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Journal of Modern Physics 2012年第9期3卷 902-917页

作者： Pablo Carlos López Vázquez Gustavo López Vázquez Departamento de Física Universidad de Guadalajara Guadalajara Mexico

We develop in the weak coupling approximation a quasi-non-Markovian master equation and study the phenomenon of decoherence during the operation of a controlled-not (CNOT) quantum gate in a quantum computer model formed by a linear chain of three nuclear spins system with second neighbor Ising interaction between them. We compare with the behavior of the Markovian counterpart for temperature different from zero (thermalization) and at zero temperature for low and high dissipation rates. At low dissipation there is a very small difference between Markovian and quasi no-Markovian at any temperature which is unlikely to be measured, and at high dissipation there is a difference which is likely to be measured at any temperature.

关键词： decoherence Chain of Nuclear Spins Controlled-Not

Time Dependent Entropy and decoherence in a Modified Quantum Damped Harmonic Oscillator

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Journal of Quantum Information Science 2014年第4期4卷 214-226页

作者： F. B. Pelap A. Fomethe A. J. Fotue M. P. Djemmo Tabue Laboratoire de Mécanique et de Modélisation des Systèmes Physiques (L2MSP) Faculté des Sciences Université de Dschang Dschang Cameroon Laboratory of Mesoscopy and Multilayers Structures Faculty of Science University of Dschang Dschang Cameroon

The time dependence of probability and Shannon entropy of a modified damped harmonic oscillator is studied by using single and double Gaussian wave functions through the Feynman path method. We establish that the damped coefficient as well as the system frequency and the distance separating two consecutive waves of the initial double Gaussian function influences the coherence of the system and can be used to control its decoherence.

关键词： Modified Damped Harmonic Oscillator Feynman Path Integral decoherence Shannon Entropy Distribution Probability

Study of decoherence on the Teleportation Algorithm in a Chain of Three Nuclear Spins System

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Journal of Modern Physics 2013年第1期4卷 68-75页

作者： G. V. López P. López Departamento de Física Universidad de Guadalajara Blvd. Marcelino García Barragán y Calzada Olímpica Guadalajara Mexico

We make a numerical study of decoherence on the teleportation algorithm implemented in a linear chain of three nuclear spins system. We study different types of environments, and we determine the associated decoherence time as a function of the dissipative parameter. We found that the dissipation parameter to get a well defined quantum gates (without significant decoherence) must be within the range of γ≤4×10-4 for not thermalized case, which was determined by using the purity parameter calculated at the end of the algorithm. For the thermalized case the decoherence is stablished for very small dissipation parameter, making almost not possible to implement this algorithm for not zero temperature.

关键词： Teleportation decoherence Nuclear Spin

Study of decoherence of Entangled States Made up of Two Basic States in a Linear Chain of Three Qubits

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Journal of Modern Physics 2015年第11期6卷 1701-1710页

作者： Gustavo López Velázquez Gustavo Montes Cabrera Departamento de Física Universidad de Guadalajara Blvd. Marcelino García Barragan y Calzada Olímpica Guadalajara Mexico

Using Lindblad approach to study decoherence of quantum systems, we study the decoherence and decay of entangled states, formed by two basic states of a chain of thee qubits. We look on these states for a possible regular dependence on their decay as a function of their energy separation between the basic states under different types of environments. We didn’t find regular or significant dependence on this energy separation for the type of environment considered.

关键词： Study of decoherence of Entangled States Made up of Two Basic States in a Linear Chain of Three Qubits decoherence Entangled States Three Quits Linear Chain

Study of decoherence of Elementary Gates Implemented in a Chain of Few Nuclear Spins Quantum Computer Model

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Journal of Modern Physics 2012年第1期3卷 85-101页

作者： G. V. López P. López 不详

We study the phenomenon of decoherence during the operation of one qubit transformation, controlled-not (CNOT) and controlled-controlled-not (C2NOT) quantum gates in a quantum computer model formed by a linear chain of three nuclear spins system. We make this study with different type of environments, and we determine the associated decoherence time as a function of the dissipative parameter. We found that the dissipation parameter to get a well defined quantum gates (without significant decoherence) must be within the range of . We also study the behavior of the purity parameter for these gates and different environments and found linear or quadratic decays of this parameter depending on the type of environments.

关键词： decoherence Not Gate Controlled-Not Gates Controlled-Controlled-Not Gate Nuclear Spin Chain Quantum Computer

Feedback Control of decoherence:Systems Theoretical Approach

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Feedback Control of Decoherence:Systems Theoretical Approach

Restoring electronic coherence/decoherence for a trajectory-based nonadiabatic molecular dynamics

第25届中国控制会议

作者： Narayan Ganesan Tzyh Jong Tarn Electrical and Systems Engineering Washington University in St．LouisM0-63130USA Electrical and Systems Engineering Washington University in St．LouisM0-63130USA

＜正＞This paper outlines the recent work on control of decoherence in Open Quantum systems using systems and control techniques and the corresponding theoretical results obtained.

关键词： Quantum Control decoherence Geometric Control

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Restoring electronic coherence/decoherence for a trajectory-...

