20,162 research outputs found
Engineering the unitary charge-conjugation operator of quantum field theory for particle-antiparticle using trapped ions and light fields in cavity QED
We present a method to engineer the unitary charge conjugation operator, as
given by quantum field theory, in the highly controlled context of quantum
optics, thus allowing one to simulate the creation of charged particles with
well-defined momenta simultaneously with their respective antiparticles. Our
method relies on trapped ions driven by a laser field and interacting with a
single mode of a light field in a high Q cavity.Comment: 10 pages, no figur
On a heuristic point of view related to quantum nonequilibrium statistical mechanics
In this paper I propose a new way for counting the microstates of a system
out of equilibrium. As, according to quantum mechanics, things happen as if a
given particle can be found in more than one state at once, I extend this
concept to propose the coherent access by a particle to the available states of
a system. By coherent access I mean the possibility for the particle to act as
if it is populating more than one microstate at once. This hypothesis has
experimental implications, since the thermodynamical probability and, as a
consequence, the Bose-Einstein distribution as well as the argument of the
Boltzmann factor is modified.Comment: 5 page
Renormalizability in -dimensional higher-order gravity
A simple expression for calculating the classical potential concerning
-dimensional gravitational models is obtained through a method based on the
generating functional. The prescription is then used as a mathematical tool to
probe the conjecture that renormalizable higher-order gravity models --- which
are, of course, nonunitary --- are endowed with a classical potential that is
nonsingular at the origin. It is also shown that the converse of this statement
is not true, which implies that the finiteness of the classical potential at
the origin is a necessary but not a sufficient condition for the
renormalizability of the model. The systems we have utilized to verify the
conjecture were fourth- and sixth- order gravity models in -dimensions. A
discussion about the polemic question related to the renormalizability of new
massive gravity, which Oda claimed to be renormalizable in 2009 and three years
late was shown to be nonrenormalizable by Muneyuki and Ohta, is considered. We
remark that the solution of this issue is straightforward if the aforementioned
conjecture is employed. We point out that our analysis is restricted to local
models in which the propagator has simple and real poles.Comment: Accepted for publication in Physical Review
Cooling by heating in the quantum optics domain
A class of Hamiltonians that are experimentally feasible in several contexts
within quantum optics and lead to so-called cooling by heating for fermionic as
well as for bosonic systems has been analyzed numerically. We have found a
large range of parameters for which cooling by heating can be observed either
for the fermionic system alone or for the combined fermionic and bosonic
systems. Analyzing the experimental requirements, we conclude that cooling by
heating is achievable with present-day technology, especially in the context of
trapped-ion and cavity QED, thus contributing to the understanding of this
interesting and counterintuitive effect
Superposition of coherent states prepared in one mode of a dissipative bimodal cavity
We solve the problem of the temporal evolution of one of two-modes embedded
in a same dissipative environment and investigate the role of the losses after
the preparation of a coherent state in only one of the two modes. Based on
current cavity QED technology, we present a calculation of the fidelity of a
superposition of coherent states engineered in a bimodal high-Q cavity. Our
calculation demonstrates that the engineered superposition retains coherence
for large times when the mean photon number of the prepared mode is on the
order of unity.Comment: 7 pages, 1 figure, submitted to J. Phys.
Interesting features of a general class of higher derivative theories of quantum gravity
We investigate some classical and quantum aspects of a general class of
higher derivative theories of gravity. We propose a generalized version of the
so-called Teyssandier gauge condition and we investigative its implications on
the linearized field equations. An exhaustive investigation on the particle
spectra is done, including a discussion on the appearance of ghost-like
particles. We investigate the UV properties and we determine the power-counting
renormalizability of the theory. Finally we probe a conjecture which relates
renormalizability with the cancellation of Newtonian singularities
Unambiguous discrimination of nonorthogonal quantum states in cavity QED
We propose an oversimplified scheme to unambiguously discriminate
nonorthogonal quantum field states inside high-Q cavities. Our scheme, which is
based on positive operator-valued mea- sures (POVM) technique, uses a single
three-level atom interacting resonantly with a single mode of a cavity-field
and selective atomic state detectors. While the single three-level atom takes
the role of the ancilla, the single cavity mode field represents the system we
want to obtain information. The efficiency of our proposal is analyzed
considering the nowadays achievements in the context of cavity QED.Comment: 7 page
Negative response with optical cavity and traveling wave fields
We present a feasible protocol using traveling wave field to experimentally
observe negative response, i.e., to obtain a decrease in the output field
intensity when the input field intensity is increased. Our protocol uses one
beam splitter and two mirrors to direct the traveling wave field into a lossy
cavity in which there is a three-level atom in a lambda configuration. In our
scheme, the input field impinges on a beam splitter and, while the transmitted
part is used to drive the cavity mode, the reflected part is used as the
control field to obtain negative response of the output field. We show that the
greater cooperativity of the atom-cavity system, the more pronounced the
negative response. The system we are proposing can be used to protect devices
sensitive to intense fields, since the intensity of the output field, which
should be directed to the device to be protected, is diminished when the
intensity of the input field increases.Comment: 5 pages, 5 figure
A proposal to implement a quantum delayed choice experiment assisted by a cavity QED
We propose a scheme feasible with current technology to implement a quantum
delayed-choice experiment in the realm of cavity QED. Our scheme uses two-level
atoms interacting on and off resonantly with a single mode of a high Q cavity.
At the end of the protocol, the state of the cavity returns to its ground
state, allowing new sequential operations. The particle and wave behavior,
which are verified in a single experimental setup, are postselected after the
atomic states are selectively detected.Comment: 3 pages, 3 figures. arXiv admin note: text overlap with
arXiv:1208.0802 by other author
Analytic solutions for links and triangles distributions in finite Barab\'asi-Albert networks
Barab\'asi-Albert model describes many different natural networks, often
yielding sensible explanations to the subjacent dynamics. However, finite size
effects may prevent from discerning among different underlying physical
mechanisms and from determining whether a particular finite system is driven by
Barab\'asi-Albert dynamics. Here we propose master equations for the evolution
of the degrees, links and triangles distributions, solve them both analytically
and by numerical iteration, and compare with numerical simulations. The
analytic solutions for all these distributions predict the network evolution
for systems as small as 100 nodes. The analytic method we developed is
applicable for other classes of networks, representing a powerful tool to
investigate the evolution of natural networks
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