278 research outputs found
Extension of worldline computational algorithms for QCD to open fermionic contours
The worldline casting of a gauge field system with spin-1/2 matter fields has
provided a, particle-based, first quantization formalism in the framework of
which the Bern-Kosower algorithms for efficient computations in QCD acquire a
simple interpretation. This paper extends the scope of applicability of the
worldline scheme so as to include open fermionic paths. Specific algorithms are
established which address themselves to the fermionic propagator and which are
directly applicable to any other process involving external fermionic states.
It is also demonstrated that in this framework the sole agent of dynamics
operating in the system is the Wilson line (loop) operator, which makes a
natural entrance in the worldline action; everything else is associated with
geometrical properties of particle propagation, of which the most important
component is Polyakov's spin factor.Comment: 24 page
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
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