12,923 research outputs found
Single-Pulse Preparation of the Uniform Superpositional State used in Quantum Algorithms
We examine a single-pulse preparation of the uniform superpositional wave
function, which includes all basis states, in a spin quantum computer. The
effective energy spectrum and the errors generated by this pulse are studied in
detail. We show that, in spite of the finite width of the energy spectrum
bands, amplitude and phase errors can be made reasonably small.Comment: RevTex, 5 pages, 7 eps figure
ABTRAJ on-site tracking prediction program
Computer program, ABTRAJ, provides Deep Space Network tracking stations with the capability of generating spacecraft predictions with on-site computers. The program is comprised of two major sections - the main prediction portion and a trajectory subroutine which spans the desired predict interval with spacecraft ephemeris data written on magnetic tapes
Stability of the Ground State of a Harmonic Oscillator in a Monochromatic Wave
Classical and quantum dynamics of a harmonic oscillator in a monochromatic
wave is studied in the exact resonance and near resonance cases. This model
describes, in particular, a dynamics of a cold ion trapped in a linear ion trap
and interacting with two lasers fields with close frequencies. Analytically and
numerically a stability of the ``classical ground state'' (CGS) -- the vicinity
of the point () -- is analyzed. In the quantum case, the method for
studying a stability of the quantum ground state (QGS) is suggested, based on
the quasienergy representation. The dynamics depends on four parameters: the
detuning from the resonance, , where and
are, respectively, the wave and the oscillator's frequencies; the
positive integer (resonance) number, ; the dimensionless Planck constant,
, and the dimensionless wave amplitude, . For , the CGS
and the QGS are unstable for resonance numbers . For small
, the QGS becomes more stable with increasing and decreasing
. When increases, the influence of chaos on the stability of the
QGS is analyzed for different parameters of the model, , and
.Comment: RevTeX, 38 pages, 24 figure
Understanding delocalization in the Continuous Random Dimer model
We propose an explanation of the bands of extended states appearing in random
one dimensional models with correlated disorder, focusing on the Continuous
Random Dimer model [A.\ S\'{a}nchez, E.\ Maci\'a, and F.\ Dom\'\i nguez-Adame,
Phys.\ Rev.\ B {\bf 49}, 147 (1994)]. We show exactly that the transmission
coefficient at the resonant energy is independent of the number of host sites
between two consecutive dimers. This allows us to understand why are there
bands of extended states for every realization of the model as well as the
dependence of the bandwidths on the concentration. We carry out a perturbative
calculation that sheds more light on the above results. In the conclusion we
discuss generalizations of our results to other models and possible
applications which arise from our new insight of this problem.Comment: REVTeX 3.0, 4 pages, 4 figures (hard copy on request from
[email protected]), Submitted to Phys Rev
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
Irregular Dynamics in a One-Dimensional Bose System
We study many-body quantum dynamics of -interacting bosons confined
in a one-dimensional ring. Main attention is payed to the transition from the
mean-field to Tonks-Girardeau regime using an approach developed in the theory
of interacting particles. We analyze, both analytically and numerically, how
the Shannon entropy of the wavefunction and the momentum distribution depend on
time for a weak and strong interactions. We show that the transition from
regular (quasi-periodic) to irregular ("chaotic") dynamics coincides with the
onset of the Tonks-Girardeau regime. In the latter regime the momentum
distribution of the system reveals a statistical relaxation to a steady state
distribution. The transition can be observed experimentally by studying the
interference fringes obtained after releasing the trap and letting the boson
system expand ballistically.Comment: 4 pages 4 picture
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