9 research outputs found
High coherence photon pair source for quantum communication
This paper reports a novel single mode source of narrow-band entangled photon
pairs at telecom wavelengths under continuous wave excitation, based on
parametric down conversion. For only 7 mW of pump power it has a created
spectral radiance of 0.08 pairs per coherence length and a bandwidth of 10 pm
(1.2 GHz). The effectively emitted spectral brightness reaches 3.9*10^5 pairs
/(s pm). Furthermore, when combined with low jitter single photon detectors,
such sources allow for the implementation of quantum communication protocols
without any active synchronization or path length stabilization. A HOM-Dip with
photons from two autonomous CW sources has been realized demonstrating the
setup's stability and performance.Comment: 12 pages, 4 figure
Intrinsically narrowband pair photon generation in microstructured fibres
In this paper we study the tailoring of photon spectral properties generated
by four-wave mixing in a birefringent photonic crystal fibre (PCF). The aim is
to produce intrinsically narrow-band photons and hence to achieve high
non-classical interference visibility and generate high fidelity entanglement
without any requirement for spectral filtering, leading to high effective
detection efficiencies. We show unfiltered Hong-Ou-Mandel interference
visibilities of 77% between photons from the same PCF, and 80% between separate
sources. We compare results from modelling the PCF to these experiments and
analyse photon purities.Comment: 23 pages, 17 figures, Comments Welcom
Entangling Independent Photons by Time Measurement
A quantum system composed of two or more subsystems can be in an entangled
state, i.e. a state in which the properties of the global system are well
defined but the properties of each subsystem are not. Entanglement is at the
heart of quantum physics, both for its conceptual foundations and for
applications in information processing and quantum communication. Remarkably,
entanglement can be "swapped": if one prepares two independent entangled pairs
A1-A2 and B1-B2, a joint measurement on A1 and B1 (called a "Bell-State
Measurement", BSM) has the effect of projecting A2 and B2 onto an entangled
state, although these two particles have never interacted or shared any common
past[1,2]. Experiments using twin photons produced by spontaneous parametric
down-conversion (SPDC) have already demonstrated entanglement swapping[3-6],
but here we present its first realization using continuous wave (CW) sources,
as originally proposed[2]. The challenge was to achieve sufficiently sharp
synchronization of the photons in the BSM. Using narrow-band filters, the
coherence time of the photons that undergo the BSM is significantly increased,
exceeding the temporal resolution of the detectors. Hence pulsed sources can be
replaced by CW sources, which do not require any synchronization[6,7], allowing
for the first time the use of completely autonomous sources. Our experiment
exploits recent progress in the time precision of photon detectors, in the
efficiency of photon pair production by SPDC with waveguides in nonlinear
crystals[8], and in the stability of narrow-band filters. This approach is
independent of the form of entanglement; we employed time-bin entangled
photons[9] at telecom wavelengths. Our setup is robust against thermal or
mechanical fluctuations in optical fibres thanks to cm-long coherence lengths.Comment: 13 pages, 3 figure