1,720,990 research outputs found
Pseudomode treatment of strong-coupling quantum thermodynamics
Full text linkThe treatment of quantum thermodynamic systems beyond weak coupling is of
increasing relevance, yet extremely challenging. The evaluation of
thermodynamic quantities in strong-coupling regimes requires a nonperturbative
knowledge of the bath dynamics, which in turn relies on heavy numerical
simulations. To tame these difficulties, considering thermal bosonic baths
linearly coupled to the open system, we derive expressions for heat, work, and
average system-bath interaction energy that only involve the autocorrelation
function of the bath and two-time expectation values of system operators. We
then exploit the pseudomode approach, which replaces the physical continuous
bosonic bath with a small finite number of damped, possibly interacting, modes,
to numerically evaluate these relevant thermodynamic quantities. We show in
particular that this method allows for an efficient numerical evaluation of
thermodynamic quantities in terms of one-time expectation values of the open
system and the pseudomodes. We apply this framework to the investigation of two
paradigmatic situations. In the first instance, we study the entropy production
for a two-level system coupled to an ohmic bath, simulated via interacting
pseudomodes, allowing for the presence of time-dependent driving. Secondly, we
consider a quantum thermal machine composed of a two-level system interacting
with two thermal baths at different temperatures, showing that an appropriate
sinusoidal modulation of the coupling with the cold bath only is enough to
obtain work extraction.Comment: 23 pages, 5 figure
684. WE-Heraeus-Seminar
No full textQuantum mechanics has shown unprecedented success as a physical theory, but it has forced a new view on the description of physical reality. In recent years, important progress has been achieved both in the theory of open quantum systems and in the experimental realization and control of such systems. A great deal of the new results is concerned with the characterization and quantification of quantum memory effects. From this perspective, the 684. WE-Heraeus-Seminar has brought together scientists from different communities, both theoretical and experimental, sharing expertise on open quantum systems, as well as the commitment to the understanding of quantum mechanics. This book consists of many contributions addressing the diversified physics community interested in foundations of quantum mechanics and its applications and it reports about recent results in open quantum systems and their connection with the most advanced experiments testing quantum mechanics
Experimentally determining the incompatibility of two qubit measurements
Full text linkWe describe and realize an experimental procedure for assessing the incompatibility of two qubit measurements. The experiment consists in a state discrimination task where either measurement is used according to some partial intermediate information. The success statistics of the task provides an upper bound for the amount of incompatibility of the two measurements, as it is quantified by means of their incompatibility robustness. For a broad class of unbiased and possibly noisy qubit measurements, one can make this upper bound coincide with the true value of the robustness by suitably tuning the preparation of the experiment. We demonstrate this fact in an optical setup, where the qubit states are encoded into the photons' polarization degrees of freedom, and incompatibility is directly accessed by virtue of a refined control on the amplitude, phase and purity of the final projection stage of the measurements. Our work thus establishes the practical feasibility of a recently proposed method for the detection of quantum incompatibility
Dissipative extension of the Ghirardi-Rimini-Weber model
Full text linkIn this paper, we present an extension of the Ghirardi-Rimini-Weber model for the spontaneous collapse of the wave function. Through the inclusion of dissipation, we avoid the divergence of the energy on the long-time scale, which affects the original model. In particular, we define jump operators, which depend on the momentum of the system and lead to an exponential relaxation of the energy to a finite value. The finite asymptotic energy is naturally associated to a collapse noise with a finite temperature, which is a basic realistic feature of our extended model. Remarkably, even in the presence of a low-temperature noise, the collapse model is effective. The action of the jump operators still localizes the wave function and the relevance of the localization increases with the size of the system, according to the so-called amplification mechanism, which guarantees a unified description of the evolution of microscopic and macroscopic systems. We study in detail the features of our model, at the level of both the trajectories in the Hilbert space and the master equation for the average state of the system. In addition, we show that the dissipative Ghirardi-Rimini-Weber model, as well as the original one, can be fully characterized in a compact way by means of a proper stochastic differential equation
Non-Markov Processes in Quantum Theory
No full textThe study of quantum dynamics featuring memory effects has always been a topic of interest within the theory of open quantum system. The latter is concerned with providing useful conceptual and theoretical tools for the description of the reduced dynamics of a system interacting with an external environment. Definitions of non-Markovian processes have been introduced trying to capture the notion of memory effect by studying features of the quantum dynamical map providing the evolution of the system states, or changes in the distinguishability of the system states themselves. We introduce basic notions in the framework of open quantum systems. We stress in particular analogies and differences with models used for introducing modifications of quantum mechanics which should help in dealing with the measurement problem. We further discuss recent developments in the treatment of non-Markovian processes and their role in considering more general modifications of quantum mechanics
Quantum Non-Markovian Piecewise Dynamics from Collision Models
Full text linkRecently, a large class of quantum non-Markovian piecewise dynamics for an open quantum system obeying closed evolution equations has been introduced [1]. These dynamics have been defined in terms of a waiting-time distribution between quantum jumps, along with quantum maps describing the effect of jumps and the system evolution between them. Here, we present a quantum collision model with memory, whose reduced dynamics in the continuous-time limit reproduces the above class of non-Markovian piecewise dynamics, thus providing an explicit microscopic realization
Quantum renewal processes
Full text linkWe introduce a general construction of master equations with memory kernel whose solutions are given by completely positive trace-preserving maps. These dynamics going beyond the Lindblad paradigm are obtained with reference to classical renewal processes, so that they are termed quantum renewal processes. They can be described by means of semigroup dynamics interrupted by jumps, separated by independently distributed time intervals, following suitable waiting time distributions. In this framework, one can further introduce modified processes, in which the first few events follow different distributions. A crucial role, marking an important difference with respect to the classical case, is played by operator ordering. Indeed, for the same choice of basic quantum transformations, different quantum dynamics arise. In particular, for the case of modified processes, it is natural to consider the time inverted operator ordering, in which the last few events are distributed differently
Comparison of distances and entropic distinguishability quantifiers for the detection of memory effects
Full text linkWe consider a recently introduced framework for the description of memory effects based on quantum state distinguishability quantifiers, in which entropic quantifiers can be included. After briefly presenting the approach, we validate it considering the performance of different quantifiers in the characterization of the reduced dynamics of a two-level system undergoing decoherence. We investigate the different behaviors of these quantifiers in the dependence on physical features of the model, such as environmental temperature and coupling strength. It appears that the performance of the different quantifiers conveys the same physical information, though with different sensitivities, thus supporting robustness of the approach
Frontiers of Open Quantum System Dynamics
Full text linkWe briefly examine recent developments in the field of open quantum system theory, devoted to the introduction of a satisfactory notion of memory for a quantum dynamics. In particular, we will consider a possible formalization of the notion of non-Markovian dynamics, as well as the construction of quantum evolution equations featuring a memory kernel. Connections will be draw to the corresponding notions in the framework of classical stochastic processes, thus pointing to the key differences between a quantum and classical formalization of the notion of memory effects
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