1,721,232 research outputs found
Dissipative scheme to approach the boundary of two-qubit entangled mixed states
No full textWe discuss the generation of states close to the boundary family of maximally entangled mixed states as defined by the use of concurrence and linear entropy. The coupling of two qubits to a dissipation-affected bosonic mode is able to produce a bipartite state having, for all practical purposes, the entanglement and mixedness properties of one of such boundary states. We thoroughly study the effects that thermal and squeezed characters of the bosonic mode have in such a process and we discuss tolerance to qubit phase-damping mechanisms. The nondemanding nature of the scheme makes it realizable in a matter-light-based physical setup, which we address in some details. © 2009 The American Physical Society
Shortcut-to-adiabaticity Otto engine: A twist to finite-time thermodynamics
Full text linkWe consider a finite-time Otto engine operating on a quantum harmonic oscillator and driven by shortcut-to-adiabaticity (STA) techniques to speed up its cycle. We study its efficiency and power when internal friction, time-averaged work, and work fluctuations are used as quantitative figures of merit, showing that time-averaged efficiency and power are useful cost functions for the characterization of the performance of the engine. We then use the minimum allowed time for validity of STA protocol relation to establish a physically relevant bound to the efficiency at maximum power of the STA-driven cycle
Implications of non-Markovian dynamics on information-driven engine
Full text linkThe understanding of memory effects arising from the interaction between system and environment is a key for engineering quantum thermodynamic devices beyond the standard Markovian limit. We study the performance of measurement-based thermal machine whose working medium dynamics is subject to backflow of information from the reservoir via collision based model. In this study, the nonMarkovian effect is introduced by allowing for additional unitary interactions between the environments. We present two strategies of realizing non-Markovian dynamics and study their influence on the performance of the engine. Moreover, the role of system-environment memory effects on the engine work extraction and information gain through measurement can be beneficial in short time
Composite Discordant States and Quantum Darwinism
Full text linkThe framework of Quantum Darwinism strives at characterizing the quantum-to-classical transition by introducing the concept of redundancy of information—as measured by Mutual Information—that a set of observers would acquire on the state of a physical system of interest. Further development on this concept, in the form of Strong Quantum Darwinism and Spectrum Broadcast Structures, has recently led to a more fine-grained identification of the nature of such information, which should not involve any quantum correlations between observing and observed systems, while the assessment of information proliferation from individual systems has attracted most of the attention so far, the way such mechanism takes place in more complex states is open to exploration. To this end, we shall consider a two-qubit state, sharing initial quantum correlations in the form of Quantum Discord, and different dephasing-like interactions between them and an observing environment. We will focus on the amount of information regarding the subsystem not involved in the interaction that is proliferated to the environment. We shall refer to this as mediated redundancy. We will show that, in some cases, the channel capacity of the subsystems, given these interactions, can exceed that of the fragments
Quantum work statistics with initial coherence
Full text linkThe two-point measurement scheme for computing the thermodynamic work performed on a system requires it to be initially in equilibrium. The Margenau–Hill scheme, among others, extends the previous approach to allow for a non-equilibrium initial state. We establish a quantitative comparison between both schemes in terms of the amount of coherence present in the initial state of the system, as quantified by the l1-coherence measure. We show that the difference between the two first moments of work, the variances of work, and the average entropy production obtained in both schemes can be cast in terms of such initial coherence. Moreover, we prove that the average entropy production can take negative values in the Margenau–Hill framework
Multipartite optomechanical entanglement from competing nonlinearities
Full text linkWe investigate the nature of the three-mode interaction inside an optomechanically active microtoroid with a sizable ?(2) coefficient. Experimental techniques are quickly advancing to the point where structures with the necessary properties can be made, and we argue that these provide a natural setting in which to observe rich dynamics leading, for instance, to genuine tripartite steady-state entanglement. We also show that this approach lends itself to a full characterization of the three-mode state of the system
Implications of non-Markovian quantum dynamics for the Landauer bound
Full text linkWe study the dynamics of a spin-1/2 particle interacting with a multi-spin environment, modelling the corresponding open system dynamics through a collision-based model. The environmental particles are prepared in individual thermal states, and we investigate the effects of a distribution of temperatures across the spin environment on the evolution of the system, particularly how thermalisation in the long-time limit is affected. We study the phenomenology of the heat exchange between system and environment and consider the information-to-energy conversion process, induced by the system-environment interaction and embodied by the Landauer principle. Furthermore, by considering an interacting-particles environment, we tune the dynamics of the system from an explicit Markovian evolution up to a strongly non-Markovian one, investigating the connections between non-Markovianity, the establishment of system-environment correlations, and the breakdown of the validity of Landauer principle
Optimal quantum control via genetic algorithms for quantum state engineering in driven-resonator mediated networks
Full text linkWe employ a machine learning-enabled approach to quantum state engineering based on evolutionary algorithms. In particular, we focus on superconducting platforms and consider a network of qubits—encoded in the states of artificial atoms with no direct coupling—interacting via a common single-mode driven microwave resonator. The qubit-resonator couplings are assumed to be in the resonant regime and tunable in time. A genetic algorithm is used in order to find the functional time-dependence of the couplings that optimise the fidelity between the evolved state and a variety of targets, including three-qubit GHZ and Dicke states and four-qubit graph states. We observe high quantum fidelities (above 0.96 in the worst case setting of a system of effective dimension 96), fast preparation times, and resilience to noise, despite the algorithm being trained in the ideal noise-free setting. These results show that the genetic algorithms represent an effective approach to control quantum systems of large dimensions
Modelling mechanical equilibration processes of closed quantum systems: a case-study
Full text linkWe model the dynamics of a closed quantum system brought out of mechanical
equilibrium, undergoing a non-driven, spontaneous, thermodynamic
transformation. In particular, we consider a quantum particle in a box with a
moving and insulating wall, subjected to a constant external pressure. Under
the assumption that the wall undergoes classical dynamics, we obtain a system
of differential equations that describes the evolution of the quantum system
and the motion of the wall. We study the dynamics of such system and the
thermodynamics of the process of compression and expansion of the box. Our
approach is able to capture several properties of the thermodynamic
transformations considered and goes beyond a description in terms of an ad-hoc
time-dependent Hamiltonian, considering instead the mutual interactions between
the dynamics of the quantum system and the parameters of its Hamiltonian.Comment: 10 pages, 11 figure
Efficient excitation-transfer across fully connected networks via local-energy optimization
Full text linkWe study the excitation transfer across a fully connected quantum network
whose sites energies can be artificially designed. Starting from a simplified
model of a broadly-studied physical system, we systematically optimize its
local energies to achieve high excitation transfer for various environmental
conditions, using an adaptive Gradient Descent technique and Automatic
Differentiation. We show that almost perfect transfer can be achieved with and
without local dephasing, provided that the dephasing rates are not too large.
We investigate our solutions in terms of resilience against variations in
either the network connection strengths, or size, as well as coherence losses.
We highlight the different features of a dephasing-free and dephasing-driven
transfer. Our work gives further insight into the interplay between coherence
and dephasing effects in excitation-transfer phenomena across fully connected
quantum networks. In turn, this will help designing optimal transfer in
artificial open networks through the simple manipulation of local energies.Comment: 11 pages, 8 figure
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