Progress in superconducting qubits from the perspective of coherence and readout

第十五届全国化学动力学会议

作者：朱超原 Department of Applied Chemistry Chaio-Tung University

Trajectory-based molecular dynamics（MD） simulations assume nuclear motions governed by Newton equations associated with the potential energy surfaces. MD simulation on a single potential energy surface results in average reaction probability and rate constant in accordance with exact calculation of quantum wavepacket. This is because trajectory simulation averages out quantum interference from different vibrational quantum states. On the other hand, nonadiabatic MD simulation on coupled potential energy surfaces results in semiclassical nonadiabatic switching probability that may overestimate or underestimate nonadiabatic quantum interference of exact quantum wavepacket. As the result, semiclassical methods usually add electronic coherence/decoherence into simulation of nonadiabatic switching probability. This is because numerically obtained nonadiabatic switching probability suffers overcoherent problems and these coupled semiclassical electronic states must decohere. In particular, Tully’s fewest switching and semicalssical Ehrenfest hopping algorithms that are suitable for large-scale nonadiabatic molecular dynamics simulations have attracted the great attention. Various efforts have been made to improve decoherence/coherence effects to some extent but at either high computational cost or through the use of complicated algorithms. We have recently figured out simple but accurate new coupled equations with minimum modification to original coupled electronic semiclassical equations, and within the new coupled equations both Tully’s fewest switching and semicalssical Ehrenfest hopping algorithms present nonadiabatic switching probability in excellent agreement with exact quantum simulations [1].

关键词： Coherence decoherence Molecular dynamics Nonadiabatic transition Quantum wavepacket

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Chinese Physics B 2013年第11期22卷 76-90页

作者：钟有鹏李春燕王浩华陈宇 Department of Physics Zhejiang University Department of Physics University of CaliforniaSanta Barbara

Superconducting qubits are Josephson junction-based circuits that exhibit macroscopic quantum behavior and can be manipulated as artificial atoms. Benefiting from the well-developed technology of microfabrication and microwave engineering, superconducting qubits have great advantages in design flexibility, controllability, and scalability. Over the past decade, there has been rapid progress in the field, which greatly improved our understanding of qubit decoherence and circuit optimization. The single-qubit coherence time has been steadily raised to the order of 10 to 100 p.s, allowing for the demonstration of high-fidelity gate operations and measurement-based feedback control. Here we review recent progress in the coherence and readout of superconducting qubits.

关键词： superconducting qubit Josephson junction quantum non-demolition measurement decoherence

Superconducting phase qubits with shadow-evaporated Josephson junctions

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Chinese Physics B 2017年第6期26卷 61-65页

作者：宿非凡刘伟洋徐晖凯邓辉李志远田野朱晓波郑东宁吕力赵士平 Beijing National Laboratory for Condensed Matter Physics Institute of Physics Chinese Academy of Sciences Beijing 100190 China School of Physical Sciences University of Chinese Academy of Sciences (CAS) Beijing 100049 China National Laboratory of Solid State Microstructures School of Physics Nanjing University Nanjing 210093 China CAS Center for Excellence and Synergetic Innovation Center in Quantum Information and Quantum Physics University of Science and Technology of China Hefei 230026 China Collaborative Innovation Center of Quantum Matter Beijing China

We develop a fabrication process for the superconducting phase qubits in which Josephson junctions for both the qubit and superconducting quantum interference device（SQUID） detector are prepared by shadow evaporation with a suspended bridge. Al junctions with areas as small as 0.05 μm^2 are fabricated for the qubit, in which the number of the decoherencecausing two-level systems（TLS） residing in the tunnel barrier and proportional to the junction area are greatly reduced. The measured energy spectrum shows no avoided crossing arising from coherent TLS in the experimentally reachable flux bias range of the phase qubit, which demonstrates the energy relaxation time T1 and dephasing time Tφ on the order of 100 ns and 50 ns, respectively. We discuss several possible origins of decoherence from incoherent or weakly-coupled coherent TLS and further improvements of the qubit performance.

关键词： superconducting phase qubit two-level system decoherence shadow evaporated junction

Dynamics of a multi-mode maximum entangled coherent state over an amplitude damping channel

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Chinese Physics B 2011年第11期20卷 67-73页

作者： A.El Allati Y.Hassouni N.Metwally Faculté des Sciences Laboratoire de Physique Theorique URAC 13Université Mohammed V-Agdal The Abdus Salam International Centre for Theoretical Physics Mathematics Department College of ScienceUniversity of Bahrain Mathematics Department Faculty of ScienceSouth Valley University

The dynamics of the maximum entangled coherent state traveling through an amplitude damping channel is investigated. For small values of the transmissivity rate, the traveling state is very fragile to this noise channel, which suffers from the phase flip error with high probability. The entanglement decays smoothly for larger values of the transmissivity rate and speedily for smaller values of this rate. As the number of modes increases, the traveling state over this noise channel quickly loses its entanglement. The odd and even states vanish at the same value of field intensity.

关键词： entanglement quantum communication decoherence coherent states