8,697 research outputs found
Deterministic Plug-and-Play for Quantum Communication
We present a scheme for secure deterministic quantum communication without
using entanglement, in a Plug-and-Play fashion. The protocol is completely
deterministic, both in the encoding procedure and in the control one, thus
doubling the communication rate with respect to other setups; moreover,
deterministic nature of transmission, apart from rendering unnecessary bases
revelation on the public channel, allows the realization of protocols like
`direct communication' and `quantum dialogue'. The encoding exploits the phase
degree of freedom of a photon, thus paving the way to an optical fiber
implementation, feasible with present day technology.Comment: 4 pages, 2 figures; one reference update
Dynamical aspects in the Quantizer-Dequantizer formalism
The use of the quantizer-dequantizer formalism to describe the evolution of a
quantum system is reconsidered. We show that it is possible to embed a manifold
in the space of quantum states of a given auxiliary system by means of an
appropriate quantizer-dequantizer system. If this manifold of states is
invariant with respect to some unitary evolution, the quantizer-dequantizer
system provides a classical-like realization of such dynamics, which in general
is non linear. Integrability properties are also discussed. Weyl systems and
generalized coherente states are used as a simple illustration of these ideas.Comment: 15 page
Schwinger's Picture of Quantum Mechanics IV: Composition and independence
The groupoids description of Schwinger's picture of quantum mechanics is
continued by discussing the closely related notions of composition of systems,
subsystems, and their independence. Physical subsystems have a neat algebraic
description as subgroupoids of the Schwinger's groupoid of the system. The
groupoids picture offers two natural notions of composition of systems: Direct
and free products of groupoids, that will be analyzed in depth as well as their
universal character. Finally, the notion of independence of subsystems will be
reviewed, finding that the usual notion of independence, as well as the notion
of free independence, find a natural realm in the groupoids formalism. The
ideas described in this paper will be illustrated by using the EPRB experiment.
It will be observed that, in addition to the notion of the non-separability
provided by the entangled state of the system, there is an intrinsic
`non-separability' associated to the impossibility of identifying the entangled
particles as subsystems of the total system.Comment: 32 pages. Comments are welcome
Robust Unconditionally Secure Quantum Key Distribution with Two Nonorthogonal and Uninformative States
We introduce a novel form of decoy-state technique to make the single-photon
Bennett 1992 protocol robust against losses and noise of a communication
channel. Two uninformative states are prepared by the transmitter in order to
prevent the unambiguous state discrimination attack and improve the phase-error
rate estimation. The presented method does not require strong reference pulses,
additional electronics or extra detectors for its implementation.Comment: 7 pages, 2 figure
The Elephant Quantum Walk
We explore the impact of long-range memory on the properties of a family of
quantum walks in a one-dimensional lattice and discrete time, which can be
understood as the quantum version of the classical "Elephant Random Walk"
non-Markovian process. This Elephant Quantum Walk is robustly superballistic
with the standard deviation showing a constant exponent, , whatever the quantum coin operator, on which the diffusion coefficient is
dependent. On the one hand, this result indicates that contrarily to the
classical case, the degree of superdiffusivity in quantum non- Markovian
processes of this kind is mainly ruled by the extension of memory rather than
other microscopic parameters that explicitly define the process. On the other
hand, these parameters reflect on the diffusion coefficient.Comment: 4 figures, any comments is welcome. Accepted in PR
Covariant Jacobi Brackets for Test Particles
We show that the space of observables of test particles carries a natural
Jacobi structure which is manifestly invariant under the action of the
Poincar\'{e} group. Poisson algebras may be obtained by imposing further
requirements. A generalization of Peierls procedure is used to extend this
Jacobi bracket on the space of time-like geodesics on Minkowski space-time.Comment: 13 pages Submitted to MPL
Geometry from divergence functions and complex structures
Motivated by the geometrical structures of quantum mechanics, we introduce an
almost-complex structure on the product of any parallelizable
statistical manifold . Then, we use to extract a pre-symplectic form and
a metric-like tensor on from a divergence function. These tensors
may be pulled back to , and we compute them in the case of an N-dimensional
symplex with respect to the Kullback-Leibler relative entropy, and in the case
of (a suitable unfolding space of) the manifold of faithful density operators
with respect to the von Neumann-Umegaki relative entropy.Comment: 19 pages, comments are welcome
Covariant Variational Evolution and Jacobi Brackets: Fields
The analysis of the covariant brackets on the space of functions on the
solutions to a variational problem in the framework of contact geometry
initiated in the companion letter Ref.19 is extended to the case of the
multisymplectic formulation of the free Klein-Gordon theory and of the free
Schr\"{o}dinger equation.Comment: 16 page
Performance Assessment of Different Roof Integrated Photovoltaic Modules under Mediterranean Climate
AbstractMany countries, for aesthetic purposes, offer economic advantages (tax deductions, incentives, etc..) for the installation of building integrated photovoltaic modules (BIPV), with water-tightness capability and adequate mechanical resistance in order to substitute tile covering or part of it. Nevertheless, poor or absent ventilation under BIPV panels could cause them to overheat and reduce their efficiency.It is well established that the presence of an air gap between a photovoltaic (PV) module and roof covering facilitates ventilation cooling under the device and consequently reduces cell temperature and improves its performance.In this study, we investigated the thermal performance of PV modules installed in a real scale experimental building over a traditional clay tile pitched roof in Italy for almost one year (from August 2009 to June 2010). One PV module was rack-mounted over the roof covering with a 0.2 m air gap; the others were fully integrated and installed at the same level of the roof covering (one with an air gap of 0.04 m, the other mounted directly in contact with the insulation). Temperature and heat flux measurements for each panel, and environmental parameters were recorded.Experimental results demonstrate that even though the rack-mounted PV module constantly maintains cell temperature below that of the other full-building integrated modules, due to the presence of a higher air gap, the difference in the energy produced by the PV modules estimated for the entire monitoring period is less than 4%
Quantum dynamics of a vibrational mode of a membrane within an optical cavity
Optomechanical systems are a promising candidate for the implementation of
quantum interfaces for storing and redistributing quantum information. Here we
focus on the case of a high-finesse optical cavity with a thin vibrating
semitransparent membrane in the middle. We show that robust and stationary
optomechanical entanglement could be achieved in the system, even in the
presence of nonnegligible optical absorption in the membrane. We also present
some preliminary experimental data showing radiation-pressure induced optical
bistability.Comment: 6 pages, 2 figures. Work presented at the conference QCMC 2010 held
on 19-23 July 2010 at the University of Queensland, Brisbane, Australi
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