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1.
Dissipation and decoherence, and the evolution from pure to mixed states in quantum physics, are handled through master equations for the density matrix. By embedding elements of this matrix in a higher-dimensional Liouville-Bloch equation, the methods of unitary integration are adapted to solve for the density matrix as a function of time, including the nonunitary effects of dissipation and decoherence. The input requires only solutions of classical, initial value time-dependent equations. Results are illustrated for a damped, driven two-level system. 相似文献
2.
3.
Nayereh Majd Jahangir Payamara Fariba Daliri 《The European Physical Journal B - Condensed Matter and Complex Systems》2014,87(3):1-12
We have investigated the quantum phase transition in the ground state of collective Lipkin-Meshkov-Glick model (LMG model) subjected to decoherence due to its interaction, represented by a quantum channel, with an environment. We discuss the behavior of quantum and classical pair wise correlations in the system, with the quantumness of correlations measured by quantum discord (QD), entanglement of formation (EOF), measurement-induced disturbance (MID) and the Clauser-Horne-Shimony-Holt-Bell function (CHSH-Bell function). The time evolution established by system-environment interactions is assumed to be Markovian in nature and the quantum channels studied include the amplitude damping (AD), phase damping (PD), bit-flip (BF), phase-flip (PF), and bit-phase-flip (BPF) channels. One can identify appropriate quantities associated with the dynamics of quantum correlations signifying quantum phase transition in the model. Surprisingly, the CHSH-Bell function is found to detect all the phase transitions, even when quantum and classical correlations are zero for the relevant ground state. 相似文献
4.
A. K. Pal I. Bose 《The European Physical Journal B - Condensed Matter and Complex Systems》2012,85(1):36
The transverse Ising Model (TIM) in one dimension is the simplest model which exhibits a quantum phase transition (QPT). Quantities
related to quantum information theoretic measures like entanglement, quantum discord (QD) and fidelity are known to provide
signatures of QPTs. The issue is less well explored when the quantum system is subjected to decoherence due to its interaction,
represented by a quantum channel, with an environment. In this paper we study the dynamics of the mutual information I(ρ
AB
), the classical correlations C(ρ
AB
) and the quantum correlations Q(ρ
AB
), as measured by the QD, in a two-qubit state the density matrix of which is the reduced density matrix obtained from the
ground state of the TIM in 1d. The time evolution brought about by system-environment interactions is assumed to be Markovian
in nature and the quantum channels considered are amplitude damping, bit-flip, phase-flip and bit-phase-flip. Each quantum
channel is shown to be distinguished by a specific type of dynamics. In the case of the phase-flip channel, there is a finite
time interval in which the quantum correlations are larger in magnitude than the classical correlations. For this channel
as well as the bit-phase-flip channel, appropriate quantities associated with the dynamics of the correlations can be derived
which signal the occurrence of a QPT. 相似文献
5.
Irreversibility of a quantum walk induced by controllable decoherence employing random unitary operations 下载免费PDF全文
Quantum walk is different from random walk in reversibility and interference. Observation of the reduced re- versibility in a realistic quantum walk is of scientific interest in understanding the unique quantum behavior. We propose an idea to experimentally investigate the decoherence-induced irreversibility of quantum walks with trapped ions in phase space via the average fidelity decay. By introducing two controllable decoherence sources, i.e., the phase damping channel (i.e., dephasing) and the high temperature amplitude reservoir (i.e., dissipation), in the intervals between the steps of quantum walk, we find that the high temperature amplitude reservoir shows more detrimental effects than the phase damping channel on quantum walks. Our study also shows that the average fidelity decay works better than the position variance for characterizing the transition from quantum walks to random walk. Experimental feasibility to monitor the irreversibility is justified using currently available techniques. 相似文献
6.
运用量子轨迹和量子Monte Carlo仿真的方法,研究耗散退相干对周期驱动的量子Harper (quantum kicked Harper, QKH)模型量子计算的影响.数值仿真结果表明,一定强度的耗散干扰将破坏QKH特征状态的动态局域化以及相空间的随机网结构.以相位阻尼信道噪声模型为例分析了保真度的衰减规律以及可信计算时间尺度.与静态干扰相比,在干扰强度小于某一阈值时,耗散干扰下的可信计算时间尺度随量子比特的增加而快速下降;而在干扰强度大于该阈值时,静态干扰下的可信计算时间尺度下降更快. 相似文献
7.
运用量子轨迹和量子Monte Carlo仿真的方法,研究耗散退相干对周期驱动的量子Harper (quantum kicked Harper, QKH)模型量子计算的影响.数值仿真结果表明,一定强度的耗散干扰将破坏QKH特征状态的动态局域化以及相空间的随机网结构.以相位阻尼信道噪声模型为例分析了保真度的衰减规律以及可信计算时间尺度.与静态干扰相比,在干扰强度小于某一阈值时,耗散干扰下的可信计算时间尺度随量子比特的增加而快速下降;而在干扰强度大于该阈值时,静态干扰下的可信计算时间尺度下降更快.
