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Incoherent control of two classes of finite-level quantum systems

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Journal of Systems Engineering and Electronics 2011年第4期22卷 679-683页

作者： Chunlin Chen 1,2 and Zhenquan Qin 3,1.Department of control and System Engineering,Nanjing University,Nanjing 210093,P.R.China 2.State Key Laboratory for Novel Software Technology,Nanjing University,Nanjing 210093,P.R.China 3.School of Software,Dalian University of Technology,Dalian 116620,P.R.China Department of control and System Engineering Nanjing University Nanjing 210093 P. R. China State Key Laboratory for Novel Software Technology Nanjing University Nanjing 210093 P. R. China School of Software Dalian University of Technology Dalian 116620 P. R. China

The incoherent control of finite-level quantum systems is investigated. Following a brief introduction to coherent control paradigms in quantum control, a control problem that can not be accomplished using only coherent control is presented. For such a control problem, it is proved that it can be accomplished using incoherent control based on projective measurement and coherent control for two classes of finite-level quantum systems, i.e., eigenstate controllable quantum systems and wavefunction controllable quantum systems.

关键词： quantum control eigenstate controllability wavefunction controllability coherent control incoherent control.

STATE TRANSFER control OF quantum SYSTEMS ON THE BLOCH SPHERE

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Journal of Systems Science & Complexity 2011年第3期24卷 506-518页

作者： Yuesheng LOU Shuang CONG Department of Automation University of Science & Technology of China Hefei 230027 China

The state transfer under control fields is analyzed based on the Bloch sphere representation of a single qubit. In order to achieve the target from an arbitrary initial state to a target state, the conditions that parameters should satisfy are deduced separately in two different requirements： One is in the case of the rotation angle around the x-axis being fixed and another is in the situation with a given evolution time. Several typical states trajectories are demonstrated by numerical simulations on the Bloch sphere. The relations between parameters and the trajectories are analyzed.

关键词： quantum control qubit state transfer trajectory the Bloch sphere.

control Protocol of Finite Dimensional quantum Systems

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Communications in Theoretical Physics 2013年第12期60卷 731-737页

作者：唐剑炬付洪忱 School of Physical Sciences and Technology Shenzhen University

An analytic control protocol of two types of finite dimensional quantum systems is proposed. The system can be driven to an arbitrary target state using cosine classical fields in finite cycles. The control parameters which are time periods of interaction between systems and control fields in each cycle are connected with the probability amplitudes of target states via trigonometrical functions and can be determined analytically.

关键词： quantum control control protocol control fields

Optimal control of quantum systems with SU(1,1)dynamical symmetry

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control Theory and Technology 2015年第3期13卷 211-220页

作者： Wenbin DONG Rebing WU Jianwu WU Chunwen LI Tzyh-Jong TARN Department of Automation Tsinghua University Center for quantum Information Science and Technology Tsinghua National Laboratory for Information Science and Technology(TNlist) Beijing Aerospace Automatic control Institute Electrical and Systems Engineering Department Washington University in St.Louis

SU（1,1） dynamical symmetry is of fundamental importance in analyzing unbounded quantum systems in theoretical and applied physics. In this paper, we study the control of generalized coherent states associated with quantum systems with SU（1,1） dynamical symmetry. Based on a pseudo Riemannian metric on the SU（1,1） group, we obtain necessary conditions for minimizing the field fluence of controls that steer the system to the desired final state. Further analyses show that the candidate optimal control solutions can be classified into normal and abnormal extremals. The abnormal extremals can only be constant functions when the control Hamiltonian is non-parabolic, while the normal extremals can be expressed by Weierstrass elliptic functions according to the parabolicity of the control Hamiltonian. As a special case, the optimal control solution that maximally squeezes a generalized coherent state is a sinusoidal field, which is consistent with what is used in the laboratory.

关键词： quantum control optimal control dynamical symmetry

Experimental demonstration of concatenated composite pulses robustness to non-static errors

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Science China(Physics,Mechanics & Astronomy) 2016年第9期59卷 46-51页

作者： Xing-Long Zhen Tao Xin Fei-Hao Zhang Gui-Lu Long State Key Laboratory of Low-Dimensional quantum Physics and Department of Physics Tsinghua University Beijing 100084 China Innovation Centre of quantum Matter Beijing 100084 China Tsinghua National Laboratory For Information Science and Technology Tsinghua University Beijing 100084 China

We examine the robustness of composite pulses to non-static classic noise in the NMR facility. Though these pulses are proposed to eliminate static, systematic errors, they are shown to be robust to time-varying noise with high-cut frequency up to near 10% of the Rabi frequency in a recent theoretical work. The CP pulses that are only robust to one kind of error have been implemented in various experiment platforms. In this paper we have compared the performance of reduced CinSK rc pulse, which is designed to cancel both the pulse length error and the off resonance error, to that of the primitive n pulse in a hybrid error environment. In order to achieve this target we have simultaneously injected noise to the RF output wave. The filter function formalism is employed to predict the evolution fidelity decay, which shows great consistency with the experiment data. Our work not only validates the superiority of reduced CinSK pulse but also indicates its sensitivity to the initial states, providing practical guidance in the noise suppression domain.

