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Direct measurement of density-matrix elements with a phase-shifting technique on a quantum photonic chip

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Physical Review A 2022年第6期105卷 062414-062414页

作者： Congxiu Li Yaxin Wang Tianfeng Feng Zhihao Li Changliang Ren Xiaoqi Zhou School of Physics and State Key Laboratory of Optoelectronic Materials and Technologies Sun Yat-sen University Guangzhou 510000 China Key Laboratory of Low-Dimensional Quantum Structures and Quantum Control of Ministry of Education Key Laboratory for Matter Microstructure and Function of Hunan Province Department of Physics and Synergetic Innovation Center for Quantum Effects and Applications Hunan Normal University Changsha 410081 China

A direct measurement protocol allows reconstructing specific elements of the density matrix of a quantum state without using quantum state tomography. Until now, most direct measurement protocols have relied on ancillary pointers, which add complexity and are not always easy to implement experimentally. In this paper, we experimentally validate a direct measurement protocol requiring no ancillary pointers that calculates the value of a specific element of a quantum state's density matrix using only six projection measurements. We prepare path-encoded arbitrary four-dimensional quantum states on a silicon-based quantum photonic chip and measure the density-matrix elements of the four-dimensional quantum states using this protocol, with experimental results deviating from ideal values by an average of only 0.010±0.004. This approach has the potential to be applied to quantum information applications where only partial information about the quantum state needs to be extracted, for example, problems such as entanglement witnessing, fidelity estimation of quantum systems, and quantum coherence estimation.

关键词： Integrated optics Quantum information architectures & platforms Quantum information processing Quantum tomography

Interface engineering of ferroelectricity in thin films of thiophosphate ABP2X6 (A = Cu, Ag;B = In, Bi, Cr, V;and X = S, Se)

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arXiv 2021年

作者： Yu, Guoliang Pan, Anlian Chen, Mingxing Key Laboratory for Matter Microstructure and Function of Hunan Province Key Laboratory of Low-Dimensional Quantum Structures and Quantum Control of Ministry of Education School of Physics and Electronics Hunan Normal University Changsha410081 China Key Laboratory for Micro-Nano Physics and Technology of Hunan Province College of Materials Science and Engineering Hunan University Changsha410082 China

Two-dimensional ferroelectrics (FEs) are promising in the miniaturization of memory devices with ultra-high-density data storage and low power consumption. However, many thiophosphate monolayers, i.e., analogs of CuInP2S6 and referred to as ABP2X6, lose ferroelectricity and instead exhibit an antiferroelectric (AFE) or paraelectric ordering. We propose to tune the AFE ABP2X6 monolayers into the FE ordering through interface engineering. The mechanism is that there are couplings between the charge polarizations of the ABP2X6 monolayers and the local dipoles as well as the induced electronic polarizations in the substrate which have a tendency to stabilize the FE ordering. We further perform first-principles calculations for CuInP2Se6 and CuCrP2S6 monolayers and their van der Waals heterostructures. We find that an AFE CuInP2Se6 monolayer becomes FE as interfaced with graphene, MoS2, and h-BN monolayers. In contrast, the CuCrP2S6 monolayer remains AFE since there is a large energy difference between the AFE and FE phases. Interfacing it with a MoTe2 monolayer induces a metal-insulator transition for the heterostructure, whereas interfacing with a polar surface MgO(111) can drive it into FE. The interfacing effect can also be used to manipulate the FE properties of ABP2X6 multilayers. We further find that the AFE-to-FE transition is electrically switchable in these systems. In particular, it is accompanied by an indirect-direct band-gap transition for the CuInP2Se6 monolayer. Our study offers an effective approach to tune the FE and electronic properties of ABP2X6 thin films for applications in electronics and optoelectronics. © 2021, CC BY.

关键词： Monolayers

Entanglement-enhanced quantum ranging in the near-Earth spacetime

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arXiv 2022年

作者： Liu, Qianqian Wen, Cuihong Jing, Jiliang Wang, Jieci Department of Physics and Synergetic Innovation Center for Quantum Effects Key Laboratory of Low-Dimensional Quantum Structures and Quantum Control of Ministry of Education Key Laboratory for Matter Microstructure and Function of Hunan Province Hunan Normal University Changsha410081 China

We propose a quantum ranging protocol to determine the distance between an observer and a target at the line of sight in the near-Earth curved spacetime. Unlike the quantum illumination scheme, here we employ multiple quantum hypothesis testing to decide the presence and location of the target at the same time. In the present protocol, the gravity of the Earth influences the propagation of photons and the performance of quantum ranging. We find that the maximum potential advantages of the quantum ranging strategy in the curved spacetime outperform its flat spacetime counterpart. This is because the effect of gravitational red-shift and blue-shift on the entangled signal photons can be canceled out, while the thermal photons only suffers from the gravitational blue-shift effect. We also show that the number of transmitted modes can promote the maximum potential advantage of the quantum ranging tasks. The maximum potential advantage of quantum ranging in the curved spacetime can not be raised sharply by dividing the range into multiple slices. Copyright © 2022, The Authors. All rights reserved.