关键词:
量子计算
量子Harper模型
主方程
量子Monte Carlo方法 相似文献
8.
We have studied the effect of environment induced pure decoherence on the generalized Jaynes-Cummings model (JCM). This generalized
JCM is introduced to take into account both atom-field interaction and a class of spin-orbit interactions in the same framework.
For generalized JCM with atom-field interaction, it is shown that along with the suppression of the oscillatory behaviour
of the atomic and field variables, in the steady state, atomic energy is transferred to the field or vice versa through the
dressed state coherence depending on the initial condition of the atom-field system and the model under consideration. It
is also shown that initial Poissonian field acquires a sub-Poissonian character in the steady state and thus all the nonclassical
properties are not erased by the decoherence in JCM. An interesting effect of this decoherence mechanism is that it affects
the population and coherence properties of the individual subsystem in a different way. As an example of generalized JCM with
spin-orbit interaction, the dynamics of spin of the hydrogen atom in a magnetic field is studied to show the effect of decoherence. 相似文献
9.
J. Bouda M. Koniorczyk A. Varga 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2009,53(3):365-372
Channels encrypting quantum bits by the application of randomly
chosen unitary operators are studied. Quantities based on averages of
linear entropies which characterize certain aspects
of the encoding quality and the non-malleability of the
channels are introduced. The relation between the entropy of the classical key and
the choice of the encryption operators with the behaviour of these
properties is discussed. The extension of exact private quantum
channels in order to improve non-malleability via additional
encryption operators is considered. 相似文献
10.
A. S. Sanz F. Borondo 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,44(2):319-326
A complete theoretical treatment in many problems relevant to
physics, chemistry, and biology requires considering the action
of the environment over the system of interest.
Usually the environment involves a relatively large number of degrees
of freedom, this making the problem numerically intractable from a
purely quantum-mechanical point of view.
To overcome this drawback, a new class of quantum trajectories is
proposed.
These trajectories, based on the same grounds as Bohmian ones, are
solely associated to the system reduced density matrix, since the
evolution of the environment degrees of freedom is not considered
explicitly.
Within this approach, environment effects come into play through a
time-dependent damping factor that appears in the system equations
of motion.
Apart from their evident computational advantage, this type of
trajectories also results very insightful to understand the system
decoherence.
In particular, here we show the usefulness of these trajectories
analyzing decoherence effects in interference phenomena, taking as
a working model the well-known double-slit experiment. 相似文献
11.
Zafer Gedik 《Solid State Communications》2006,138(2):82-85
We study an analytically solvable model for decoherence of a two spin system embedded in a large spin environment. As a measure of entanglement, we evaluate the concurrence for the Bell states (Einstein-Podolsky-Rosen pairs). We find that while for two separate spin baths all four Bell states lose their coherence with the same time dependence, for a common spin bath, two of the states decay faster than the others. We explain this difference by the relative orientation of the individual spins in the pair. We also examine how the Bell inequality is violated in the coherent regime. Both for one bath and two bath cases, we find that while two of the Bell states always obey the inequality, the other two violate the inequality at early times. 相似文献
12.
We study dynamics of nonclassical correlations by exactly solving a model consisting of two atomic qubits with spontaneous emission. We find that the nonclassical correlations defined by different measures give different qualitative characterizations of those correlations. The relative behaviors of those correlation measures are presented explicitly for various quantum states in the two-qubit atomic system. In particular, we find that the robustness of quantum correlations can be greatly enhanced by performing appropriate local unitary operations on the initial state of the system. 相似文献
13.
Perets HB Lahini Y Pozzi F Sorel M Morandotti R Silberberg Y 《Physical review letters》2008,100(17):170506
Quantum random walks are the quantum counterpart of classical random walks, and were recently studied in the context of quantum computation. Physical implementations of quantum walks have only been made in very small scale systems severely limited by decoherence. Here we show that the propagation of photons in waveguide lattices, which have been studied extensively in recent years, are essentially an implementation of quantum walks. Since waveguide lattices are easily constructed at large scales and display negligible decoherence, they can serve as an ideal and versatile experimental playground for the study of quantum walks and quantum algorithms. We experimentally observe quantum walks in large systems ( approximately 100 sites) and confirm quantum walks effects which were studied theoretically, including ballistic propagation, disorder, and boundary related effects. 相似文献
14.
We study entanglement teleportation in the two‐qubit XX Heisenberg model with pure phase decoherence taken into account. For some initial entangled states, pure phase decoherence has no effect on the teleported entanglement, while for others pure phase decoherence has a pronounced effect. In addition, entanglement sudden death happens in the latter case. 相似文献
15.
