Irreversible decay of nonlocal entanglement via a reservoir of a single degree of freedom

The Quantum Jump Approach to Dissipative Dynamics in Quantum Optics

Dissipation, the irreversible loss of energy and coherence, from a microsystem, is the result of coupling to a much larger macrosystem (or reservoir) which is so large that one has no chance of keeping track of all of its degrees of freedom. The microsystem evolution is then described by tracing over the reservoir states, resulting in an irreversible decay as excitation leaks out of the initially excited microsystems into the outer reservoir environment. Earlier treatments of this dissipation described an ensemble of microsystems using density matrices, either in Schroedinger picture with Mast…

On exact identity between thermodynamic and informatic entropies in a unitary model of friction

An elementary collision model of a molecular reservoir is considered upon which an external field is applied and the work is dissipated into heat. To realize macroscopic irreversibility at the microscopic level, we introduce a ``graceful'' irreversible map which randomly mixes the identities of the molecules. This map is expected to generate informatic entropy exactly equal to the independently calculable irreversible thermodynamic entropy.

Long-time Protection of Nonlocal Entanglement

We investigate how nonlocal entanglement, as identified by violations of a Bell inequality, may be protected during the evolution. Our system consists of two qubits each embedded in a bosonic reservoir evolving independently and initially in an entangled mixed state. We show that the violation of the Bell inequality can be related to the single-qubit population of excited state in such a way that, by appropriately choosing structured environments that give rise to sufficiently high values of population trapping, long-time protection of nonlocal entanglement can be correspondingly achieved.

Weak Measurement effects on dynamics of quantum correlations in a Two-atom System in Thermal Reservoirs

The dynamical behavior of quantum correlations captured by different forms Measurement-Induced Nonlocality (MIN) between two atoms coupled with thermal reservoirs is investigated and compared with the entanglement. It is shown that the MIN quantities are more robust, while noise causes sudden death in entanglement. Further, we quantified the quantum correlation with weak measurement, and the effect of measurement strength is observed. The role of mean photon number and weak measurement on quantum correlation is also highlighted.

Random Lindblad equations from complex environments

In this paper we demonstrate that Lindblad equations characterized by a random rate variable arise after tracing out a complex structured reservoir. Our results follows from a generalization of the Born-Markov approximation, which relies in the possibility of splitting the complex environment in a direct sum of sub-reservoirs, each one being able to induce by itself a Markovian system evolution. Strong non-Markovian effects, which microscopically originate from the entanglement with the different sub-reservoirs, characterize the average system decay dynamics. As an example, we study the anomal…

Relaxation of a two-level system strongly coupled to a reservoir: Anomalously slow decoherence

Relaxation of a two-level system (TLS) into a resonant infinite-temperature reservoir with a Lorentzian spectrum is studied. The reservoir is described by a complex Gaussian-Markovian field coupled to the nondiagonal elements of the TLS Hamiltonian. The theory can be relevant for electromagnetic interactions in microwave high-$Q$ cavities and muon spin depolarization. Analytical results are obtained for the strong-coupling regime, $Ω_0\ggν$, where $Ω_0$ is the rms coupling amplitude (Rabi frequency) and $ν$ is the width of the reservoir spectrum. In this regime, the population difference and h…

Steady state entanglement beyond thermal limits

Classical engines turn thermal resources into work, which is maximized for reversible operations. The quantum realm has expanded the range of useful operations beyond energy conversion, and incoherent resources beyond thermal reservoirs. This is the case of entanglement generation in a driven-dissipative protocol, which we hereby analyze as a continuous quantum machine. We show that for such machines the more irreversible the process the larger the concurrence. Maximal concurrence and entropy production are reached for the hot reservoir being at negative effective temperature, beating the limi…

熵流与异常点结构在双模压缩浴动力学中

Entropy Flow and Exceptional-Point Structure in Two-Mode Squeezed-Bath Dynamics

本文研究了双模压缩浴动力学中熵流与异常点结构，揭示压缩参数对PT对称性的影响及非线性熵生成机制。

通用纠缠盗用与来自一般局部混沌量子演化的发散非局域魔法

Universal entanglement embezzlement and divergent nonlocal magic from generic local chaotic quantum evolution

本文证明一般局部混沌量子演化从乘积态生成具有多尺度纠缠谱的中间态，实现通用纠缠盗用并伴随发散非局域魔法，无需精细调谐即可形成通用催化储库。

Decoherent many-body dynamics of a nano- mechanical resonator coupled to charge qubits

The dynamics of charge qubits coupled to a nanomechanical resonator under influence of both a phonon bath in contact with the resonator and irreversible decay of the qubits is considered. The focus of our analysis is devoted to multi partite entanglement and the effects arising from the coupling to the reservoir. It is shown that despite losses, entanglement formation may still persist for relatively long times and it is especially robust against temperature dependence of the reservoir. Together with control of system parameters, the system may therefore be especially suited for quantum inform…

Internal dissipation and heat leaks in quantum thermodynamic cycles

The direction of the steady-state heat currents across a generic quantum system connected to multiple baths may be engineered so as to realize virtually any thermodynamic cycle. In spite of their versatility such continuous energy-conversion systems are generally unable to operate at maximum efficiency due to non-negligible sources of irreversible entropy production. In this paper we introduce a minimal model of irreversible absorption chiller. We identify and characterize the different mechanisms responsible for its irreversibility, namely heat leaks and internal dissipation, and gauge their …

Degree of entanglement in a quantum measurement process

We suggest a quantum measurement model in an ion trap which specifies the probability distribution of two, distinct internal ground states of a trapped four-level ion. The external degrees of motion of the four-level ion constitute the meter which, in turn, is coupled to the environment by engineered reservoirs. In a previous publication, a similar measurement model was employed to test decoherence effects on quantum nonlocality in phase space on the basis of coincidence measurements of the entangled system-meter scheme. Here, we study the effects of decoherence on the entanglement of formatio…

开放量子系统中的稳态纠缠标度：若干主方程之间的比较

Steady-state entanglement scaling in open quantum systems: A comparison between several master equations

本文比较非局域 Lindblad、Redfield 与 ULE 三种主方程，研究受驱耗散临界链稳态 FLN 的标度，发现弱耦合下均为对数增长，而 Redfield 与 ULE 在更强耦合时转为超对数标度。