Heeger (SSH) model and its extension incorporating with next-nearest-neighbor coupling. This approach provides compelling experimental evidence for the precise identification of topological invariants and can be extended to more complex topological systems. △ Less

Submitted 27 May, 2025; originally announced May 2025.

Comments: 21 pages,4 figures

Solving the encoding bottleneck: of the HHL algorithm, by the HHL algorithm

Authors: Guang Ping He

Abstract: The Harrow-Hassidim-Lloyd (HHL) algorithm offers exponential speedup for solving the quantum linear-system problem. But some caveats for the speedup could be hard to met. One of the difficulties is the encoding bottleneck, i.e., the efficient preparation of the initial quantum state. To prepare an arbitrary $N$-dimensional state exactly, existing state-preparation approaches generally require a ru… ▽ More The Harrow-Hassidim-Lloyd (HHL) algorithm offers exponential speedup for solving the quantum linear-system problem. But some caveats for the speedup could be hard to met. One of the difficulties is the encoding bottleneck, i.e., the efficient preparation of the initial quantum state. To prepare an arbitrary $N$-dimensional state exactly, existing state-preparation approaches generally require a runtime of $O(N)$, which will ruin the speedup of the HHL algorithm. Here we show that the states can be prepared approximately with a runtime of $O(poly(\log N))$ by employing a slightly modified version of the HHL algorithm itself. Thus, applying this approach to prepare the initial state of the original HHL algorithm can preserve the exponential speedup advantage. It can also serve as a standalone solution for other applications demanding fast state preparation. △ Less

Submitted 9 March, 2025; v1 submitted 19 February, 2025; originally announced February 2025.

Comments: Added a diagram of the quantum circuit of our algorithm

Quantum noise spectroscopy of superconducting dynamics in thin film Bi$_2$Sr$_2$CaCu$_2$O$_{8+δ}$

Authors: Zhongyuan Liu, Ruotian Gong, Jaewon Kim, Oriana K. Diessel, Qiaozhi Xu, Zackary Rehfuss, Xinyi Du, Guanghui He, Abhishek Singh, Yun Suk Eo, Erik A. Henriksen, G. D. Gu, Norman Y. Yao, Francisco Machado, Sheng Ran, Shubhayu Chatterjee, Chong Zu

Abstract: Characterizing the low-energy dynamics of quantum materials is crucial to our understanding of strongly correlated electronic states. Yet, it remains experimentally challenging to investigate such dynamics with high spectroscopic resolution in both frequency and momentum space, particularly in two-dimensional correlated systems. Here, we leverage Nitrogen-Vacancy (NV) centers in diamond as a power… ▽ More Characterizing the low-energy dynamics of quantum materials is crucial to our understanding of strongly correlated electronic states. Yet, it remains experimentally challenging to investigate such dynamics with high spectroscopic resolution in both frequency and momentum space, particularly in two-dimensional correlated systems. Here, we leverage Nitrogen-Vacancy (NV) centers in diamond as a powerful and non-invasive tool to study thin-film Bi$_2$Sr$_2$CaCu$_2$O$_{8+δ}$ (BSCCO), revealing several distinct dynamical phenomena across the superconducting phase diagram. At zero magnetic field and low temperatures, NV depolarization ($T_1$) noise spectroscopy captures the low-frequency (GHz-scale) magnetic noise generated by nodal superconducting quasiparticle excitations, in agreement with Bardeen-Cooper-Schrieffer (BCS) mean-field theory. Near the critical temperature $T_c \approx 90$ K, supercurrent-fluctuation-induced noise leads to a sharp reduction of the NV $T_1$. By carefully analyzing the temperature-scaling of $T_1$, we observe clear deviations from the BCS prediction, reflecting the importance of order parameter fluctuations and enabling the determination of both static and dynamical critical exponents. When a small field is applied, we detect a broad and asymmetric reduction of NV $T_1$ near $T_c$; the field-induced smearing of the transition unveils the presence of a vortex liquid phase. Finally, NV decoherence ($T_2$) noise spectroscopy allows us to characterize magnetic noise at even lower MHz-scale frequencies and obtain evidence for complex vortex-solid fluctuations well below $T_c$. Our results establish quantum noise spectroscopy as a versatile platform for probing dynamical phenomena in superconductors, with frequency and length scales complementary to existing techniques. △ Less

Submitted 27 February, 2025; v1 submitted 6 February, 2025; originally announced February 2025.

Comments: [Version 2] revised with Methods and Supplementary Information. 9 pages, 4 figures in main. 4 pages, 2 figures in methods. 7 pages, 5 figures in supplementary information. [Original Version] 9 pages, 4 figures in main text

Probing Stress and Magnetism at High Pressures with Two-Dimensional Quantum Sensors

Authors: Guanghui He, Ruotian Gong, Zhipan Wang, Zhongyuan Liu, Jeonghoon Hong, Tongxie Zhang, Ariana L. Riofrio, Zachary Rehfuss, Mingfeng Chen, Changyu Yao, Thomas Poirier, Bingtian Ye, Xi Wang, Sheng Ran, James H. Edgar, Shixiong Zhang, Norman Y. Yao, Chong Zu

Abstract: Pressure serves as a fundamental tuning parameter capable of drastically modifying all properties of matter. The advent of diamond anvil cells (DACs) has enabled a compact and tabletop platform for generating extreme pressure conditions in laboratory settings. However, the limited spatial dimensions and ultrahigh pressures within these environments present significant challenges for conventional s… ▽ More Pressure serves as a fundamental tuning parameter capable of drastically modifying all properties of matter. The advent of diamond anvil cells (DACs) has enabled a compact and tabletop platform for generating extreme pressure conditions in laboratory settings. However, the limited spatial dimensions and ultrahigh pressures within these environments present significant challenges for conventional spectroscopy techniques. In this work, we integrate optical spin defects within a thin layer of two-dimensional (2D) materials directly into the high-pressure chamber, enabling an in situ quantum sensing platform for mapping local stress and magnetic environments up to 4~GPa. Compared to nitrogen-vacancy (NV) centers embedded in diamond anvils, our 2D sensors exhibit around three times stronger response to local stress and provide nanoscale proximity to the target sample in heterogeneous devices. We showcase the versatility of our approach by imaging both stress gradients within the high-pressure chamber and a pressure-driven magnetic phase transition in a room-temperature self-intercalated van der Waals ferromagnet, Cr$_{1+δ}$Te$_2$. Our work demonstrates an integrated quantum sensing device for high-pressure experiments, offering potential applications in probing pressure-induced phenomena such as superconductivity, magnetism, and mechanical deformation. △ Less

Submitted 6 January, 2025; originally announced January 2025.

Comments: 9 pages, 7 figures

Journal ref: Nat Commun 16, 8162 (2025)

Phonon Dephasing, Entanglement and Exchange-Only Toffoli Gate Sequence in Quantum Dot Spin Chains

Authors: Guanjie He

Abstract: The quantum dot spin chain system is vital for quantum simulation and studying collective electron behaviors, necessitating an understanding of its mechanisms and control protocols. Chapter 1 introduces key concepts, focusing on the extended Hubbard model, double quantum dot systems, and electron-phonon coupling. Chapter 2 explores electron-phonon coupling in multielectron double quantum dots unde… ▽ More The quantum dot spin chain system is vital for quantum simulation and studying collective electron behaviors, necessitating an understanding of its mechanisms and control protocols. Chapter 1 introduces key concepts, focusing on the extended Hubbard model, double quantum dot systems, and electron-phonon coupling. Chapter 2 explores electron-phonon coupling in multielectron double quantum dots under unbiased and biased scenarios via detuning variations. In the unbiased case, dephasing due to electron-phonon coupling generally increases with more electrons in the right dot; this trend is inconsistent in the biased case, suggesting potential advantages of multielectron quantum dots under certain conditions. Chapter 3 investigates entanglement entropy in a multielectron quantum dot spin chain described by the extended Hubbard model. Local and pairwise entanglement are influenced by Coulomb interactions, tunneling strengths, electronic configurations, and site potential energies. The entanglement diagram reveals phase transitions significantly impacted by coupling strength ratios and potential energy variations; adjusting the potential energy of a specific dot critically influences ground state configurations and entanglement entropy. Chapter 4, inspired by the decoherence-free subspace concept, explores operation sequences in a nine-spin, nine-quantum-dot system defined by the Heisenberg model, with bases determined by total angular momentum quantum numbers. Employing the Krotov method of quantum optimal control, we identify a more efficient pulse-level operation sequence for an exchange-only quantum dot spin chain, offering a superior alternative to conventional quantum gate decomposition and potentially enhancing the development of more concise quantum algorithm representations. △ Less

Submitted 20 October, 2024; v1 submitted 23 September, 2024; originally announced September 2024.

