11,587 research outputs found
General-Purpose Parallel Simulator for Quantum Computing
With current technologies, it seems to be very difficult to implement quantum
computers with many qubits. It is therefore of importance to simulate quantum
algorithms and circuits on the existing computers. However, for a large-size
problem, the simulation often requires more computational power than is
available from sequential processing. Therefore, the simulation methods using
parallel processing are required.
We have developed a general-purpose simulator for quantum computing on the
parallel computer (Sun, Enterprise4500). It can deal with up-to 30 qubits. We
have performed Shor's factorization and Grover's database search by using the
simulator, and we analyzed robustness of the corresponding quantum circuits in
the presence of decoherence and operational errors. The corresponding results,
statistics and analyses are presented.Comment: 15 pages, 15 figure
A Magnetic Resonance Force Microscopy Quantum Computer with Tellurium Donors in Silicon
We propose a magnetic resonance force microscopy (MRFM)-based nuclear spin
quantum computer using tellurium impurities in silicon. This approach to
quantum computing combines the well-developed silicon technology with expected
advances in MRFM.Comment: 9 pages, 1 figur
The photon blockade effect in optomechanical systems
We analyze the photon statistics of a weakly driven optomechanical system and
discuss the effect of photon blockade under single photon strong coupling
conditions. We present an intuitive interpretation of this effect in terms of
displaced oscillator states and derive analytic expressions for the cavity
excitation spectrum and the two photon correlation function . Our
results predict the appearance of non-classical photon correlations in the
combined strong coupling and sideband resolved regime, and provide a first
detailed understanding of photon-photon interactions in strong coupling
optomechanics
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
Quantum Measurement of a Single Spin using Magnetic Resonance Force Microscopy
Single-spin detection is one of the important challenges facing the
development of several new technologies, e.g. single-spin transistors and
solid-state quantum computation. Magnetic resonance force microscopy with a
cyclic adiabatic inversion, which utilizes a cantilever oscillations driven by
a single spin, is a promising technique to solve this problem. We have studied
the quantum dynamics of a single spin interacting with a quasiclassical
cantilever. It was found that in a similar fashion to the Stern-Gerlach
interferometer the quantum dynamics generates a quantum superposition of two
quasiclassical trajectories of the cantilever which are related to the two spin
projections on the direction of the effective magnetic field in the rotating
reference frame. Our results show that quantum jumps will not prevent a
single-spin measurement if the coupling between the cantilever vibrations and
the spin is small in comparison with the amplitude of the radio-frequency
external field.Comment: 16 pages RevTeX including 4 figure
Dynamics of a Quantum Control-Not Gate for an Ensemble of Four-Spin Molecules at Room Temperature
We investigate numerically a single-pulse implementation of a quantum
Control-Not (CN) gate for an ensemble of Ising spin systems at room
temperature. For an ensemble of four-spin ``molecules'' we simulate the
time-evolution of the density matrix, for both digital and superpositional
initial conditions. Our numerical calculations confirm the feasibility of
implementation of quantum CN gate in this system at finite temperature, using
electromagnetic -pulse.Comment: 7 pages 3 figure
Two Qubit Quantum Computing in a Projected Subspace
A formulation for performing quantum computing in a projected subspace is
presented, based on the subdynamical kinetic equation (SKE) for an open quantum
system. The eigenvectors of the kinetic equation are shown to remain invariant
before and after interaction with the environment. However, the eigenvalues in
the projected subspace exhibit a type of phase shift to the evolutionary
states. This phase shift does not destroy the decoherence-free (DF) property of
the subspace because the associated fidelity is 1. This permits a universal
formalism to be presented - the eigenprojectors of the free part of the
Hamiltonian for the system and bath may be used to construct a DF projected
subspace based on the SKE. To eliminate possible phase or unitary errors
induced by the change in the eigenvalues, a cancellation technique is proposed,
using the adjustment of the coupling time, and applied to a two qubit computing
system. A general criteria for constructing a DF projected subspace from the
SKE is discussed. Finally, a proposal for using triangulation to realize a
decoherence-free subsystem based on SKE is presented. The concrete formulation
for a two-qubit model is given exactly. Our approach is novel and general, and
appears applicable to any type of decoherence. Key Words: Quantum Computing,
Decoherence, Subspace, Open System PACS number: 03.67.Lx,33.25.+k,.76.60.-kComment: 24 pages. accepted by Phys. Rev.
Effects of motion in cavity QED
We consider effects of motion in cavity quantum electrodynamics experiments
where single cold atoms can now be observed inside the cavity for many Rabi
cycles. We discuss the timescales involved in the problem and the need for good
control of the atomic motion, particularly the heating due to exchange of
excitation between the atom and the cavity, in order to realize nearly unitary
dynamics of the internal atomic states and the cavity mode which is required
for several schemes of current interest such as quantum computing. Using a
simple model we establish ultimate effects of the external atomic degrees of
freedom on the action of quantum gates. The perfomance of the gate is
characterized by a measure based on the entanglement fidelity and the motional
excitation caused by the action of the gate is calculated. We find that schemes
which rely on adiabatic passage, and are not therefore critically dependent on
laser pulse areas, are very much more robust against interaction with the
external degrees of freedom of atoms in the quantum gate.Comment: 10 pages, 5 figures, REVTeX, to be published in Walls Symposium
Special Issue of Journal of Optics
Duality Invariant M-theory: Gauged supergravities and Scherk-Schwarz reductions
We consider the reduction of the duality invariant approach to M-theory by a
U-duality group valued Scherk-Schwarz twist. The result is to produce
potentials for gauged supergravities that are normally associated with
non-geometric compactifications. The local symmetry reduces to gauge
transformations with the gaugings exactly matching those of the embedding
tensor approach to gauged supergravity. Importantly, this approach now includes
a nontrivial dependence of the fields on the extra coordinates of the extended
space.Comment: 22 pages Latex; v2: typos corrected and references adde
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