The important applications of quantum dot system are to implement logic operations and achieve universal quantum computing based on different quantum nonlocalities. Here, we characterize the quantum steering, Bell nonlocality, and nonlocal advantage of quantum coherence (NAQC) of quantum dot system suffering nonunital and unital channels. The results reveal that quantum steering, Bell nonlocality, and NAQC can display the traits of dissipation, enhancement, and freezing. One can achieve the detections of quantum steering, Bell nonlocality, and NAQC of quantum dot system in different situations. Among these quantum nonlocalities, NAQC is the most fragile, and it is most easily influenced by different system parameters. Furthermore, considering quantum dot system coupling with amplitude damping channel and phase damping channel, these quantum nonlocalities degenerate with the enlargement of the channel parameters $t$ and $\varGamma$. Remarkably, measurement reversal can effectively control and enhance quantum steering, Bell nonlocality, and NAQC of quantum dot system suffering from decoherence, especially in the scenarios of the amplitude damping channel and strong operation strength. 相似文献
16.
M. A.?de?Ponte A.?Cacheffo C. J.?Villas-B?as S. S.?Mizrahi M. H.Y.?Moussa 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2010,59(3):487-496
In this work, we identify the set of time-dependent pure states building the
statistical mixture to which a system, initially in a pure state, is driven by
the reservoir. This set of time-dependent pure states, composing what we term
a pure basis, are those that diagonalize the reduced density operator
of the system. Next, we show that the evolution of the pure-basis
states reveals an interesting phenomenon as the system, after decoherence,
evolves toward the equilibrium: the spontaneous recoherence of quantum
states. Around our defined recoherence time, the statistical mixture
associated with a special kind of initial states termed even-symmetric,
spontaneously undergoes a recoherence process, by which the initial state of
the system emerges from the mixture except for its reduced excitation drained
into the reservoir. This phenomenon reveals that the reservoir only shuffle
the original information carried out by the initial state of the system
instead of erasing it. Moreover, as the spontaneously recohered state occurs
only for asymptotic time, we also present a protocol to extract it from the
mixture through specific projective measurements. The password to retrieve the
original information stems is the knowledge of both the initial state itself
and the associated pure basis. A definition of the decoherence time of
an N-state superposition is also presented. 相似文献
17.
通过求解系统的Milburn方程,研究了两个二能级原子和单模场相互作用系统中原子间纠缠和贝尔不等式破坏随时间的演化特性,讨论了偶极相互作用、场与原子的失谐量对纠缠度以及贝尔不等式破坏的影响.结果表明:原子间偶极-偶极相互作用对纠缠度和贝尔不等式破坏有显著影响,失谐量增大会使两原子的纠缠度和贝尔不等式破坏变大,并且两原子所能达到稳定的纠缠受偶极相互作用系数与失谐量两者之差的影响.同时还发现两原子的纠缠与贝尔不等式破坏并不是单调的函数关系,很小的纠缠也可以产生贝尔不等式破坏.
关键词:
Milburn理论
偶极-偶极相互作用
失谐量
贝尔不等式破坏 相似文献
18.
Superconductive quantum circuits comprise quantized energy levels that may be coupled via microwave electromagnetic fields. Described in this way, one may draw a close analogy to atoms with internal (electronic) levels coupled by laser light fields. In this Letter, we present a superconductive analog to electromagnetically induced transparency that utilizes superconductive quantum circuit designs of present day experimental consideration. We discuss how a superconductive analog to electromagnetically induced transparency can be used to establish macroscopic coherence in such systems and, thereby, be utilized as a sensitive probe of decoherence. 相似文献
19.
Diósi L 《Physical review letters》2004,92(17):170401
The theory of decoherent histories is checked for the requirement of statistical independence of subsystems. Strikingly, this is satisfied only when the decoherence functional is diagonal in both its real and imaginary parts. Although the weakened condition of consistency (or weak decoherence), allowing a nondiagonal imaginary part, is sufficient for the assignment of probabilities, it may easily violate the statistical independence of subsystems. Therefore, weakened consistency conditions and various related generalizations of the concept of decoherent histories appear to be ruled out. The same conclusion is obtained independently, by claiming a plausible dynamical robustness of decoherent histories. 相似文献
20.
Among the most important parameters for the usefulness of quantum computers are the size of the quantum register and the decoherence time for the quantum information. The decoherence time is expected to get shorter with the number of correlated qubits, but experimental data are only available for small numbers of qubits. Solid-state nuclear magnetic resonance allows one to correlate large numbers of qubits (several hundred) and measure their decoherence rates. We use a modified magnetic dipole-dipole interaction to correlate the proton spins in a solid sample and observe the decay of the resulting highly correlated states. By systematically varying the number of correlated spins, we measure the increase of the decoherence rate with the size of the quantum register. 相似文献