Bosonic Reservoir Research Articles

多个玻色库下的自旋压缩动力学

多个玻色库下的自旋压缩动力学

Protection of quantum Fisher information for multiple phases in open quantum systems

We study the protection of quantum Fisher information (QFI) of two phases encoded in an open V-type three-level atom embedded in a zero-temperature bosonic reservoir and driven by a classical field. By transforming the problem into the model of an open driving-free V-type atom, we can then solve the dynamics analytically and study the evolution of QFI numerically. It is found that the QFI of both of the two phases can be protected effectively when the strength of the driving field is adequate. The protective effect enhances with the decrease in detuning between the frequency of the classical driving field and the frequency of the atomic transitions. Narrow width of the environmental spectrum is also beneficial for the protection of QFI of the phases.

Quantum measurements in spin-boson model under non-Markovian environment

We propose a control approach of the parameter estimation for a two-level quantum system interacting with a bosonic reservoir considering non-Markovian open, dissipative quantum system. We show that the precision of the estimation significantly affected and behaves differently within the framework of the markovian and non-Markovian regimes. The influence of memory effects for an Ohmic reservoir with Lorentz-Drude regularization on the estimation-parameter precision are numerically demonstrated under the following three conditions: ω0⪡ωc, ω0≈ωc or ω0⪢ωc, where ω0 is the characteristic frequency of the two-level system, and ωc is the cut-off frequency of Ohmic reservoir. We investigate the precision rate in high temperature, intermediate temperature, and low temperature reservoirs for various values of the ratio r=ωc/ω0 considering manifold external fields. We reveal that the enhancement and preservation of the measurement precision, highly depend on the combination of the external control field, reservoir parameters, and non-Markovian effects.

Entropic uncertainty relations for Markovian and non-Markovian processes under a structured bosonic reservoir

The uncertainty relation is a fundamental limit in quantum mechanics and is of great importance to quantum information processing as it relates to quantum precision measurement. Due to interactions with the surrounding environment, a quantum system will unavoidably suffer from decoherence. Here, we investigate the dynamic behaviors of the entropic uncertainty relation of an atom-cavity interacting system under a bosonic reservoir during the crossover between Markovian and non-Markovian regimes. Specifically, we explore the dynamic behavior of the entropic uncertainty relation for a pair of incompatible observables under the reservoir-induced atomic decay effect both with and without quantum memory. We find that the uncertainty dramatically depends on both the atom-cavity and the cavity-reservoir interactions, as well as the correlation time, τ, of the structured reservoir. Furthermore, we verify that the uncertainty is anti-correlated with the purity of the state of the observed qubit-system. We also propose a remarkably simple and efficient way to reduce the uncertainty by utilizing quantum weak measurement reversal. Therefore our work offers a new insight into the uncertainty dynamics for multi-component measurements within an open system, and is thus important for quantum precision measurements.

Quantum Fisher Information of Driven Multi-particle Systems in Structured Bosonic Reservoirs**Supported by the National Natural Science Foundation of China under Grant No. 11274054, the Creative Project of Graduate in University of Suzhou Science and Technology in No. SKCX16-006, the Innovation Project of Graduate Education of Jiangsu Province No. JGLX15-150

We investigate the dynamics of the precision of the parameter estimation in many driven atoms, each of which interacts with a local structured bosonic reservoir respectively. The evolution of quantum states for single driven atom is described by the time local quantum master equation. The dynamics of the quantum Fisher information for many entangled atoms is obtained by means of the supreoperator mapping. The estimation limit is superior to the standard quantum limit during a characteristic interval. At a given time, the precision of parameter estimation can be improved to a maximal value if the number of entangled atoms is chosen to be an optimal value. The optimal number of entangled atoms is determined by the dynamical property. The decay of quantum Fisher information is accelerated with the increase of the number of entangled atoms.

Geometric phase of an atomic qubit coupled to a Lorentzian reservoir

We calculate the geometric phase for an atomic qubit coupled to a zero-temperature bosonic reservoir with a Lorentzian spectral density. The geometric phase is obtained without tracing out the degrees of freedom of the reservoir. It is shown that the phase accumulated by the total system is purely geometric and exhibits an oscillation behaviour in both the Markovian and non-Markovian regimes.

Fundamental limits for cooling of linear quantum refrigerators.

