3,584 research outputs found
Gain-tunable optomechanical cooling in a laser cavity
We study the optical cooling of the resonator mirror in a
cavity-optomechanical system that contains an optical gain medium. We find that
the optical damping rate is vanishingly small for an incoherently pumped laser
above threshold. In the presence of an external coherent drive however, the
optical damping rate can be enhanced substantially with respect to that of a
passive cavity. We show that the strength of the incoherent pump provides a
conduit to tune the damping rate and the minimum attainable phonon number with
the same radiation pressure force, and the latter can be lowered from that of a
passive cavity if the thermal contribution is nonnegligible. We also show that
the system can undergo a transition from the weak optomechanical coupling
regime to the strong optomechanical coupling regime as the incoherent pump
strength is varied.Comment: 7 pages, 5 figure
Transverse angular momentum of photons
We develop the quantum theory of transverse angular momentum of light beams.
The theory applies to paraxial and quasi-paraxial photon beams in vacuum, and
reproduces the known results for classical beams when applied to coherent
states of the field. Both the Poynting vector, alias the linear momentum, and
the angular momentum quantum operators of a light beam are calculated including
contributions from first-order transverse derivatives. This permits a correct
description of the energy flow in the beam and the natural emergence of both
the spin and the angular momentum of the photons. We show that for collimated
beams of light, orbital angular momentum operators do not satisfy the standard
commutation rules. Finally, we discuss the application of our theory to some
concrete cases.Comment: 10 pages, 2 figure
TIRS Cryocooler: Spacecraft Integration and Test and Early Flight Data
The Thermal Infrared Sensor (TIRS) is an instrument on Landsat 8, launched in February 2013. The focal plane is cooled by a two-stage Ball Aerospace Stirling cycle cryocooler, with a coldfinger operating at 40K. This paper describes events during the spacecraft integration and test program, and results from early orbit operation of the cryocooler
Quantum squeezing of motion in a mechanical resonator
As a result of the quantum, wave-like nature of the physical world, a
harmonic oscillator can never be completely at rest. Even in the quantum ground
state, its position will always have fluctuations, called the zero-point
motion. Although the zero-point fluctuations are unavoidable, they can be
manipulated. In this work, using microwave frequency radiation pressure, we
both prepare a micron-scale mechanical system in a state near the quantum
ground state and then manipulate its thermal fluctuations to produce a
stationary, quadrature-squeezed state. We deduce that the variance of one
motional quadrature is 0.80 times the zero-point level, or 1 dB of
sub-zero-point squeezing. This work is relevant to the quantum engineering of
states of matter at large length scales, the study of decoherence of large
quantum systems, and for the realization of ultra-sensitive sensing of force
and motion
Controlled Dephasing of Electrons by Non-Gaussian Shot Noise
In a 'controlled dephasing' experiment [1-3], an interferometer loses its
coherence due to entanglement with a controlled quantum system ('which path'
detector). In experiments that were conducted thus far in mesoscopic systems
only partial dephasing was achieved. This was due to weak interactions between
many detector electrons and the interfering electron, resulting in a Gaussian
phase randomizing process [4-10]. Here, we report the opposite extreme: a
complete destruction of the interference via strong phase randomization only by
a few electrons in the detector. The realization was based on interfering edge
channels (in the integer quantum Hall effect regime, filling factor 2) in a
Mach-Zehnder electronic interferometer, with an inner edge channel serving as a
detector. Unexpectedly, the visibility quenched in a periodic lobe-type form as
the detector current increased; namely, it periodically decreased as the
detector current, and thus the detector's efficiency, increased. Moreover, the
visibility had a V-shape dependence on the partitioning of the detector
current, and not the expected dependence on the second moment of the shot
noise, T(1-T), with T the partitioning. We ascribe these unexpected features to
the strong detector-interferometer coupling, allowing only 1-3 electrons in the
detector to fully dephase the interfering electron. Consequently, in this work
we explored the non-Gaussian nature of noise [11], namely, the direct effect of
the shot noise full counting statistics [12-15].Comment: 14 pages, 4 figure
Coupled multimode optomechanics in the microwave regime
The motion of micro- and nanomechanical resonators can be coupled to
electromagnetic fields. This allows to explore the mutual interaction and
introduces new means to manipulate and control both light and mechanical
motion. Such optomechanical systems have recently been implemented in
nanoelectromechanical systems involving a nanomechanical beam coupled to a
superconducting microwave resonator. Here, we propose optomechanical systems
that involve multiple, coupled microwave resonators. In contrast to similar
systems in the optical realm, the coupling frequency governing photon exchange
between microwave modes is naturally comparable to typical mechanical
frequencies. For instance this enables new ways to manipulate the microwave
field, such as mechanically driving coherent photon dynamics between different
modes. In particular we investigate two setups where the electromagnetic field
is coupled either linearly or quadratically to the displacement of a
nanomechanical beam. The latter scheme allows to perform QND Fock state
detection. For experimentally realistic parameters we predict the possibility
to measure an individual quantum jump from the mechanical ground state to the
first excited state.Comment: 6 pages, 4 figures, 1 tabl
Electron-nuclei spin relaxation through phonon-assisted hyperfine interaction in a quantum dot
We investigate the inelastic spin-flip rate for electrons in a quantum dot
due to their contact hyperfine interaction with lattice nuclei. In contrast to
other works, we obtain a spin-phonon coupling term from this interaction by
taking directly into account the motion of nuclei in the vibrating lattice. In
the calculation of the transition rate the interference of first and second
orders of perturbation theory turns out to be essential. It leads to a
suppression of relaxation at long phonon wavelengths, when the confining
potential moves together with the nuclei embedded in the lattice. At higher
frequencies (or for a fixed confining potential), the zero-temperature rate is
proportional to the frequency of the emitted phonon. We address both the
transition between Zeeman sublevels of a single electron ground state as well
as the triplet-singlet transition, and we provide numerical estimates for
realistic system parameters. The mechanism turns out to be less efficient than
electron-nuclei spin relaxation involving piezoelectric electron-phonon
coupling in a GaAs quantum dot.Comment: 8 pages, 1 figur
Spin Relaxation in a Quantum Dot due to Nyquist Noise
We calculate electron and nuclear spin relaxation rates in a quantum dot due
to the combined action of Nyquist noise and electron-nuclei hyperfine or
spin-orbit interactions. The relaxation rate is linear in the resistance of the
gate circuit and, in the case of spin-orbit interaction, it depends essentially
on the orientations of both the static magnetic field and the fluctuating
electric field, as well as on the ratio between Rashba and Dresselhaus
interaction constants. We provide numerical estimates of the relaxation rate
for typical system parameters, compare our results with other, previously
discussed mechanisms, and show that the Nyquist mechanism can have an
appreciable effect for experimentally relevant systems.Comment: v2: New discussion of arbitrary gate setups (1 new figure), more
Comments on experiments; 6 pages, 4 figure
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