40,586 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
Nonviolation of Bell's Inequality in Translation Invariant Systems
The nature of quantum correlations in strongly correlated systems has been a
subject of intense research. In particular, it has been realized that
entanglement and quantum discord are present at quantum phase transitions and
able to characterize it. Surprisingly, it has been shown for a number of
different systems that qubit pairwise states, even when highly entangled, do
not violate Bell's inequalities, being in this sense local. Here we show that
such a local character of quantum correlations is in fact general for
translation invariant systems and has its origins in the monogamy trade-off
obeyed by tripartite Bell correlations. We illustrate this result in a quantum
spin chain with a soft breaking of translation symmetry. In addition, we extend
the monogamy inequality to the -qubit scenario, showing that the bound
increases with and providing examples of its saturation through uniformly
generated random pure states.Comment: Published erratum added at the en
Multipartite Entanglement Signature of Quantum Phase Transitions
We derive a general relation between the non-analyticities of the ground
state energy and those of a subclass of the multipartite generalized global
entanglement (GGE) measure defined by T. R. de Oliveira et al. [Phys. Rev. A
73, 010305(R) (2006)] for many-particle systems. We show that GGE signals both
a critical point location and the order of a quantum phase transition (QPT). We
also show that GGE allows us to study the relation between multipartite
entanglement and QPTs, suggesting that multipartite but not bipartite
entanglement is favored at the critical point. Finally, using GGE we were able,
at a second order QPT, to define a diverging entanglement length (EL) in terms
of the usual correlation length. We exemplify this with the XY spin-1/2 chain
and show that the EL is half the correlation length.Comment: Published version. Incorporates correction made in erratu
The mechanism for the electrooxidation of procarbazine pharmaceutical preparation in alkaline media and its mathematical description
The mechanism for the electrooxidation of procarbazine in alkaline media has been proposed. The process is realized completely on the electrode surface and is adsorption-controlled. The oscillatory behavior in this case is more probable, than for neutral media and may be caused by influences of electrochemical oxidation and salt dissolution from the electrode surface
- …