This paper shows that a proposal for implementing all possible two-operator positive-operator-value measurements of single spin qubit can be obtained via introducing another spin qubit as ancilla. The realization proc...This paper shows that a proposal for implementing all possible two-operator positive-operator-value measurements of single spin qubit can be obtained via introducing another spin qubit as ancilla. The realization process is accomplished from the free evolution of the Heisenberg XX model by considering nearest-neighbour spin interaction. A controlled- NOT gate, which is a significant operator for this scheme is also constructed and the generalisation to multiple-operator is considered finally.展开更多
We present a scheme for implementing robust quantum gates in decoherence-free subspaces(DFSs) with double-dot spin qubits. Through the resonator-assisted interaction, the controllable interqubit couplings can be achie...We present a scheme for implementing robust quantum gates in decoherence-free subspaces(DFSs) with double-dot spin qubits. Through the resonator-assisted interaction, the controllable interqubit couplings can be achieved only by adjusting the qubit transition frequencies. We construct a set of logic gates on the DFS-encoded qubits to eliminate the collective noise effects, and thus the gate fidelities can be enhanced remarkably. This proposal may offer a potential approach to realize the robust quantum computing with spin qubits.展开更多
We consider two typical approximations that are used in the microscopic calculations of double-quantum dot spin qubits, namely,the Heitler-London(HL) and the Hund-Mulliken(HM) approximations, which use linear combinat...We consider two typical approximations that are used in the microscopic calculations of double-quantum dot spin qubits, namely,the Heitler-London(HL) and the Hund-Mulliken(HM) approximations, which use linear combinations of Fock-Darwin states to approximate the two-electron states under the double-well confinement potential. We compared these results to a case in which the solution to a one-dimensional Schr ¨odinger equation was exactly known and found that typical microscopic calculations based on Fock-Darwin states substantially underestimate the value of the exchange interaction, which is the key parameter that controls the quantum dot spin qubits. This underestimation originates from the lack of tunneling of Fock-Darwin states, which is accurate only in the case with a single potential well. Our results suggest that the accuracies of the current two-dimensional molecularorbit-theoretical calculations based on Fock-Darwin states should be revisited since underestimation could only deteriorate in dimensions that are higher than one.展开更多
Thirty years of effort in semiconductor quantum dots has resulted in significant developments in the control of spin quantum bits（qubits）. The natural two-energy level of spin states provides a path toward quantum i...Thirty years of effort in semiconductor quantum dots has resulted in significant developments in the control of spin quantum bits（qubits）. The natural two-energy level of spin states provides a path toward quantum information processing. In particular, the experimental implementation of spin control with high fidelity provides the possibility of realizing quantum computing. In this review, we will discuss the basic elements of spin qubits in semiconductor quantum dots and summarize some important experiments that have demonstrated the direct manipulation of spin states with an applied electric field and/or magnetic field. The results of recent experiments on spin qubits reveal a bright future for quantum information processing.展开更多
We study an anisotropic spin cluster of 3 spin S=1/2 particles with antiferromagnetic exchange interactionwith non-uniform coupling constants.A time-dependent magnetic field is applied to control the time evolution of...We study an anisotropic spin cluster of 3 spin S=1/2 particles with antiferromagnetic exchange interactionwith non-uniform coupling constants.A time-dependent magnetic field is applied to control the time evolution of thecluster.It is well known that for an odd number of sites a spin cluster qubit can be defined in terms of the ground statedoublet.The universal one-qubit logic gate can be constructed from the time evolution operator of the non-autonomousmany-body system,and the six basic one-qubit gates can be realized by adjusting the applied time-dependent magneticfield.展开更多
We propose a deterministic generation and purification of decoherence-free spin entangled states with singlet-triplet spins in nanowire double quantum dots via resonator-assisted charge manipulation and measurement te...We propose a deterministic generation and purification of decoherence-free spin entangled states with singlet-triplet spins in nanowire double quantum dots via resonator-assisted charge manipulation and measurement techniques. Each spin qubit corresponds to two electrons in a double quantum dot in the nanowire, with the singlet and one of the triplets as the decoherence-free qubit states. The logical qubits are immunized against the dominant source of decoherence- dephasing--while the influences of additional errors are shown by numerical simulations. We analyse the performance and stability of all required operations and emphasize that all techniques are feasible in current experimental conditions.展开更多
