共查询到20条相似文献,搜索用时 31 毫秒
1.
The speed of evolution of a qubit undergoing a nonequilibrium environment with spectral density of general ohmic form is investigated. First we reveal non-Markovianity of the model, and find that the non-Markovianity quantified by information backflow of Breuer et al. [Phys. Rev. Lett. 103 210401(2009)] displays a nonmonotonic behavior for different values of the ohmicity parameter s in fixed other parameters and the maximal non-Markovianity can be achieved at a specified value s. We also find that the non-Markovianity displays a nonmonotonic behavior with the change of a phase control parameter. Then we further discuss the relationship between quantum speed limit(QSL) time and non-Markovianity of the open-qubit system for any initial states including pure and mixed states. By investigation, we find that the QSL time of a qubit with any initial states can be expressed by a simple factorization law: the QSL time of a qubit with any qubitinitial states are equal to the product of the coherence of the initial state and the QSL time of maximally coherent states,where the QSL time of the maximally coherent states are jointly determined by the non-Markovianity, decoherence factor and a given driving time. Moreover, we also find that the speed of quantum evolution can be obviously accelerated in the wide range of the ohmicity parameter, i.e., from sub-Ohmic to Ohmic and super-Ohmic cases, which is different from the thermal equilibrium environment case. 相似文献
2.
G. Augello D. Valenti A. L. Pankratov B. Spagnolo 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,70(1):145-151
We study the transient statistical properties of short and long Josephson junctions under the influence of thermal and correlated
fluctuations. In particular, we investigate the lifetime
of the superconductive metastable state finding the presence of noise induced phenomena. For short Josephson junctions we
investigate the lifetime as a function both of the frequency of the current driving signal and the noise intensity and we
find how these noise-induced effects are modified by the presence of a correlated noise source. For long Josephson junctions
we integrate numerically
the sine-Gordon equation calculating the lifetime as a function of the length of the junction both for inhomogeneous and homogeneous
bias current distributions. We obtain a non-monotonic behavior of the lifetime as a function of the frequency of the current
driving signal and the correlation time of the noise. Moreover we find two maxima in the non-monotonic behaviour of the mean
escape time as a
function of the correlated noise intensity. 相似文献
3.
We study the noise in a quantum dot which is coupled to metallic leads by using the non-equation of motion technique at the Kondo temperature TK. We compute the out of equilibrium density of states, the current and the shot noise. We find that the shot noise exhibits a nonmonotonic dependence on the voltage when variation of εd values of the QD energy in the absence of the external magnetic field occurs. We also find that the amplitude of current exhibits a saturation behavior when driving field is increased. 相似文献
4.
S. Fugmann D. Hennig L. Schimansky-Geier I.M. Sokolov 《The European physical journal. Special topics》2010,191(1):187-210
We study collective escape phenomena in nonlinear chain models. First we investigate the fragmentation of an overdamped polymer
chain due to thermal fluctuations in the absence of an external force. We calculate the activation times of individual bonds
in the coupled chain system and compare them with times obtained from Brownian dynamics simulations. We also consider a grafted
chain exposed to an external force which monotonically grows as time goes on. In underdamped situations we show that collective
localized excitations in a nonlinear force field with absorbing states can cause polymer fragmentation. In a similar fashion,
localized modes assist a thermally activated escape of interacting particles in a metastable potential landscape which is
additionally subjected to a periodic driving. The latter is necessary to obtain overcritical elongations which create localized
modes even in case of stronger damping. 相似文献
5.
We study, within the spin-boson dynamics, the synchronization of a quantum tunneling system with an external, time-periodic driving signal. As a main result, we find that at a sufficiently large system-bath coupling strength (i.e., for a friction strength alpha > 1) the thermal noise plays a constructive role in yielding forced synchronization. This noise-induced synchronization can occur when the driving frequency is larger than the zero-temperature tunneling rate. As an application evidencing the effect, we consider the charge transfer dynamics in molecular complexes. 相似文献
6.
We study the dynamics of a single excitation in a Heisenberg spin-chain subjected to a sequence of periodic pulses from an external, parabolic, magnetic field. We show that, for experimentally reasonable parameters, a pair of counterpropagating coherent states is ejected from the center of the chain. We find an illuminating correspondence with the quantum time evolution of the well-known paradigm of quantum chaos, the quantum kicked rotor. From this we can analyze the entanglement production and interpret the ejected coherent states as a manifestation of the so-called "accelerator modes" of a classically chaotic system. 相似文献
7.
