12,439 research outputs found
Naturalness in emergent spacetime
Effective field theories (EFTs) have been widely used as a framework in order
to place constraints on the Planck suppressed Lorentz violations predicted by
various models of quantum gravity. There are however technical problems in the
EFT framework when it comes to ensuring that small Lorentz violations remain
small -- this is the essence of the "naturalness" problem. Herein we present an
"emergent" space-time model, based on the "analogue gravity'' programme, by
investigating a specific condensed-matter system that is in principle capable
of simulating the salient features of an EFT framework with Lorentz violations.
Specifically, we consider the class of two-component BECs subject to
laser-induced transitions between the components, and we show that this model
is an example for Lorentz invariance violation due to ultraviolet physics.
Furthermore our model explicitly avoids the "naturalness problem", and makes
specific suggestions regarding how to construct a physically reasonable quantum
gravity phenomenology.Comment: V1:4 pages, revtex4; V2: slight changes in title, presentation, and
conclusions. This version to appear in Physical Review Letter
Entanglement Entropy and Mutual Information Production Rates in Acoustic Black Holes
A method to investigate acoustic Hawking radiation is proposed, where
entanglement entropy and mutual information are measured from the fluctuations
of the number of particles. The rate of entropy radiated per one-dimensional
(1D) channel is given by , where is the sound
acceleration on the sonic horizon. This entropy production is accompanied by a
corresponding formation of mutual information to ensure the overall
conservation of information. The predictions are confirmed using an \emph{ab
initio} analytical approach in transonic flows of 1D degenerate ideal Fermi
fluids.Comment: 4 pages, 1 figure. Supplemental Material (pdf) included in the source
of this manuscrip
Greenberger-Horne-Zeilinger paradoxes for many qudits
We construct GHZ contradictions for three or more parties sharing an
entangled state, the dimension d of each subsystem being an even integer
greater than 2. The simplest example that goes beyond the standard GHZ paradox
(three qubits) involves five ququats (d=4). We then examine the criteria a GHZ
paradox must satisfy in order to be genuinely M-partite and d-dimensional.Comment: 5 pages RevTe
A lattice calculation of the pion form factor with Ginsparg-Wilson-type fermions
Results for Monte Carlo calculations of the electromagnetic vector and scalar
form factors of the pion in a quenched simulation are presented. We work with
two different lattice volumes up to a spatial size of 2.4 fm at a lattice
spacing of 0.148 fm. The pion form factors in the space-like region are
determined for pion masses down to 340 MeV.Comment: REVTeX 4, 8 pages, 9 figures, 4 tables; final versio
Landau-Zener Tunnelling in Waveguide Arrays
Landau-Zener tunnelling is discussed in connection with optical waveguide
arrays. Light injected in a specific band of the Bloch spectrum in the
propagation constant can be transmitted to another band, changing its physical
properties. This is achieved using two waveguide arrays with different
refractive indices, which amounts to consider a Schr\"odinger equation in a
periodic potential with a step. The step causes wave "acceleration" and thus
induces Landau-Zener tunnelling. The region of physical parameters where this
phenomenon can occur is analytically determined and a realistic experimental
setup is suggested. Its application could allow the realization of light
filters.Comment: 4 pages, 6 figure
One-dimensional lattice of oscillators coupled through power-law interactions: Continuum limit and dynamics of spatial Fourier modes
We study synchronization in a system of phase-only oscillators residing on
the sites of a one-dimensional periodic lattice. The oscillators interact with
a strength that decays as a power law of the separation along the lattice
length and is normalized by a size-dependent constant. The exponent of
the power law is taken in the range . The oscillator frequency
distribution is symmetric about its mean (taken to be zero), and is
non-increasing on . In the continuum limit, the local density of
oscillators evolves in time following the continuity equation that expresses
the conservation of the number of oscillators of each frequency under the
dynamics. This equation admits as a stationary solution the unsynchronized
state uniform both in phase and over the space of the lattice. We perform a
linear stability analysis of this state to show that when it is unstable,
different spatial Fourier modes of fluctuations have different stability
thresholds beyond which they grow exponentially in time with rates that depend
on the Fourier modes. However, numerical simulations show that at long times,
all the non-zero Fourier modes decay in time, while only the zero Fourier mode
(i.e., the "mean-field" mode) grows in time, thereby dominating the instability
process and driving the system to a synchronized state. Our theoretical
analysis is supported by extensive numerical simulations.Comment: 7 pages, 4 figures. v2: new simulation results added, close to the
published versio
Side-channel-free quantum key distribution
Quantum key distribution (QKD) offers the promise of absolutely secure
communications. However, proofs of absolute security often assume perfect
implementation from theory to experiment. Thus, existing systems may be prone
to insidious side-channel attacks that rely on flaws in experimental
implementation. Here we replace all real channels with virtual channels in a
QKD protocol, making the relevant detectors and settings inside private spaces
inaccessible while simultaneously acting as a Hilbert space filter to eliminate
side-channel attacks. By using a quantum memory we find that we are able to
bound the secret-key rate below by the entanglement-distillation rate computed
over the distributed states.Comment: Considering general quantum systems, we extended QKD to the presence
of an untrusted relay, whose measurement creates secret correlations in
remote stations (achievable rate lower-bounded by the coherent information).
This key ingredient, i.e., the use of a measurement-based untrusted relay,
has been called 'measurement-device independence' in another arXiv submission
(arXiv:1109.1473
The Theory of a Quantum Noncanonical Field in Curved Spacetimes
Much attention has been recently devoted to the possibility that quantum
gravity effects could lead to departures from Special Relativity in the form of
a deformed Poincar\`e algebra. These proposals go generically under the name of
Doubly or Deformed Special Relativity (DSR). In this article we further explore
a recently proposed class of quantum field theories, involving noncanonically
commuting complex scalar fields, which have been shown to entail a DSR-like
symmetry. An open issue for such theories is whether the DSR-like symmetry has
to be taken as a physically relevant symmetry, or if in fact the "true"
symmetries of the theory are just rotations and translations while boost
invariance has to be considered broken. We analyze here this issue by extending
the known results to curved spacetime under both of the previous assumptions.
We show that if the symmetry of the free theory is taken to be a DSR-like
realization of the Poincar\'e symmetry, then it is not possible to render such
a symmetry a gauge symmetry of the curved physical spacetime. However, it is
possible to introduce an auxiliary spacetime which allows to describe the
theory as a standard quantum field theory in curved spacetime. Alternatively,
taking the point of view that the noncanonical commutation of the fields
actually implies a breakdown of boost invariance, the physical spacetime
manifold has to be foliated in surfaces of simultaneity and the field theory
can be coupled to gravity by making use of the ADM prescription.Comment: 9 pages, no figure
On the Possibility of a Trans-Planckian Duality
We investigate the possibility of a trans-Planckian duality, which exchanges
a manifold of events (space-time), with a manifold of momenta
(energy-momentum). Gravity has a dual counter-part, that is, a geometric theory
defined on the manifold of momenta. We provide a mathematical framework that
can possibly realize this idea, and analyze its classical behaviour.Comment: 21 pages, 4 figure
- …