1,931 research outputs found
Efficiency of optically pumping a quantum battery and a two-stroke heat engine
In this work, we study the efficiency of charging a quantum battery through
optical pumping. The battery consists of a qutrit and it is connected to a
natural thermal reservoir and an external coherent drive in the limit where its
upper energy level can be adiabatically eliminated from the dynamics. In this
scenario, the drive plus spontaneous emission optically pumps the intermediate
energy level of the qutrit and the battery can be understood as being charged
by an effective higher temperature reservoir that takes it out of equilibrium
with the natural reservoir and stores useful energy in it. We also analyse the
efficiency of using this battery and charging scheme as the work fluid of a
two-stroke thermal machine
Criteria for two distinguishable fermions to behave like a boson
We study the necessary conditions for bosons composed of two distinguishable
fermions to exhibit bosonic-like behaviour. We base our analysis on tools of
quantum information theory such as entanglement and the majorization criterion
for probability distributions. In particular we scrutinize a recent interesting
hypothesis by C. K. Law in the Ref. Phys. Rev. A 71, 034306 (2005) that
suggests that the amount of entanglement between the constituent fermions is
related to the bosonic properties of the composite boson. We show that a large
amount of entanglement does not necessarily imply a good boson-like behaviour
by constructing an explicit counterexample. Moreover, we identify more
precisely the role entanglement may play in this situation.Comment: 6 pages, 1 figure (in color
Screening mechanisms in hybrid metric-Palatini gravity
We investigate the efficiency of screening mechanisms in the hybrid
metric-Palatini gravity. The value of the field is computed around spherical
bodies embedded in a background of constant density. We find a thin shell
condition for the field depending on the background field value. In order to
quantify how the thin shell effect is relevant, we analyze how it behaves in
the neighborhood of different astrophysical objects (planets, moons or stars).
We find that the condition is very well satisfied except only for some peculiar
objects. Furthermore we establish bounds on the model using data from solar
system experiments such as the spectral deviation measured by the Cassini
mission and the stability of the Earth-Moon system, which gives the best
constraint to date on theories. These bounds contribute to fix the range
of viable hybrid gravity models.Comment: 7 pages, 2 figures. Accepted for publication in Phys. Rev.
Cooperative isentropic charging of hybrid quantum batteries
Quantum batteries are quantum systems used to store energy to be later
extracted by an external agent in the form of work to perform some task. Here
we study the charging of a hybrid quantum battery via a collisional model
mediated by an anti-Jaynes Cummings interaction obtained from an off-resonant
Raman configuration. The battery is made of two distinct components: a
stationary infinite dimensional single quantum system (e.g. an harmonic
oscillator) and a stream of small dimensional ones (e.g. qutrits). The charging
protocol consists of sequentially interacting the harmonic oscillator with each
element of the stream, one at a time, under the action of an external energy
source and the goal is to analyze how the charging of both the harmonic
oscillator and the qutrits is affected by the correlation properties of the
stream.Comment: 6 captioned figure
Vacuum enhanced charging of a quantum battery
Quantum batteries are quantum systems that store energy which can then be
used for quantum tasks. One relevant question about such systems concerns the
differences and eventual advantages over their classical counterparts, whether
in the efficiency of the energy transference, input power, total stored energy
or other relevant physical quantities. Here, we show how a purely quantum
effect related to the vacuum of the electromagnetic field can enhance the
charging of a quantum battery. In particular, we demonstrate how an anti-Jaynes
Cummings interaction derived from an off-resonant Raman configuration can be
used to increase the stored energy of an effective two-level atom when compared
to its classically driven counterpart, eventually achieving full charging of
the battery with zero entropic cost
Laser from a Manybody Correlated Medium
We consider a non-equilibrium system of interacting emitters described by the
XXZ model, whose excitonic transitions are spatially and spectrally coupled to
a single mode cavity. We demonstrate that the output radiation field is
sensitive to an interplay between the hopping () and the interactions ()
of the excitons. Moderate values of the short-ranged interaction are shown to
induce laser with maximal output at the Heisenberg point (). In the laser
regime, charge-charge correlations emerge and they are shown to strongly depend
on the interaction-hopping ratio. In particular, the system shows
charge-density correlations below the Heisenberg point and ferromagnetic
correlations beyond the Heisenberg point. This contrast to the equilibrium
behavior of the XXZ chain occurs since the laser explores highly excited states
of the emitters
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