Single-electron spins in quantum dots are the leading platform for qubits,while magnons in solids are one of the emerging candidates for quantum technologies.How to manipulate a composite system composed of both syste...Single-electron spins in quantum dots are the leading platform for qubits,while magnons in solids are one of the emerging candidates for quantum technologies.How to manipulate a composite system composed of both systems is an outstanding challenge.Here,we use spin-charge hybridization to effectively couple the single-electron spin state in quantum dots to the cavity and further to the magnons.Through this coupling,quantum dots can entangle and detect magnon states.The detection efficiency can reach 0.94 in a realistic experimental situation.We also demonstrate the electrical tunability of the scheme for various parameters.These results pave a practical pathway for applications of composite systems based on quantum dots and magnons.展开更多
Using the effective non-Markovian measure proposed by Breuer et al. recently, we study the memory effect of a central qubit system coupled to a spin chain environment with Dzyaloshinskii-Moriya interaction in a transv...Using the effective non-Markovian measure proposed by Breuer et al. recently, we study the memory effect of a central qubit system coupled to a spin chain environment with Dzyaloshinskii-Moriya interaction in a transverse field. It is discovered that the central qubit system presents different memory effects in different environment phases with the different oscillatory behaviors of the decoherence factor. Moreover, it is revealed that the Dzyaloshinskii-Moriya interaction has a prominent influence on the memory effect of a central qubit system via modifying the amplitude and period of the decoherence factor under certain conditions.展开更多
基金supported by the National Natural Science Foundation of China (Grant No.60667001)
文摘This paper shows that a proposal for implementing all possible two-operator positive-operator-value measurements of single spin qubit can be obtained via introducing another spin qubit as ancilla. The realization process is accomplished from the free evolution of the Heisenberg XX model by considering nearest-neighbour spin interaction. A controlled- NOT gate, which is a significant operator for this scheme is also constructed and the generalisation to multiple-operator is considered finally.
基金Supported by the National Natural Science Foundation of China under Grant Nos.11047006,11304267Programs for Science and Technology Innovation Talents in Universities of Henan Province under Grant No.13HASTIT049+2 种基金Young Backbone Teachers in Universities of Henan Province under Grant No.2012GGJS-173Prominent Young Backbone Talents of Xuchang Universitythe Natural Science Foundation of Zhejiang Province under Grant No.Y6110250
文摘We present a scheme for implementing robust quantum gates in decoherence-free subspaces(DFSs) with double-dot spin qubits. Through the resonator-assisted interaction, the controllable interqubit couplings can be achieved only by adjusting the qubit transition frequencies. We construct a set of logic gates on the DFS-encoded qubits to eliminate the collective noise effects, and thus the gate fidelities can be enhanced remarkably. This proposal may offer a potential approach to realize the robust quantum computing with spin qubits.
基金supported by the Research Grants Council of the Hong Kong Special Administrative Region of China(Grant No.City U 21300116)the National Natural Science Foundation of China(Grant No.11604277)the Guangdong Innovative and Entrepreneurial Research Team Program(Grant No.2016ZT06D348)
文摘We consider two typical approximations that are used in the microscopic calculations of double-quantum dot spin qubits, namely,the Heitler-London(HL) and the Hund-Mulliken(HM) approximations, which use linear combinations of Fock-Darwin states to approximate the two-electron states under the double-well confinement potential. We compared these results to a case in which the solution to a one-dimensional Schr ¨odinger equation was exactly known and found that typical microscopic calculations based on Fock-Darwin states substantially underestimate the value of the exchange interaction, which is the key parameter that controls the quantum dot spin qubits. This underestimation originates from the lack of tunneling of Fock-Darwin states, which is accurate only in the case with a single potential well. Our results suggest that the accuracies of the current two-dimensional molecularorbit-theoretical calculations based on Fock-Darwin states should be revisited since underestimation could only deteriorate in dimensions that are higher than one.