Comments: PhD Thesis. 161 pages, 31 figures, 13 tables. Please feel free to contact me if you're interested in further discussion or collaboration. Let's work together to advance our field! email: guanjiehe2-c@my.cityu.edu.hk

Frequency-dependent squeezing via Einstein-Podolsky-Rosen entanglement based on silicon nitride microring resonators

Authors: Haodong Xu, Zijun Shu, Nianqin Li, Yang Shen, Bo Ji, Yongjun Yang, Tengfei Wu, Mingliang Long, Guangqiang He

Abstract: Significant efforts have been made to enhance the performance of displacement sensors limited by quantum noise, such as gravitational wave detectors. Techniques like frequency-dependent squeezing have overcome the standard quantum limit in optomechanical force measurements, leading to substantial overall progress. These advancements, coupled with major developments in integrated photonics, have pa… ▽ More Significant efforts have been made to enhance the performance of displacement sensors limited by quantum noise, such as gravitational wave detectors. Techniques like frequency-dependent squeezing have overcome the standard quantum limit in optomechanical force measurements, leading to substantial overall progress. These advancements, coupled with major developments in integrated photonics, have paved the way for the emergence of integrated Kerr quantum frequency combs (QFCs). A platform has been established for designing EPR entangled quantum frequency combs using on-chip silicon nitride microring resonators, enabling thorough analysis and optimization of entanglement performance, as well as effective noise reduction adjustments. This platform, incorporating the quantum dynamics of Kerr nonlinear microresonators, supports at least 12 continuous-variable quantum modes in the form of 6 simultaneous two-mode squeezed pairs (EPR entangled pairs). Additionally, by selecting the detection angle of the idler mode, a single-mode squeezed state is generated in the signal mode. Given the frequency-dependent nature of the detection angle, frequency-dependent squeezing is achieved. A comparative analysis of the results under different dispersion conditions is also conducted. △ Less

Submitted 22 October, 2024; v1 submitted 14 September, 2024; originally announced September 2024.

Training quantum machine learning models on cloud without uploading the data

Authors: Guang Ping He

Abstract: Based on the linearity of quantum unitary operations, we propose a method that runs the parameterized quantum circuits before encoding the input data. This enables a dataset owner to train machine learning models on quantum cloud computation platforms, without the risk of leaking the information about the data. It is also capable of encoding a vast amount of data effectively at a later time using… ▽ More Based on the linearity of quantum unitary operations, we propose a method that runs the parameterized quantum circuits before encoding the input data. This enables a dataset owner to train machine learning models on quantum cloud computation platforms, without the risk of leaking the information about the data. It is also capable of encoding a vast amount of data effectively at a later time using classical computations, thus saving runtime on quantum computation devices. The trained quantum machine learning models can be run completely on classical computers, meaning the dataset owner does not need to have any quantum hardware, nor even quantum simulators. Moreover, our method mitigates the encoding bottleneck by reducing the required circuit depth from $O(2^{n})$ to $O(n)$, and relax the tolerance on the precision of the quantum gates for the encoding. These results demonstrate yet another advantage of quantum and quantum-inspired machine learning models over existing classical neural networks, and broaden the approaches to data security. △ Less

Submitted 7 October, 2024; v1 submitted 6 September, 2024; originally announced September 2024.

Comments: Added experimental results and the flow chart of our method

Simultaneous Generation of Quantum Frequency Combs across Distinct Modal Families in a Single $Si_3 N_4$ Whispering Gallery Mode Resonator

Authors: Bo Ji, Yongjun Yang, Tengfei Wu, Nianqin Li, Guangqiang He

Abstract: Quantum frequency combs (QFCs) are versatile resources for multi-mode entanglement, such as cluster states, crucial for quantum communication and computation. On-chip whispering gallery mode resonators (WGMRs) can generate these states at ultra-low threshold power. This work demonstrates the simultaneous generation of multiple QFCs using a single on-chip silicon nitride WGMR across distinct modal… ▽ More Quantum frequency combs (QFCs) are versatile resources for multi-mode entanglement, such as cluster states, crucial for quantum communication and computation. On-chip whispering gallery mode resonators (WGMRs) can generate these states at ultra-low threshold power. This work demonstrates the simultaneous generation of multiple QFCs using a single on-chip silicon nitride WGMR across distinct modal families. It presents a micro-ring resonator with a radius of 240 $\mathrm{μm}$, capable of supporting four modal families within the 130 to 260 $\mathrm{THz}$ frequency range for consistency regulation. The results indicate that, by carefully designing the structure of silicon nitride WGMRs, it is possible to generate quantum entangled frequency combs across distinct modal families simultaneously using monochromatic pump light. It is achieved by modulating the pump mode profiles with a spatial light modulator (SLM) or an on-chip inverse-designed mode converter. This approach offers a simple and low-cost method to achieve higher-density entanglement integration on-chip. △ Less

Submitted 19 November, 2024; v1 submitted 24 June, 2024; originally announced June 2024.

Comments: 20 pages, 9 figures

Exploring Entanglement Spectrum and Phase Diagram in multi-electron Quantum Dot Chains

Authors: Guanjie He, Xin Wang

Abstract: We investigate the entanglement properties in semiconductor quantum dot systems modeled by extended Hubbard model, focusing on the impact of potential energy variations and electron interactions within a four-site quantum dot spin chain. Our study explores local and pairwise entanglement across configurations with electron counts N=4 and N=6, under different potential energy settings. By adjusting… ▽ More We investigate the entanglement properties in semiconductor quantum dot systems modeled by extended Hubbard model, focusing on the impact of potential energy variations and electron interactions within a four-site quantum dot spin chain. Our study explores local and pairwise entanglement across configurations with electron counts N=4 and N=6, under different potential energy settings. By adjusting the potential energy in specific dots and examining the entanglement across various interaction regimes, we identify significant variations in the ground states of quantum dots. Our results reveal that local potential modifications lead to notable redistributions of electron configurations, significantly affecting the entanglement properties. These changes are depicted in phase diagrams that show entanglement dependencies on interaction strengths and potential energy adjustments, highlighting complex entanglement dynamics and phase transitions triggered by inter-dot interactions. △ Less

Submitted 9 May, 2024; originally announced May 2024.

