202 research outputs found
Impedance model for the polarization-dependent optical absorption of superconducting single-photon detectors
We measured the single-photon detection efficiency of NbN superconducting
single photon detectors as a function of the polarization state of the incident
light for different wavelengths in the range from 488 nm to 1550 nm. The
polarization contrast varies from ~5% at 488 nm to ~30% at 1550 nm, in good
agreement with numerical calculations. We use an optical-impedance model to
describe the absorption for polarization parallel to the wires of the detector.
For lossy NbN films, the absorption can be kept constant by keeping the product
of layer thickness and filling factor constant. As a consequence, we find that
the maximum possible absorption is independent of filling factor. By
illuminating the detector through the substrate, an absorption efficiency of
~70% can be reached for a detector on Si or GaAs, without the need for an
optical cavity.Comment: 15 pages, 5 figures, submitted to Journal of Applied Physic
Efficient and robust fiber coupling of superconducting single photon detectors
We applied a recently developed fiber coupling technique to superconducting
single photon detectors (SSPDs). As the detector area of SSPDs has to be kept
as small as possible, coupling to an optical fiber has been either inefficient
or unreliable. Etching through the silicon substrate allows fabrication of a
circularly shaped chip which self aligns to the core of a ferrule terminated
fiber in a fiber sleeve. In situ alignment at cryogenic temperatures is
unnecessary and no thermal stress during cooldown, causing misalignment, is
induced. We measured the quantum efficiency of these devices with an attenuated
tunable broadband source. The combination of a lithographically defined chip
and high precision standard telecommunication components yields near unity
coupling efficiency and a system detection efficiency of 34% at a wavelength of
1200 nm. This quantum efficiency measurement is confirmed by an absolute
efficiency measurement using correlated photon pairs (with = 1064 nm)
produced by spontaneous parametric down-conversion. The efficiency obtained via
this method agrees well with the efficiency measured with the attenuated
tunable broadband source
Correlated photon-pair generation in a periodically poled MgO doped stoichiometric lithium tantalate reverse proton exchanged waveguide
We demonstrate photon-pair generation in a reverse proton exchanged waveguide
fabricated on a periodically poled magnesium doped stoichiometric lithium
tantalate substrate. Detected pairs are generated via a cascaded second order
nonlinear process where a pump laser at wavelength of 1.55 m is first
doubled in frequency by second harmonic generation and subsequently
downconverted around the same spectral region. Pairs are detected at a rate of
42 per second with a coincidence to accidental ratio of 0.7. This cascaded pair
generation process is similar to four-wave-mixing where two pump photons
annihilate and create a correlated photon pair
Fast Purcell-enhanced single photon source in 1,550-nm telecom band from a resonant quantum dot-cavity coupling
High-bit-rate nanocavity-based single photon sources in the 1,550-nm telecom
band are challenges facing the development of fibre-based long-haul quantum
communication networks. Here we report a very fast single photon source in the
1,550-nm telecom band, which is achieved by a large Purcell enhancement that
results from the coupling of a single InAs quantum dot and an InP photonic
crystal nanocavity. At a resonance, the spontaneous emission rate was enhanced
by a factor of 5 resulting a record fast emission lifetime of 0.2 ns at 1,550
nm. We also demonstrate that this emission exhibits an enhanced anti-bunching
dip. This is the first realization of nanocavity-enhanced single photon
emitters in the 1,550-nm telecom band. This coupled quantum dot cavity system
in the telecom band thus provides a bright high-bit-rate non-classical single
photon source that offers appealing novel opportunities for the development of
a long-haul quantum telecommunication system via optical fibres.Comment: 16 pages, 4 figure
Photon Pair Generation in Silicon Micro-Ring Resonator with Reverse Bias Enhancement
Photon sources are fundamental components for any quantum photonic
technology. The ability to generate high count-rate and low-noise correlated
photon pairs via spontaneous parametric down-conversion using bulk crystals has
been the cornerstone of modern quantum optics. However, future practical
quantum technologies will require a scalable integration approach, and
waveguide-based photon sources with high-count rate and low-noise
characteristics will be an essential part of chip-based quantum technologies.
Here, we demonstrate photon pair generation through spontaneous four-wave
mixing in a silicon micro-ring resonator, reporting a maximum
coincidence-to-accidental (CAR) ratio of 602 (+-) 37, and a maximum photon pair
generation rate of 123 MHz (+-) 11 KHz. To overcome free-carrier related
performance degradations we have investigated reverse biased p-i-n structures,
demonstrating an improvement in the pair generation rate by a factor of up to
2, with negligible impact on CAR.Comment: 5 pages, 3 figure
Quantum interference and manipulation of entanglement in silicon wire waveguide quantum circuits
Integrated quantum photonic waveguide circuits are a promising approach to
realizing future photonic quantum technologies. Here, we present an integrated
photonic quantum technology platform utilising the silicon-on-insulator
material system, where quantum interference and the manipulation of quantum
states of light are demonstrated in components orders of magnitude smaller than
in previous implementations. Two-photon quantum interference is presented in a
multi-mode interference coupler, and manipulation of entanglement is
demonstrated in a Mach-Zehnder interferometer, opening the way to an
all-silicon photonic quantum technology platform.Comment: 7 page
Enhancement of the electron electric dipole moment in gadolinium garnets
Effects caused by the electron electric dipole moment (EDM) in gadolinium
garnets are considered. Experimental studies of these effects could improve
current upper limit on the electron EDM by several orders of magnitude. We
suggest a consistent theoretical model and perform calculations of observable
effects in gadolinium gallium garnet and gadolinium iron garnet. Our
calculation accounts for both direct and exchange diagrams.Comment: 9 page
Generation of correlated photon pairs in a chalcogenide As2S3 waveguide
We demonstrate the first 1550 nm correlated photon-pair source in an
integrated glass platform-a chalcogenide As2S3 waveguide. A measured pair
coincidence rate of 80 per second was achieved using 57 mW of continuous-wave
pump. The coincidence to accidental ratio was shown to be limited by
spontaneous Raman scattering effects that are expected to be mitigated by using
a pulsed pump source.Comment: 3 pages, 4 figure
Superconducting nanowire single-photon detectors: physics and applications
Single-photon detectors based on superconducting nanowires (SSPDs or SNSPDs)
have rapidly emerged as a highly promising photon-counting technology for
infrared wavelengths. These devices offer high efficiency, low dark counts and
excellent timing resolution. In this review, we consider the basic SNSPD
operating principle and models of device behaviour. We give an overview of the
evolution of SNSPD device design and the improvements in performance which have
been achieved. We also evaluate device limitations and noise mechanisms. We
survey practical refrigeration technologies and optical coupling schemes for
SNSPDs. Finally we summarize promising application areas, ranging from quantum
cryptography to remote sensing. Our goal is to capture a detailed snapshot of
an emerging superconducting detector technology on the threshold of maturity.Comment: 27 pages, 5 figures, Review article preprint versio
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