12,887 research outputs found
Temperature Measurement and Phonon Number Statistics of a Nanoelectromechanical Resonator
Measuring thermodynamic quantities can be easy or not, depending on the
system that is being studied. For a macroscopic object, measuring temperatures
can be as simple as measuring how much a column of mercury rises when in
contact with the object. At the small scale of quantum electromechanical
systems, such simple methods are not available and invariably detection
processes disturb the system state. Here we propose a method for measuring the
temperature on a suspended semiconductor membrane clamped at both ends. In this
method, the membrane is mediating a capacitive coupling between two
transmission line resonators (TLR). The first TLR has a strong dispersion, that
is, its decaying rate is larger than its drive, and its role is to pump in a
pulsed way the interaction between the membrane and the second TLR. By
averaging the pulsed measurements of the quadrature of the second TLR we show
how the temperature of the membrane can be determined. Moreover the statistical
description of the state of the membrane, which is directly accessed in this
approach is significantly improved by the addition of a Josephson Junction
coupled to the second TLR.Comment: 9 pages, 5 figures. To appear in New Journal of Physic
Interplay between disorder, quantum and thermal fluctuations in ferromagnetic alloys: The case of UCu2Si(2-x)Ge(x)
We consider, theoretically and experimentally, the effects of structural
disorder, quantum and thermal fluctuations in the magnetic and transport
properties of certain ferromagnetic alloys.We study the particular case of
UCu2Si(2-x)Ge(x). The low temperature resistivity, rho(T,x), exhibits Fermi
liquid (FL) behavior as a function of temperature T for all values of x, which
can be interpreted as a result of the magnetic scattering of the conduction
electrons from the localized U spins. The residual resistivity, rho(0,x),
follows the behavior of a disordered binary alloy. The observed non-monotonic
dependence of the Curie temperature, Tc(x), with x can be explained within a
model of localized spins interacting with an electronic bath whose transport
properties cross-over from ballistic to diffusive regimes. Our results clearly
show that the Curie temperature of certain alloys can be enhanced due to the
interplay between quantum and thermal fluctuations with disorder.Comment: 4 pages, 3 figures, to appear in Phys. Rev. Let
Effective Actions for 0+1 Dimensional Scalar QED and its SUSY Generalization at
We compute the effective actions for the 0+1 dimensional scalar field
interacting with an Abelian gauge background, as well as for its supersymmetric
generalization at finite temperature.Comment: 5 pages, Latex fil
Quantum radiation in a plane cavity with moving mirrors
We consider the electromagnetic vacuum field inside a perfect plane cavity
with moving mirrors, in the nonrelativistic approximation. We show that low
frequency photons are generated in pairs that satisfy simple properties
associated to the plane geometry. We calculate the photon generation rates for
each polarization as functions of the mechanical frequency by two independent
methods: on one hand from the analysis of the boundary conditions for moving
mirrors and with the aid of Green functions; and on the other hand by an
effective Hamiltonian approach. The angular and frequency spectra are discrete,
and emission rates for each allowed angular direction are obtained. We discuss
the dependence of the generation rates on the cavity length and show that the
effect is enhanced for short cavity lengths. We also compute the dissipative
force on the moving mirrors and show that it is related to the total radiated
energy as predicted by energy conservation.Comment: 17 pages, 1 figure, published in Physical Review
Capacitive Coupling of Two Transmission Line Resonators Mediated by the Phonon Number of a Nanoelectromechanical Oscillator
Detection of quantum features in mechanical systems at the nanoscale
constitutes a challenging task, given the weak interaction with other elements
and the available technics. Here we describe how the interaction between two
monomodal transmission-line resonators (TLRs) mediated by vibrations of a
nano-electromechanical oscillator can be described. This scheme is then
employed for quantum non-demolition detection of the number of phonons in the
nano-electromechanical oscillator through a direct current measurement in the
output of one of the TLRs. For that to be possible an undepleted field inside
one of the TLR works as a amplifier for the interaction between the mechanical
resonator and the remaining TLR. We also show how how the non-classical nature
of this system can be used for generation of tripartite entanglement and
conditioned mechanical coherent superposition states, which may be further
explored for detection processes.Comment: 6 pages, 5 figure
Operatorial quantization of Born-Infeld Skyrmion model and hidden symmetries
The SU(2) collective coordinates expansion of the Born-Infeld\break Skyrmion
Lagrangian is performed. The classical Hamiltonian is computed from this
special Lagrangian in approximative way: it is derived from the expansion of
this non-polynomial Lagrangian up to second-order variable in the collective
coordinates. This second-class constrained model is quantized by Dirac
Hamiltonian method and symplectic formalism. Although it is not expected to
find symmetries on second-class systems, a hidden symmetry is disclosed by
formulating the Born-Infeld Skyrmion %model as a gauge theory. To this end we
developed a new constraint conversion technique based on the symplectic
formalism. Finally, a discussion on the role played by the hidden symmetry on
the computation of the energy spectrum is presented.Comment: A new version of hep-th/9901133. To appear in JP
- …