Comments: 14 pages, 9 figures

Journal ref: Entropy 27, 479 (2025)

Temperature dependent spin-phonon coupling of boron-vacancy centers in hexagonal boron nitride

Authors: Zhongyuan Liu, Ruotian Gong, Benchen Huang, Yu Jin, Xinyi Du, Guanghui He, Eli Janzen, Li Yang, Erik Henriksen, James Edgar, Giulia Galli, Chong Zu

Abstract: The negatively charged boron-vacancy center ($\mathrm{V}_{\mathrm{B}}^-$) in hexagonal boron nitride (hBN) has recently emerged as a highly promising quantum sensor. Compared to the nitrogen-vacancy (NV) center in diamond, the change with temperature of the spin transition energy of $\mathrm{V}_{\mathrm{B}}^-$ is more than an order of magnitude larger, making it a potential nanoscale thermometer w… ▽ More The negatively charged boron-vacancy center ($\mathrm{V}_{\mathrm{B}}^-$) in hexagonal boron nitride (hBN) has recently emerged as a highly promising quantum sensor. Compared to the nitrogen-vacancy (NV) center in diamond, the change with temperature of the spin transition energy of $\mathrm{V}_{\mathrm{B}}^-$ is more than an order of magnitude larger, making it a potential nanoscale thermometer with superior sensitivity. However, the underlying mechanism of the observed large temperature dependence remains an open question. In this work, using isotopically purified $\mathrm{h}{}^{10}\mathrm{B}{}^{15}\mathrm{N}$, we systematically characterize the zero-field splitting, hyperfine interaction, and spin relaxation time of $\mathrm{V}_{\mathrm{B}}^-$ from 10 to 350$~$K. We carry out first-principle calculations of the $\mathrm{V}_{\mathrm{B}}^-$ spin-phonon interaction and show that a second-order effect from finite-temperature phonon excitations is responsible for the observed changes in experiments. By fitting our experimental results to a physically motivated model, we extract the dominant phonon mode which agrees well with our simulations. Finally, we investigate the dynamic nuclear spin polarization process at cryogenic temperatures. Our results provide key insights in $\mathrm{V}_{\mathrm{B}}^-$ centers and their utilization as nanoscale thermometers and phonon sensors. △ Less

Submitted 10 December, 2024; v1 submitted 23 April, 2024; originally announced April 2024.

Comments: [Version 2] 7 pages, 4 figures and 1 table in main. 11 pages and 8 figures in supplemental material. Updated for revision, revised manuscript and figures, added more references and addtional supplementary figures. [Original Version] 7 pages, 4 figures and 1 table in main. 9 pages and 5 figures in supplemental material

Report number: 2469-9950/2025/111(2)/024108(7)

Journal ref: Physical Review B 111, 024108 (2025)

Experimental Realization of Discrete Time Quasi-Crystals

Authors: Guanghui He, Bingtian Ye, Ruotian Gong, Changyu Yao, Zhongyuan Liu, Kater W. Murch, Norman Y. Yao, Chong Zu

Abstract: Floquet (periodically driven) systems can give rise to unique non-equilibrium phases of matter without equilibrium analogs. The most prominent example is the realization of discrete time crystals. An intriguing question emerges: what other novel phases can manifest when the constraint of time periodicity is relaxed? In this study, we explore quantum systems subjected to a quasi-periodic drive. Lev… ▽ More Floquet (periodically driven) systems can give rise to unique non-equilibrium phases of matter without equilibrium analogs. The most prominent example is the realization of discrete time crystals. An intriguing question emerges: what other novel phases can manifest when the constraint of time periodicity is relaxed? In this study, we explore quantum systems subjected to a quasi-periodic drive. Leveraging a strongly interacting spin ensemble in diamond, we identify the emergence of long-lived discrete time quasi-crystals. Unlike conventional time crystals, time quasi-crystals exhibit robust sub-harmonic responses at multiple incommensurate frequencies. Furthermore, we show that the multi-frequency nature of the quasi-periodic drive allows for the formation of diverse patterns associated with different discrete time quasi-crystalline phases. Our findings demonstrate the existence of non-equilibrium phases in quasi-Floquet settings, significantly broadening the catalog of novel phenomena in driven many-body quantum systems. △ Less

Submitted 26 March, 2024; originally announced March 2024.

Comments: 7+5 pages, 4+5 figures

Journal ref: Physical Review X 15, 011055 (2025)

Manipulating multiple optical parametric processes in photonic topological insulators

Authors: Zhen Jiang, Bo Ji, Yanghe Chen, Chun Jiang, Guangqiang He

Abstract: Topological quantum optics, an emerging area of study, holds the potential to bring about substantial enhancements for integrated quantum devices. Here we propose integrated topological quantum devices performing various functions including optical parametric amplification, frequency division, and frequency entangled biphoton generation. We show two distinct edge modes corresponding to different f… ▽ More Topological quantum optics, an emerging area of study, holds the potential to bring about substantial enhancements for integrated quantum devices. Here we propose integrated topological quantum devices performing various functions including optical parametric amplification, frequency division, and frequency entangled biphoton generation. We show two distinct edge modes corresponding to different frequency ranges in both sandwich kagome and honeycomb topological designs that emulate the quantum valley Hall effect. These two topological edge modes enable two types of optical parametric processes through four-wave mixing, specifically inter-band and intra-band cases. The devices emulating photonic valley-Hall insulators allow the frequency division of two transverse modes, and furthermore, enable the separation of two quantum functionalities - optical parametric amplification and frequency entangled biphoton state generation. More importantly, the parametric processes are inborn topological protected, showing robustness against sharp bends and disorders. Our proposal significantly widens the possibilities for robust, multifunctional topological quantum devices on-chip, which may find applications in quantum information processing. △ Less

Submitted 12 January, 2024; originally announced January 2024.

Comments: 18pages, 12 figures

On-chip topological transport of optical frequency combs in silicon-based valley photonic crystals

Authors: Zhen Jiang, Hongwei Wang, Yuechen Yang, Yang Shen, Bo Ji, Yanghe Chen, Yong Zhang, Lu Sun, Zheng Wang, Chun Jiang, Yikai Su, Guangqiang He

Abstract: The generation and control of optical frequency combs in integrated photonic systems enables complex, high-controllable, and large-scale devices. In parallel, harnessing topological physics in multipartite systems has allowed them with compelling features such as robustness against fabrication imperfections. Here we experimentally demonstrate on-chip topological transport for optical frequency com… ▽ More The generation and control of optical frequency combs in integrated photonic systems enables complex, high-controllable, and large-scale devices. In parallel, harnessing topological physics in multipartite systems has allowed them with compelling features such as robustness against fabrication imperfections. Here we experimentally demonstrate on-chip topological transport for optical frequency combs at telecommunication wavelengths, both in classical and nonclassical domains. We access both the quantum frequency combs and dissipative Kerr soliton combs with a micro-resonator. The quantum frequency comb, that is, a coherent superposition of multiple frequency modes, is proven to be a frequency-entangled qudit state. We also show that dissipative Kerr soliton combs are highly coherent and mode-locked due to the collective coherence or self-organization of solitons. Moreover, the valley kink states allow both quantum frequency combs and dissipative Kerr soliton combs with robustness against sharp bends. Our topologically protected optical frequency combs could enable the inherent robustness in integrated complex photonic systems. △ Less

Submitted 24 October, 2023; originally announced October 2023.

Comments: 20 pages,12 figures

Comment on "Masking quantum information is impossible"

Authors: Guang Ping He

Abstract: The no-masking theorem (Phys. Rev. Lett. 120, 230501 (2018)) claims that arbitrary quantum states cannot be masked. Based on this result, the authors further suggested that qubit commitment is not possible. Here we show that this connection does not hold in general. The no-masking theorem (Phys. Rev. Lett. 120, 230501 (2018)) claims that arbitrary quantum states cannot be masked. Based on this result, the authors further suggested that qubit commitment is not possible. Here we show that this connection does not hold in general. △ Less

Submitted 4 August, 2023; originally announced August 2023.

