69 research outputs found
Henri Temianka correspondence, Gurs
https://digitalcommons.chapman.edu/beach_gurs_et_al_correspondence/1001/thumbnail.jp
Simulation of Many-Body Fermi Systems on a Universal Quantum Computer
We provide fast algorithms for simulating many body Fermi systems on a
universal quantum computer. Both first and second quantized descriptions are
considered, and the relative computational complexities are determined in each
case. In order to accommodate fermions using a first quantized Hamiltonian, an
efficient quantum algorithm for anti-symmetrization is given. Finally, a
simulation of the Hubbard model is discussed in detail.Comment: Submitted 11/7/96 to Phys. Rev. Lett. 10 pages, 0 figure
Quantum Search with Two-atom Collisions in Cavity QED
We propose a scheme to implement two-qubit Grover's quantum search algorithm
using Cavity Quantum Electrodynamics. Circular Rydberg atoms are used as
quantum bits (qubits). They interact with the electromagnetic field of a
non-resonant cavity . The quantum gate dynamics is provided by a
cavity-assisted collision, robust against decoherence processes. We present the
detailed procedure and analyze the experimental feasibility.Comment: 4 pages, 2 figure
Resolved-sideband Raman cooling to the ground state of an optical lattice
We trap neutral Cs atoms in a two-dimensional optical lattice and cool them
close to the zero-point of motion by resolved-sideband Raman cooling. Sideband
cooling occurs via transitions between the vibrational manifolds associated
with a pair of magnetic sublevels and the required Raman coupling is provided
by the lattice potential itself. We obtain mean vibrational excitations
\bar{n}_x \approx \bar{n}_y \approx 0.01, corresponding to a population \sim
98% in the vibrational ground state. Atoms in the ground state of an optical
lattice provide a new system in which to explore quantum state control and
subrecoil laser coolingComment: PDF file, 13 pages including 3 figure
A quantum-mechanical Maxwell's demon
A Maxwell's demon is a device that gets information and trades it in for
thermodynamic advantage, in apparent (but not actual) contradiction to the
second law of thermodynamics. Quantum-mechanical versions of Maxwell's demon
exhibit features that classical versions do not: in particular, a device that
gets information about a quantum system disturbs it in the process. In
addition, the information produced by quantum measurement acts as an additional
source of thermodynamic inefficiency. This paper investigates the properties of
quantum-mechanical Maxwell's demons, and proposes experimentally realizable
models of such devices.Comment: 13 pages, Te
Interaction-free generation of entanglement
In this paper, we study how to generate entanglement by interaction-free
measurement. Using Kwiat et al.'s interferometer, we construct a two-qubit
quantum gate that changes a particle's trajectory according to the other
particle's trajectory. We propose methods for generating the Bell state from an
electron and a positron and from a pair of photons by this gate. We also show
that using this gate, we can carry out the Bell measurement with the
probability of 3/4 at the maximum and execute a controlled-NOT operation by the
method proposed by Gottesman and Chuang with the probability of 9/16 at the
maximum. We estimate the success probability for generating the Bell state by
our procedure under imperfect interaction.Comment: 18 pages, Latex2e, 11 eps figures, v2: minor corrections and one
reference added, v3: a minor correctio
Quantum Logic Gates in Optical Lattices
We propose a new system for implementing quantum logic gates: neutral atoms
trapped in a very far-off-resonance optical lattice. Pairs of atoms are made to
occupy the same well by varying the polarization of the trapping lasers, and
then a near-resonant electric dipole is induced by an auxiliary laser. A
controlled-NOT can be implemented by conditioning the target atomic resonance
on a resolvable level shift induced by the control atom. Atoms interact only
during logical operations, thereby suppressing decoherence.Comment: Revised version, To appear in Phys. Rev. Lett. Three separate
postscript figure
Quantum gates on hybrid qudits
We introduce quantum hybrid gates that act on qudits of different dimensions.
In particular, we develop two representative two-qudit hybrid gates (SUM and
SWAP) and many-qudit hybrid Toffoli and Fredkin gates. We apply the hybrid SUM
gate to generating entanglement, and find that operator entanglement of the SUM
gate is equal to the entanglement generated by it for certain initial states.
We also show that the hybrid SUM gate acts as an automorphism on the Pauli
group for two qudits of different dimension under certain conditions. Finally,
we describe a physical realization of these hybrid gates for spin systems.Comment: 8 pages and 1 figur
Classical interventions in quantum systems. I. The measuring process
The measuring process is an external intervention in the dynamics of a
quantum system. It involves a unitary interaction of that system with a
measuring apparatus, a further interaction of both with an unknown environment
causing decoherence, and then the deletion of a subsystem. This description of
the measuring process is a substantial generalization of current models in
quantum measurement theory. In particular, no ancilla is needed. The final
result is represented by a completely positive map of the quantum state
(possibly with a change of the dimensions of ). A continuous limit of the
above process leads to Lindblad's equation for the quantum dynamical semigroup.Comment: Final version, 14 pages LaTe
Quantum search without entanglement
Entanglement of quantum variables is usually thought to be a prerequisite for
obtaining quantum speed-ups of information processing tasks such as searching
databases. This paper presents methods for quantum search that give a speed-up
over classical methods, but that do not require entanglement. These methods
rely instead on interference to provide a speed-up. Search without entanglement
comes at a cost: although they outperform analogous classical devices, the
quantum devices that perform the search are not universal quantum computers and
require exponentially greater overhead than a quantum computer that operates
using entanglement. Quantum search without entanglement is compared to
classical search using waves.Comment: 9 pages, TeX, submitted to Physical Review Letter
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