357 research outputs found
Multilevel Holstein-Primakoff approximation and its application to atomic spin squeezing and ensemble quantum memories
We show that an ensemble of identical d-level atoms can be efficiently
described by d-1 collective oscillator degrees of freedom in the vicinity of a
product state with all atoms in the same, but otherwise arbitrary
single-particle state. We apply our description to two different kinds of spin
squeezing: (i) when each spin-F atom is individually squeezed without creating
interatomic entanglement and (ii) when a particular collective atomic
oscillator mode is squeezed via quantum non-demolition (QND) measurement and
feedback. When combined in sequence, the order of the two methods is relevant
in the final degree of squeezing. We also discuss the role of the two kinds of
squeezing when multi-sublevel atoms are used as quantum memories for light.Comment: 12 pages, 3 figure
Quantum state reconstruction with imperfect rotations on an inhomogeneously broadened ensemble of qubits
We present a method for performing quantum state reconstruction on qubits and
qubit registers in the presence of decoherence and inhomogeneous broadening.
The method assumes only rudimentary single qubit rotations as well as knowledge
of decoherence and loss mechanisms. We show that full state reconstruction is
possible even in the case where single qubit rotations may only be performed
imperfectly. Furthermore we show that for ensemble quantum computing proposals,
quantum state reconstruction is possible even if the ensemble experiences
inhomogeneous broadening and if only imperfect qubit manipulations are
available during state preparation and reconstruction.Comment: 6 pages, 5 figure
Molecule Formation in Optical Lattice Wells by Resonantly Modulated Magnetic Fields
We present a theoretical model for formation of molecules in an optical
lattice well where a resonant coupling of atomic and molecular states is
provided by small oscillations of a magnetic field in the vicinity of a
Feshbach resonance. As opposed to an adiabatic sweep over the full resonance,
this provides a coherent coupling with a frequency that can be tuned to meet
resonance conditions in the system. The effective Rabi frequencies for this
coupling are calculated and simulations show perfect Rabi oscillations. Robust
production of molecules with an adiabatic sweep of the modulation frequency is
demonstrated. For very large oscillation amplitudes, the Rabi oscillations are
distorted but still effective and fast association is possible.Comment: 5 pages, 6 figure
Wave packet dynamics of the matter wave field of a Bose-Einstein condensate
We show in the framework of a tractable model that revivals and fractional
revivals of wave packets afford clear signatures of the extent of departure
from coherence and from Poisson statistics of the matter wave field in a
Bose-Einstein condensate, or of a suitably chosen initial state of the
radiation field propagating in a Kerr-like medium.Comment: 10 pages, 4 figures, RevTeX
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