We study the asymptotic dynamics of arbitrary linear quantum open systems that are periodically driven while coupled with generic bosonic reservoirs. We obtain exact results for the heat flowing from each reservoir, and these results are valid beyond the weak-coupling or Markovian approximations. We prove the validity of the dynamical third law of thermodynamics (Nernst unattainability principle), showing that the ultimate limit for cooling is imposed by a fundamental heating mechanism that dominates at low temperatures, namely the nonresonant creation of excitation pairs in the reservoirs induced by the driving field. This quantum effect, which is missed in the weak-coupling approximation, restores the unattainability principle, the validity of which was recently challenged.

Radiative heat transfer as a Landauer-Büttiker problem.

We study the radiative heat transfer between two semi-infinite half-spaces, bounded by conductive surfaces in contact with vacuum. This setup is interpreted as a four-terminal mesoscopic transport problem. The slabs and interfaces are viewed as bosonic reservoirs, coupled perfectly to a scattering center consisting of the two planes and vacuum. Using Rytov's fluctuational electrodynamics and assuming Kirchhoff's circuital law, we calculate the heat flow in each bath. This allows for explicit evaluation of a conductance matrix, from which one readily verifies Büttiker symmetry. Thus, radiative heat transfer in layered media with conductive interfaces becomes a Landauer-Büttiker transport problem.

Enforcing Thermal Entanglement of Three Coupled Qubits by Dissipation

The stationary state entanglement in a chain with three spins is reported. Each of spins couples to its own separate bosonic reservoir. The master equation for such spins’ system is derived under the Born-Markovian approximation. The result presents that the coupling between the middle spin and its bosonic bath in some special temperature region reinforce the entanglement between the spins. By analyzing the heat current between the middle spin and its bosonic bath, we find a tight relationship between the direction of heat current from the middle spin to its bosonic bath and the reinforcement of the entanglement. The entanglement increases with the heat current between the middle spin and its bosonic bath almost linearly.

Theoretical approach to characterize the non-Markovianity and diffusion through the influx of the information

In this paper, we study the Fisher information for a quantum system consisting of two identical qubits, each of them locally interacting with a bosonic reservoir in the same environment for non-Markovian open, dissipative quantum system. Based on the influx of the information, we propose an information-theoretical approach for characterizing the time-dependent memory effect of environment and diffusion function under the effect of the physical parameters. More precisely, an interesting monotonic relation between the time derivative of quantum Fisher information (QFI) and diffusion function behavior is observed during the time evolution. The phenomenon is that the QFI, namely the precision of estimation, changes dramatically with the environment structure. The dependence of the physical parameters shows that the increasing in the temperature will damage the amount of the QFI with respect of the ratio between the reservoir cutoff frequency and the system oscillation frequency.

Bosonic Josephson effect in the Fano-Anderson model

We investigate the coherent dynamics of a non-interacting Bose-Einstein condensate in a system consisting of two bosonic reservoirs coupled via a spatially localized mode. We describe this system by a two-terminal Fano-Anderson model and investigate analytically the time evolution of observables such as the bosonic Josephson current. In doing so, we find that the Josephson current sensitively depends on the on-site energy of the localized mode. This facilitates to use this setup as a transistor for a Bose-Einstein condensate. We identify two regimes. In one regime, the system exhibits well-behaved long-time dynamics with a slowly oscillating and undamped Josephson current. In a second regime, the Josephson current is a superposition of an extremely weakly damped slow oscillation and an undamped fast oscillation. Our results are confirmed by finite-size simulations.

Evolution of entropy in different types of non-Markovian three-level systems: Single reservoir vs. two independent reservoirs

We solve the Nakajima–Zwanzig (NZ) non-Markovian master equation to study the dynamics of different types of three-level atomic systems interacting with bosonic Lorentzian reservoirs at zero temperature. Von Neumann entropy (S) is used to show the evolution of the degree of entanglement of the subsystems. The results presented are also compared with some recently published reports.

Dynamics of quantum Fisher information in a two-level system coupled to multiple bosonic reservoirs**Project supported by the Hunan Provincial Innovation Foundation for Postgraduate, China (Grant No. CX2014B194) and the Scientific Research Foundation of Hunan Provincial Education Department, China (Grant No. 13C039).

We consider the optimal parameter estimation for a two-level system coupled to multiple bosonic reservoirs. By using quantum Fisher information (QFI), we investigate the effect of the Markovian reservoirs’ number N on QFI in both weak and strong coupling regimes for a two-level system surrounded by N zero-temperature reservoirs of field modes initially in the vacua. The results show that the dynamics of QFI non-monotonically decays to zero with revival oscillations at some time in the weak coupling regime depending on the reservoirs’ parameters. Furthermore, we also present the relations between the QFI flow, the flows of energy and information, and the sign of the decay rate to gain insight into the physical processes characterizing the dynamics.