基金Project supported by the National Key R&D Program of China(Grant No.2016YFA0301700)the National Natural Science Foundation of China(Grant Nos.11674300,61674132,11575172,and 11625419)the Fundamental Research Fund for the Central Universities,China
文摘Thirty years of effort in semiconductor quantum dots has resulted in significant developments in the control of spin quantum bits（qubits）. The natural two-energy level of spin states provides a path toward quantum information processing. In particular, the experimental implementation of spin control with high fidelity provides the possibility of realizing quantum computing. In this review, we will discuss the basic elements of spin qubits in semiconductor quantum dots and summarize some important experiments that have demonstrated the direct manipulation of spin states with an applied electric field and/or magnetic field. The results of recent experiments on spin qubits reveal a bright future for quantum information processing.
文摘We study an anisotropic spin cluster of 3 spin S=1/2 particles with antiferromagnetic exchange interactionwith non-uniform coupling constants.A time-dependent magnetic field is applied to control the time evolution of thecluster.It is well known that for an odd number of sites a spin cluster qubit can be defined in terms of the ground statedoublet.The universal one-qubit logic gate can be constructed from the time evolution operator of the non-autonomousmany-body system,and the six basic one-qubit gates can be realized by adjusting the applied time-dependent magneticfield.
基金supported by the National Natural Science Foundation of China (Grant No. 11004029)the Natural Science Foundation of Jiangsu Province, China (Grant No. BK2010422)+2 种基金the Ph. D. Program Foundation of the Ministry of Education of Chinathe Excellent Young Teachers Program of Southeast Universitythe National Basic Research Development Program of China(Grant No. 2011CB921203)
文摘We propose a deterministic generation and purification of decoherence-free spin entangled states with singlet-triplet spins in nanowire double quantum dots via resonator-assisted charge manipulation and measurement techniques. Each spin qubit corresponds to two electrons in a double quantum dot in the nanowire, with the singlet and one of the triplets as the decoherence-free qubit states. The logical qubits are immunized against the dominant source of decoherence- dephasing--while the influences of additional errors are shown by numerical simulations. We analyse the performance and stability of all required operations and emphasize that all techniques are feasible in current experimental conditions.
基金Project supported by the National Natural Science Foundation of China(Grant No.11974336)the National Key Research and Development Program of China(Grant No.2017YFA0304100)
文摘Single-electron spins in quantum dots are the leading platform for qubits,while magnons in solids are one of the emerging candidates for quantum technologies.How to manipulate a composite system composed of both systems is an outstanding challenge.Here,we use spin-charge hybridization to effectively couple the single-electron spin state in quantum dots to the cavity and further to the magnons.Through this coupling,quantum dots can entangle and detect magnon states.The detection efficiency can reach 0.94 in a realistic experimental situation.We also demonstrate the electrical tunability of the scheme for various parameters.These results pave a practical pathway for applications of composite systems based on quantum dots and magnons.
基金supported by the National Natural Science Foundation of China(Grant Nos.11075101 and 11275119)
文摘Using the effective non-Markovian measure proposed by Breuer et al. recently, we study the memory effect of a central qubit system coupled to a spin chain environment with Dzyaloshinskii-Moriya interaction in a transverse field. It is discovered that the central qubit system presents different memory effects in different environment phases with the different oscillatory behaviors of the decoherence factor. Moreover, it is revealed that the Dzyaloshinskii-Moriya interaction has a prominent influence on the memory effect of a central qubit system via modifying the amplitude and period of the decoherence factor under certain conditions.
