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Nonlinear time-reversal interferometry with arbitrary quadratic collective-spin interaction

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Chinese Physics B 2024年第8期33卷 63-70页

作者：胡知遥李其贤张轩晨张贺宾黄龙刚刘永椿 State Key Laboratory of Low-Dimensional Quantum Physics Department of PhysicsTsinghua UniversityBeijing 100084China School of Physics Xi'an Jiaotong UniversityXi'an 710049China China Fire and Rescue Institute Beijing 102202China Frontier Science Center for Quantum Information Beijing 100084China

Atomic nonlinear interferometry has wide applications in quantum metrology and quantum information *** we propose a nonlinear time-reversal interferometry scheme with high robustness and metrological gain based on the spin squeezing generated by arbitrary quadratic collective-spin interaction,which could be described by the Lipkin–Meshkov–Glick(LMG)*** optimize the squeezing process,encoding process,and anti-squeezing process,finding that the two particular cases of the LMG model,one-axis twisting and two-axis twisting outperform in robustness and precision,***,we propose a Floquet driving method to realize equivalent time reverse in the atomic system,which leads to high performance in precision,robustness,and *** study sets a benchmark for achieving high precision and high robustness in atomic nonlinear interferometry.

关键词： time-reversal interferometry spin squeezing quantum metrology

Macroscopic mechanical systems are entering the quantum world

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National Science Review 2015年第1期2卷 9-10页

作者： yong-chun liu Yun-Feng Xiao School of Physics Peking University Collaborative Innovation Center of Quantum Matter

In the classic Chinese novel Journey to the West,the Monkey King has a special power that enables him to be in two or more places ***,an amazing thing such as this could never happen in real ***,in the quantum world,where the motions of objects obey the rules of quantum mechanics,this could *** weird quantum rules usually only apply in the

关键词： In Macroscopic mechanical systems are entering the quantum world

Optimal phase sensitivity of atomic Ramsey interferometers with coherent spin states

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Frontiers of physics 2011年第3期6卷 251-257页

作者： Guang-ri JIN yong-chun liu Li YOU Department of Physics Beijing Jiaotong University Beijing 100044 China Department of Physics Tsinghua University Beijing 100085 China

We present a detailed analysis of phase sensitivity for a nonlinear Ramsey interferometer, which utilize effective mean-field interaction of a two-component Bose-Einstein condensate in phase ac- cumulation. For large enough particle number N and small phase shift φ, analytical results of the Ramsey signal and the phase sensitivity are derived for a product coherent state θ, 0）. When collisional dephasing is absent, we confirm that the optimal sensitivity scales as 2/N3/2 for polar angle of the initial state θ = π/4 or 3π/4. The best-sensitivity phase satisfies different transcendental equations, depending upon the initial state and the observable being measured after the phase accumulation. In the presence of the collisional dephasing, we show that the N-3/2-scaling rule of the sensitivity maintains with spin operators jx and jy measurements. A slightly better sensitivity is attainable for optimal coherent state with θ = π/6 or 5π/6.

关键词： Ramsey interferometry phase estimation Bose-Einstein condensates phase decay,one-axis twisting model

Loss-induced nonreciprocity

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Light(Science & Applications) 2021年第2期10卷 256-263页

作者： Xinyao Huang Cuicui Lu Chao Liang Honggeng Tao yong-chun liu State Key Laboratory of Low-Dimensional Quantum Physics Department of PhysicsTsinghua UniversityBeijing 100084China Key Laboratory of Advanced Optoelectronic Quantum Architecture and Measurements of Ministry of Education Beijing Key Laboratory of Nanophotonics and Ultrafine Optoelectronic SystemsSchool of PhysicsBeijing Institute of TechnologyBeijing 100081China Collaborative Innovation Center of Light Manipulations and Applications Shandong Normal UniversityJinan 250358China Frontier Science Center for Quantum Information Beijing 100084China

Nonreciprocity is important in both optical information processing and topological photonics *** principles for realizing non reciprocity rely on magnetic fields,spatiotemporal modulation,or *** we propose a generic principle for generating nonreciprocity by taking advantage of energy loss,which is usually regarded as *** loss in a resonance mode induces a phase lag,which is independent of the energy transmission *** multichannel lossy resonance modes are combined,the resulting interference gives rise to nonreciprocity,with different coupling strengths for the forward and backward directions,and unidirectional energy *** study opens a new avenue for the design of nonreciprocal devices without stringent requirements.

关键词： backward generating directions

Optomechanical sensing with on-chip microcavities

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Frontiers of physics 2013年第5期8卷 475-490页

作者： Yi-Wen Hu Yun-Feng Xiao yong-chun liu Qihuang Gong State Key Laboratory for Artificial Microstructure and Mesoscopic Physics School of Physics Peking University Beijing 100871 China

The coupling between optical and mechanical degrees of freedom has been of broad interest for a long time. However, it is only until recently, with the rapid development of optical mierocavity research, that we are able to manipulate and utilize this coupling process. When a high Q microeavity couples to a mechanical resonator, they can consolidate into an optomeehanieal system. Benefitting from the unique characteristics offered by optomeehanical coupling, this hybrid system has become a promising platform for ultrasensitive sensors to detect displacement, mass, force and acceleration. In this review, we introduce the basic physical concepts of cavity optomechanies, and describe some of the most typical experimental cavity optomechanical systems for sensing applications. Finally, we discuss the noise arising from various sources and show the potentiality of optomechanical sensing towards quantum-noise-limited detection.

关键词： optical microcavities mechanical resonators cavity optomechanics optical sensing,integrated photonics

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What limits limits?

