11 research outputs found
Bogoliubov space of a Bose--Einstein condensate and quantum spacetime fluctuations
In the present work we consider the role that metric fluctuations could have
upon the properties of a Bose--Einstein condensate. In particular we consider
the Bogoliubov space associated to it and show that there are, at least, two
independent ways in which the average size of these metric fluctuations could
be, experimentally, determined. Indeed, we prove that the pressure and the
speed of sound of the ground state define an expression allowing us to
determine the average size of these fluctuations. Afterwards, an
interferometric experiment involving Bogoliubov excitations of the condensate
and the pressure (or the speed of sound of the ground state) provides a second
and independent way in which this average size could be determined,
experimentally
Space--time fluctuations and the spreading of wavepackets
Using a density matrix description in space we study the evolution of
wavepackets in a fluctuating space-time background. We assume that space-time
fluctuations manifest as classical fluctuations of the metric. From the
non-relativistic limit of a non-minimally coupled Klein-Gordon equation we
derive a Schr\"odinger equation with an additive gaussian random potential.
This is transformed into an effective master equation for the density matrix.
The solutions of this master equation allow to study the dynamics of
wavepackets in a fluctuating space-time, depending on the fluctuation scenario.
We show how different scenarios alter the diffusion properties of wavepackets.Comment: 11 page
Test of constancy of speed of light with rotating cryogenic optical resonators
A test of Lorentz invariance for electromagnetic waves was performed by
comparing the resonance frequencies of two optical resonators as a function of
orientation in space. In terms of the Robertson-Mansouri-Sexl theory, we obtain
, a ten-fold improvement compared to
the previous best results. We also set a first upper limit for a so far unknown
parameter of the Standard Model Extension test theory,
.Comment: 4 pages, 2 figures, accepted for publication Phys. Rev. A (2005
Metric fluctuations and decoherence
Recently a model of metric fluctuations has been proposed which yields an
effective Schr\"odinger equation for a quantum particle with a modified
inertial mass, leading to a violation of the weak equivalence principle. The
renormalization of the inertial mass tensor results from a local space average
over the fluctuations of the metric over a fixed background metric. Here, we
demonstrate that the metric fluctuations of this model lead to a further
physical effect, namely to an effective decoherence of the quantum particle. We
derive a quantum master equation for the particle's density matrix, discuss in
detail its dissipation and decoherence properties, and estimate the
corresponding decoherence time scales. By contrast to other models discussed in
the literature, in the present approach the metric fluctuations give rise to a
decay of the coherences in the energy representation, i. e., to a localization
in energy space.Comment: 7 page
Quantum spacetime fluctuations: Lamb Shift and hyperfine structure of the hydrogen atom
We consider the consequences of the presence of metric fluctuations upon the
properties of a hydrogen atom. Particularly, we introduce these metric
fluctuations in the corresponding effective Schroedinger equation and deduce
the modifications that they entail upon the hyperfine structure related to a
hydrogen atom. We will find the change that these effects imply for the ground
state energy of the system and obtain a bound for its size comparing our
theoretical predictions against the experimental uncertainty reported in the
literature. In addition, we analyze the corresponding Lamb shift effect
emerging from these fluctuations of spacetime. Once again, we will set a bound
to these oscillations resorting to the current experimental outcomesComment: 26 page
Dephasing of a non-relativistic quantum particle due to a conformally fluctuating spacetime
We investigate the dephasing suffered by a nonrelativistic quantum particle
within a conformally fluctuating spacetime geometry. Starting from a minimally
coupled massive Klein-Gordon field, the low velocity limit yields an effective
Schrodinger equation where the wave function couples to gravity through an
effective nonlinear potential induced by the conformal fluctuations. The
quantum evolution is studied through a Dyson expansion scheme up to second
order. We show that only the nonlinear part of the potential can induce
dephasing. This happens through an exponential decay of the off diagonal terms
of the particle density matrix. The bath of conformal radiation is modeled in
3-dimensions and its statistical properties are described in general in terms
of a power spectral density. The case of a Lorentz invariant spectral density,
allowing to model vacuum fluctuations at a low energy domain, is investigated
and a general formula describing the loss of coherence derived. This depends
quadratically on the particle mass and on the inverse cube of a typical
particle dependent cutoff scale. Finally, the possibilities for experimental
verification are discussed. It is shown that current interferometry experiments
cannot detect such an effect. However this conclusion may improve by using high
mass entangled quantum states.Comment: 30 pages, 4 figures; to appear in Class. Quantum Grav. (2009
STE-QUEST - Test of the Universality of Free Fall Using Cold Atom Interferometry
The theory of general relativity describes macroscopic phenomena driven by the influence of gravity while quantum mechanics brilliantly accounts for microscopic effects. Despite their tremendous individual success, a complete unification of fundamental interactions is missing and remains one of the most challenging and important quests in modern theoretical physics. The STE-QUEST satellite mission, proposed as a medium-size mission within the Cosmic Vision program of the European Space Agency (ESA), aims for testing general relativity with high precision in two experiments by performing a measurement of the gravitational redshift of the Sun and the Moon by comparing terrestrial clocks, and by performing a test of the Universality of Free Fall of matter waves in the gravitational field of Earth comparing the trajectory of two Bose-Einstein condensates of Rb85 and Rb87. The two ultracold atom clouds are monitored very precisely thanks to techniques of atom interferometry. This allows to reach down to an uncertainty in the E\"otv\"os parameter of at least 2x10E-15. In this paper, we report about the results of the phase A mission study of the atom interferometer instrument covering the description of the main payload elements, the atomic source concept, and the systematic error sources