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Invalidity of Geometrical Interpretation of F-Spin Structure of Nuclear Rotations by Otsuka’s View

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Chinese Physics Letters 1995年第6期12卷 342-343页

作者： long guilu Department of Physics Tsinghua UniversityBeijing 100084

In Otsuka's view of nuclear rotations neutrons and protons are not rotating around a common axis,but rather around separate *** this letter,we pointed out that this invalidates the geometrical interpretation of F-spin structure of the neutron-proton interacting boson model,where the angle between the axis of symmetries of neutron ellipsoid and proton ellipsoid is used to determine whether a state is F-spin symmetric or mixed symmetric.

关键词： symmetric validity rotating

Entanglement purification for memory nodes in a quantum network

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Science China(Physics,Mechanics & Astronomy) 2020年第2期63卷 47-54页

作者： GuanYu Wang guilu long State Key Laboratory of Low-Dimensional Quantum Physics and Department of Physics Tsinghua UniversityBeijing 100084China Tsinghua National Laboratory of Information Science and Technology Beijing 100084China Collaborative Innovation Center of Quantum Matter Beijing 100084China

The entanglement between quantum memory nodes is a prerequisite in a quantum network, and the diamond nitrogen-vacancy(NV) center is a promising candidate serving as a quantum memory node. Here, we investigate the possibility of achieving an entanglement purification protocol(EPP) for entangled NV centers in distant diamonds. To construct the EPP, we design a nondestructive parity-check detector(PCD) utilizing an auxiliary polarization-entangled photon pair, which makes our EPP less time consuming and insensitive to the phase fluctuation of the optical path length. The satisfied fidelity of an NV center pair after purification and efficiency of obtaining a purified NV center pair with our EPP can be obtained with current experimental techniques in the realistic condition. This EPP is useful for a quantum network in which NV centers are used as quantum memory nodes.

关键词： entanglement purification memory nodes quantum network nitrogen-vacancy center system parity-check detectors

The q^2-Dependence of the Spin-Dependent Cross Section of WIMPs in the Single Particle Model

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Chinese journal of nuclear physics 1995年第2期17卷 113-117页

作者： long, guilu Tsinghua Univ Beijing China

The dependence on the momentum transfer of the spin-dependent cross sec-tion of weakly interacting massive particles(WIMPs) is studied in a single *** are obtained for various candidate detector nuclei.

关键词： Cross section Dark matter Neutralino

Experimental realization of single-shot nonadiabatic holonomic gates in nuclear spins

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Science China(Physics,Mechanics & Astronomy) 2017年第8期60卷 1-7页

作者： Hang Li Yang Liu guilu long State Key Laboratory of Low-Dimensional Quantum Physics and Department of Physics Tsinghua University Collaborative Innovation Centre of Quantum Matter School of Nuclear Science and Engineering North China Electric Power University Tsinghua National Laboratory for Information Science and Technology

Nonadiabatic holonomic quantum computation has received increasing attention due to its robustness against control errors. However, all the previous schemes have to use at least two sequentially implemented gates to realize a general one-qubit gate. Based on two recent reports, we construct two Hamiltonians and experimentally realized nonadiabatic holonomic gates by a single-shot implementation in a two-qubit nuclear magnetic resonance （NMR） system. Two noncommuting one-qubit holonomic gates, rotating along .~ and ~ axes respectively, are implemented by evolving a work qubit and an ancillary qubit nonadiabatically following a quantum circuit designed. Using a sequence compiler developed for NMR quantum information processor, we optimize the whole pulse sequence, minimizing the total error of the implementation. Finally, all the nonadiabatic holonomic gates reach high unattenuated experimental fidelities over 98%.

关键词： nonadiabatic holonomic quantum computation nuclear magnetic resonance quantum process tomography

Experimental quantum deletion in an NMR quantum information processor

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Science China(Physics,Mechanics & Astronomy) 2014年第7期57卷 1256-1261页

作者： long Yu FENG GuanRu PEARSON Jasong long guilu State Key Laboratory of Low-dimensional Quantum Physics and Department of Physics Tsinghua University Collaborative Innovation Center of Quantum Matter Tsinghua National Laboratory for Information Science and Technology Tsinghua University

We report an NMR experimental realization of a rapid quantum deletion algorithm that deletes marked states in an unsorted *** classical deletion,where search and deletion are equivalent,quantum deletion can be implemented with only a single query,which achieves exponential speed-up compared to the optimal classical *** the experimental realization,the GRAPE algorithm was used to obtain an optimized NMR pulse sequence,and the efficient method of maximum-likelihood has been used to reconstruct the experimental output state.