Comments: 2 pages

Journal ref: Results in Physics 57, 107346 (2023)

Approaching the standard quantum limit of a Rydberg-atom microwave electrometer

Authors: Hai-Tao Tu, Kai-Yu Liao, Guo-Dong He, Yi-Fei Zhu, Si-Yuan Qiu, Hao Jiang, Wei Huang, Wu Bian, Hui Yan, Shi-Liang Zhu

Abstract: The development of a microwave electrometer with inherent uncertainty approaching its ultimate limit carries both fundamental and technological significance. Recently, the Rydberg electrometer has garnered considerable attention due to its exceptional sensitivity, small-size, and broad tunability. This specific quantum sensor utilizes low-entropy laser beams to detect disturbances in atomic intern… ▽ More The development of a microwave electrometer with inherent uncertainty approaching its ultimate limit carries both fundamental and technological significance. Recently, the Rydberg electrometer has garnered considerable attention due to its exceptional sensitivity, small-size, and broad tunability. This specific quantum sensor utilizes low-entropy laser beams to detect disturbances in atomic internal states, thereby circumventing the intrinsic thermal noise encountered by its classical counterparts. However, due to the thermal motion of atoms, the advanced Rydberg-atom microwave electrometer falls considerably short of the standard quantum limit by over three orders of magnitude. In this study, we utilize an optically thin medium with approximately 5.2e5 laser-cooled atoms to implement heterodyne detection. By mitigating a variety of noises and strategically optimizing the parameters of the Rydberg electrometer, our study achieves an electric-field sensitivity of 10.0 nV/cm/Hz^1/2 at a 100 Hz repetition rate, reaching a factor of 2.6 above the standard quantum limit and a minimum detectable field of 540 pV/cm. We also provide an in-depth analysis of noise mechanisms and determine optimal parameters to bolster the performance of Rydberg-atom sensors. Our work provides insights into the inherent capacities and limitations of Rydberg electrometers, while offering superior sensitivity for detecting weak microwave signals in numerous applications. △ Less

Submitted 13 November, 2023; v1 submitted 28 July, 2023; originally announced July 2023.

Comments: 12 pages

Computing the gradients with respect to all parameters of a quantum neural network using a single circuit

Authors: Guang Ping He

Abstract: Finding gradients is a crucial step in training machine learning models. For quantum neural networks, computing gradients using the parameter-shift rule requires calculating the cost function twice for each adjustable parameter in the network. When the total number of parameters is large, the quantum circuit must be repeatedly adjusted and executed, leading to significant computational overhead. H… ▽ More Finding gradients is a crucial step in training machine learning models. For quantum neural networks, computing gradients using the parameter-shift rule requires calculating the cost function twice for each adjustable parameter in the network. When the total number of parameters is large, the quantum circuit must be repeatedly adjusted and executed, leading to significant computational overhead. Here we propose an approach to compute all gradients using a single circuit only, significantly reducing both the circuit depth and the number of classical registers required. We experimentally validate our approach on both quantum simulators and IBM's real quantum hardware, demonstrating that our method significantly reduces circuit compilation time compared to the conventional approach, resulting in a substantial speedup in total runtime. △ Less

Submitted 30 January, 2025; v1 submitted 16 July, 2023; originally announced July 2023.

Comments: Fixed an incomplete link

Isotope engineering for spin defects in van der Waals materials

Authors: Ruotian Gong, Xinyi Du, Eli Janzen, Vincent Liu, Zhongyuan Liu, Guanghui He, Bingtian Ye, Tongcang Li, Norman Y. Yao, James H. Edgar, Erik A. Henriksen, Chong Zu

Abstract: Spin defects in van der Waals materials offer a promising platform for advancing quantum technologies. Here, we propose and demonstrate a powerful technique based on isotope engineering of host materials to significantly enhance the coherence properties of embedded spin defects. Focusing on the recently-discovered negatively charged boron vacancy center ($\mathrm{V}_{\mathrm{B}}^-$) in hexagonal b… ▽ More Spin defects in van der Waals materials offer a promising platform for advancing quantum technologies. Here, we propose and demonstrate a powerful technique based on isotope engineering of host materials to significantly enhance the coherence properties of embedded spin defects. Focusing on the recently-discovered negatively charged boron vacancy center ($\mathrm{V}_{\mathrm{B}}^-$) in hexagonal boron nitride (hBN), we grow isotopically purified $\mathrm{h}{}^{10}\mathrm{B}{}^{15}\mathrm{N}$ crystals. Compared to $\mathrm{V}_{\mathrm{B}}^-$ in hBN with the natural distribution of isotopes, we observe substantially narrower and less crowded $\mathrm{V}_{\mathrm{B}}^-$ spin transitions as well as extended coherence time $T_2$ and relaxation time $T_1$. For quantum sensing, $\mathrm{V}_{\mathrm{B}}^-$ centers in our $\mathrm{h}{}^{10}\mathrm{B}{}^{15}\mathrm{N}$ samples exhibit a factor of $4$ ($2$) enhancement in DC (AC) magnetic field sensitivity. For additional quantum resources, the individual addressability of the $\mathrm{V}_{\mathrm{B}}^-$ hyperfine levels enables the dynamical polarization and coherent control of the three nearest-neighbor ${}^{15}\mathrm{N}$ nuclear spins. Our results demonstrate the power of isotope engineering for enhancing the properties of quantum spin defects in hBN, and can be readily extended to improving spin qubits in a broad family of van der Waals materials. △ Less

Submitted 3 January, 2024; v1 submitted 12 July, 2023; originally announced July 2023.

Comments: 8+5+12 pages, 4+5+8 figures

Journal ref: Nature Communications 15, 104 (2024)

A no-go result on observing quantum superpositions

Authors: Guang Ping He

Abstract: We give a general proof showing that once irreversible processes are involved, a class of projective measurements is impossible. Applying this no-go result to the Schroedinger's cat paradox implies that if something is claimed to be a real Schroedinger's cat, there will be no measurable difference between it and a trivial classical mixture of ordinary cats in any physically implementable process,… ▽ More We give a general proof showing that once irreversible processes are involved, a class of projective measurements is impossible. Applying this no-go result to the Schroedinger's cat paradox implies that if something is claimed to be a real Schroedinger's cat, there will be no measurable difference between it and a trivial classical mixture of ordinary cats in any physically implementable process, otherwise raising the dead will become reality. Other similar macroscopic quantum superpositions cannot be observed either due to the lack of non-commuting measurement bases. Our proof does not involve any quantum interpretation theory and hypothesis. △ Less

Submitted 10 May, 2023; v1 submitted 6 April, 2023; originally announced April 2023.

Comments: 7 pages

Journal ref: Found. Phys. 54, 23 (2024)

Quasi-Floquet prethermalization in a disordered dipolar spin ensemble in diamond

Authors: Guanghui He, Bingtian Ye, Ruotian Gong, Zhongyuan Liu, Kater W. Murch, Norman Y. Yao, Chong Zu

Abstract: Floquet (periodic) driving has recently emerged as a powerful technique for engineering quantum systems and realizing non-equilibrium phases of matter. A central challenge to stabilizing quantum phenomena in such systems is the need to prevent energy absorption from the driving field. Fortunately, when the frequency of the drive is significantly larger than the local energy scales of the many-body… ▽ More Floquet (periodic) driving has recently emerged as a powerful technique for engineering quantum systems and realizing non-equilibrium phases of matter. A central challenge to stabilizing quantum phenomena in such systems is the need to prevent energy absorption from the driving field. Fortunately, when the frequency of the drive is significantly larger than the local energy scales of the many-body system, energy absorption is suppressed. The existence of this so-called prethermal regime depends sensitively on the range of interactions and the presence of multiple driving frequencies. Here, we report the observation of Floquet prethermalization in a strongly interacting dipolar spin ensemble in diamond, where the angular dependence of the dipolar coupling helps to mitigate the long-ranged nature of the interaction. Moreover, we extend our experimental observation to quasi-Floquet drives with multiple incommensurate frequencies. In contrast to a single-frequency drive, we find that the existence of prethermalization is extremely sensitive to the smoothness of the applied field. Our results open the door to stabilizing and characterizing non-equilibrium phenomena in quasi-periodically driven systems. △ Less

Submitted 28 September, 2023; v1 submitted 21 December, 2022; originally announced December 2022.

