Decoherence Factor Research Articles

Improving the estimation of environment parameters via a two-qubit scheme

We demonstrate how using two qubits can drastically improve the estimation of environment parameters compared to using only a single qubit. The two qubits are coupled to a common harmonic oscillator environment, and the properties of the environment are imprinted upon the dynamics of the two qubits. The reduced density matrix of only one of these qubits contains a decoherence factor and an additional factor taking into account the indirect interaction induced between the qubits due to the interaction with their common environment. This additional factor can drastically improve the estimation of the environment parameters, as quantified by the quantum Fisher information. In particular, we investigate the estimation of the cutoff frequency, the coupling strength, and the temperature using our two-qubit scheme compared to simply using a single qubit. We find that the precision of the estimates can be improved by orders of magnitude.

Dynamics of quantum coherence and correlations in a transverse Ising spin chain environment

In this paper, we study the dynamical processes of quantum coherence and correlations for two central qubits system coupled with a transverse Ising spin chain. Suppose the initial state of quantum system is the Werner state and the initial state of environment is the ground state of spin chain, and the corresponding time evolution operator, decoherence factor and reduced density matrix are given. We deduce the analytical expressions of evolution of quantum coherence, entanglement and quantum discord. We find that when the spin chain undergoes quantum phase transition (QPT), the entanglement vanished at time [Formula: see text], and the coherence and discord vanished when the decoherence factor decayed to zero. Besides, we also find that the environmental scale N, coupling strength g and parameter P of Werner state do not change the evolution rules of quantum correlation, but accelerate their decay rate with these parameters’ increase.

Dephasing Dynamics in a Non-Equilibrium Fluctuating Environment.

We performed a theoretical study of the dephasing dynamics of a quantum two-state system under the influences of a non-equilibrium fluctuating environment. The effect of the environmental non-equilibrium fluctuations on the quantum system is described by a generalized random telegraph noise (RTN) process, of which the statistical properties are both non-stationary and non-Markovian. Due to the time-homogeneous property in the master equations for the multi-time probability distribution, the decoherence factor induced by the generalized RTN with a modulatable-type memory kernel can be exactly derived by means of a closed fourth-order differential equation with respect to time. In some special limit cases, the decoherence factor recovers to the expression of the previous ones. We analyzed in detail the environmental effect of memory modulation in the dynamical dephasing in four types of dynamics regimes. The results showed that the dynamical dephasing of the quantum system and the conversion between the Markovian and non-Markovian characters in the dephasing dynamics under the influence of the generalized RTN can be effectively modulated via the environmental memory kernel.

Decoherence factor as a convolution: an interplay between a Gaussian and an exponential coherence loss

We identify and investigate the origin and nature of the transition between Gaussian and exponential forms of decoherence: the decoherence factor (that controls the time dependence of the off-diagonal terms of the density matrix expressed in the pointer basis representation) is the convolution of the Fourier transforms of the spectral density and of the overlap (between the eigenstates the environment with and without couplings to the system). Spectral density alone tends to lead to the (approximately) Gaussian decay of coherence while the overlap alone results in a (largely) exponential decay. We show that these two contributions combine as a convolution, their relative importance controlled by the strength of the system-environment coupling. The resulting decoherence factor in the strong and weak coupling limits leads to predominantly Gaussian or exponential decay, respectively, as is demonstrated with two paradigmatic examples of decoherence—a spin-bath model and the quantum Brownian motion.

Quantum security and theory of decoherence

We sketch a relation between two crucial, yet independent, fields in quantum information research, viz. quantum decoherence and quantum cryptography. We investigate here how the standard cryptographic assumption of shielded laboratory, stating that data generated by a secure quantum device remain private unless explicitly published, is disturbed by the einselection mechanism of quantum Darwinism explaining the measurement process by interaction with the external environment. We illustrate the idea with a paradigmatic example of a quantum random number generator compromised by a quantum analog of the Van Eck phreaking. In particular, we derive a trade-off relation between the eavesdropper’s guessing probability and the collective decoherence factor Γ of the simple form .