Xue-Jian Sun Wen-Xiao Liu Hao Chen Cheng-Yuan Wang Hui-Zhong Ma Hong-Rong Li 《理论物理通讯》2022,74(6):65101
In this work, we propose a high-fidelity phonon-mediated entangling gate in a hybrid mechanical system based on two silicon-vacancy color centers in diamond. In order to suppress the influence of the spin decoherence on the entangling gate, we use a continuous dynamical decoupling approach to create new dressed spin states, which are less sensitive to environmental fluctuations and exhibit an extended ${T}_{2}^{* }$ spin dephasing time. The effective spin–spin Hamiltonian modified by the mechanical driving field and the corresponding master equation are derived in the dispersive regime. We show that in the presence of the mechanical driving field, the effective spin–spin coupling can be highly controlled. By calculating the entangling gate fidelity in the dressed basis, we find that once the mechanical field is turned on, the gate fidelity can be significantly improved. In particular, under an optimized spin-phonon detuning and a stronger Rabi frequency of the mechanical driving field, the two-qubit gate is capable of reaching fidelity exceeding 0.99. Moreover, by employing appropriate driving modulation, we show that a high-fidelity full quantum gate can be also realized, in which the initial and final spin states are on a bare basis. Our work provides a promising scheme for realizing high-fidelity quantum information processing. 相似文献
8.
In this paper, we consider the thermal bath Lindblad master equation to describe the quantum nonunitary dynamics of quantum states in a multi-mode bosonic system. For the two-mode bosonic system interacting with an environment, we analyse how both the coupling between the modes and the coupling with the environment characterised by the frequency and the relaxation rate vectors affect dynamics of the entanglement. We discuss how the revivals of entanglement can be induced by the dynamic coupling between the different modes. For the system, initially prepared in a two-mode squeezed state, we find the logarithmic negativity as defined by the magnitude and orientation of the frequency and the relaxation rate vectors. We show that, in the regime of finite-time disentanglement, reorientation of the relaxation rate vector may significantly increase the time of disentanglement. 相似文献
9.
10.
We theoretically investigated a hybrid absorptive-dispersive optical bistability and multistability behaviour in a three-level V-type system using a microwave field driving a hyperfine transition between two upper excited states inside a unidirectional ring cavity. We find that the intensity and the frequency detuning of the coupling field as well as the intensity of the microwave field can affect the OM behaviour dramatically, which can be used to control the transition from OM to OB or vice versa without need to resort the effect of the quantum interference. The effects of the phase, the quantum interference and the atomic cooperation parameter on the OM are also studied. Our scheme may be used for building more efficient all-optical switches and logic-gate devices for optical computing and quantum information processing. 相似文献
11.
《Physica A》2005,351(1):117-125
A Markovian dichotomic system driven by a deterministic time-periodic force is analyzed in terms of the statistical properties of the switching events between the states. The consideration of the counting process of the switching events leads us to define a discrete phase. We obtain expressions for the instantaneous output frequency and phase diffusion associated to the dichotomic process, as well as for their cycle averages. These expressions are completely determined by the rates of escape from both states. They are a convenient starting point for the study of the stochastic frequency and phase synchronization in a wide range of situations (both classical and quantum) in which two metastable states are involved. 相似文献
12.
《Fortschritte der Physik》2017,65(1)
By analyzing the key properties of black holes from the point of view of quantum information, we derive a model‐independent picture of black hole quantum computing. It has been noticed that this picture exhibits striking similarities with quantum critical condensates, allowing the use of a common language to describe quantum computing in both systems. We analyze such quantum computing by allowing coupling to external modes, under the condition that the external influence must be soft‐enough in order not to offset the basic properties of the system. We derive model‐independent bounds on some crucial time‐scales, such as the times of gate operation, decoherence, maximal entanglement and total scrambling. We show that for black hole type quantum computers all these time‐scales are of the order of the black hole half‐life time. Furthermore, we construct explicitly a set of Hamiltonians that generates a universal set of quantum gates for the black hole type computer. We find that the gates work at maximal energy efficiency. Furthermore, we establish a fundamental bound on the complexity of quantum circuits encoded on these systems, and characterize the unitary operations that are implementable. It becomes apparent that the computational power is very limited due to the fact that the black hole life‐time is of the same order of the gate operation time. As a consequence, it is impossible to retrieve its information, within the life‐time of a black hole, by externally coupling to the black hole qubits. However, we show that, in principle, coupling to some of the internal degrees of freedom allows acquiring knowledge about the micro‐state. Still, due to the trivial complexity of operations that can be performed, there is no time advantage over the collection of Hawking radiation and subsequent decoding. 相似文献
13.
