34,468 research outputs found
Effects of multiple pairs on visibility measurements of entangled photons generated by spontaneous parametric processes
Entangled photon-pair sources based on spontaneous parametric processes are
widely used in photonic quantum information experiments. In this paper, we
clarify the relationship between average photon-pair number and the visibility
of two-photon interference (TPI) using those entanglement sources. We consider
sources that generate distinguishable and indistinguishable entangled photon
pairs, assuming coincidence measurements that use threshold detectors. We
present formulas for the TPI visibility of a polarization entanglement that
take account of all the high-order multi-pair emission events. Moreover, we
show that the formulas can be approximated with simple functions of the average
pair number when the photon collection efficiency is small. As a result, we
reveal that an indistinguishable entangled pair provides better visibility than
a distinguishable one
Correlated photon-pair generation in reverse-proton-exchange PPLN waveguides with integrated mode demultiplexer at 10 GHz clock
We report 10-ps correlated photon pair generation in periodically-poled
reverse-proton-exchange lithium niobate waveguides with integrated mode
demultiplexer at a wavelength of 1.5-um and a clock of 10 GHz. Using
superconducting single photon detectors, we observed a coincidence to
accidental count ratio (CAR) as high as 4000. The developed photon-pair source
may find broad application in quantum information systems as well as quantum
entanglement experiments.Comment: 6 pages, 4 figures, presented at 2007 CLEO conferenc
Active Temporal Multiplexing of Photons
Photonic qubits constitute a leading platform to disruptive quantum
technologies due to their unique low-noise properties. The cost of the photonic
approach is the non-deterministic nature of many of the processes, including
single-photon generation, which arises from parametric sources and negligible
interaction between photons. Active temporal multiplexing - repeating a
generation process in time and rerouting to single modes using an optical
switching network - is a promising approach to overcome this challenge and will
likely be essential for large-scale applications with greatly reduced resource
complexity and system sizes. Requirements include the precise synchronization
of a system of low-loss switches, delay lines, fast photon detectors, and
feed-forward. Here we demonstrate temporal multiplexing of 8 'bins' from a
double-passed heralded photon source and observe an increase in the heralding
and heralded photon rates. This system points the way to harnessing temporal
multiplexing in quantum technologies, from single-photon sources to large-scale
computation.Comment: Minor revision
Cross-polarized photon-pair generation and bi-chromatically pumped optical parametric oscillation on a chip
Nonlinear optical processes are one of the most important tools in modern optics with a broad spectrum of applications in, for example, frequency conversion, spectroscopy, signal processing and quantum optics. For practical and ultimately widespread implementation, on-chip devices compatible with electronic integrated circuit technology offer great advantages in terms of low cost, small footprint, high performance and low energy consumption. While many on-chip key components have been realized, to date polarization has not been fully exploited as a degree of freedom for integrated nonlinear devices. In particular, frequency conversion based on orthogonally polarized beams has not yet been demonstrated on chip. Here we show frequency mixing between orthogonal polarization modes in a compact integrated microring resonator and demonstrate a bi-chromatically pumped optical parametric oscillator. Operating the device above and below threshold, we directly generate orthogonally polarized beams, as well as photon pairs, respectively, that can find applications, for example, in optical communication and quantum optics
Searching for links between magnetic fields and stellar evolution. I. A survey of magnetic fields in open cluster A- and B-type stars with FORS1
About 5% of upper main sequence stars are permeated by a strong magnetic
field, the origin of which is still matter of debate.
With this work we provide observational material to study how magnetic fields
change with the evolution of stars on the main sequence, and to constrain
theory explaining the presence of magnetic fields in A and B-type stars.
Using FORS1 in spectropolarimetric mode at the ESO VLT, we have carried out a
survey of magnetic fields in early-type stars belonging to open clusters and
associations of various ages.
We have measured the magnetic field of 235 early-type stars with a typical
uncertainty of about 100 G. In our sample, 97 stars are Ap or Bp stars. For
these targets, the median error bar of our field measurements was about 80 G. A
field has been detected in about 41 of these stars, 37 of which were not
previously known as magnetic stars. For the 138 normal A and B-type stars, the
median error bar was 136 G, and no field was detected in any of them.Comment: Accepted by A&A; 15 pages (article)+15 pages (tables), 8 figure
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