3,883 research outputs found
Decoherence induced by an interacting spin environment in the transition from integrability to chaos
We investigate the decoherence properties of a central system composed of two
spins 1/2 in contact with a spin bath. The dynamical regime of the bath ranges
from a fully integrable integrable limit to complete chaoticity. We show that
the dynamical regime of the bath determines the efficiency of the decoherence
process. For perturbative regimes, the integrable limit provides stronger
decoherence, while in the strong coupling regime the chaotic limit becomes more
efficient. We also show that the decoherence time behaves in a similar way. On
the contrary, the rate of decay of magnitudes like linear entropy or fidelity
does not depend on the dynamical regime of the bath. We interpret the latter
results as due to a comparable complexity of the Hamiltonian for both the
integrable and the fully chaotic limits.Comment: Submitted to Phys. Rev.
Fermionic Mach-Zehnder interferometer subject to a quantum bath
We study fermions in a Mach-Zehnder interferometer, subject to a
quantum-mechanical environment leading to inelastic scattering, decoherence,
renormalization effects, and time-dependent conductance fluctuations. Both the
loss of interference contrast as well as the shot noise are calculated, using
equations of motion and leading order perturbation theory. The full dependence
of the shot-noise correction on setup parameters, voltage, temperature and the
bath spectrum is presented. We find an interesting contribution due to
correlations between the fluctuating renormalized phase shift and the output
current, discuss the limiting behaviours at low and high voltages, and compare
with simpler models of dephasing.Comment: 5 pages, 3 figure
Introduction to Quantum Noise, Measurement and Amplification
The topic of quantum noise has become extremely timely due to the rise of
quantum information physics and the resulting interchange of ideas between the
condensed matter and AMO/quantum optics communities. This review gives a
pedagogical introduction to the physics of quantum noise and its connections to
quantum measurement and quantum amplification. After introducing quantum noise
spectra and methods for their detection, we describe the basics of weak
continuous measurements. Particular attention is given to treating the standard
quantum limit on linear amplifiers and position detectors using a general
linear-response framework. We show how this approach relates to the standard
Haus-Caves quantum limit for a bosonic amplifier known in quantum optics, and
illustrate its application for the case of electrical circuits, including
mesoscopic detectors and resonant cavity detectors.Comment: Substantial improvements over initial version; include supplemental
appendices
Optomechanical circuits for nanomechanical continuous variable quantum state processing
We propose and analyze a nanomechanical architecture where light is used to
perform linear quantum operations on a set of many vibrational modes. Suitable
amplitude modulation of a single laser beam is shown to generate squeezing,
entanglement, and state-transfer between modes that are selected according to
their mechanical oscillation frequency. Current optomechanical devices based on
photonic crystals may provide a platform for realizing this scheme.Comment: 11 pages, 5 figure
Recommended from our members
Previously Identified Genetic Variants in ADGRL3 Are not Associated with Risk for Equine Degenerative Myeloencephalopathy across Breeds.
Equine neuroaxonal dystrophy/equine degenerative myeloencephalopathy (eNAD/EDM) is a neurologic disease that has been reported in young horses from a wide range of breeds. The disease is inherited and associated with vitamin E deficiency during the first two years of life, resulting in bilateral symmetric ataxia. A missense mutation (chr3:71,917,591 C > T) within adhesion G protein-coupled receptor L3 (ADGRL3) was recently associated with risk for EDM in the Caspian breed. In order to confirm these findings, genotyping of this missense mutation, along with the three other associated single nucleotide polymorphisms (SNPs) in the genomic region, was carried out on 31 postmortem-confirmed eNAD/EDM cases and 43 clinically phenotyped controls from various breeds. No significant association was found between eNAD/EDM confirmed cases and genotype at any of the four identified SNPs (P > 0.05), including the nonsynonymous variant (EquCab2.0 chr3:71,917,591; allelic P = 0.85). These findings suggest that the four SNPs, including the missense variant in the ADGRL3 region, are not associated with risk for eNAD/EDM across multiple breeds of horses
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
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
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
Optomechanical cooling of levitated spheres with doubly-resonant fields
Optomechanical cooling of levitated dielectric particles represents a
promising new approach in the quest to cool small mechanical resonators towards
their quantum ground state. We investigate two-mode cooling of levitated
nanospheres in a self-trapping regime. We identify a rich structure of split
sidebands (by a mechanism unrelated to usual strong-coupling effects) and
strong cooling even when one mode is blue detuned. We show the best regimes
occur when both optical fields cooperatively cool and trap the nanosphere,
where cooling rates are over an order of magnitude faster compared to
corresponding single-sideband cooling rates.Comment: 8 Pages, 7 figure
Optimal control of circuit quantum electrodynamics in one and two dimensions
Optimal control can be used to significantly improve multi-qubit gates in
quantum information processing hardware architectures based on superconducting
circuit quantum electrodynamics. We apply this approach not only to dispersive
gates of two qubits inside a cavity, but, more generally, to architectures
based on two-dimensional arrays of cavities and qubits. For high-fidelity gate
operations, simultaneous evolutions of controls and couplings in the two
coupling dimensions of cavity grids are shown to be significantly faster than
conventional sequential implementations. Even under experimentally realistic
conditions speedups by a factor of three can be gained. The methods immediately
scale to large grids and indirect gates between arbitrary pairs of qubits on
the grid. They are anticipated to be paradigmatic for 2D arrays and lattices of
controllable qubits.Comment: Published version
- …