关键词： Photons

Thermal-noise-resistant optomechanical entanglement via general dark-mode control

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Physical Review A 2022年第6期106卷 063506-063506页

作者： Jian Huang Deng-Gao Lai Jie-Qiao Liao Key Laboratory of Low-Dimensional Quantum Structures and Quantum Control of Ministry of Education Key Laboratory for Matter Microstructure and Function of Hunan Province Department of Physics and Synergetic Innovation Center for Quantum Effects and Applications Hunan Normal University Changsha 410081 China Theoretical Quantum Physics Laboratory RIKEN Cluster for Pioneering Research Wako-shi Saitama 351-0198 Japan

Quantum entanglement not only plays an important role in the study of the fundamentals of quantum theory, but also is considered as a crucial resource in quantum information science. The generation of macroscopic entanglement involving multiple optical and mechanical modes is a desired task in cavity optomechanics. However, the dark-mode effect is a critical obstacle against the generation of quantum entanglement in multimode optomechanical systems consisting of multiple degenerate or near-degenerate mechanical modes coupled to a common cavity mode. Here we propose an auxiliary-cavity-mode method to enhance optomechanical entanglement in a multimode optomechanical system by breaking the dark-mode effect. We find that the introduction of the auxiliary cavity mode not only assists the entanglement creation between the cavity mode and the mechanical modes, but also improves the immunity of the optomechanical entanglement to the thermal excitations by about three orders of magnitude. We also study the optomechanical entanglement in the network-coupled optomechanical system consisting of two mechanical modes and two cavity modes. By analyzing the correspondence between the optomechanical entanglement and the dark-mode effect, we find that optomechanical entanglement can be largely enhanced once the dark mode is broken. In addition, we study the mechanical entanglement and find that it is negligibly small. We also present some discussions on the experimental implementation with a microwave optomechanical setup, on the relationship between the dark-mode-breaking mechanism and the center-of-mass and relative coordinates, and on the explanation of the important role of the dark-mode breaking in the enhancement of optomechanical entanglement. Our results pave the way towards the preparation of entangled optomechanical networks and noise-resistant quantum resources.

关键词： Optics & lasers Optomechanics

Gaussian quantum steering under the influence of a dilaton black hole

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arXiv 2021年

作者： Hu, Biwei Wen, Cuihong Wang, Jieci Jing, Jiliang Department of Physics Synergetic Innovation Center for Quantum Effects Key Laboratory of Low-Dimensional Quantum Structures and Quantum Control Ministry of Education Key Laboratory for Matter Microstructure and Function of Hunan Province Hunan Normal University Changsha410081 China

We study the dynamics of Gaussian quantum steering in the background of a Garfinkle-Horowitz-Strominger dilaton black hole. It is found that the gravity induced by dilaton field will destroy the quantum steerability between the inertial observer Alice and the observer Bob who hovers outside the event horizon, while it generates steering-type quantum correlations between the causally disconnected regions. Therefore, the observers can steer each other's state by local measurements even though they are separated by the event horizon. Unlike quantum entanglement in the dilaton spacetime, the quantum steering experiences catastrophic behaviors such as "sudden death" and "sudden birth" with increasing dilaton charge. In addition, the dilaton gravity destroys the symmetry of Gaussian steering and the latter is always asymmetric in the dilation spacetime. Interestingly, the attainment of maximal steering asymmetry indicates the critical point between one-way and two-way steering for the two-mode Gaussian state in the dilaton spacetime. Copyright © 2021, The Authors. All rights reserved.

关键词： Gravitation

Multifunctional near-infrared polarized photodetector driven by the anisotropic photogalvanic effect in a two-dimensional MnSSe/TaIrS4/MnSSe magnetic tunnel junction

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Physical Review Applied 2024年第5期22卷 054042-054042页

作者： Degao Xu Jianing Tan Meng Ge Guowei Yang Gang Ouyang Key Laboratory of Low-Dimensional Quantum Structures and Quantum Control of Ministry of Education Key Laboratory for Matter Microstructure and Function of Hunan Province School of Physics and Electronics Hunan Normal University Changsha 410081 China State Key Laboratory of Optoelectronic Materials and Technologies Nanotechnology Research Center School of Materials Science & Engineering Sun Yat-sen University Guangzhou 510275 Guangdong China

Traditional polarized photodetectors have faced critical challenges, such as limited functionality, integration complexities, and subpar photosensitivity. In this study, we propose a kind of multifunctional coupled polarized photodetector based on an anisotropic MnSSe/TaIrS4/MnSSe lateral magnetic tunnel junction (MTJ) that integrates self-powered, near-infrared photodetection, spin valve, pure spin current, and multichannel optical communication induced by the photogalvanic effect. Profiting from the synergistic interplay between optical transition and spin-tunneling selection rules within the MTJ, seamless toggling between perfect spin filtering and pure spin current can be achieved in the self-powered mode. Furthermore, the remarkable performance metrics, including an anisotropy ratio of 481.84, an extinction ratio of 725.43, and a tunneling magnetoresistance ratio of 100%, underscore the exceptional capabilities of the multifunctional polarized photodetector. Building upon these achievements, a proof-of-concept three-channel optical communication scheme is shown to amplify the output efficiency of binary signals by an additional 50%. Our research provides insights into the development of multifunctional and high-performance photodetectors and presents an interesting platform for advancing coupled optoelectronic and spintronic applications.