Time-Delayed Quantum Feedback Control.

A theory of time-delayed coherent quantum feedback is developed. More specifically, we consider a quantum system coupled to a bosonic reservoir creating a unidirectional feedback loop. It is shown that the dynamics can be mapped onto a fictitious series of cascaded quantum systems, where the system is driven by past versions of itself. The derivation of this model relies on a tensor network representation of the system-reservoir time propagator. For concreteness, this general theory is applied to a driven two-level atom scattering into a coherent feedback loop. We demonstrate how delay effects can qualitatively change the dynamics of the atom and how quantum control can be implemented in the presence of time delays.

Multiscale dynamics of open three-level quantum systems with two quasi-degenerate levels

We consider a three-level quantum system interacting with a bosonic thermal reservoir. Two energy levels of the system are nearly degenerate but well separated from the third one. The system-reservoir interaction constant is larger than the energy difference of the degenerate levels, but it is smaller than the separation between the latter and the remaining level. We show that the quasi-degeneracy of energy levels leads to the existence of a manifold of quasi-stationary states, and the dynamics exhibits two characteristic time scales. On the first, shorter one, initial states approach the quasi-stationary manifold. Then, on the much longer second time scale, the final unique equilibrium is reached.

Thermal rectification in the nonequilibrium quantum-dots-system

We study thermal rectification of a two-quantum-dots system with Dzyaloshinskii–Moriya (DM) interaction and coupling to two bosonic reservoirs. Compared with other proposals (Zhang et al., 2009 [9]), our model can offer larger rectification efficiency through different modulations in small size systems (N=2).

Enhancing Atomic Entanglement in a Common Reservoir by Weak Measurement and its Reversal

The three two-level atoms, initially prepared in like-W state, interact with a common bosonic reservoir. To suppress environment decoherence and obtain much better entanglement, we firstly perform weak measurement on these atoms before they pass the reservoir, and then, when they have experienced the decoherence environment, the receiver carry out a quantum reversal on all atoms. The results show both the tripartite and bipartite entanglement can be enhanced and the post-reversal measurement is more obvious to promote atomic entanglements than the weak measurement. Increasing the strength of reversal measurement can always improve entanglement. As a price, the success probability decreases with the much greater measure strength.

Non-Markovian dynamics of the mixed-state geometric phase of dissipative qubits

We investigate the geometric phase of a two-level atom (qubit) coupled to a bosonic reservoir with Lorentzian spectral density and find that for the non-Markovian dynamics in which the rotating-wave approximation (RWA) is performed, the geometric phase has a $\ensuremath{\pi}$-phase jump at the nodal point. However, the exact result without the RWA given by the hierarchical equations of motion method shows that there is no such phase jump or nodal structure in the geometric phase. Thus our results demonstrate that the counterrotating terms significantly contribute to the geometric phase in the multimode Hamiltonian under certain circumstances.

Non-Markovianity of a two-level system transversally coupled to multiple bosonic reservoirs

Dynamics of a two-level open system transversally coupled to a single zero-temperature bosonic reservoir may be Markovian or non-Markovian, depending on whether the system-reservoir coupling is weak or strong. In this paper, we show that when the system is simultaneously coupled to $N$ reservoirs its dynamics is always non-Markovian, provided that $N\ensuremath{\ge}{N}_{\mathrm{cr}},$ with ${N}_{\mathrm{cr}}$ a critical number depending on the reservoirs' parameters. Quantitatively, the non-Markovianity $\mathcal{N}$ is shown proportional to the number of contributed reservoirs. We explain our results in terms of the pseudomode theory, finding out that when $N\ensuremath{\ge}{N}_{\mathrm{cr}}$ the pseudomodes of all the reservoirs can always partially return information back to the system, no matter how strong the couplings between the system and each individual reservoir.

Relaxation dynamics of meso-reservoirs

We study the phenomenology of maximum-entropy meso-reservoirs, where we assume that their local thermal equilibrium state changes consistently with the heat transferred between the meso-reservoirs. Depending on heat and matter carrying capacities, the chemical potentials and temperatures are allowed to vary in time, and using global conservation relations we solve their evolution equations. We compare two-terminal transport between bosonic and fermionic meso-reservoirs via systems that tightly couple energy and matter currents and systems that do not. For bosonic reservoirs, we observe the temporary formation of a Bose–Einstein condensate in one of the meso-reservoirs from an initial nonequilibrium setup.