National Science Review 2021年第1期8卷 11-14页

作者： yong-chun liu Kun Huang Yun-Feng Xiao Lan Yang Cheng-Wei Qiu State Key Laboratory of Low-Dimensional Quantum Physics Department of Physics Frontier Science Center for Quantum Information Tsinghua University Department of Optics and Optical Engineering University of Science and Technology of China State Key Laboratory for Mesoscopic Physics and Frontiers Science Center for Nano-optoelectronics School of Physics Peking University Department of Electrical and Systems Engineering Washington University Department of Electrical and Computer Engineering National University of Singapore

There are fundamental rules and principles setting the limits of physical systems. It triggers an interesting thought—can we break the limits under specific circumstances? A realistic system can only provide limited functionalities because its performance is physically constrained by some fundamental principles.‘Breaking the limit’, which usually implies that the capability of a system could be enhanced significantly,

关键词： CAVITIES

A concise review of Rydberg atom based quantum computation and quantum simulation

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Chinese Physics B 2021年第2期30卷 1-22页

作者： Xiaoling Wu Xinhui Liang Yaoqi Tian Fan Yang Cheng Chen yong-chun liu Meng Khoon Te Li You State Key Laboratory of Low Dimensional Quantum Physics Department of PhysicsTsinghua UniversityBeijing 100084China School of Physical Sciences University of Chinese Academy of SciencesBeijing 100049China CAS Key Laboratory of Theoretical Physics Institute of Theoretical PhysicsChinese Academy of SciencesBeijing 100190China Frontier Science Center for Quantum Information Beijing 100084China Beijing Academy of Quantum Information Sciences Beijing 100193China

Quantum information processing based on Rydberg atoms emerged as a promising direction two decades *** experimental and theoretical progresses have shined exciting light on this *** this concise review,we will briefly introduce the basics of Rydberg atoms and their recent applications in associated areas of neutral atom quantum computation and *** shall also include related discussions on quantum optics with Rydberg atomic ensembles,which are increasingly used to explore quantum computation and quantum simulation with photons.

关键词： quantum computation quantum simulation Rydberg atom quantum nonlinear optics

On-chip topological nanophotonic devices

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Chip 2022年第4期1卷 1-21页

作者： Cui-Cui Lu Hong-Yi Yuan Hong-Yu Zhang Wen Zhao Nian-En Zhang Yan-Ji Zheng Sayed Elshahat yong-chun liu Key Laboratory of Advanced Optoelectronic Quantum Architecture and Mea-surements of Ministry of Education Beijing Key Laboratory of Nanophotonics and Ultrafine Optoelectronic SystemsSchool of PhysicsBeijing Institute of TechnologyBeijing 100081China State Key Laboratory of Low-Dimensional Quantum Physics Department of PhysicsFrontier Science Center for Quantum InformationTsinghua UniversityBeijing 100084China

On-chip topological nanophotonic devices,which take photons as in-formation carriers with topological protection during light propaga-tion,have great application potential in the next generation photonic *** topological photonic states enable the nanophotonic de-vices to be robust and stable,immune to scattering even with imper-fect *** development,opportunities and challenges of the on-chip topological nanophotonic devices have attracted great atten-tion of scholars,and desired to be *** this review,topologi-cal devices were introduced in the order of functionalities on an in-tegrated photonic chip,*** light source,topological light waveguiding,topological light division and selection,topological light manipulation and topological light ***,we gave out-looks for predicting and promoting the performances of on-chip topo-logical nanophotonic devices from the angles of non-Hermitian sys-tems,non-Abelian topology,metasurfaces,intelligent algorithms and multiple functional topological nanophotonic *** review provides rich knowledge about on-chip topological nanophotonic *** insights in this paper will spark inspiration and inspire new thinking for the realization of topological photonic chips.

关键词： Topological photonics Nanophotonic devices Photonic chip

Pb induced dislocation defects of PtCo systems: Strain-triggered oxygen reduction reaction for PEMFC

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Nano Research 2024年第4期17卷 2462-2472页

作者： chun Jin Qiheng Wang Jingjun liu Beijing Key Laboratory of Electrochemical Process and Technology for Materials Beijing 100029China Beijing University of Chemical Technology Beijing 100029China

Design and development of advanced electrocatalysts with high performance and low Pt consumption are crucial for reducing the kinetic energy barrier of the cathode oxygen reduction reaction(ORR)and improving the efficiency of proton exchange membrane fuel cells(PEMFC).In this study,we demonstrate a Pb-modulated PtCo system for efficient ORR,in which the inclusion of Pb in ternary alloys induces dislocation defects due to the significant difference in atomic ***-PtCoPb was confirmed to exhibit significantly higher ORR activity and stability in acidic *** practical PEMFC applications,it outperforms the corresponding commercial Pt/C with a mass activity of 0.58 A·mgPt^(-1),making it a promising alternative to state-of-the-art Pt-based *** combination of experimental results and density functional theory(DFT)calculations offers valuable atomic-level insights into the dislocation *** with a larger atomic radius is located in the lattice stretching region below the dislocation slip plane,forming a structure similar to a Cottrell atmosphere,which reduces the dislocation energy and puts the system in a lower energy *** Cottrell atmosphere pins the dislocation structure and stabilizes the ternary *** adjusting the amount of added Pb,a moderate level of dislocation density induces a tuned strain effect,thereby enhancing the electrocatalytic mechanism by optimizing the electronic structure of the alloy surface and the adsorption and desorption of oxygen *** work provides valuable insights into the design and development of lattice dislocation defect structures to trigger strain effects for improving ORR performance.

关键词： dislocation defect strain effect Pb-modulated oxygen reduction reaction