13,613 research outputs found
Influence of qubit displacements on quantum logic operations in a silicon-based quantum computer with constant interaction
The errors caused by qubit displacements from their prescribed locations in
an ensemble of spin chains are estimated analytically and calculated
numerically for a quantum computer based on phosphorus donors in silicon. We
show that it is possible to polarize (initialize) the nuclear spins even with
displaced qubits by using Controlled NOT gates between the electron and nuclear
spins of the same phosphorus atom. However, a Controlled NOT gate between the
displaced electron spins is implemented with large error because of the
exponential dependence of exchange interaction constant on the distance between
the qubits. If quantum computation is implemented on an ensemble of many spin
chains, the errors can be small if the number of chains with displaced qubits
is small
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
Resonant Perturbation Theory of Decoherence and Relaxation of Quantum Bits
We describe our recent results on the resonant perturbation theory of
decoherence and relaxation for quantum system with many qubits. The approach
represents a rigorous analysis of the phenomenon of decoherence and relaxation
for general -level systems coupled to reservoirs of the bosonic fields. We
derive a representation of the reduced dynamics valid for all times
and for small but fixed interaction strength. Our approach does not involve
master equation approximations and applies to a wide variety of systems which
are not explicitly solvable
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
Transition from isolated to overlapping resonances in the open system of interacting fermions
We study the statistical properties of resonance widths and spacings in an
open system of interacting fermions at the transition between isolated and
overlapping resonances, where a radical change in the width distribution
occurs. Our main interest is to reveal how this transition is influenced by the
onset of chaos in the internal dynamics as the strength of random two-body
interaction between the particles increases. We have found that in the region
of overlapped resonances, the fluctuations of the widths (rather than their
mean values) are strongly affected by the onset of an internal chaos. The
results may be applied to the analysis of neutron cross sections, as well as in
the physics of mesoscopic devices with strongly interacting electrons.Comment: 4 pages, 5 figures, corrected version, figures are replace
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
Stability of Nonlinear Normal Modes in the FPU- Chain in the Thermodynamic Limit
All possible symmetry-determined nonlinear normal modes (also called by
simple periodic orbits, one-mode solutions etc.) in both hard and soft
Fermi-Pasta-Ulam- chains are discussed. A general method for studying
their stability in the thermodynamic limit, as well as its application for each
of the above nonlinear normal modes are presented
Creation of Two-Particle Entanglement in Open Macroscopic Quantum Systems
We consider an open quantum system of N not directly interacting spins
(qubits) in contact with both local and collective thermal environments. The
qubit-environment interactions are energy conserving. We trace out the
variables of the thermal environments and N-2 qubits to obtain the
time-dependent reduced density matrix for two arbitrary qubits. We numerically
simulate the reduced dynamics and the creation of entanglement (concurrence) as
a function of the parameters of the thermal environments and the number of
qubits, N. Our results demonstrate that the two-qubit entanglement generally
decreases as N increases. We show analytically that in the limit N tending to
infinity, no entanglement can be created. This indicates that collective
thermal environments cannot create two-qubit entanglement when many qubits are
located within a region of the size of the environment coherence length. We
discuss possible applications of our approach to the development of a new
quantum characterization of noisy environments
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