Memory effects on bidirectional teleportation

In this contribution, we have investigated the bidirectional quantum teleportation (BQT) of single qubit states using a Bell state influenced by decoherence channels with memory, dephasing and amplitude damping channels. The expressions of the partial transposed density operator, as a measure of the entanglement remaining in the BQT quantum channel, the teleportation fidelities and the quantum Fisher information are also evaluated. We find that both these last quantities depend on the survival amount of entanglement in the BQT quantum channel, on the decoherence factor and on the correlation degree of the decoherence channel. We show that in the Markovian regime, the Negativity, the teleportation average fidelities and the quantum Fisher information are slightly enhanced by considering the classical channel correlations. Besides, in the non-Markovian regime, these three quantities could be improved for a long period of time.

Quantum Decoherence Technique for Two Two-level Interacting Atomic Engineering in Dissipative Field.

In order to improve the in-depth understanding and research on the dissipative field of atomic engineering, the research object of this paper is the dissipative field of atomic engineering. Through the engineering of two two-level interacting atoms as the background, an in-depth study of two two-level atoms is carried out, so the decoherence factor of two two-level atoms is obtained. In this paper, the numerical simulation calculation experiment of the dissipative field of atomic engineering is carried out, and the evolution of the quantum coherent oscillation of the dissipative field to the quantum decoherence is discussed. The results indicate that the dissipation coefficient and strength of the atom-light field interaction not only affect the oscillation of the quantum coherent evolution of atomic states but also the periodicity of the evolution. All preliminary results throw light on the nature of two-level interacting atoms in the dissipative field of atomic engineering, which also provides a reference value for related researchers.

Quantum version of Prisoners’ Dilemma under interacting environment

Quantum game theory is a rapidly evolving subject that extends beyond physics. In this research work, a schematic picture of quantum game theory has been provided with the help of the famous game Prisoners’ Dilemma, where both of the prisoners possess an entangled qubit. Increasing the payoffs of the prisoners, quantum theory introduces a new Nash equilibrium. It has been considered that the shared qubits may interact with the environment, which is a bath of simple harmonic oscillators. This interaction introduces decoherence. Calculating the decoherence factor, we have shown that as time increases, the new Nash equilibrium disappears and accordingly the corresponding payoffs reduce. The decoherence factor has been analyzed for different time regions, and a characteristic time scale of decoherence has also been provided. A critical time scale, below which Alice and Bob can use the quantum strategy to achieve a higher payoff, has been described with its connection to the off-diagonal elements of the reduced density matrix of the prisoners. The critical time scale has also been discussed based on whether the decoherence occurred once or twice. A comparative discussion establishes that the process of decoherence is faster when it occurs twice. It needs to be mentioned here that the total time of decoherence is the same in both cases.

Decoherence and objectivity in higher spin environments

We analyze decoherence and objectivization processes in spin-spin models for arbitrary spins. We first derive the most general analytic form of the decoherence factor in the measurement limit, where the interaction Hamiltonian dominates the rest. We then analyze thermal environments and derive exact, analytic formulas for both the decoherence factor and the state fidelity of post-interaction environment states. This allows to analyze the objectivization process of the state of the central spin during the interaction. We do so using, so called, Spectrum Broadcast Structures (SBS), which are specific multipartite quantum states encoding a certain operation notion of objectivity. We analyze analytically (for short times) and numerically how higher spin influences the efficiency of decoherence and objectivization processes. As expected, the higher the spin of the environment, the more efficient decoherence and objectivization become. This work is a generalization of previous studies, limited to spin-$1/2$ systems only, and we hope will be useful in future objectivity experiments.