关键词： composite pulse filter function quantum control NMR

Simulations of superconducting quantum gates by digital flux tuner for qubits

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Chinese Physics B 2024年第7期33卷 210-222页

作者：耿霄何楷泳刘建设陈炜 Laboratory of Superconducting quantum Information Processing School of Integrated CircuitsTsinghua UniversityBeijing 100084China Beijing Innovation Center for Future Chips Tsinghua UniversityBeijing 100084China Beijing National Research Center for Information Science and Technology Beijing 100084China26

The interconnection bottleneck caused by limitations of cable number, inner space and cooling power of dilution refrigerators has been an outstanding challenge for building scalable superconducting quantum computers with the increasing number of qubits in quantum processors. To surmount such an obstacle, it is desirable to integrate qubits with quantum–classical interface(QCI) circuits based on rapid single flux quantum(RSFQ) circuits. In this work, a digital flux tuner for qubits(DFTQ) is proposed for manipulating flux of qubits as a crucial part of the interface circuit. A schematic diagram of the DFTQ is presented, consisting of a coarse tuning unit and a fine-tuning unit for providing magnetic flux with different precision to qubits. The method of using DFTQ to provide flux for gate operations is discussed from the optimization of circuit design and input signal. To verify the effectiveness of the method, simulations of a single DFTQ and quantum gates including a Z gate and an iSWAP gate with DFTQs are performed for flux-tunable transmons. The quantum process tomography corresponding to the two gates is also carried out to analyze the sources of gate error. The results of tomography show that the gate fidelities independent of the initial states of the Z gate and the iSWAP gate are 99.935% and 99.676%,respectively. With DFTQs inside, the QCI would be a powerful tool for building large-scale quantum computers.

关键词： quantum computation superconducting electronics quantum control

Experimental measurement of the quantum geometric tensor using coupled qubits in diamond

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National Science Review 2020年第2期7卷 254-260页

作者： Min Yu Pengcheng Yang Musang Gong Qingyun Cao Qiuyu Lu Haibin Liu Shaoliang Zhang Martin B.Plenio Fedor Jelezko Tomoki Ozawa Nathan Goldman Jianming Cai School of Physics Huazhong University of Science and Technology International Joint Laboratory on quantum Sensing and quantum Metrology Huazhong University of Science and Technology Institut für Quantenoptik & IQST Albert-Einstein Allee 11Universit?t Ulm Institut für Theoretische Physik & IQST Albert-Einstein Allee 11Universit?t Ulm Interdisciplinary Theoretical and Mathematical Sciences Program(iTHEMS) 6. Center for Nonlinear Phenomena and Complex Systems Université Libre de Bruxelles

Geometry and topology are fundamental concepts, which underlie a wide range of fascinating physical phenomena such as topological states of matter and topological defects. In quantum mechanics, the geometry of quantum states is fully captured by the quantum geometric tensor. Using a qubit formed by an NV center in diamond, we perform the first experimental measurement of the complete quantum geometric tensor. Our approach builds on a strong connection between coherent Rabi oscillations upon parametric modulations and the quantum geometry of the underlying states. We then apply our method to a system of two interacting qubits, by exploiting the coupling between the NV center spin and a neighboring13C nuclear spin. Our results establish coherent dynamical responses as a versatile probe for quantum geometry,and they pave the way for the detection of novel topological phenomena in solid state.

关键词： quantum geometry topological physics quantum measurement quantum control quantum information

Generation of two-axis countertwisting squeezed spin states via Uhrig dynamical decoupling

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Science China(Information Sciences) 2021年第2期64卷 227-236页

作者： Jiying ZHANG Shan WU Yongchang ZHANG Zhengwei ZHOU Institute for Interdisciplinary Research Jianghan University Department of Physics and Astronomy Aarhus University Key Laboratory of quantum Information University of Science and Technology of ChinaChinese Academy of Sciences

We propose a scheme to generate two-axis countertwisting squeezed spin states from a one-axis twisting Hamiltonian via Uhrig dynamical decoupling. The proposed scheme significantly reduces the number of control pulses or requires shorter evolution time compared to previous proposals. The minimum number of applied pulses changes relative to the spin number almost linearly. The proposed scheme significantly relieves the experimental demand on the applied pulses or the evolution time, and we expect it would be within the reach of current spin squeezing experiment.

关键词： squeezed spin states Uhrig dynamical decoupling control pulses quantum control quantum metrology quantum information science

Comparison of differential evolution, particle swarm optimization,quantum-behaved particle swarm optimization, and quantum evolutionary algorithm for preparation of quantum states

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Chinese Physics B 2023年第2期32卷 53-59页

作者：程鑫鲁秀娟刘亚楠匡森 Department of Automation University of Science and Technology of ChinaHefei 230027China Department of Mechanical Engineering The University of Hong KongHong Kong 999077China quantum Machines Unit Okinawa Institute of Science and Technology Graduate UniversityOkinawa 904-0495Japan

Four intelligent optimization algorithms are compared by searching for control pulses to achieve the preparation of target quantum states for closed and open quantum systems, which include differential evolution(DE), particle swarm optimization(PSO), quantum-behaved particle swarm optimization(QPSO), and quantum evolutionary algorithm(QEA).We compare their control performance and point out their differences. By sampling and learning for uncertain quantum systems, the robustness of control pulses found by these four algorithms is also demonstrated and compared. The resulting research shows that the QPSO nearly outperforms the other three algorithms for all the performance criteria *** conclusion provides an important reference for solving complex quantum control problems by optimization algorithms and makes the QPSO be a powerful optimization tool.

关键词： quantum control state preparation intelligent optimization algorithm