2,501 research outputs found
Quantum entanglement and disentanglement of multi-atom systems
We present a review of recent research on quantum entanglement, with special
emphasis on entanglement between single atoms, processing of an encoded
entanglement and its temporary evolution. Analysis based on the density matrix
formalism are described. We give a simple description of the entangling
procedure and explore the role of the environment in creation of entanglement
and in disentanglement of atomic systems. A particular process we will focus on
is spontaneous emission, usually recognized as an irreversible loss of
information and entanglement encoded in the internal states of the system. We
illustrate some certain circumstances where this irreversible process can in
fact induce entanglement between separated systems. We also show how
spontaneous emission reveals a competition between the Bell states of a two
qubit system that leads to the recently discovered "sudden" features in the
temporal evolution of entanglement. An another problem illustrated in details
is a deterministic preparation of atoms and atomic ensembles in long-lived
stationary squeezed states and entangled cluster states. We then determine how
to trigger the evolution of the stable entanglement and also address the issue
of a steered evolution of entanglement between desired pairs of qubits that can
be achieved simply by varying the parameters of a given system.Comment: Review articl
Coexistence of thermal noise and squeezing in the intensity fluctuations of small laser diodes
The intensity fluctuations of laser light are derived from photon number rate
equations. In the limit of short times, the photon statistics for small laser
devices such as typical semiconductor laser diodes show thermal characteristics
even above threshold. In the limit of long time averages represented by the low
frequency component of the noise, the same devices exhibit squeezing. It is
shown that squeezing and thermal noise can coexist in the multi-mode output
field of laser diodes. This result implies that the squeezed light generated by
regularly pumped semiconductor laser diodes is qualitatively different from
single mode squeezed light. In particular, no entanglement between photons can
be generated using this type of collective multi-mode squeezing.Comment: 9 pages, 8 figures, submitted to J. Opt. Soc. Am. B, added references
and clarifications of the contex
Ultra-bright omni-directional collective emission of correlated photon pairs from atomic vapors
Spontaneous four-wave mixing can generate highly correlated photon pairs from
atomic vapors. We show that multi-photon pumping of dipole-forbidden
transitions in a recoil-free geometry can result in ultra-bright pair-emission
in the full 4\pi solid angle, while strongly suppresses background Rayleigh
scattering and associated atomic heating, Such a system can produce photon
pairs at rates of ~ 10 ^12 per second, given only moderate optical depths of 10
~ 100, or alternatively, the system can generate paired photons with
sub-natural bandwidths at lower production rates. We derive a rate-equation
based theory of the collective atomic population and coherence dynamics, and
present numerical simulations for a toy model, as well as realistic model
systems based on 133 Cs and 171 Yb level structures. Lastly, we demonstrate
that dark-state adiabatic following (EIT) and/or timescale hierarchy protects
the paired photons from reabsorption as they propagate through an optically
thick sample
Heralded single photon absorption by a single atom
The emission and absorption of single photons by single atomic particles is a
fundamental limit of matter-light interaction, manifesting its quantum
mechanical nature. At the same time, as a controlled process it is a key
enabling tool for quantum technologies, such as quantum optical information
technology [1, 2] and quantum metrology [3, 4, 5, 6]. Controlling both emission
and absorption will allow implementing quantum networking scenarios [1, 7, 8,
9], where photonic communication of quantum information is interfaced with its
local processing in atoms. In studies of single-photon emission, recent
progress includes control of the shape, bandwidth, frequency, and polarization
of single-photon sources [10, 11, 12, 13, 14, 15, 16, 17], and the
demonstration of atom-photon entanglement [18, 19, 20]. Controlled absorption
of a single photon by a single atom is much less investigated; proposals exist
but only very preliminary steps have been taken experimentally such as
detecting the attenuation and phase shift of a weak laser beam by a single atom
[21, 22], and designing an optical system that covers a large fraction of the
full solid angle [23, 24, 25]. Here we report the interaction of single
heralded photons with a single trapped atom. We find strong correlations of the
detection of a heralding photon with a change in the quantum state of the atom
marking absorption of the quantum-correlated heralded photon. In coupling a
single absorber with a quantum light source, our experiment demonstrates
previously unexplored matter-light interaction, while opening up new avenues
towards photon-atom entanglement conversion in quantum technology.Comment: 10 pages, 4 figure
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