3,768 research outputs found
Transforming squeezed light into a large amplitude coherent state superposition
A quantum superposition of two coherent states of light with small amplitude
can be obtained by subtracting a photon from a squeezed vacuum state. In
experiments this preparation can be made conditioned on the detection of a
photon in the field from a squeezed light source. We propose and analyze an
extended measurement strategy which allows generation of high fidelity coherent
state superpositions with larger amplitude.Comment: 6 pages, 4 figures, v2: published versio
Giant Kerr nonlinearities in Circuit-QED
The very small size of optical nonlinearities places wide ranging
restrictions on the types of novel physics one can explore. For an ensemble of
multi-level systems one can synthesize a large effective optical nonlinearity
using quantum coherence effects but such non-linearities are technically
extremely challenging to demonstrate at the single atom level. In this work we
describe how a single artificial multi-level Cooper Pair Box molecule,
interacting with a superconducting microwave coplanar waveguide resonator, when
suitably driven, can generate extremely large optical nonlinearities at
microwave frequencies, with no associated absorption. We describe how the giant
self-Kerr effect can be detected by measuring the second-order correlation
function and quadrature squeezing spectrum.Comment: 4 pages, 4 figures, 1 table; version accepted by PRL edito
Observation of dressed intra-cavity dark states
Cavity electromagnetically induced transparency in a coherently prepared
cavity-atom system is manifested as a narrow transmission peak of a weak probe
laser coupled into the cavity mode. We show that with a resonant pump laser
coupling the cavity-confined four-level atoms from free space, the narrow
transmission peak of the cavity EIT is split into two peaks. The two peaks
represent the dressed intra-cavity dark states and have a frequency separation
approximately equal to the Rabi frequency of the free-space pump laser. We
observed experimentally the dressed intra-cavity dark states in cold Rb atoms
confined in a cavity and the experimental results agree with theoretical
calculations based on a semiclassical analysis.Comment: 10 pages, 6 figure
On-demand single-photon state generation via nonlinear absorption
We propose a method for producing on-demand single-photon states based on
collision-induced exchanges of photons and unbalanced linear absorption between
two single-mode light fields. These two effects result in an effective
nonlinear absorption of photons in one of the modes, which can lead to single
photon states. A quantum nonlinear attenuator based on such a mechanism can
absorb photons in a normal input light pulse and terminate the absorption at a
single-photon state. Because the output light pulses containing single photons
preserve the properties of the input pulses, we expect this method to be a
means for building a highly controllable single photon source.Comment: 5 pages, 2 figures, to appear in PRA. To be published in PR
Decoherence induced by a phase-damping reservoir
A phase damping reservoir composed by -bosons coupled to a system of
interest through a cross-Kerr interaction is proposed and its effects on
quantum superpo sitions are investigated. By means of analytical calculations
we show that: i-) the reservoir induces a Gaussian decay of quantum coherences,
and ii-) the inher ent incommensurate character of the spectral distribution
yields irreversibility . A state-independent decoherence time and a master
equation are both derived an alytically. These results, which have been
extended for the thermodynamic limit, show that nondissipative decoherence can
be suitably contemplated within the EI D approach. Finally, it is shown that
the same mechanism yielding decoherence ar e also responsible for inducing
dynamical disentanglement.Comment: 8 pages, 3 figure
Light scattering from ultracold atoms in optical lattices as an optical probe of quantum statistics
We study off-resonant collective light scattering from ultracold atoms
trapped in an optical lattice. Scattering from different atomic quantum states
creates different quantum states of the scattered light, which can be
distinguished by measurements of the spatial intensity distribution, quadrature
variances, photon statistics, or spectral measurements. In particular,
angle-resolved intensity measurements reflect global statistics of atoms (total
number of radiating atoms) as well as local statistical quantities (single-site
statistics even without an optical access to a single site) and pair
correlations between different sites. As a striking example we consider
scattering from transversally illuminated atoms into an optical cavity mode.
For the Mott insulator state, similar to classical diffraction, the number of
photons scattered into a cavity is zero due to destructive interference, while
for the superfluid state it is nonzero and proportional to the number of atoms.
Moreover, we demonstrate that light scattering into a standing-wave cavity has
a nontrivial angle dependence, including the appearance of narrow features at
angles, where classical diffraction predicts zero. The measurement procedure
corresponds to the quantum non-demolition (QND) measurement of various atomic
variables by observing light.Comment: 15 pages, 5 figure
The two-level atom laser: analytical results and the laser transition
The problem of the two-level atom laser is studied analytically. The
steady-state solution is expressed as a continued fraction, and allows for
accurate approximation by rational functions. Moreover, we show that the abrupt
change observed in the pump dependence of the steady-state population is
directly connected with the transition to the lasing regime. The condition for
a sharp transition to Poissonian statistics is expressed as a scaling limit of
vanishing cavity loss and light-matter coupling, , ,
such that stays finite and , where
is the rate of atomic losses. The same scaling procedure is also shown to
describe a similar change to Poisson distribution in the Scully-Lamb laser
model too, suggesting that the low-, low- asymptotics is of a more
general significance for the laser transition.Comment: 23 pages, 3 figures. Extended discussion of the paper aim (in the
Introduction) and of the results (Conclusions and Discussion). Results
unchange
Non-critically squeezed light via spontaneous rotational symmetry breaking
We theoretically address squeezed light generation through the spontaneous
breaking of the rotational invariance occuring in a type I degenerate optical
parametric oscillator (DOPO) pumped above threshold. We show that a DOPO with
spherical mirrors, in which the signal and idler fields correspond to first
order Laguerre-Gauss modes, produces a perfectly squeezed vacuum with the shape
of a Hermite-Gauss mode, within the linearized theory. This occurs at any
pumping level above threshold, hence the phenomenon is non-critical.
Imperfections of the rotational symmetry, due e.g. to cavity anisotropy, are
shown to have a small impact, hence the result is not singular.Comment: 4 pages, 1 figure, replaced with resubmitted versio
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