300 research outputs found
The Unruh Quantum Otto Engine
We introduce a quantum heat engine performing an Otto cycle by using the
thermal properties of the quantum vacuum. Since Hawking and Unruh, it has been
established that the vacuum space, either near a black hole or for an
accelerated observer, behaves as a bath of thermal radiation. In this work, we
present a fully quantum Otto cycle, which relies on the Unruh effect for a
single quantum bit (qubit) in contact with quantum vacuum fluctuations. By
using the notions of quantum thermodynamics and perturbation theory we obtain
that the quantum vacuum can exchange heat and produce work on the qubit.
Moreover, we obtain the efficiency and derive the conditions to have both a
thermodynamic and a kinematic cycle in terms of the initial populations of the
excited state, which define a range of allowed accelerations for the Unruh
engine.Comment: 31 pages, 11 figure
Global Quantum Discord in Multipartite Systems
We propose a global measure for quantum correlations in multipartite systems,
which is obtained by suitably recasting the quantum discord in terms of
relative entropy and local von Neumann measurements. The measure is symmetric
with respect to subsystem exchange and is shown to be non-negative for an
arbitrary state. As an illustration, we consider tripartite correlations in the
Werner-GHZ state and multipartite correlations at quantum criticality. In
particular, in contrast with the pairwise quantum discord, we show that the
global quantum discord is able to characterize the infinite-order quantum phase
transition in the Ashkin-Teller spin chain.Comment: v3: 7 pages, 6 figures. Published versio
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