698 research outputs found
Diffusion Processes and Coherent States
It is shown that stochastic processes of diffusion type possess, in all
generality, a structure of uncertainty relations and of coherent and squeezed
states. This fact is used to obtain, via Nelson stochastic formulation of
quantum mechanics, the harmonic-oscillator coherent and squeezed states. The
method allows to derive new minimum uncertainty states in time-dependent
oscillator potentials and for the Caldirola-Kanai model of quantum damped
oscillator.Comment: 11 pages, plain LaTe
Quantum Groups, Coherent States, Squeezing and Lattice Quantum Mechanics
By resorting to the Fock--Bargmann representation, we incorporate the quantum
Weyl--Heisenberg (-WH) algebra into the theory of entire analytic functions.
The main tool is the realization of the --WH algebra in terms of finite
difference operators. The physical relevance of our study relies on the fact
that coherent states (CS) are indeed formulated in the space of entire analytic
functions where they can be rigorously expressed in terms of theta functions on
the von Neumann lattice. The r\^ole played by the finite difference operators
and the relevance of the lattice structure in the completeness of the CS system
suggest that the --deformation of the WH algebra is an essential tool in the
physics of discretized (periodic) systems. In this latter context we define a
quantum mechanics formalism for lattice systems.Comment: 22 pages, TEX file, DFF188/9/93 Firenz
Influence of trapping potentials on the phase diagram of bosonic atoms in optical lattices
We study the effect of external trapping potentials on the phase diagram of
bosonic atoms in optical lattices. We introduce a generalized Bose-Hubbard
Hamiltonian that includes the structure of the energy levels of the trapping
potential, and show that these levels are in general populated both at finite
and zero temperature. We characterize the properties of the superfluid
transition for this situation and compare them with those of the standard
Bose-Hubbard description. We briefly discuss similar behaviors for fermionic
systems.Comment: 4 pages, 3 figures; final version, to be published in Phys. Rev.
Tunable non-Gaussian resources for continuous-variable quantum technologies
We introduce and discuss a set of tunable two-mode states of
continuous-variable systems, as well as an efficient scheme for their
experimental generation. This novel class of tunable entangled resources is
defined by a general ansatz depending on two experimentally adjustable
parameters. It is very ample and flexible as it encompasses Gaussian as well as
non-Gaussian states. The latter include, among others, known states such as
squeezed number states and de-Gaussified photon-added and photon-subtracted
squeezed states, the latter being the most efficient non-Gaussian resources
currently available in the laboratory. Moreover, it contains the classes of
squeezed Bell states and even more general non-Gaussian resources that can be
optimized according to the specific quantum technological task that needs to be
realized. The proposed experimental scheme exploits linear optical operations
and photon detections performed on a pair of uncorrelated two--mode Gaussian
squeezed states. The desired non-Gaussian state is then realized via ancillary
squeezing and conditioning. Two independent, freely tunable experimental
parameters can be exploited to generate different states and to optimize the
performance in implementing a given quantum protocol. As a concrete instance,
we analyze in detail the performance of different states considered as
resources for the realization of quantum teleportation in realistic conditions.
For the fidelity of teleportation of an unknown coherent state, we show that
the resources associated to the optimized parameters outperform, in a
significant range of experimental values, both Gaussian twin beams and
photon-subtracted squeezed states.Comment: 13 pages, 7 figure
Optimal estimation of losses at the ultimate quantum limit with non-Gaussian states
We address the estimation of the loss parameter of a bosonic channel probed
by arbitrary signals. Unlike the optimal Gaussian probes, which can attain the
ultimate bound on precision asymptotically either for very small or very large
losses, we prove that Fock states at any fixed photon number saturate the bound
unconditionally for any value of the loss. In the relevant regime of low-energy
probes, we demonstrate that superpositions of the first low-lying Fock states
yield an absolute improvement over any Gaussian probe. Such few-photon states
can be recast quite generally as truncations of de-Gaussified photon-subtracted
states.Comment: 4 pages, 3 figure
DYNAMICAL CONTROL OF THE HALO IN PARTICLE BEAMS: A STOCHASTIC–HYDRODYNAMIC APPROACH
In this paper we describe the beam distribution in particle accelerators in the framework of a stochastic–hydrodynamic scheme. In this scheme the possible reproduction of the halo after its elimination is a consequence of the stationarity of the transverse distribution which plays the role of an attractor for every other distribution. The relaxation time toward the halo is estimated, and a few examples of controlled transitions toward a permanent halo elimination are discussed
Hierarchies of Geometric Entanglement
We introduce a class of generalized geometric measures of entanglement. For
pure quantum states of elementary subsystems, they are defined as the
distances from the sets of -separable states (). The entire set
of generalized geometric measures provides a quantification and hierarchical
ordering of the different bipartite and multipartite components of the global
geometric entanglement, and allows to discriminate among the different
contributions. The extended measures are applied to the study of entanglement
in different classes of -qubit pure states. These classes include and
states, and their symmetric superpositions; symmetric multi-magnon
states; cluster states; and, finally, asymmetric generalized -like
superposition states. We discuss in detail a general method for the explicit
evaluation of the multipartite components of geometric entanglement, and we
show that the entire set of geometric measures establishes an ordering among
the different types of bipartite and multipartite entanglement. In particular,
it determines a consistent hierarchy between and states, clarifying
the original result of Wei and Goldbart that states possess a larger global
entanglement than states. Furthermore, we show that all multipartite
components of geometric entanglement in symmetric states obey a property of
self-similarity and scale invariance with the total number of qubits and the
number of qubits per party.Comment: 16 pages, 7 figures. Final version, to appear in Phys. Rev.
Dietary habits and gut microbiota in healthy adults: Focusing on the right diet. a systematic review
Diet is the first to affect our intestinal microbiota and therefore the state of eubiosis. Several studies are highlighting the potential benefits of taking certain nutritional supplements, but a dietary regime that can ensure the health of the intestinal microbiota, and the many pathways it governs, is not yet clearly defined. We performed a systematic review of the main studies concerning the impact of an omnivorous diet on the composition of the microbiota and the production of short-chain fatty acids (SCFAs). Some genera and phyla of interest emerged significantly and about half of the studies evaluated consider them to have an equally significant impact on the production of SCFAs, to be a source of nutrition for our colon cells, and many other processes. Although numerous randomized trials are still needed, the Mediterranean diet could play a valuable role in ensuring our health through direct interaction with our microbiota
Dynamics of Ordering of Heisenberg Spins with Torque --- Nonconserved Case. I
We study the dynamics of ordering of a nonconserved Heisenberg magnet. The
dynamics consists of two parts --- an irreversible dissipation into a heat bath
and a reversible precession induced by a torque due to the local molecular
field. For quenches to zero temperature, we provide convincing arguments, both
numerically (Langevin simulation) and analytically (approximate closure scheme
due to Mazenko), that the torque is irrelevant at late times. We subject the
Mazenko closure scheme to systematic numerical tests. Such an analysis, carried
out for the first time on a vector order parameter, shows that the closure
scheme performs respectably well. For quenches to , we show, to , that the torque is irrelevant at the Wilson-Fisher fixed
point.Comment: 13 pages, REVTEX, and 19 .eps figures, compressed, Submitted to Phys.
Rev.
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