14 research outputs found
Mutual information and Bose-Einstein condensation
In the present work we are studying a bosonic quantum field system at finite
temperature, and at zero and non-zero chemical potential. For a simple spatial
partition we derive the corresponding mutual information, a quantity that
measures the total amount of information of one of the parts about the other.
In order to find it, we first derive the geometric entropy corresponding to the
specific partition and then we substract its extensive part which coincides
with the thermal entropy of the system. In the case of non-zero chemical
potential, we examine the influence of the underlying Bose-Einstein
condensation on the behavior of the mutual information, and we find that its
thermal derivative possesses a finite discontinuity at exactly the critical
temperature
Entropy production in Gaussian bosonic transformations using the replica method: application to quantum optics
In spite of their simple description in terms of rotations or symplectic
transformations in phase space, quadratic Hamiltonians such as those modeling
the most common Gaussian operations on bosonic modes remain poorly understood
in terms of entropy production. For instance, determining the von Neumann
entropy produced by a Bogoliubov transformation is notably a hard problem, with
generally no known analytical solution. Here, we overcome this difficulty by
using the replica method, a tool borrowed from statistical physics and quantum
field theory. We exhibit a first application of this method to the field of
quantum optics, where it enables accessing entropies in a two-mode squeezer or
optical parametric amplifier. As an illustration, we determine the entropy
generated by amplifying a binary superposition of the vacuum and an arbitrary
Fock state, which yields a surprisingly simple, yet unknown analytical
expression
Heralded noiseless amplification and attenuation of non-gaussian states of light
We examine the behavior of non-Gaussian states of light under the action of
probabilistic noiseless amplification and attenuation. Surprisingly, we find
that the mean field amplitude may decrease in the process of noiseless
amplification -- or increase in the process of noiseless attenuation, a
counterintuitive effect that Gaussian states cannot exhibit. This striking
phenomenon could be tested with experimentally accessible non-Gaussian states,
such as single-photon added coherent states. We propose an experimental scheme,
which is robust with respect to the major experimental imperfections such as
inefficient single-photon detection and imperfect photon addition. In
particular, we argue that the observation of mean field amplification by
noiseless attenuation should be feasible with current technology
Majorization relations and entanglement generation in a beam splitter
We prove that a beam splitter, one of the most common optical components, fulfills several classes of majorization relations, which govern the amount of quantum entanglement that it can generate. First, we show that the state resulting from k photons impinging on a beam splitter majorizes the corresponding state with any larger photon number k > k, implying that the entanglement monotonically grows with k. Then we examine parametric infinitesimal majorization relations as a function of the beam-splitter transmittance and find that there exists a parameter region where majorization is again fulfilled, implying a monotonic increase of entanglement by moving towards a balanced beam splitter. We also identify regions with a majorization default, where the output states become incomparable. In this latter situation, we find examples where catalysis may nevertheless be used in order to recover majorization. The catalyst states can be as simple as a path-entangled single-photon state or a two-mode squeezed vacuum state
A probabilistic phase-insensitive optical squeezer in peaceful coexistence with causality
A non trace-preserving map describing a probabilistic but heralded noiseless
linear amplifier has recently been proposed and experimentally demonstrated.
Here, we exhibit another remarkable feature of this peculiar transformation,
namely its ability to serve as a universal single-mode squeezer regardless of
the quadrature that is initially squeezed. Hence, it acts as an heralded
phase-insensitive optical squeezer, conserving the signal-to-noise ratio just
as a phase-sensitive optical amplifier but for all quadratures at the same
time, which may offer new perspectives in quantum optical communications.
Although this ability to squeeze all quadratures seemingly opens a way to
instantaneous signaling by circumventing the quantum no-cloning theorem, we
explain the subtle mechanism by which the probability for such a causality
violation vanishes, even on an heralded basis
Bounding the quantum limits of precision for phase estimation with loss and thermal noise
Majorization relations and entanglement generation in a beam splitter
We prove that a beam splitter, one of the most common optical components,
fulfills several classes of majorization relations, which govern the amount of
quantum entanglement that it can generate. First, we show that the state
resulting from k photons impinging on a beam splitter majorizes the
corresponding state with any larger photon number k'>k, implying that the
entanglement monotonically grows with k. Then, we examine parametric
infinitesimal majorization relations as a function of the beam-splitter
transmittance, and find that there exists a parameter region where majorization
is again fulfilled, implying a monotonic increase of entanglement by moving
towards a balanced beam splitter. We also identify regions with a majorization
default, where the output states become incomparable. In this latter situation,
we find examples where catalysis may nevertheless be used in order to recover
majorization. The catalyst states can be as simple as a path-entangled
single-photon state or a two-mode vacuum squeezed state