Comments: 7+13 pages, 3+8 figures

Journal ref: Physical Review Letters 131, 130401 (2023)

Coherent dynamics of strongly interacting electronic spin defects in hexagonal boron nitride

Authors: Ruotian Gong, Guanghui He, Xingyu Gao, Peng Ju, Zhongyuan Liu, Bingtian Ye, Erik A. Henriksen, Tongcang Li, Chong Zu

Abstract: Optically active spin defects in van der Waals materials are promising platforms for modern quantum technologies. Here we investigate the coherent dynamics of strongly interacting ensembles of negatively charged boron-vacancy ($\mathrm{V}_{\mathrm{B}}^-$) centers in hexagonal boron nitride (hBN) with varying defect density. By employing advanced dynamical decoupling sequences to selectively isolat… ▽ More Optically active spin defects in van der Waals materials are promising platforms for modern quantum technologies. Here we investigate the coherent dynamics of strongly interacting ensembles of negatively charged boron-vacancy ($\mathrm{V}_{\mathrm{B}}^-$) centers in hexagonal boron nitride (hBN) with varying defect density. By employing advanced dynamical decoupling sequences to selectively isolate different dephasing sources, we observe more than 5-fold improvement in the measured coherence times across all hBN samples. Crucially, we identify that the many-body interaction within the $\mathrm{V}_{\mathrm{B}}^-$ ensemble plays a substantial role in the coherent dynamics, which is then used to directly estimate the concentration of $\mathrm{V}_{\mathrm{B}}^-$. We find that at high ion implantation dosage, only a small portion of the created boron vacancy defects are in the desired negatively charged state. Finally, we investigate the spin response of $\mathrm{V}_{\mathrm{B}}^-$ to the local charged defects induced electric field signals, and estimate its ground state transverse electric field susceptibility. Our results provide new insights on the spin and charge properties of $\mathrm{V}_{\mathrm{B}}^-$, which are important for future use of defects in hBN as quantum sensors and simulators. △ Less

Submitted 12 July, 2023; v1 submitted 20 October, 2022; originally announced October 2022.

Comments: 8+8+4 pages, 4+5+1 figures

Journal ref: Nature Communications 14, 3299 (2023)

Theory on electron-phonon spin dehphasing in GaAs multi-electron double quantum dots

Authors: Guanjie He, Guo Xuan Chan, Xin Wang

Abstract: Recent studies reveal that a double-quantum-dot system hosting more than two electrons may be superior in certain aspects as compared to the traditional case in which only two electrons are confined (a singlet-triplet qubit). We study the electron-phonon dephasing occurring in a GaAs multi-electron double-quantum-dot system, in a biased case in which the singlet state is hybridized, as well as in… ▽ More Recent studies reveal that a double-quantum-dot system hosting more than two electrons may be superior in certain aspects as compared to the traditional case in which only two electrons are confined (a singlet-triplet qubit). We study the electron-phonon dephasing occurring in a GaAs multi-electron double-quantum-dot system, in a biased case in which the singlet state is hybridized, as well as in an unbiased case in which the hybridization is absent. We have found that while the electron-phonon dephasing rate increases with the number of electrons confined in the unbiased case, this does not hold in the biased case. We define a merit figure as a ratio between the exchange energy and the dephasing rate, and have shown that in experimentally relevant range of the exchange energy, the merit figure actually increases with the number of electrons in the biased case. Our results show that the multi-electron quantum-dot system has another advantage in mitigating the effect of electron-phonon dephasing, which is previously under-appreciated in the literature. △ Less

Submitted 30 March, 2022; originally announced March 2022.

Comments: 9+ pages, 6 figures

Journal ref: Adv. Quantum Technol. 2023, 2200074 (2023)

Robust violation of a multipartite Bell inequality from the perspective of a single-system game

Authors: Gang-Gang He, Xing-Yan Fan, Fu-Lin Zhang

Abstract: Recently, Fan \textit{et al.} [Mod. Phys. Lett. A 36, 2150223 (2021)], presented a generalized Clauser-Horne-Shimony-Holt (CHSH) inequality, to identify $N$-qubit Greenberger-Horne-Zeilinger (GHZ) states. They showed an interesting phenomenon that the maximal violation of the generalized CHSH inequality is robust under some specific noises. In this work, we map the inequality to the CHSH game, and… ▽ More Recently, Fan \textit{et al.} [Mod. Phys. Lett. A 36, 2150223 (2021)], presented a generalized Clauser-Horne-Shimony-Holt (CHSH) inequality, to identify $N$-qubit Greenberger-Horne-Zeilinger (GHZ) states. They showed an interesting phenomenon that the maximal violation of the generalized CHSH inequality is robust under some specific noises. In this work, we map the inequality to the CHSH game, and consequently to the CHSH* game in a single-qubit system. This mapping provides an explanation for the robust violations in $N$-qubit systems. Namely, the robust violations, resulting from the degeneracy of the generalized CHSH operators correspond to the symmetry of the maximally entangled two-qubit states and the identity transformation in the single-qubit game. This explanation enables us to exactly demonstrate that the degeneracy is $2^{N-2}$. △ Less

Submitted 8 June, 2022; v1 submitted 11 February, 2022; originally announced February 2022.

Comments: 9 pages, 2 figures

Journal ref: Mod. Phys. Lett.A 37,(2022) 2250082

Measurement-device-independent quantum key distribution with classical Bob and no joint measurement

Authors: Guang Ping He

Abstract: Measurement-device-independent quantum key distribution (MDI-QKD) provides a method for secret communication whose security does not rely on trusted measurement devices. In all existing MDI-QKD protocols, the participant Charlie has to perform the Bell state measurement or other joint measurements. Here we propose an MDI-QKD protocol which requires individual measurements only. Meanwhile, all oper… ▽ More Measurement-device-independent quantum key distribution (MDI-QKD) provides a method for secret communication whose security does not rely on trusted measurement devices. In all existing MDI-QKD protocols, the participant Charlie has to perform the Bell state measurement or other joint measurements. Here we propose an MDI-QKD protocol which requires individual measurements only. Meanwhile, all operations of the receiver Bob are classical, without the need for preparing and measuring quantum systems. Thus the implementation of the protocol has a lower technical requirement on Bob and Charlie. △ Less

Submitted 11 August, 2021; originally announced August 2021.

Comments: 6 pages, 1 figure

Journal ref: Quantum Inf. Process. 21, 32 (2022)

Preparation of quantum correlations assisted by a steering Maxwell demon

Authors: Gang-Gang He, Fu-Lin Zhang

Abstract: A Maxwell demon can reduce the entropy of a quantum system by performing measurements on its environment. The nonsignaling theorem prevents the demon from affecting the average state of the system. We study the preparations of quantum correlations from a system qubit and an auxiliary qubit, assisted by a demon who obtains information of the system qubit from measurements on its environment. The de… ▽ More A Maxwell demon can reduce the entropy of a quantum system by performing measurements on its environment. The nonsignaling theorem prevents the demon from affecting the average state of the system. We study the preparations of quantum correlations from a system qubit and an auxiliary qubit, assisted by a demon who obtains information of the system qubit from measurements on its environment. The demon can affect the postmeasured states of system by choosing different measurements, which establishes the relationships between quantum steering and other correlations in the thermodynamic framework. We present the optimal protocols for creating mutual information, entanglement, and Bell-nonlocality. These maximal correlations are found to relate exactly to the steerable boundary of the system-environment state with maximally mixed marginals. We also present upper bounds of the prepared correlations by utilizing classical environment-system correlation, which can be regarded as steering-type inequalities bounding the correlations created with the aid of classical demons. △ Less

Submitted 18 July, 2022; v1 submitted 4 March, 2021; originally announced March 2021.

