66 research outputs found
Phase gate and readout with an atom/molecule hybrid platform
We suggest a combined atomic/molecular system for quantum computation, which
takes advantage of highly developed techniques to control atoms and recent
experimental progress in manipulation of ultracold molecules. We show that two
atoms of different species in a given site, {\it e.g.}, in an optical lattice,
could be used for qubit encoding, initialization and readout, with one atom
carrying the qubit, the other enabling a gate. In particular, we describe how a
two-qubit phase gate can be realized by transferring a pair of atoms into the
ground rovibrational state of a polar molecule with a large dipole moment, and
allowing two molecules to interact via their dipole-dipole interaction. We also
discuss how the reverse process of coherently transferring a molecule into a
pair of atoms could be used as a readout tool for molecular quantum computers
Collective Lamb Shift and Modified Linewidth of An Interacting Atomic Gas
Finding a comprehensive and general description of the collective Lamb shift
and cooperative broadening in a radiatively interacting system is a
long-standing open question. Both energy levels and linewidth of individual
atoms are modified by the exchange of real and virtual photons making up the
dipole-dipole interaction. We introduce a method to theoretically study
weakly-driven, low-excited ensembles of two-level atoms, and obtain an analytic
description of the collective Lamb shift and linewidth via a self-consistent
formalism including infinite order of correlations which stem from only
two-body interactions. We predict the dependency of these quantities, as
measurables, on system parameters: the number density of the ensemble, the
detuning of an external probe field, and the geometry of the sample.Comment: 8 pages, 4 figure
Radiative atom-atom interactions in optically dense media: Quantum corrections to the Lorentz-Lorenz formula
Abstract: Generalized single-atom Maxwell-Bloch equations for optically dense media are derived taking into account non-cooperative radiative atom-atom interactions. Applying a Gaussian approximation and formally eliminating the degrees of freedom of the quantized radiation field and of all but a probe atom leads to an effective time-evolution operator for the probe atom. The mean coherent amplitude of the local field seen by the atom is shown to be given by the classical Lorentz-Lorenz relation. The second-order correlations of the field lead to terms that describe relaxation or pump processes and level shifts due to multiple scattering or reabsorption of spontaneously emitted photons. In the Markov limit a non-linear and nonlocal single-atom density matrix equation is derived. To illustrate the effects of the quantum corrections we discuss amplified spontaneous emission and radiation trapping in a dense ensemble of initially inverted two-level atoms and the effects of radiative interactions on intrinsic optical bistability in coherently driven systems
Superglass formation in an atomic BEC with competing long-range interactions
The complex dynamical phases of quantum systems are dictated by atomic
interactions that usually evoke an emergent periodic order. Here, we study a
quantum many-body system with two competing and substantially different
long-range interaction potentials where the dynamical instability towards
density order can give way to a superglass phase, i. e., a superfluid
disordered amorphous solid, which exhibits local density modulations but no
long-range periodic order. We consider a two-dimensional BEC in the
Rydberg-dressing regime coupled to an optical standing wave resonator. The
dynamic pattern formation in this system is governed by the competition between
the two involved interaction potentials: repulsive soft-core interactions
arising due to Rydberg dressing and infinite-range sign changing interactions
induced by the cavity photons. The superglass phase is found when the two
interaction potentials introduce incommensurate length scales. The dynamic
formation of this peculiar phase without any externally added disorder is
driven by quantum fluctuations and can be attributed to frustration induced by
the two competing interaction energies and length scales.Comment: new title, added reference
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