Quantum coherence of photons to cosmological distances

We identify potential sources of decoherence for $U(1)$ gauge bosons from a cosmological standpoint. Besides interactions with different species in the cosmological medium, we also consider effects due to the expansion of the Universe, which can produce particles (especially scalars) that can potentially interact with the photon in a quantum state. We look in particular at the case of axionlike particles and their predicted decay channels in our analysis. These interactions are shown to have a negligible effect as far as decoherence goes. Interaction rates with cosmic microwave background radiation or through Thomson scattering are small, so that the interstellar medium remains the biggest decoherence factor. Thus, quantum teleportation experiments with photon energies in the range 1--10 keV should be feasible at cosmological distances up to the galaxy formation epoch or beyond ($z\ensuremath{\sim}100$).

Sensing quantum chaos through the non-unitary geometric phase

Quantum chaos is usually characterized through its statistical implications on the energy spectrum of a given system. In this work we propose a decoherent mechanism for sensing quantum chaos. The chaotic nature of a many-body quantum system is sensed by studying the implications that it produces in the long-time dynamics of a probe coupled to it under a dephasing interaction. By introducing the notion of an effective averaged decoherence factor, we show that the correction to the geometric phase acquired by the probe with respect to its unitary evolution can be exploited as a robust tool for sensing the integrable to chaos transition of the many-body quantum system to which it is coupled. This sensing mechanism is verified for several systems with different types of symmetries, disorder and even in the presence of long-range interactions, evidencing its universality.

Decoherence dynamics of a charged particle within a non-demolition type interaction in non-commutative phase-space

This paper studies decoherence without dissipation of charged magneto-oscillator in the framework of quantum non-demolition type interaction in non-commutative phase-space. The master equation is derived considering the non-commutativity effects of a bath of harmonic oscillators to study the dynamics of such a system, and its possible exact solution is presented. By analyzing this solution, it turns out that the process involving decoherence without energy dissipation can be observed explicitly. In addition, the decoherence factor and the measure of coherence via linear entropy dynamic are deduced for two types of reservoir, namely the ohmic and super-ohmic reservoirs at low and high temperature limits. Numerical results obtained show that the coherence is better preserved in the system when non-commutativity effects are taken into account at low temperature, while the inverse phenomenon is observed at high temperature. Moreover, by kindly adjusting the non-commutative parameters, it is possible to improve the coherence time scale of the system. Another interesting result can be observed from the system’s coherence time scale, which is very sensitive to the magnetic field and thus adding to non-commutative parameters, it may be useful to control decoherence in the system.

Analyzing entropic uncertainty bound in two qubits coupled to a spin environment

By assuming a general pure state and a mixed Werner state as two initial states, we investigate the time evolution of entropic uncertainty bound in the presence of quantum memory for a two-qubit system interacting with an XY spin chain regarded as an environment constrained to carry the energy current. We obtain an explicit relationship between the entropic uncertainty bound and decoherence factor, and analytically study the dynamical process of entropic uncertainty bound for both weak and strong-coupling cases in two initial states. Our results reveal that the evolution of entropic uncertainty bound depends not only on the energy current, the system-environment couplings and the anisotropy parameter but also on the size of the environmental XY spin chain. Interestingly, we find that the entropic uncertainty bound can be suppressed by reducing the energy current on the environmental spin chain in a weak-coupling region, however, it has no sensitivity to the energy current in a strong-coupling region.

Geometry for a Symmetrıc 2-Path Atom Interferometer Model

It is often argued that the sensitivity of atom interferometer depends on the geometry of the interfering atom paths, conventionally, atom interferometer are usually configured to be sensitive to all deformations including tensor and scalar field deformations, it is a promising and robust tool for obtaining a highly sensitive and accurate measurements of gravitational signals, as such they are potentially capable of testing a wide range of fundamental physics questions including gravitational decoherence. Therefore, motivated by the recent search to improve the sensitivity of the next generation atom interferometer, we derived a broad class of equations that obeys a specific geometric configuration for the interfering paths for a 2-level atom interferometer model, and in doing so, we further analysed various configurations for the geometric interpretation, in addition to interferometric influence phase shift and a possible decoherence factor which could lead to a systematic theoretical framework for future sensing of weak forces, due to, for example, gravitational waves and light dark matter.