Comments: 8 pages, 3 figures. Published version

Journal ref: Phys. Rev. E 106, 014119 (2022)

Locality of three-qubit Greenberger-Horne-Zeilinger-symmetric states

Authors: Dian Zhu, Gang-Gang He, Fu-Lin Zhang

Abstract: The hierarchy of nonlocality and entanglement in multipartite systems is one of the fundamental problems in quantum physics. We study this topic in three-qubit systems considering the entanglement classification of stochastic local operations and classical communication (SLOCC). The equivalence under SLOCC divides threequbit states into separable, biseparable, W, and Greenberger-Horne-Zeilinger (G… ▽ More The hierarchy of nonlocality and entanglement in multipartite systems is one of the fundamental problems in quantum physics. We study this topic in three-qubit systems considering the entanglement classification of stochastic local operations and classical communication (SLOCC). The equivalence under SLOCC divides threequbit states into separable, biseparable, W, and Greenberger-Horne-Zeilinger (GHZ) classes. The W and GHZ are two subclasses of genuine tripartite entanglement.We adopt the family of GHZ-symmetric states as a research subject, which share the symmetries of the GHZ state and have a complete characterization of SLOCC classes. In the biseparable region (with bipartite entanglement), there exist GHZ-symmetric states that are found to be fully local. In addition, there are bilocal states in both theW and GHZ classes. That is, neither of the subclasses of genuine tripartite entanglement can ensure genuinely tripartite nonlocality. △ Less

Submitted 6 June, 2022; v1 submitted 12 February, 2021; originally announced February 2021.

Comments: 4 figures, 7 pages

Journal ref: Phys. Rev. A 105, 062202 (2022)

Realizing the "fictitious" beam splitter -- A stationary implementation of semi-counterfactual interaction-free imaging

Authors: Guang Ping He

Abstract: Based on quantum counterfactual interaction-free measurement, we propose an implementation scheme for a beam splitter with anomalous reflection and transmission properties that looks impossible at first glance. Our scheme is stationary without requiring switchable mirrors and polarization rotators. Using the scheme for imaging will ensure that the optical radiation received by the object being ima… ▽ More Based on quantum counterfactual interaction-free measurement, we propose an implementation scheme for a beam splitter with anomalous reflection and transmission properties that looks impossible at first glance. Our scheme is stationary without requiring switchable mirrors and polarization rotators. Using the scheme for imaging will ensure that the optical radiation received by the object being imaged can be arbitrarily low. Thus it enables applications such as stealthy night vision devices that can work without detectable ambient light, or being used as a hackware against some counterfactual quantum cryptographic protocols. △ Less

Submitted 11 November, 2022; v1 submitted 6 July, 2020; originally announced July 2020.

Comments: This paper has been withdrawn by the author, because the proposed scheme does not work

Tunable Optomechanically Induced Sideband Comb

Authors: Jun-Hao Liu, Guangqiang He, Qin Wu, Ya-Fei Yu, Jin-Dong Wang, Zhi-Ming Zhang

Abstract: Cavity optomechanical system can exhibit higher-order sideband comb effect when it is driven by a control field $ω_{c}$ and a probe field $ω_{p}$, and works in the non-perturbative regime, as was shown in a previous work [Xiong et al., Opt. Lett. 38, 353 (2013)]. The repetition frequency of such a comb is equal to the mechanical frequency $ω_{b}$ and is untunable, which limits the precision of the… ▽ More Cavity optomechanical system can exhibit higher-order sideband comb effect when it is driven by a control field $ω_{c}$ and a probe field $ω_{p}$, and works in the non-perturbative regime, as was shown in a previous work [Xiong et al., Opt. Lett. 38, 353 (2013)]. The repetition frequency of such a comb is equal to the mechanical frequency $ω_{b}$ and is untunable, which limits the precision of the comb. Here we address this problem by driving the system with an additional strong probe field $ω_{f}$, and the detuning between $ω_{f}$ and $ω_{c}$ is equal to $ω_{b}/n$ (here $n$ is an integer), i.e., this detuning is a fraction of the mechanical frequency. In this case, we obtain some interesting results. We find that not only the integer-order (higher-order) sidebands, but also the fraction-order sidebands, and the sum and difference sidebands between the integer- and fraction-order sidebands, will appear in the output spectrum. The generated nonlinear sidebands constitute an optomechanically induced sideband comb (OMISC). The frequency range and the repetition frequency of the OMISC are proportional to the sideband cutoff-order number and the sideband interval, respectively. We show that we can extend the frequency range of the OMISC by increasing the intensity of the probe field $ω_{p}$. More importantly, we can decrease the repetition frequency, and consequently, improve the precision of the OMISC by increasing $n$ and the intensity of the probe field $ω_{f}$. △ Less

Submitted 9 May, 2020; v1 submitted 20 April, 2020; originally announced April 2020.

Comments: 6 pages, 4 figures

Heterogeneously integrated, superconducting silicon-photonic platform for measurement-device-independent quantum key distribution

Authors: Xiaodong Zheng, Peiyu Zhang, Renyou Ge, Liangliang Lu, Guanglong He, Qi Chen, Fangchao Qu, Labao Zhang, Xinlun Cai, Yanqing Lu, Shining Zhu, Peiheng Wu, Xiao-Song Ma

Abstract: Integrated photonics provides a route both to miniaturize quantum key distribution (QKD) devices and to enhance their performance. A key element for achieving discrete-variable QKD is a single-photon detector. It is highly desirable to integrate detectors onto a photonic chip to enable the realization of practical and scalable quantum networks. We realize an integrated heterogeneous superconductin… ▽ More Integrated photonics provides a route both to miniaturize quantum key distribution (QKD) devices and to enhance their performance. A key element for achieving discrete-variable QKD is a single-photon detector. It is highly desirable to integrate detectors onto a photonic chip to enable the realization of practical and scalable quantum networks. We realize an integrated heterogeneous superconducting-silicon-photonic chip. Harnessing the unique high-speed feature of our optical waveguide-integrated superconducting detector, we perform the first optimal Bell-state measurement (BSM) of time-bin encoded qubits generated from two independent lasers. The optimal BSM enables an increased key rate of measurement-device-independent QKD, which is immune to all attacks against the detection system, and hence provides the basis for a QKD network with untrusted relays. Together with the time-multiplexed technique, we have enhanced the sifted key rate by almost one order of magnitude. With a 125 MHz clock rate, we obtain a secure key rate of 6.166 kbps over 24.0 dB loss, which is comparable to the state-of-the-art MDI-QKD experimental results with GHz clock rate. Combined with integrated QKD transmitters, a scalable, chip-based and cost-effective QKD network should become realizable in the near future. △ Less

Submitted 30 October, 2021; v1 submitted 19 December, 2019; originally announced December 2019.

Comments: Major updates: 1. Realize optimal Bell-state measurement for time-bin qubits; 2. With a 125 MHz clock rate, the generated secure key rate is comparable to the state-of-the-art MDI-QKD experimental results with GHz clock rate

Journal ref: Adv. Photon. 3(5), 055002 (2021)

An optical implementation of quantum bit commitment using infinite-dimensional systems

Authors: Guang Ping He

Abstract: Unconditionally secure quantum bit commitment (QBC) was widely believed to be impossible for more than two decades. But recently, based on an anomalous behavior found in quantum steering, we proposed a QBC protocol which can be unconditionally secure in principle. The protocol requires the use of infinite-dimensional systems, therefore it may seem less feasible in practice. Here we propose a quant… ▽ More Unconditionally secure quantum bit commitment (QBC) was widely believed to be impossible for more than two decades. But recently, based on an anomalous behavior found in quantum steering, we proposed a QBC protocol which can be unconditionally secure in principle. The protocol requires the use of infinite-dimensional systems, therefore it may seem less feasible in practice. Here we propose a quantum optical method based on Mach-Zehnder interferometer, which gives a very good approximation to such infinite-dimensional systems. Thus, it enables a proof-of-principle experimental implementation of our protocol, which can also serve as a practically secure QBC scheme. Other multi-party cryptographic protocols such as quantum coin tossing can be built upon it too. Our approach also reveals a relationship between infinity and non-locality, which may have an impact on the research of fundamental theories. △ Less

Submitted 22 July, 2023; v1 submitted 21 September, 2019; originally announced September 2019.

