362 research outputs found
Exploring the limits of multiplexed photon-pair sources for the preparation of pure single-photon states
Current sources of heralded single photons based on nonlinear optics operate
in a probabilistic manner. In order to build quantum-enhanced devices based
around the use of single photons, compact, turn-key and deterministic sources
are required. A possible solution is to multiplex a number of sources to
increase the single-photon generation probability and in so doing reducing the
waiting time to deliver large numbers of photons simultaneously, from
independent sources. Previously it has been shown that, in the ideal case, 17
multiplexed sources allow deterministic generation of heralded single photons
[Christ and Silberhorn, Phys. Rev. A 85, 023829 (2012)]. Here we extend this
analysis to include undesirable effects of detector inefficiency and photon
loss on a number of multiplexed sources using a variety of different detectors
for heralding. We compare these systems for fixed signal-to-noise ratio to
allow a direct comparison of performance for real- world heralded single photon
sources.Comment: 10 pages, 7 figures. Equation 18 changed to include power of a half
in the binomial facto
Temporal Loop Multiplexing: A resource efficient scheme for multiplexed photon-pair sources
Single photons are a vital resource for photonic quantum information
processing. However, even state-of-the-art single photon sources based on
photon-pair generation and heralding detection have only a low probability of
delivering a single photon when one is requested. We analyse a scheme that uses
a switched fibre delay loop to increase the delivery probability per time bin
of single photons from heralded sources. We show that, for realistic
experimental parameters, combining the output of up to 15 pulses can yield a
performance improvement of a factor of 10. We consider the future performance
of this scheme with likely component improvements.Comment: 5 pages, 4 figure
A bright, pulsed two-mode squeezer
We report the realization of a bright ultrafast two-mode squeezer based on
type II parametric downconversion (PDC) in periodically poled
(PP-KTP) waveguides. It produces a pulsed two-mode squeezed
vacuum state: a photon-number entangled pair of truly single-mode pulses or, in
terms of continuous variables quantum optics, a pulsed, single mode
Einstein-Podolsky-Rosen (EPR) state in the telecom regime. We prove the single
mode character of our source by measuring its correlation function
and demonstrate a mean photon number of up to 2.5 per pulse, equivalent to 11dB
of two-mode squeezing.Comment: 4 pages, 3 figure
Characterizing the variation of propagation constants in multicore fibre
We demonstrate a numerical technique that can evaluate the core-to-core
variations in propagation constant in multicore fibre. Using a Markov Chain
Monte Carlo process, we replicate the interference patterns of light that has
coupled between the cores during propagation. We describe the algorithm and
verify its operation by successfully reconstructing target propagation
constants in a fictional fibre. Then we carry out a reconstruction of the
propagation constants in a real fibre containing 37 single-mode cores. We find
that the range of fractional propagation constant variation across the cores is
approximately .Comment: 17 pages; preprint format; 5 figures. Submitted to Optics Expres
Single-shot measurement of photonic topological invariant
Topological design enables physicists to engineer robustness into a system. When connected to a topological invariant, the propagation of light remains unchanged in the presence of disorder. However, a general challenge remains to directly characterise the topological properties of systems by experiment. In this work, we demonstrate a novel technique for directly observing a photonic winding number using a single measurement. By propagating light with a sufficiently broad spectrum along a topological photonic crystal fibre, we calculate the winding number invariant from the output intensity pattern. We quantify the limitations of this single-shot method, which works even for surprisingly narrow and asymmetric spectral distributions. Furthermore, we dynamically evaluate the effectiveness of our method by uncovering the loss of the bulk invariant as we twist the fibre. The characterisation method that we present is highly accessible and transferable across topological photonic platforms
Direct Measurement of the Spatial-Spectral Structure of Waveguided Parametric Down-Conversion
We present a study of the propagation of higher-order spatial modes in a
waveguided parametric down-conversion photon pair source. Observing the
multimode photon pair spectrum from a periodically poled KTiOPO waveguide
allowed us to isolate individual spatial modes through their distinctive
spectral properties. We have measured directly the spatial distribution of each
mode of the photon pairs, confirming the findings of our waveguide model, and
demonstrated by coincidence measurements that the total parity of the modes is
conserved in the nonlinear interaction. Furthermore, we show that we can
combine the advantages of a waveguide source with the potential to generate
spatially entangled photon pairs as in bulk crystal down-converters.Comment: 4 pages, 5 figure
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