Enhancing nonlocal advantage of quantum coherence in correlated quantum channels

We explore decay behaviors of the nonlocal advantage of quantum coherence (NAQC) for two qubits traversing the phase flap, bit flip, bit-phase flip, and depolarizing channels. For the input Bell and Bell-diagonal states, we showed analytically that the NAQC of the output states can always be noticeably enhanced due to the correlations between consecutive uses of these quantum channels, and the degree of minimum correlation needed for achieving the NAQC increases with an increase in the decoherence factor. We also explored a colored dephasing channel which enables one to compare the cooperation mechanism of two different origins of memory effects in enhancing the NAQC.

Geometric decoherence in diffusive open quantum systems

Based on a generic quantum open system model, we study the geometric nature of decoherence by defining a complex-valued geometric phase through stochastic pure states describing non-unitary, non-cyclic and non-adiabatic evolutions. The ensemble average of the complex geometric phases for the pure stochastic states yields a conventional geometric phase together with an amplitude factor. We show that the decoherence process described by the decaying amplitude can be a geometric quantity independent of the system's dynamics. It is a remarkable fact that the geometric phase of a quantum system can serve as an ideal realisation of quantum gates due to its robustness against dynamical errors, however, in this paper we show that, for some open quantum systems, a desirable geometric phase may be accompanied by an unwanted robust geometric decoherence factor. Two exactly solvable models are studied to demonstrate that, while the decoherence is a purely dynamical effect for a dephasing two-level model, the decoherence in a dissipative two-level model can be a geometric process. Finally, we show that such a geometric decoherence effect may be eliminated by a non-perturbative control scheme.

Quantum Dynamics in a Fluctuating Environment

We theoretically investigate the dynamics of a quantum system which is coupled to a fluctuating environment based on the framework of Kubo-Anderson spectral diffusion. By employing the projection operator technique, we derive two types of dynamical equations, namely, time-convolution and time-convolutionless quantum master equations, respectively. We derive the exact quantum master equations of a qubit system with both diagonal splitting and tunneling coupling when the environmental noise is subject to a random telegraph process and a Ornstein-Uhlenbeck process, respectively. For the pure decoherence case with no tunneling coupling, the expressions of the decoherence factor we obtained are consistent with the well-known existing ones. The results are significant to quantum information processing and helpful for further understanding the quantum dynamics of open quantum systems.

Decoherence factor in quantum phase transition

As a fundamental quantity in quantum dynamics, decoherence factor reflects the influence on the system brought by the environment. In this work, we mainly investigate the dynamical behavior of decoherence factor in the quantum phase transition progresses, from the perspective of its phase information, amplitude information, real part information, and imaginary part information. Through two significant models, we show that most of these quantities can act as a witness of quantum phase transition phenomena and correctly reveal the locations of the critical points.

Non-Markovian decoherence dynamics in nonequilibrium environments

We theoretically investigate the non-Markovian dynamical decoherence of a quantum system coupled to nonequilibrium environments with nonstationary statistical properties. We show the time evolution of the decoherence factor in real-imaginary space to study the environment-induced energy renormalization and backaction of coherence which are associated with the unitary and nonunitary parts of the quantum master equation, respectively. It is also shown that the nonequilibrium decoherence dynamics displays a transition between Markovian and non-Markovian and the transition boundary depends on the environmental parameters. The results are helpful for further understanding non-Markovian dynamics and coherence backaction on an open quantum system from environments.

Steady-state measurement-induced nonlocality in thermal reservoir

We examined measurement-induced nonlocality (MIN) of a central system for which every of the constituent qubit is embedded in its respective independent thermal reservoir. By introducing anisotropy to the Heisenberg XY interaction of the qubits, we showed that the strength of the MIN can be enhanced apparently. The anisotropy of the spin interaction can also be employed to generate MIN from the initial zero-MIN states. In the infinite-time limit, the steady-state MIN is independent of the initial states and is determined solely by the anisotropic parameter of the system and the decoherence factor of the thermal reservoir.