Comments: Very close to the published version

Journal ref: Applied Sciences 13, 7692 (2023)

Cryptanalysis and improvement of Wu-Cai-Wu-Zhang's quantum private comparison protocol

Authors: Guang Ping He

Abstract: In a recent paper (Int. J. Quantum Inf. 17 (2019) 1950026), the authors discussed the shortcomings in the security of a quantum private comparison protocol that we previously proposed (Int. J. Quantum Inf. 15 (2017) 1750014). They also proposed a new protocol aimed to avoid these problems. Here we analysis the information leaked in their protocol, and find that it is even less secure than our prot… ▽ More In a recent paper (Int. J. Quantum Inf. 17 (2019) 1950026), the authors discussed the shortcomings in the security of a quantum private comparison protocol that we previously proposed (Int. J. Quantum Inf. 15 (2017) 1750014). They also proposed a new protocol aimed to avoid these problems. Here we analysis the information leaked in their protocol, and find that it is even less secure than our protocol in certain cases. We further propose an improved version which has the following advantages: (1) no entanglement needed, (2) quantum memory is no longer required, and (3) less information leaked. Therefore, better security and great feasibility are both achieved. △ Less

Submitted 22 July, 2023; v1 submitted 24 August, 2019; originally announced August 2019.

Comments: Very close to the published version

Journal ref: Int. J. Quantum Inf. 18, 2050041 (2020)

Copenhagen interpretation can survive the upgraded Schroedinger's cat Gedankenexperiment

Authors: Guang Ping He

Abstract: Recently, Frauchiger and Renner proposed a Gedankenexperiment, which was claimed to be able to prove that quantum theory cannot consistently describe the use of itself. Here we show that the conclusions of Frauchiger and Renner actually came from their incorrect description of some quantum states. With the correct description there will be no inconsistent results, no matter which quantum interpret… ▽ More Recently, Frauchiger and Renner proposed a Gedankenexperiment, which was claimed to be able to prove that quantum theory cannot consistently describe the use of itself. Here we show that the conclusions of Frauchiger and Renner actually came from their incorrect description of some quantum states. With the correct description there will be no inconsistent results, no matter which quantum interpretation theory is used. Especially, the Copenhagen interpretation can satisfy all the three assumptions (C), (Q), and (S) of Frauchiger and Renner simultaneously, thus it has no problem consistently describing the use of itself. △ Less

Submitted 15 June, 2020; v1 submitted 16 October, 2018; originally announced October 2018.

Comments: Published version

Journal ref: Found. Phys. 50, 715 (2020)

Practical quantum oblivious transfer with a single photon

Authors: Guang Ping He

Abstract: Quantum oblivious transfer (QOT) is an essential cryptographic primitive. But unconditionally secure QOT is known to be impossible. Here we propose a practical QOT protocol, which is perfectly secure against dishonest sender without relying on any technological assumption. Meanwhile, it is also secure against dishonest receiver in the absence of long-term quantum memory and complicated collective… ▽ More Quantum oblivious transfer (QOT) is an essential cryptographic primitive. But unconditionally secure QOT is known to be impossible. Here we propose a practical QOT protocol, which is perfectly secure against dishonest sender without relying on any technological assumption. Meanwhile, it is also secure against dishonest receiver in the absence of long-term quantum memory and complicated collective measurements. The protocol is extremely feasible, as it can be implemented using currently available Mach-Zehnder interferometer, and no quantum memory, collective measurements nor entanglement are needed for honest participants. More importantly, comparing with other practical QOT schemes, our protocol has an unbeatable efficiency since it requires the transmission of a single photon only. △ Less

Submitted 24 July, 2018; v1 submitted 1 May, 2018; originally announced May 2018.

Comments: 7 pages, 2 figures

Journal ref: Laser Phys. 29, 035201 (2019)

Device-independent quantum private comparison protocol without a third party

Authors: Guang Ping He

Abstract: Since unconditionally secure quantum two-party computations are known to be impossible, most existing quantum private comparison (QPC) protocols adopted a third party. Recently, we proposed a QPC protocol which involves two parties only, and showed that although it is not unconditionally secure, it only leaks an extremely small amount of information to the other party. Here we further propose the… ▽ More Since unconditionally secure quantum two-party computations are known to be impossible, most existing quantum private comparison (QPC) protocols adopted a third party. Recently, we proposed a QPC protocol which involves two parties only, and showed that although it is not unconditionally secure, it only leaks an extremely small amount of information to the other party. Here we further propose the device-independent version of the protocol, so that it can be more convenient and dependable in practical applications. △ Less

Submitted 24 July, 2018; v1 submitted 13 October, 2017; originally announced October 2017.

Comments: Published version. arXiv admin note: text overlap with arXiv:1604.06834

Journal ref: Phys. Scr. 93, 095001 (2018)

Unconditionally secure quantum bit commitment based on the uncertainty principle

Authors: Guang Ping He

Abstract: Unconditionally secure quantum bit commitment (QBC) was considered impossible. But the no-go proofs are based on the Hughston-Jozsa-Wootters (HJW) theorem (a.k.a. the Uhlmann theorem). Recently it was found that in high-dimensional systems, there exist some states which can display a chaos effect in quantum steering, so that the attack strategy based on the HJW theorem has to require the capabilit… ▽ More Unconditionally secure quantum bit commitment (QBC) was considered impossible. But the no-go proofs are based on the Hughston-Jozsa-Wootters (HJW) theorem (a.k.a. the Uhlmann theorem). Recently it was found that in high-dimensional systems, there exist some states which can display a chaos effect in quantum steering, so that the attack strategy based on the HJW theorem has to require the capability of discriminating quantum states with very subtle difference, to the extent that is not allowed by the uncertainty principle. With the help of this finding, here we propose a simple QBC protocol which manages to evade the no-go proofs. △ Less

Submitted 25 July, 2018; v1 submitted 1 September, 2017; originally announced September 2017.

Comments: 7 pages. Security proof extended. No change to the protocol

Journal ref: Proc. R. Soc. A. 475, 20180543 (2019)

Chaos in quantum steering in high-dimensional systems

Authors: Guang Ping He

Abstract: Quantum steering means that in some bipartite quantum systems, the local measurements on one side can determine the state of the other side. Here we show that in high-dimensional systems, there exists a specific entangled state which can display a kind of chaos effect when being adopted for steering. That is, a subtle difference in the measurement results on one side can steer the other side into… ▽ More Quantum steering means that in some bipartite quantum systems, the local measurements on one side can determine the state of the other side. Here we show that in high-dimensional systems, there exists a specific entangled state which can display a kind of chaos effect when being adopted for steering. That is, a subtle difference in the measurement results on one side can steer the other side into completely orthogonal states. Moreover, by expanding the result to infinite-dimensional systems, we find two sets of states for which, contrary to common belief, even though their density matrices approach being identical, the steering between them is impossible. This property makes them very useful for quantum cryptography. △ Less

Submitted 26 April, 2018; v1 submitted 30 August, 2017; originally announced August 2017.

Comments: Published version

Journal ref: Phys. Rev. A 97, 042340 (2018)

Quantum private comparison protocol without a third party

Authors: Guang Ping He

Abstract: To evade the well-known impossibility of unconditionally secure quantum two-party computations, previous quantum private comparison protocols have to adopt a third party. Here we study how far we can go with two parties only. We propose a very feasible and efficient protocol. Intriguingly, although the average amount of information leaked cannot be made arbitrarily small, we find that it never exc… ▽ More To evade the well-known impossibility of unconditionally secure quantum two-party computations, previous quantum private comparison protocols have to adopt a third party. Here we study how far we can go with two parties only. We propose a very feasible and efficient protocol. Intriguingly, although the average amount of information leaked cannot be made arbitrarily small, we find that it never exceeds 14 bits for any length of the bit-string being compared. △ Less

Submitted 22 April, 2016; originally announced April 2016.

