12,730 research outputs found
Dynamical Stability and Quantum Chaos of Ions in a Linear Trap
The realization of a paradigm chaotic system, namely the harmonically driven
oscillator, in the quantum domain using cold trapped ions driven by lasers is
theoretically investigated. The simplest characteristics of regular and chaotic
dynamics are calculated. The possibilities of experimental realization are
discussed.Comment: 24 pages, 17 figures, submitted to Phys. Rev
A compact micro-wave synthesizer for transportable cold-atom interferometers
We present the realization of a compact micro-wave frequency synthesizer for
an atom interferometer based on stimulated Raman transitions, applied to
transportable inertial sensing. Our set-up is intended to address the hyperfine
transitions of Rubidium 87 atoms at 6.8 GHz. The prototype is evaluated both in
the time and the frequency domain by comparison with state-of-the-art frequency
references developed at LNE-SYRTE. In free-running mode, it features a residual
phase noise level of -65 dBrad$^2.Hz^{-1} at 10-Hz offset frequency and a white
phase noise level in the order of -120 dBrad^2.Hz^{-1} for Fourier frequencies
above 10 kHz. The phase noise effect on the sensitivity of the atomic
interferometer is evaluated for diverse values of cycling time, interrogation
time and Raman pulse duration. To our knowledge, the resulting contribution is
well below the sensitivity of any demonstrated cold atom inertial sensors based
on stimulated Raman transitions. The drastic improvement in terms of size,
simplicity and power consumption paves the way towards field and mobile
operations.Comment: accepted for publication in Review of Scientific Instruments, 6
pages, 4 figure
Dynamical fidelity of a solid-state quantum computation
In this paper we analyze the dynamics in a spin-model of quantum computer.
Main attention is paid to the dynamical fidelity (associated with dynamical
errors) of an algorithm that allows to create an entangled state for remote
qubits. We show that in the regime of selective resonant excitations of qubits
there is no any danger of quantum chaos. Moreover, in this regime a modified
perturbation theory gives an adequate description of the dynamics of the
system. Our approach allows to explicitly describe all peculiarities of the
evolution of the system under time-dependent pulses corresponding to a quantum
protocol. Specifically, we analyze, both analytically and numerically, how the
fidelity decreases in dependence on the model parameters.Comment: 9 pages, 6 figures, submitted to PR
Spin Diffusion and Relaxation in a Nonuniform Magnetic Field
We consider a quasiclassical model that allows us to simulate the process of
spin diffusion and relaxation in the presence of a highly nonuniform magnetic
field. The energy of the slow relaxing spins flows to the fast relaxing spins
due to the dipole-dipole interaction between the spins. The magnetic field
gradient suppresses spin diffusion and increases the overall relaxation time in
the system. The results of our numerical simulations are in a good agreement
with the available experimental data.Comment: 11 pages and 6 figure
Cascade atom in high-Q cavity: The spectrum for non-Markovian decay
The spontaneous emission spectrum for a three level cascade configuration
atom in a single mode high-Q cavity coupled to a zero temperature reservoir of
continuum external modes is determined from the atom-cavity mode master
equation using the quantum regression theorem. Initially the atom is in its
upper state and the cavity mode empty of photons. Following Glauber, the
spectrum is defined via the response of a detector atom. Spectra are calculated
for the detector located inside the cavity (case A), outside the cavity end
mirror (Case B-end emission), or placed for emission out the side of the cavity
(Case C). The spectra for case A and case B are found to be essentially the
same. In all the cases the predicted lineshapes are free of instrumental
effects and only due to cavity decay. Spectra are presented for intermediate
and strong coupling regime situations (where both atomic transitions are
resonant with the cavity frequency), for cases of non-zero cavity detuning, and
for cases where the two atomic transition frequencies differ. The spectral
features for Cases B(A) and C are qualitatively similar, with six spectral
peaks for resonance cases and eight for detuned cases. These general features
of the spectra can be understood via the dressed atom model. However, Case B
and C spectra differ in detail, with the latter exhibiting a deep spectral hole
at the cavity frequency due to quantum interference effects.Comment: 29 pages, 14 figures; v2: very minor correction to two equations,
thicker lines in some figure
Solid-State Quantum Computer Based on Scanning Tunneling Microscopy
We propose a solid-state nuclear spin quantum computer based on application
of scanning tunneling microscopy (STM) and well-developed silicon technology.
It requires the measurement of tunneling current modulation caused by the
Larmor precession of a single electron spin.
Our envisioned STM quantum computer would operate at the high magnetic field
(T) and at low temperature K.Comment: 3pages RevTex including 2 figure
Avoiding Quantum Chaos in Quantum Computation
We study a one-dimensional chain of nuclear spins in an external
time-dependent magnetic field. This model is considered as a possible candidate
for experimental realization of quantum computation. According to the general
theory of interacting particles, one of the most dangerous effects is quantum
chaos which can destroy the stability of quantum operations. According to the
standard viewpoint, the threshold for the onset of quantum chaos due to an
interaction between spins (qubits) strongly decreases with an increase of the
number of qubits. Contrary to this opinion, we show that the presence of a
magnetic field gradient helps to avoid quantum chaos which turns out to
disappear with an increase of the number of qubits. We give analytical
estimates which explain this effect, together with numerical data supportingComment: RevTex, 5 pages including 3 eps-figure
Accelerator dynamics of a fractional kicked rotor
It is shown that the Weyl fractional derivative can quantize an open system.
A fractional kicked rotor is studied in the framework of the fractional
Schrodinger equation. The system is described by the non-Hermitian Hamiltonian
by virtue of the Weyl fractional derivative. Violation of space symmetry leads
to acceleration of the orbital momentum. Quantum localization saturates this
acceleration, such that the average value of the orbital momentum can be a
direct current and the system behaves like a ratchet. The classical counterpart
is a nonlinear kicked rotor with absorbing boundary conditions.Comment: Submitted for publication in Phys. Rev.
Single electron capacitance spectroscopy of vertical quantum dots using a single electron transistor
We have incorporated an aluminum single electron transistor (SET) directly on
top of a vertical quantum dot, enabling the use of the SET as an electrometer
that is extremely responsive to the motion of charge into and out of the dot.
Charge induced on the SET central island from single electron additions to the
dot modulates the SET output, and we describe two methods for demodulation that
permit quantitative extraction of the quantum dot capacitance signal. The two
methods produce closely similar results for the determined single electron
capacitance peaks.Comment: Submitted to Applied Physics Letters (reformatted to fit correctly on
a page
Double-Slit Interferometry with a Bose-Einstein Condensate
A Bose-Einstein "double-slit" interferometer has been recently realized
experimentally by (Y. Shin et. al., Phys. Rev. Lett. 92 50405 (2004)). We
analyze the interferometric steps by solving numerically the time-dependent
Gross-Pitaevski equation in three-dimensional space. We focus on the
adiabaticity time scales of the problem and on the creation of spurious
collective excitations as a possible source of the strong dephasing observed
experimentally. The role of quantum fluctuations is discussed.Comment: 4 pages, 3 figure
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