Zhi-Rong Zhong Lei Chen Jian-Qi Sheng Li-Tuo Shen Shi-Biao Zheng 《Frontiers of Physics》2022,17(1):12501
In this paper,we propose a scheme to achieve a multiphonon-resonance quantum Rabi model and adiabatic passage in a strong-coupling cavity optomechanical system.In the scheme,when the driving bichromatic laser beam is adjusted to the off-resonant j-order red-and blue-sideband,the interaction between the cavity and mechanical oscillator leads to a j-phonon resonance quantum Rabi model.Moreover,we show that there exists a resonant multi-phonon coupling via intermediate states connected by counter-rotating processes when the frequency of the simulated bosonic mode is near a fraction of the transition frequency of the simulated two-level system.As a typical example,we theoretically analyze the two-phonon resonance quantum Rabi model,and derive an effective Hamiltonian of the six-phonon coupling.Finally,we present a method of six-phonon generation based on adiabatic passage across the resonance.Numerical simulations confirm the validity of the proposed scheme.Theoretically,the proposed scheme can be extended to the realization of 3j-phonon state. 相似文献
14.
Peter Ashwin Jennifer Creaser Krasimira Tsaneva-Atanasova 《The European physical journal. Special topics》2018,227(10-11):1091-1100
We explore sequential escape behaviour of coupled bistable systems under the influence of stochastic perturbations. We consider transient escapes from a marginally stable “quiescent” equilibrium to a more stable “active” equilibrium. The presence of coupling introduces dependence between the escape processes: for diffusive coupling there is a strongly coupled limit (fast domino regime) where the escapes are strongly synchronised while for intermediate coupling (slow domino regime) without partially escaped stable states, there is still a delayed effect. These regimes can be associated with bifurcations of equilibria in the low-noise limit. In this paper, we consider a localized form of non-diffusive (i.e. pulse-like) coupling and find similar changes in the distribution of escape times with coupling strength. However, we find transition to a slow domino regime that is not associated with any bifurcations of equilibria. We show that this transition can be understood as a codimension-one saddle connection bifurcation for the low-noise limit. At transition, the most likely escape path from one attractor hits the escape saddle from the basin of another partially escaped attractor. After this bifurcation, we find increasing coefficient of variation of the subsequent escape times. 相似文献
15.
Sequences of residence times (RTs) associated with the escape from metastable states are observed in many fields. Here we study analytically and numerically the correlations among RTs for a bistable stochastic system driven by dichotomous noise. Our theory predicts an oscillatory behavior of the correlations with respect to the lag between RTs. Correlations vanish at all lags if the switching rate matches the hopping rate of the unperturbed system. It is also shown that RT correlations may reveal features of the driving which are not present in the single-RT statistics. 相似文献
16.
A. J. Daley J. Ye P. Zoller 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2011,65(1-2):207-217
Recent experimental progress with Alkaline-Earth atoms has opened the door to quantum computing schemes in which qubits are encoded in long-lived nuclear spin states, and the metastable electronic states of these species are used for manipulation and readout of the qubits. Here we discuss a variant of these schemes, in which gate operations are performed in nuclear-spin-dependent optical lattices, formed by near-resonant coupling to the metastable excited state. This provides an alternative to a previous scheme [Phys. Rev. Lett. 101, 170504 (2008)], which involved independent lattices for different electronic states. As in the previous case, we show how existing ideas for quantum computing with Alkali atoms such as entanglement via controlled collisions can be freed from important technical restrictions. We also provide additional details on the use of collisional losses from metastable states to perform gate operations via a lossy blockade mechanism. 相似文献
17.
We investigate the barriers separating metastable states in the spherical p-spin glass model using the instanton method. We show that the problem of finding the barrier heights can be reduced to the causal two-real-replica dynamics. We find the probability for the system to escape one of the highest energy metastable states and the energy barrier corresponding to this process. 相似文献
18.
J. Li G. S. Paraoanu 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2010,56(2):255-264
We analyze a system of two qubits embedded in two different environments. The qubits are coupled to each other and driven
on-resonance by two external classical sources.
In the secular limit, we obtain exact analytical results for the evolution of the system for several classes of two-qubit
mixed initial states. For Werner states we show that the decay of entanglement does not depend on coupling. For other initial
states with “X"-type density matrices we find that the sudden death time displays a rich dependence on the coupling energy and state parameters
due to the existence of processes of delayed sudden birth of entanglement. 相似文献
19.
We investigate the entanglement dynamics of a quantum system consisting of two two-level atoms in a cavity with classical driving fields in the presence of white noise.The cavity is initially prepared in the vacuum state.Generally,the entanglement of two atoms decreases with the intensity of the thermal fields and the coupling strength of the two-level atoms to the thermal fields.However,we find that the entanglement of the quantum system can be enhanced by adjusting the frequency and the strength of the classical driving fields in the presence of white noise. 相似文献