关键词： quantum deletion algorithm quantum computing nuclear magnetic resonance quantum search algorithm

Reconstructing unknown quantum states using variational layerwise method

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Frontiers of physics 2022年第5期17卷 137-148页

作者： Junxiang Xiao Jingwei Wen Shijie Wei guilu long State Key Laboratory of Low-Dimensional Quantum Physics and Department of Physics Tsinghua UniversityBeijing 100084China Beijing Academy of Quantum Information Sciences Beijing 100193China Frontier Science Center for Quantum Information Beijing 100084China Beijing National Research Center for Information Science and Technology Beijing 100084China

In order to gain comprehensive knowledge of an arbitrary unknown quantum state,one feasible way is to reconstruct it,which can be realized by finding a series of quantum operations that can refactor the unitary evolution producing the unknown *** design an adaptive framework that can reconstruct unknown quantum states at high fidelities,which utilizes SWAP test,parameterized quantum circuits(PQCs)and layerwise learning *** conduct benchmarking on the framework using numerical simulations and reproduce states of up to six qubits at more than 96%overlaps with original states on average using PQCs trained by our framework,revealing its high applicability to quantum systems of different scales ***,we perform experiments on a five-qubit IBM Quantum hardware to reconstruct random unknown single qubit states,illustrating the practical performance of our *** a certain reconstructing fidelity,our method can effectively construct a PQC of suitable length,avoiding barren plateaus of shadow circuits and overuse of quantum resources by deep circuits,which is of much significance when the scale of the target state is large and there is no a priori information on *** advantage indicates that it can learn credible information of unknown states with limited quantum resources,giving a boost to quantum algorithms based on parameterized circuits on near-term quantum processors.

关键词： variational quantum algorithm layerwise learning quantum state reconstructing

A Full Quantum Eigensolver for Quantum Chemistry Simulations

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Research 2020年第1期2020卷 111-121页

作者： Shijie Wei Hang Li guilu long Beijing Academy of Quantum Information Sciences Beijing 100193China State Key Laboratory of Low-Dimensional Quantum Physics and Department of Physics Tsinghua UniversityBeijing 100084China Beijing National Research Center for Information Science and Technology and School of Information Tsinghua University Beijing 100084China Frontier Science Center for Quantum Information Beijing 100084China

Quantum simulation of quantum chemistry is one of the most compelling applications of quantum *** is of particular importance in areas ranging from materials science,biochemistry,and condensed matter ***,we propose a full quantum eigensolver(FQE)algorithm to calculate the molecular ground energies and electronic structures using quantum gradient *** to existing classical-quantum hybrid methods such as variational quantum eigensolver(VQE),our method removes the classical optimizer and performs all the calculations on a quantum computer with faster *** gradient descent iteration depth has a favorable complexity that is logarithmically dependent on the system size and inverse of the ***,the FQE can be further simplified by exploiting a perturbation theory for the calculations of intermediate matrix elements and obtaining results with a precision that satisfies the requirement of chemistry *** full quantum eigensolver can be implemented on a near-term quantum *** the rapid development of quantum computing hardware,the FQE provides an efficient and powerful tool to solve quantum chemistry problems.

关键词： convergence quantum iteration

Dynamics and entanglement of a membrane-in-the-middle optomechanical system in the extremely-large-amplitude regime

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Science China(Physics,Mechanics & Astronomy) 2016年第1期59卷 45-52页

作者： Ming Gao FuChuan Lei ChunGuang Du guilu long State Key Laboratory of Low-dimensional Quantum Physics and Department of Physics tsinghua University Beiiine 100084 China Tsinghua National Laboratory of Information Science and Technology Beijing 100084 China Collaborative Innovation Center of Quantum Matter Beijing 100084 China

The study of optomechanical systems has attracted much attention, most of which are concentrated in the physics in the smallamplitude regime. While in this article, we focus on optomechanics in the extremely-large-amplitude regime and consider both classical and quantum dynamics. Firstly, we study classical dynamics in a membrane-in-the-middle optomechanical system in which a partially reflecting and flexible membrane is suspended inside an optical cavity. We show that the membrane can present self-sustained oscillations with limit cycles in the shape of sawtooth-edged ellipses and exhibit dynamical multistability. Then, we study the dynamics of the quantum fluctuations around the classical orbits. By using the logarithmic negativity, we calculate the evolution of the quantum entanglement between the optical cavity mode and the membrane during the mechanical oscillation. We show that there is some synchronism between the classical dynamical process and the evolution of the quantum entanglement.

关键词： optomechanics self-sustained oscillation entanglement membrane-in-the-middle optomechanical system MIMOS extremely-large-amplitude regime ELAR

Second-order magnetic field gradient-induced strong coupling between nitrogen-vacancy centers and a mechanical oscillator

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Science China(Physics,Mechanics & Astronomy) 2017年第7期60卷 17-24页

作者： Kang Cai RuiXia Wang ZhangQi Yin guilu long State Key Laboratory of Low-Dimensional Quantum Physics and Department of Physics Tsinghua University Beijing 100084 China Center for Quantum Information Institute for Interdisciplinary Information Sciences Tsinghua University Beijing 100084 China Tsinghua National Laboratory of Information Science and Technology Beijing 100084 China Collaborative Innovation Center of Quantum Matter Beijing 100084 China

We consider a cantilever mechanical oscillator(MO) made of diamond. A nitrogen-vacancy(NV) center lies at the end of the cantilever. Two magnetic tips near the NV center induce a strong second-order magnetic field gradient. Under coherent driving of the MO, we find that the coupling between the MO and the NV center is greatly enhanced. We studied how to generate entanglement between the MO and the NV center and realize quantum state transfer between them. We also propose a scheme to generate two-mode squeezing between different MO modes by coupling them to the same NV center. The decoherence and dissipation effects for both the MO and the NV center are numerically calculated using the present parameter values of the experimental configuration. We have achieved high fidelity for entanglement generation, quantum state transfer, and large twomode squeezing.

关键词： second-order magnetic field gradient NV center mechanical oscillator entanglement state transfer squeezing