关键词： Photogalvanic effect Spin optoelectronics Magnetic semiconductors Magnetic tunnel junctions Photodetectors Van der Waals systems Ab initio calculations Infrared techniques

Thermodynamics of Decreased Vacancy-Mediated Diffusion in High-Entropy Alloys

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SSRN

SSRN 2023年

作者： Li, Jia-Ming Liu, Zi-Ran School of Physics and Electronics Hunan Normal University Hunan Changsha410081 China Key Laboratory of Low-Dimensional Quantum Structures and Quantum Control Ministry of Education Key Laboratory for Matter Microstructure and Function of Hunan Province Department of Physics Hunan Normal University Hunan Changsha410081 China

This work presents a thermodynamic analysis to investigate the effect of increased configurational entropy on vacancy formation and diffusion in High-entropy alloys (HEAs). The calculations demonstrate that as the number of alloying elements increases, the equilibrium vacancy concentration decreases significantly due to the contribution of configurational entropy. This reduction in vacancy concentration leads to a proportional decrease in the vacancy-mediated diffusion coefficient in HEAs compared to pure metals. The diffusion coefficients follow an Arrhenius relationship with homologous temperature, where the slope remains consistent, but the intercept decreases with higher alloying complexity. The inhibition of defect formation and diffusion provides insights into the excellent mechanical properties and irradiation resistance exhibited by HEAs. © 2023, The Authors. All rights reserved.

关键词： Diffusion

Solute strengthening and softening from screw dislocation in BCC tantalum: A first-principles study

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arXiv 2024年

作者： Feng, Jiajun Zhou, Kangzhi Zhou, Xiaowei Fu, Xiao Luo, Qiuting Liu, Ziran School of Physics and Electronics Hunan Normal University Hunan Changsha410081 China Key Laboratory of Low-Dimensional Quantum Structures and Quantum Control of Ministry of Education Key Laboratory for Matter Microstructure and Function of Hunan Province Department of Physics Hunan Normal University Hunan Changsha410081 China

Improving the high-temperature performance and low-temperature plasticity of tantalum (Ta) alloys is a significant scientific challenge. We employed first-principles calculations to study the interaction between screw dislocations and solute atoms in the body-centered cubic (BCC) structure of Ta, with a particular focus on solid solution softening and hardening. We analyzed the impact of various solute elements on the generalized stacking fault energy (GSFE), energy barriers within the single-atom row displacement model, and their interaction with screw dislocations. The results indicate that Hf and Zr, either individually or in combination, exhibit notable solute softening effects in BCC Ta, significantly reducing GSFE, energy barriers, and interaction energies. In contrast, Nb shows relative insensitivity to solute effects, while Mo, W, and Ir demonstrate solute hardening effects. The calculations suggest that the interaction energy between screw dislocations and solute atoms is a reliable indicator for predicting hardening and softening effects. Additionally, we extend these predictions to ternary alloys, demonstrating that the strengthening and softening phenomena in these materials can be explained through the electronic work function at the electronic level. Copyright © 2024, The Authors. All rights reserved.

关键词： Screw dislocations

Nonequilibrium thermal transport and photon squeezing in a quadratic qubit-resonator system

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Physical Review A 2021年第3期104卷 033701-033701页

作者： Chen Wang Hua Chen Jie-Qiao Liao Department of Physics Zhejiang Normal University Jinhua 321004 Zhejiang People's Republic of China Key Laboratory of Low-Dimensional Quantum Structures and Quantum Control of Ministry of Education Key Laboratory for Matter Microstructure and Function of Hunan Province Department of Physics and Synergetic Innovation Center for Quantum Effects and Applications Hunan Normal University Changsha 410081 China

We investigate steady-state thermal transport and photon statistics in a nonequilibrium hybrid quantum system, in which a qubit shows longitudinal and quadratic coupling with an optical resonator. Our calculations are conducted with the method of the quantum dressed master equation combined with full counting statistics. The effect of negative differential thermal conductance is unravelled at finite temperature bias, which stems from the suppression of cyclic heat transitions and large mismatch of two squeezed photon modes at weak and strong qubit-resonator hybridizations, respectively. The giant thermal rectification is also exhibited at large temperature bias. It is found that the asymmetric composition of the hybrid system by spin and boson roles and negative differential thermal conductance show the cooperative contribution. Noise power and skewness, as typical current fluctuations, exhibit global maximum with strong hybridization at small and large temperature bias limits, respectively. Moreover, the effect of photon quadrature squeezing is discovered in the strong hybridization and low-temperature regime, which shows asymmetric response to two bath temperatures. These results would provide some insight to thermal functional design and photon manipulation in qubit-resonator hybrid quantum systems.

关键词： Collective effects in quantum optics Hybrid quantum systems Quantum optics Squeezing of quantum noise Quantum master equation Two-level models