34 research outputs found
Dephasing and thermal smearing in an electromechanical which-path device
In an electromechanical which-path device electrons travelling through an
Aharonov-Bohm ring with a quantum dot in one of the arms are dephased by an
interaction with the fundamental flexural mode of a radio-frequency cantilever,
leading to a reduction in the visibilty of the interference fringes. However,
at finite temperatures time-averaged measurement of the current leads to a
fringe visibility which is reduced partly by dephasing of the electrons and
partly by a thermal smearing effect. The balance between thermal smearing and
dephasing predicted by a calculation depends very strongly on the choice of
cantilever basis states used. The interaction between the cantilever and its
environment is expected to select the coherent state basis for the cantilever
and hence lead to a dephasing rate which is substantially lower than that which
would arise if instead the Fock states were selected.Comment: To appear in Phonons 2001 Proceedings (Physica B
Quantum energy flow, dissipation and decoherence in mesoscopic dielectric structures
We first present a summary of recent results concerning the phononic energy
transport properties of mesoscopic, suspended dielectric wires. We then discuss
some related open problems concerning the fundamental lower limits on the
vibrational damping rates of submicron-sized cantilever structures and also the
possibility to create and detect quantum superpositions of spatially separated
states for such structures.Comment: To appear in Physica B, Proceedings of the 9th International
Conference on Phonon Scattering (Phonons 98
Mechanical Lamb-shift analogue for the Cooper-pair box
We estimate the correction to the Cooper-pair box energy level splitting due
to the quantum motion of a coupled micromechanical gate electrode. While the
correction due to zero-point motion is very small, it should be possible to
observe thermal motion-induced corrections to the photon-assisted tunneling
current.Comment: To appear in Phonons 2001 Proceedings (Physica B
Micromechanical electrometry of single-electron transistor island charge
We consider the possibility of using a micromechanical gate electrode located
just above the island of a single-electron transistor to measure directly the
fluctuating island charge due to tunnelling electrons.Comment: To appear in Phonons 2001 Proceedings (Physica B
A cavity-Cooper pair transistor scheme for investigating quantum optomechanics in the ultrastrong coupling regime
We propose a scheme involving a Cooper pair transistor (CPT) embedded in a superconducting microwave cavity, where the CPT serves as a charge tunable quantum inductor to facilitate ultra-strong coupling between photons in the cavity and a nano- to meso-scale mechanical resonator. The mechanical resonator is capacitively coupled to the CPT, such that mechanical displacements of the resonator cause a shift in the CPT inductance and hence the cavity's resonant frequency. The amplification provided by the CPT is sufficient for the zero point motion of the mechanical resonator alone to cause a significant change in the cavity resonance. Conversely, a single photon in the cavity causes a shift in the mechanical resonator position on the order of its zero point motion. As a result, the cavity-Cooper pair transistor coupled to a mechanical resonator will be able to access a regime in which single photons can affect single phonons and vice versa. Realizing this ultra strong coupling regime will facilitate the creation of non-classical states of the mechanical resonator, as well as the means to accurately characterize such states by measuring the cavity photon field
Phonon-mediated thermal conductance of mesoscopic wires with rough edges
We present an analysis of acoustic phonon propagation through long,
free-standing, insulating wires with rough surfaces. Due to a crossover from
ballistic propagation of the lowest-frequency phonon mode at to a diffusive (or even localized) behavior upon the increase of
phonon frequency, followed by re-entrance into the quasi-ballistic regime, the
heat conductance of a wire acquires an intermediate tendency to saturate within
the temperature range .Comment: 4 pages, 3 figures included; minor changes and corrections, figures 1
and 2 replaced by better versions; to appear in PRB Brief Report
The Effect of Surface Roughness on the Universal Thermal Conductance
We explain the reduction of the thermal conductance below the predicted
universal value observed by Schwab et al. in terms of the scattering of thermal
phonons off surface roughness using a scalar model for the elastic waves. Our
analysis shows that the thermal conductance depends on two roughness
parameters: the roughness amplitude and the correlation length .
At sufficiently low temperatures the conductance decrease from the universal
value quadratically with temperature at a rate proportional to .
Values of equal to 0.22 and equal to about 0.75 of the width of
the conduction pathway give a good fit to the data.Comment: 10 pages, 5 figures. Ref. added, typo correcte
From topological to parametrized field theory
It has been proposed to study the theory resulting from setting the
gravitational constant to zero in the first order formalism for general
relativity. In this letter we investigate this theory in the presence of matter
fields, establish its equivalence with parametrized field theory on a flat
background, and relate it to previous results in topological field theory (BF
theory).Comment: 8 pages, latex, no figure
Elastic Wave Transmission at an Abrupt Junction in a Thin Plate, with Application to Heat Transport and Vibrations in Mesoscopic Systems
The transmission coefficient for vibrational waves crossing an abrupt
junction between two thin elastic plates of different widths is calculated.
These calculations are relevant to ballistic phonon thermal transport at low
temperatures in mesoscopic systems and the Q for vibrations in mesoscopic
oscillators. Complete results are calculated in a simple scalar model of the
elastic waves, and results for long wavelength modes are calculated using the
full elasticity theory calculation. We suggest that thin plate elasticty theory
provide a useful and tractable approximation to the full three dimensional
geometry.Comment: 35 pages, including 12 figure
Steering of a Bosonic Mode with a Double Quantum Dot
We investigate the transport and coherence properties of a double quantum dot
coupled to a single damped boson mode. Our numerically results reveal how the
properties of the boson distribution can be steered by altering parameters of
the electronic system such as the energy difference between the dots.
Quadrature amplitude variances and the Wigner function are employed to
illustrate how the state of the boson mode can be controlled by a stationary
electron current through the dots.Comment: 10 pages, 6 figures, to appear in Phys. Rev.