2,178 research outputs found
A Quantum Computer Architecture using Nonlocal Interactions
Several authors have described the basic requirements essential to build a
scalable quantum computer. Because many physical implementation schemes for
quantum computing rely on nearest neighbor interactions, there is a hidden
quantum communication overhead to connect distant nodes of the computer. In
this paper we propose a physical solution to this problem which, together with
the key building blocks, provides a pathway to a scalable quantum architecture
using nonlocal interactions. Our solution involves the concept of a quantum bus
that acts as a refreshable entanglement resource to connect distant memory
nodes providing an architectural concept for quantum computers analogous to the
von Neumann architecture for classical computers.Comment: 4 pages, 2 figures, Slight modifications to satisfy referee, 2 new
references, modified acknowledgement. This draft to appear in PRA Rapid
Communication
Scalable quantum computation in systems with Bose-Hubbard dynamics
Several proposals for quantum computation utilize a lattice type architecture
with qubits trapped by a periodic potential. For systems undergoing many body
interactions described by the Bose-Hubbard Hamiltonian, the ground state of the
system carries number fluctuations that scale with the number of qubits. This
process degrades the initialization of the quantum computer register and can
introduce errors during error correction. In an earlier manuscript we proposed
a solution to this problem tailored to the loading of cold atoms into an
optical lattice via the Mott Insulator phase transition. It was shown that by
adding an inhomogeneity to the lattice and performing a continuous measurement,
the unit filled state suitable for a quantum computer register can be
maintained. Here, we give a more rigorous derivation of the register fidelity
in homogeneous and inhomogeneous lattices and provide evidence that the
protocol is effective in the finite temperature regime.Comment: 12 pages, 3 figures. Expanded version of manuscript submitted to the
Journal of Modern Optics. v2 corrects typesetting error in Fig.
Pseudo-fermionization of 1-D bosons in optical lattices
We present a model that generalizes the Bose-Fermi mapping for strongly
correlated 1D bosons in an optical lattice, to cases in which the average
number of atoms per site is larger than one. This model gives an accurate
account of equilibrium properties of such systems, in parameter regimes
relevant to current experiments. The application of this model to
non-equilibrium phenomena is explored by a study of the dynamics of an atom
cloud subject to a sudden displacement of the confining potential. Good
agreement is found with results of recent experiments. The simplicity and
intuitive appeal of this model make it attractive as a general tool for
understanding bosonic systems in the strongly correlated regime.Comment: 5 pages, 4 figure
Bragg Spectroscopy of ultracold atoms loaded in an optical lattice
We study Bragg spectroscopy of ultra-cold atoms in one-dimensional optical
lattices as a method for probing the excitation spectrum in the Mott insulator
phase, in particular the one particle-hole excitation band. Within the
framework of perturbation theory we obtain an analytical expression for the
dynamic structure factor and use it to calculate the imparted
energy which has shown to be a relevant observable in recent experiments. We
test the accuracy of our approximations by comparing them with numerically
exact solutions of the Bose-Hubbard model in restricted cases and establish the
limits of validity of our linear response analysis. Finally we show that when
the system is deep in the Mott insulator regime, its response to the Bragg
perturbation is temperature dependent. We suggest that this dependence might be
used as a tool to probe temperatures of order of the Mott gap.Comment: 4 pages, 3 figure
Theoretical analysis of perfect quantum state transfer with superconducting qubits
Superconducting quantum circuits, fabricated with multiple layers, are
proposed to implement perfect quantum state transfer between nodes of a
hypercube network. For tunable devices such as the phase qubit, each node can
transmit quantum information to any other node at a constant rate independent
of the distance between qubits. The physical limits of quantum state transfer
in this network are theoretically analyzed, including the effects of disorder,
decoherence, and higher-order couplings.Comment: 7 pages, 4 figures; title changed, minor errors corrected, published
versio
Multichannel quantum-defect theory for slow atomic collisions
We present a multichannel quantum-defect theory for slow atomic collisions
that takes advantages of the analytic solutions for the long-range potential,
and both the energy and the angular-momentum insensitivities of the short-range
parameters. The theory provides an accurate and complete account of scattering
processes, including shape and Feshbach resonances, in terms of a few
parameters such as the singlet and the triplet scattering lengths. As an
example, results for Na-Na scattering are presented and compared
close-coupling calculations.Comment: 8 pages, 3 figure
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