Comments: 4 pages, 1 figure

Journal ref: Int. J. Quantum Inf. 15, 1750014 (2017)

Unconditionally secure quantum coin flipping

Authors: Guang Ping He

Abstract: Quantum coin flipping (QCF) is an essential primitive for quantum cryptography. Unconditionally secure strong QCF with an arbitrarily small bias was widely believed to be impossible. But basing on a problem which cannot be solved without quantum algorithm, here we propose such a QCF protocol, and show how it manages to evade all existing no-go proofs on QCF. Quantum coin flipping (QCF) is an essential primitive for quantum cryptography. Unconditionally secure strong QCF with an arbitrarily small bias was widely believed to be impossible. But basing on a problem which cannot be solved without quantum algorithm, here we propose such a QCF protocol, and show how it manages to evade all existing no-go proofs on QCF. △ Less

Submitted 22 July, 2023; v1 submitted 3 February, 2016; originally announced February 2016.

Comments: Very close to the published version

Journal ref: Results in Physics 48, 106398 (2023)

Continuous-variable measurement-device-independent multipartite quantum communication

Authors: Yadong Wu, Jian Zhou, Xinbao Gong, Ying Guo, Zhi-Ming Zhang, Guangqiang He

Abstract: A continuous variable measurement device independent multi-party quantum communication protocol is investigated in this paper. Utilizing distributed continuous variable Greenberger-Horne-Zeilinger state, this protocol can implement both quantum cryptographic conference and quantum secret sharing. We analyze the security of the protocol against both entangling cloner attack and coherent attack. Ent… ▽ More A continuous variable measurement device independent multi-party quantum communication protocol is investigated in this paper. Utilizing distributed continuous variable Greenberger-Horne-Zeilinger state, this protocol can implement both quantum cryptographic conference and quantum secret sharing. We analyze the security of the protocol against both entangling cloner attack and coherent attack. Entangling cloner attack is a practical individual attack, and coherent attack is the optimal attack Eve can implement. Simulation results show that coherent attack can greatly reduce the secret key rate. Different kinds of entangled attacks are compared and we finally discuss the optimal coherent attacks. △ Less

Submitted 25 January, 2016; v1 submitted 12 December, 2015; originally announced December 2015.

Comments: 10 pages, 12 figures

Journal ref: Phys. Rev. A 93, 022325 (2016)

Five-Partite Entanglement Generation in A High-Q Microresonator

Authors: Yutian Wen, Xufei Wu, Rongyu Li, Qiang Lin, Guangqiang He

Abstract: We propose to produce five-partite entanglement via cascaded four-wave mixing in a high-Q microresonator that may become a key to future one-way quantum computation on chip. A theoretical model is presented for the underlying continuous-variable entanglement among the generated comb modes that is expansible to more complicated scenarios. We analyze the entanglement condition when the van Loock and… ▽ More We propose to produce five-partite entanglement via cascaded four-wave mixing in a high-Q microresonator that may become a key to future one-way quantum computation on chip. A theoretical model is presented for the underlying continuous-variable entanglement among the generated comb modes that is expansible to more complicated scenarios. We analyze the entanglement condition when the van Loock and Furusawa criteria are violated, and discuss the device parameters for potential experimental realization that may be utilized to build an integrated compact five-partite entanglement generator. The proposed approach exhibits great potential for future large-scale integrated full optical quantum computation on chip. △ Less

Submitted 3 January, 2015; originally announced January 2015.

Comments: 7 pages, 5 figures, submitted to Physical Review A on Dec 22nd, 2014

Insecurity of a relativistic quantum commitment scheme

Authors: Guang Ping He

Abstract: We propose a cheating strategy to a relativistic quantum commitment scheme [Sci Rep 2014;4:6774] which was claimed to be unconditionally secure. It is shown that the sender Alice can cheat successfully with probability 100%, thus disproving the security claim. We propose a cheating strategy to a relativistic quantum commitment scheme [Sci Rep 2014;4:6774] which was claimed to be unconditionally secure. It is shown that the sender Alice can cheat successfully with probability 100%, thus disproving the security claim. △ Less

Submitted 22 July, 2023; v1 submitted 31 October, 2014; originally announced November 2014.

Comments: arXiv admin note: Title of previous version was: Comment on "Unconditionally secure commitment in position-based quantum cryptography"

Journal ref: Results in Physics 50, 106568 (2023)

Security bound of cheat sensitive quantum bit commitment

Authors: Guang Ping He

Abstract: Cheat sensitive quantum bit commitment (CSQBC) loosens the security requirement of quantum bit commitment (QBC), so that the existing impossibility proofs of unconditionally secure QBC can be evaded. But here we analyze the common features in all existing CSQBC protocols, and show that in any CSQBC having these features, the receiver can always learn a non-trivial amount of information on the send… ▽ More Cheat sensitive quantum bit commitment (CSQBC) loosens the security requirement of quantum bit commitment (QBC), so that the existing impossibility proofs of unconditionally secure QBC can be evaded. But here we analyze the common features in all existing CSQBC protocols, and show that in any CSQBC having these features, the receiver can always learn a non-trivial amount of information on the sender's committed bit before it is unveiled, while his cheating can pass the security check with a probability not less than 50%. The sender's cheating is also studied. The optimal CSQBC protocols that can minimize the sum of the cheating probabilities of both parties are found to be trivial, as they are practically useless. We also discuss the possibility of building a fair protocol in which both parties can cheat with equal probabilities. △ Less

Submitted 7 June, 2015; v1 submitted 28 July, 2014; originally announced July 2014.

Comments: Published version

Journal ref: Sci. Rep. 5, 9398 (2015)

Secure quantum weak oblivious transfer against individual measurements

Authors: Guang Ping He

Abstract: In quantum weak oblivious transfer, Alice sends Bob two bits and Bob can learn one of the bits at his choice. It was found that the security of such a protocol is bounded by $2P_{Alice}^{\ast }+P_{Bob}^{\ast }\geq 2$, where $P_{Alice}^{\ast }$ is the probability with which Alice can guess Bob's choice, and $P_{Bob}^{\ast }$ is the probability with which Bob can guess both of Alice's bits\ given th… ▽ More In quantum weak oblivious transfer, Alice sends Bob two bits and Bob can learn one of the bits at his choice. It was found that the security of such a protocol is bounded by $2P_{Alice}^{\ast }+P_{Bob}^{\ast }\geq 2$, where $P_{Alice}^{\ast }$ is the probability with which Alice can guess Bob's choice, and $P_{Bob}^{\ast }$ is the probability with which Bob can guess both of Alice's bits\ given that he learns one of the bits with certainty. Here we propose a protocol and show that as long as Alice is restricted to individual measurements, then both $P_{Alice}^{\ast }$ and $P_{Bob}^{\ast }$ can be made arbitrarily close to 1/2, so that maximal violation of the security bound can be reached. Even with some limited collective attacks, the security bound can still be violated. Therefore, although our protocol still cannot break the bound in principle when Alice has unlimited cheating power, it is sufficient for achieving secure quantum weak oblivious transfer in practice. △ Less

Submitted 12 June, 2015; v1 submitted 30 December, 2013; originally announced January 2014.

Comments: Published version

Journal ref: Quantum Inf. Process. 14, 2153 (2015)

Security limitation on a class of device-independent quantum key distribution

Authors: Guang Ping He

Abstract: Recently there were many proposals on device-independent (DI) quantum key distribution protocol whose security is based on the violation of the Clauser-Horne-Shimony-Holt inequality. However, as a statistical law, a certain extent of fluctuation has to be allowed. We show that the eavesdropper can make use of this property to obtain a remarkable part of the secret key by replacing some of the DI n… ▽ More Recently there were many proposals on device-independent (DI) quantum key distribution protocol whose security is based on the violation of the Clauser-Horne-Shimony-Holt inequality. However, as a statistical law, a certain extent of fluctuation has to be allowed. We show that the eavesdropper can make use of this property to obtain a remarkable part of the secret key by replacing some of the DI nonlocal boxes with local ones. On the contrary, the same cheating strategy does not apply to the device-dependent (DD) version of the protocol. Thus such kind of DI protocol is less secure than its DD counterpart. △ Less

Submitted 9 August, 2013; originally announced August 2013.

Comments: 4 pages