37,212 research outputs found
High purity bright single photon source
Using cavity-enhanced non-degenerate parametric downconversion, we have built
a frequency tunable source of heralded single photons with a narrow bandwidth
of 8 MHz, making it compatible with atomic quantum memories. The photon state
is 70% pure single photon as characterized by a tomographic measurement and
reconstruction of the quantum state, revealing a clearly negative Wigner
function. Furthermore, it has a spectral brightness of ~1,500 photons/s per MHz
bandwidth, making it one of the brightest single photon sources available. We
also investigate the correlation function of the down-converted fields using a
combination of two very distinct detection methods; photon counting and
homodyne measurement.Comment: 9 pages, 4 figures; minor changes, added referenc
The effect of grain boundaries on mechanical behavior in polycrystalline ceramics
Atomic structure and chemical composition influence on grain boundaries effect on mechanical failure in polycrystalline ceramic
Photon number states generated from a continuous-wave light source
Conditional preparation of photon number states from a continuous-wave
nondegenerate optical parametric oscillator is investigated. We derive the
phase space Wigner function for the output state conditioned on photo detection
events that are not necessarily simultaneous, and we maximize its overlap with
the desired photon number state by choosing the optimal temporal output state
mode function. We present a detailed numerical analysis for the case of
two-photon state generation from a parametric oscillator driven with an
arbitrary intensity below threshold, and in the low intensity limit, we present
a formalism that yields the optimal output state mode function and fidelity for
higher photon number states.Comment: 8 pages, 7 figures, v2: shortened versio
Control of inhomogeneous atomic ensembles of hyperfine qudits
We study the ability to control d-dimensional quantum systems (qudits)
encoded in the hyperfine spin of alkali-metal atoms through the application of
radio- and microwave-frequency magnetic fields in the presence of
inhomogeneities in amplitude and detuning. Such a capability is essential to
the design of robust pulses that mitigate the effects of experimental
uncertainty and also for application to tomographic addressing of particular
members of an extended ensemble. We study the problem of preparing an arbitrary
state in the Hilbert space from an initial fiducial state. We prove that
inhomogeneous control of qudit ensembles is possible based on a semi-analytic
protocol that synthesizes the target through a sequence of alternating rf and
microwave-driven SU(2) rotations in overlapping irreducible subspaces. Several
examples of robust control are studied, and the semi-analytic protocol is
compared to a brute force, full numerical search. For small inhomogeneities, <
1%, both approaches achieve average fidelities greater than 0.99, but the brute
force approach performs superiorly, reaching high fidelities in shorter times
and capable of handling inhomogeneities well beyond experimental uncertainty.
The full numerical search is also applied to tomographic addressing whereby two
different nonclassical states of the spin are produced in two halves of the
ensemble
Error correction in ensemble registers for quantum repeaters and quantum computers
We propose to use a collective excitation blockade mechanism to identify
errors that occur due to disturbances of single atoms in ensemble quantum
registers where qubits are stored in the collective population of different
internal atomic states. A simple error correction procedure and a simple
decoherence-free encoding of ensemble qubits in the hyperfine states of alkali
atoms are presented.Comment: 4 pages, 2 figure
A spiral-like disk of ionized gas in IC 1459: Signature of a merging collision
The authors report the discovery of a large (15 kpc diameter) H alpha + (NII) emission-line disk in the elliptical galaxy IC 1459, showing weak spiral structure. The line flux peaks strongly at the nucleus and is more concentrated than the stellar continuum. The major axis of the disk of ionized gas coincides with that of the stellar body of the galaxy. The mass of the ionized gas is estimated to be approx. 1 times 10 (exp 5) solar mass, less than 1 percent of the total mass of gas present in IC 1459. The total gas mass of 4 times 10(exp 7) solar mass has been estimated from the dust mass derived from a broad-band color index image and the Infrared Astronomy Satellite (IRAS) data. The authors speculate that the presence of dust and gas in IC 1459 is a signature of a merger event
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