494 research outputs found
Cooling of Nanomechanical Resonator Based on Periodical Coupling to Cooper Pair Box
We propose and study an active cooling mechanism for the nanomechanical
resonator (NAMR) based on periodical coupling to a Cooper pair box (CPB), which
is implemented by a designed series of magnetic flux pluses threading through
the CPB. When the initial phonon number of the NAMR is not too large, this
cooling protocol is efficient in decreasing the phonon number by two to three
orders of magnitude. Our proposal is theoretically universal in cooling various
boson systems of single mode. It can be specifically generalized to prepare the
nonclassical state of the NAMR.Comment: 5pages,3figure
The Quantum Emergence of Chaos
The dynamical status of isolated quantum systems, partly due to the linearity
of the Schrodinger equation is unclear: Conventional measures fail to detect
chaos in such systems. However, when quantum systems are subjected to
observation -- as all experimental systems must be -- their dynamics is no
longer linear and, in the appropriate limit(s), the evolution of expectation
values, conditioned on the observations, closely approaches the behavior of
classical trajectories. Here we show, by analyzing a specific example, that
microscopic continuously observed quantum systems, even far from any classical
limit, can have a positive Lyapunov exponent, and thus be truly chaotic.Comment: 4 pages, 4 figure
Quantum-Classical Transition of Photon-Carnot Engine Induced by Quantum Decoherence
We study the physical implementation of the Photon Carnot engine (PCE) based
on the cavity QED system [M. Scully et al, Science, \textbf{299}, 862 (2003)].
Here, we analyze two decoherence mechanisms for the more practical systems of
PCE, the dissipation of photon field and the pure dephasing of the input atoms.
As a result we find that (I) the PCE can work well to some extent even in the
existence of the cavity loss (photon dissipation); and (II) the short-time
atomic dephasing, which can destroy the PCE, is a fatal problem to be overcome.Comment: 6 pages, 3 figure
Persistent single-photon production by tunable on-chip micromaser with a superconducting quantum circuit
We propose a tunable on-chip micromaser using a superconducting quantum
circuit (SQC). By taking advantage of externally controllable state
transitions, a state population inversion can be achieved and preserved for the
two working levels of the SQC and, when needed, the SQC can generate a single
photon. We can regularly repeat these processes in each cycle when the
previously generated photon in the cavity is decaying, so that a periodic
sequence of single photons can be produced persistently. This provides a
controllable way for implementing a persistent single-photon source on a
microelectronic chip.Comment: 8 pages, 4 figure
Vibronic "Rabi resonances" in harmonic and hard-wall ion-traps for arbitrary laser intensity and detuning
We investigate laser-driven vibronic transitions of a single two-level atomic
ion in harmonic and hard wall traps. In the Lamb-Dicke regime, for tuned or
detuned lasers with respect to the internal frequency of the ion, and weak or
strong laser intensities, the vibronic transitions occur at well isolated "Rabi
Resonances", where the detuning-adapted Rabi frequency coincides with the level
spacing of the vibrational modes. These vibronic resonances are characterized
as avoided crossings of the dressed levels (eigenvalues of the full
Hamiltonian). Their peculiarities due to symmetry constraints and trapping
potential are also examined.Comment: 7 pages, 4 figure
A multidomain spectral method for solving elliptic equations
We present a new solver for coupled nonlinear elliptic partial differential
equations (PDEs). The solver is based on pseudo-spectral collocation with
domain decomposition and can handle one- to three-dimensional problems. It has
three distinct features. First, the combined problem of solving the PDE,
satisfying the boundary conditions, and matching between different subdomains
is cast into one set of equations readily accessible to standard linear and
nonlinear solvers. Second, touching as well as overlapping subdomains are
supported; both rectangular blocks with Chebyshev basis functions as well as
spherical shells with an expansion in spherical harmonics are implemented.
Third, the code is very flexible: The domain decomposition as well as the
distribution of collocation points in each domain can be chosen at run time,
and the solver is easily adaptable to new PDEs. The code has been used to solve
the equations of the initial value problem of general relativity and should be
useful in many other problems. We compare the new method to finite difference
codes and find it superior in both runtime and accuracy, at least for the
smooth problems considered here.Comment: 31 pages, 8 figure
Analysis of relative dispersion of two particles by Lagrangian stochastic models and DNS methods
Comparisons of the Q1D against the known Lagrangian stochastic well-mixed quadratic form models and the moments approximation models are presented. In the case of modestly large Reynolds numbers turbulence (Re λ ⋍ 240) the comparison of the Q1D model with the DNS data is made. Being in a qualitatively agreemnet with the DNS data, the Q1D model predicts higher rate of separation. Realizability of Q1D model extracted from the transport equation with a quadratic form of the conditional acceleration is shown
Real-space Manifestations of Bottlenecks in Turbulence Spectra
An energy-spectrum bottleneck, a bump in the turbulence spectrum between the
inertial and dissipation ranges, is shown to occur in the non-turbulent,
one-dimensional, hyperviscous Burgers equation and found to be the
Fourier-space signature of oscillations in the real-space velocity, which are
explained by boundary-layer-expansion techniques. Pseudospectral simulations
are used to show that such oscillations occur in velocity correlation functions
in one- and three-dimensional hyperviscous hydrodynamical equations that
display genuine turbulence.Comment: 5 pages, 2 figure
Non-Markovian Quantum Trajectories of Many-Body Quantum Open Systems
A long-standing open problem in non-Markovian quantum state diffusion (QSD)
approach to open quantum systems is to establish the non-Markovian QSD
equations for multiple qubit systems. In this paper, we settle this important
question by explicitly constructing a set of exact time-local QSD equations for
-qubit systems. Our exact time-local (convolutionless) QSD equations have
paved the way towards simulating quantum dynamics of many-body open systems
interacting with a common bosonic environment. The applicability of this
multiple-qubit stochastic equation is exemplified by numerically solving
several quantum open many-body systems concerning quantum coherence dynamics
and dynamical control.Comment: 8 pages, 2 figures. manuscript revised and reference update
- …