90 research outputs found
Single Photon Source with Individualized Single Photon Certifications
As currently implemented, single-photon sources cannot be made to produce
single photons with high probability, while simultaneously suppressing the
probability of yielding two or more photons. Because of this, single photon
sources cannot really produce single photons on demand. We describe a
multiplexed system that allows the probabilities of producing one and more
photons to be adjusted independently, enabling a much better approximation of a
source of single photons on demand. The scheme uses a heralded photon source
based on parametric downconversion, but by effectively breaking the trigger
detector area into multiple regions, we are able to extract more information
about a heralded photon than is possible with a conventional arrangement. This
scheme allows photons to be produced along with a quantitative
``certification'' that they are single photons. Some of the single-photon
certifications can be significantly better than what is possible with
conventional downconversion sources (using a unified trigger detector region),
as well as being better than faint laser sources. With such a source of more
tightly certified single photons, it should be possible to improve the maximum
secure bit rate possible over a quantum cryptographic link. We present an
analysis of the relative merits of this method over the conventional
arrangement.Comment: 11 pages, 5 figures, SPIE Free-Space Laser Communication and Laser
Imaging II. To appear in the proceeding of SPIE Free-Space Laser
Communication and Laser Imaging II, vol 482
An optical heterodyne densitometer
Researchers are developing an optical heterodyne densitometer with the potential to measure optical density over an unprecedented dynamic range with high accuracy and sensitivity. This device uses a Mach-Zender interferometer configuration with heterodyne detection to make direct comparisons between optical and RF attenuators. Researchers expect to attain measurements of filter transmittance down to 10 to the minus 12th power with better than 1 percent uncertainty. In addition, they intend to extend the technique to the problem of measuring low levels of light scattering from reflective and transmissive optics
Optimizing single-photon-source heralding efficiency at 1550 nm using periodically poled lithium niobate
We explore the feasibility of using high conversion-efficiency
periodically-poled crystals to produce photon pairs for photon-counting
detector calibrations at 1550 nm. The goal is the development of an appropriate
parametric down-conversion (PDC) source at telecom wavelengths meeting the
requirements of high-efficiency pair production and collection in single
spectral and spatial modes (single-mode fibers). We propose a protocol to
optimize the photon collection, noise levels and the uncertainty evaluation.
This study ties together the results of our efforts to model the single-mode
heralding efficiency of a two-photon PDC source and to estimate the heralding
uncertainty of such a source.Comment: 14 pages, 2 tables and 3 figures, final version accepted by
Metrologi
A throughput optimal scheduling policy for a quantum switch
We study a quantum switch that creates shared end-to-end entangled quantum states to multiple sets of users that are connected to it. Each user is connected to the switch via an optical link across which bipartite Bell-state entangled states are generated in each time-slot with certain probabilities, and the switch merges entanglements of links to create end-to-end entanglements for users. One qubit of an entanglement of a link is stored at the switch and the other qubit of the entanglement is stored at the user corresponding to the link. Assuming that qubits of entanglements of links decipher after one time-slot, we characterize the capacity region, which is defined as the set of arrival rates of requests for end-to-end entanglements for which there exists a scheduling policy that stabilizes the switch. We propose a Max-Weight scheduling policy and show that it stabilizes the switch for all arrival rates that lie in the capacity region. We also provide numerical results to support our analysis
Reduced Deadtime and Higher Rate Photon-Counting Detection using a Multiplexed Detector Array
We present a scheme for a photon-counting detection system that can be
operated at incident photon rates higher than otherwise possible by suppressing
the effects of detector deadtime. The method uses an array of N detectors and a
1-by-N optical switch with a control circuit to direct input light to live
detectors. Our calculations and models highlight the advantages of the
technique. In particular, using this scheme, a group of N detectors provides an
improvement in operation rate that can exceed the improvement that would be
obtained by a single detector with deadtime reduced by 1/N, even if it were
feasible to produce a single detector with such a large improvement in
deadtime. We model the system for continuous and pulsed light sources, both of
which are important for quantum metrology and quantum key distribution
applications.Comment: 6 figure
Experimental Bounds on Classical Random Field Theories
Alternative theories to quantum mechanics motivate important fundamental
tests of our understanding and descriptions of the smallest physical systems.
Here, using spontaneous parametric downconversion as a heralded single-photon
source, we place experimental limits on a class of alternative theories,
consisting of classical field theories which result in power-dependent
normalized correlation functions. In addition, we compare our results with
standard quantum mechanical interpretations of our spontaneous parametric
downconversion source over an order of magnitude in intensity. Our data match
the quantum mechanical expectations, and do not show a statistically
significant dependence on power, limiting on quantum mechanics alternatives
which require power-dependent autocorrelation functions.Comment: 11pages, 2 figure
Properties of entangled photon pairs generated in one-dimensional nonlinear photonic-band-gap structures
We have developed a rigorous quantum model of spontaneous parametric
down-conversion in a nonlinear 1D photonic-band-gap structure based upon
expansion of the field into monochromatic plane waves. The model provides a
two-photon amplitude of a created photon pair. The spectra of the signal and
idler fields, their intensity profiles in the time domain, as well as the
coincidence-count interference pattern in a Hong-Ou-Mandel interferometer are
determined both for cw and pulsed pumping regimes in terms of the two-photon
amplitude. A broad range of parameters characterizing the emitted
down-converted fields can be used. As an example, a structure composed of 49
layers of GaN/AlN is analyzed as a suitable source of photon pairs having high
efficiency.Comment: 14 pages, 23 figure
Experimental joint signal-idler quasi-distributions and photon-number statistics for mesoscopic twin beams
Joint signal-idler photoelectron distributions of twin beams containing
several tens of photons per mode have been measured recently. Exploiting a
microscopic quantum theory for joint quasi-distributions in parametric
down-conversion developed earlier we characterize properties of twin beams in
terms of quasi-distributions using experimental data. Negative values as well
as oscillating behaviour in quantum region are characteristic for the
subsequently determined joint signal-idler quasi-distributions of integrated
intensities. Also the conditional and difference photon-number distributions
are shown to be sub-Poissonian and sub-shot-noise, respectively.Comment: 7 pages, 6 figure
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