12 research outputs found
A relativistic quantum broadcast channel
We investigate the transmission of classical and quantum information between
three observers in a general globally hyperbolic spacetime using a quantum
scalar field as a communication channel. We build a model for a quantum
broadcast channel in which one observer (sender) wishes to transmit (classical
and quantum) information to two other observers (receivers). They possess some
localized two-level quantum system (a qubit) that can interact with the quantum
field in order to prepare an input or receive the output of this channel. The
field is supposed to be in an arbitrary quasifree state, the three observers
may be in arbitrary states of motion, and no choice of representation of the
field canonical commutation relations is made. The interaction of the field and
qubits is such that it allows us to obtain the map that describes this channel
in a non-perturbative manner. We conclude by analyzing the rates at which
information can be transmitted through this channel and by investigating
relativistic causality effects on such rates.Comment: 15 pages, 1 figur
Gravitational Waves Emitted by a Uniformly Accelerated Mass: The Role of Zero-Rindler-Energy Modes in the Classical and Quantum Descriptions
The observation of gravitational waves opens up a new window to probe the
universe and the nature of the gravitational field itself. As a result, they
serve as a new and promising tool to not only test our current theories but to
study different models that go beyond our current understanding. In this paper,
inspired by recent successes in scalar and Maxwell electrodynamics, we analyze
the role played by the (quantum) Unruh effect on the production of both
classical and quantum gravitational waves by a uniformly accelerated mass. In
particular, we show the fundamental role played by zero-energy (Rindler)
gravitons in building up the gravitational radiation, as measured by inertial
observers, emitted by the body.Comment: 20 pages, 3 figures. RevTeX 4.
From quantum to classical instability in relativistic stars
It has been shown that gravitational fields produced by realistic
classical-matter distributions can force quantum vacuum fluctuations of some
nonminimally coupled free scalar fields to undergo a phase of exponential
growth. The consequences of this unstable phase to the background spacetime
have not been addressed so far due to known difficulties concerning
backreaction in semiclassical gravity. It seems reasonable to believe, however,
that the quantum fluctuations will "classicalize" when they become large
enough, after which backreaction can be treated in the general-relativistic
context. Here we investigate the emergence of a classical regime out of the
quantum field evolution during the unstable phase. By studying the appearance
of classical correlations and loss of quantum coherence, we show that by the
time backreaction becomes important the system already behaves classically.
Consequently, the gravity-induced instability leads naturally to initial
conditions for the eventual classical description of the backreaction. Our
results give support to previous analyses which treat classically the
instability of scalar fields in the spacetime of relativistic stars, regardless
whether the instability is triggered by classical or quantum perturbations.Comment: 16 pages. Minor changes to match the published versio
Influence of detector motion in entanglement measurements with photons
We investigate how the polarization correlations of entangled photons
described by wave packets are modified when measured by moving detectors. For
this purpose, we analyze the Clauser-Horne-Shimony-Holt Bell inequality as a
function of the apparatus velocity. Our analysis is motivated by future
experiments with entangled photons designed to use satellites. This is a first
step towards the implementation of quantum information protocols in a global
scale
Influence of detector motion in Bell inequalities with entangled fermions
We investigate how relativity influences the spin correlation of entangled
fermions measured by moving detectors. In particular, we show that the
Clauser-Horne-Shimony-Holt Bell inequality is not violated by quantum mechanics
when the left and right spin detectors move fast enough.Comment: 4 pages and 5 figure