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Geometric discord for non-X states 被引量:1
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作者 刘辰 董裕力 朱士群 《Chinese Physics B》 SCIE EI CAS CSCD 2014年第6期56-62,共7页
The level surfaces of geometric discord for a class of two-qubit non-X states are investigated when the Bloch vectors are in arbitrary directions. The level surfaces of constant geometric discord are formed by three i... The level surfaces of geometric discord for a class of two-qubit non-X states are investigated when the Bloch vectors are in arbitrary directions. The level surfaces of constant geometric discord are formed by three intersecting open tubes along three orthogc^nal directions. When Bloch vectors increase, the tubes along one or two directions shrink towards the center and may either totally disappear or the open tubes may become closed tubes when the Bloch vectors reach a critical value. In the generalized amplitude damping channel, the evolution of geometric discord shows double sudden changes when the parameter γ, increases. In the phase damping channel, the freezing phenomenon of geometric discord also exists. 展开更多
关键词 geometric discord non-X states bloch vectors generalized amplitude damping channel phasedamping channel
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Geometrical representation of coherent tunneling process in two-waveguide and three-waveguide coupler
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作者 时坚 马瑞琼 +3 位作者 段作梁 梁猛 柴宝玉 董军 《Chinese Physics B》 SCIE EI CAS CSCD 2017年第12期324-331,共8页
We propose an identical geometrical representation scheme for both Landau-Zener (LZ) tunneling process in two-waveguide coupler with a cubically bent structure and stimulated Raman adiabatic passage (STIRAP) in th... We propose an identical geometrical representation scheme for both Landau-Zener (LZ) tunneling process in two-waveguide coupler with a cubically bent structure and stimulated Raman adiabatic passage (STIRAP) in three-waveguide coupler, similar to the geometrical representation of sum frequency process. The results show that although the two-waveguide coupler with a cubically bent axis has not aperiodic structure, it acts as a chirped quasi-phase-matching (QPM) grating and corrects the relative phase between the two supermodes in the curved coupler system. We present a scheme about how to choose the parameters to design the curved beam splitter. 展开更多
关键词 optical coupler adiabatic passage non-adiabatic passage bloch vector
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Nonlinear and non-CP gates for Bloch vector amplification
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作者 Michael R Geller 《Communications in Theoretical Physics》 SCIE CAS CSCD 2023年第10期51-59,共9页
Any state r=(x,y,z)of a qubit,written in the Pauli basis and initialized in the pure state r=(0,0,1),can be prepared by composing three quantum operations:two unitary rotation gates to reach a pure state r=(x^(2)+y^(2... Any state r=(x,y,z)of a qubit,written in the Pauli basis and initialized in the pure state r=(0,0,1),can be prepared by composing three quantum operations:two unitary rotation gates to reach a pure state r=(x^(2)+y^(2)+z^(2))-1/2×(x,y,z)on the Bloch sphere,followed by a depolarization gate to decrease|r|.Here we discuss the complementary state-preparation protocol for qubits initialized at the center of the Bloch ball,r=0,based on increasing or amplifying|r|to its desired value,then rotating.Bloch vector amplification increases purity and decreases entropy.Amplification can be achieved with a linear Markovian completely positive trace-preserving(CPTP)channel by placing the channel’s fixed point away from r=0,making it nonunital,but the resulting gate suffers from a critical slowing down as that fixed point is approached.Here we consider alternative designs based on linear and nonlinear Markovian PTP channels,which offer benefits relative to linear CPTP channels,namely fast Bloch vector amplification without deceleration.These gates simulate a reversal of the thermodynamic arrow of time for the qubit and would provide striking experimental demonstrations of non-CP dynamics. 展开更多
关键词 nonlinear channels non-completely positive channels bloch vector amplification
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