250 research outputs found
Nonlinear interaction between two heralded single photons
Harnessing nonlinearities strong enough to allow two single photons to
interact with one another is not only a fascinating challenge but is central to
numerous advanced applications in quantum information science. Currently, all
known approaches are extremely challenging although a few have led to
experimental realisations with attenuated classical laser light. This has
included cross-phase modulation with weak classical light in atomic ensembles
and optical fibres, converting incident laser light into a non-classical stream
of photon or Rydberg blockades as well as all-optical switches with attenuated
classical light in various atomic systems. Here we report the observation of a
nonlinear parametric interaction between two true single photons. Single
photons are initially generated by heralding one photon from each of two
independent spontaneous parametric downconversion sources. The two heralded
single photons are subsequently combined in a nonlinear waveguide where they
are converted into a single photon with a higher energy. Our approach
highlights the potential for quantum nonlinear optics with integrated devices,
and as the photons are at telecom wavelengths, it is well adapted to
applications in quantum communication.Comment: 4 pages, 4 figure
Incorporating Animal Movement Into Distance Sampling
Distance sampling is a popular statistical method to estimate the density of wild animal populations. Conventional distance sampling represents animals as fixed points in space that are detected with an unknown probability that depends on the distance between the observer and the animal. Animal movement can cause substantial bias in density estimation. Methods to correct for responsive animal movement exist, but none account for nonresponsive movement independent of the observer. Here, an explicit animal movement model is incorporated into distance sampling, combining distance sampling survey data with animal telemetry data. Detection probability depends on the entire unobserved path the animal travels. The intractable integration over all possible animal paths is approximated by a hidden Markov model. A simulation study shows themethod to be negligibly biased (\u3c5%) in scenarioswhere conventional distance sampling overestimates abundance by up to 100%. The method is applied to line transect surveys (1999– 2006) of spotted dolphins (Stenella attenuata) in the eastern tropical Pacific where abundance is shown to be positively biased by 21% on average, which can have substantial impact on the population dynamics estimated from these abundance estimates and on the choice of statistical methodology applied to future surveys. Supplementary materials for this article, including a standardized description of the materials available for reproducing the work, are available as an online supplement
Long-distance entanglement-based quantum key distribution over optical fiber
We report the first entanglement-based quantum key distribution (QKD) experiment over a 100-km optical fiber. We used superconducting single photon detectors based on NbN nanowires that provide high-speed single photon detection for the 1.5-µm telecom band, an efficient entangled photon pair source that consists of a fiber coupled periodically poled lithium niobate waveguide and ultra low loss filters, and planar lightwave circuit Mach-Zehnder interferometers (MZIs) with ultra stable operation. These characteristics enabled us to perform an entanglement-based QKD experiment over a 100-km optical fiber. In the experiment, which lasted approximately 8 hours, we successfully generated a 16 kbit sifted key with a quantum bit error rate of 6.9 % at a rate of 0.59 bits per second, from which we were able to distill a 3.9 kbit secure key
Interaction of Independent Single Photons based on Integrated Nonlinear Optics
Photons are ideal carriers of quantum information, as they can be easily
created and can travel long distances without being affected by decoherence.
For this reason, they are well suited for quantum communication. However, the
interaction between single photons is negligible under most circumstances.
Realising such an interaction is not only fundamentally fascinating but holds
great potential for emerging technologies. It has recently been shown that even
weak optical nonlinearities between single photons can be used to perform
important quantum communication tasks more efficiently than methods based on
linear optics, which have fundamental limitations. Nonlinear optical effects at
single photon levels in atomic media have been studied and demonstrated but
these are neither flexible nor compatible with quantum communication as they
impose restrictions on photons' wavelengths and bandwidths. Here we use a high
efficiency nonlinear waveguide to observe the sum-frequency generation between
a single photon and a single-photon level coherent state from two independent
sources. The use of an integrated, room-temperature device and telecom
wavelengths makes this approach to photon-photon interaction well adapted to
long distance quantum communication, moving quantum nonlinear optics one step
further towards complex quantum networks and future applications such as device
independent quantum key distribution
Spectral compression of single photons
Photons are critical to quantum technologies since they can be used for
virtually all quantum information tasks: in quantum metrology, as the
information carrier in photonic quantum computation, as a mediator in hybrid
systems, and to establish long distance networks. The physical characteristics
of photons in these applications differ drastically; spectral bandwidths span
12 orders of magnitude from 50 THz for quantum-optical coherence tomography to
50 Hz for certain quantum memories. Combining these technologies requires
coherent interfaces that reversibly map centre frequencies and bandwidths of
photons to avoid excessive loss. Here we demonstrate bandwidth compression of
single photons by a factor 40 and tunability over a range 70 times that
bandwidth via sum-frequency generation with chirped laser pulses. This
constitutes a time-to-frequency interface for light capable of converting
time-bin to colour entanglement and enables ultrafast timing measurements. It
is a step toward arbitrary waveform generation for single and entangled
photons.Comment: 6 pages (4 figures) + 6 pages (3 figures
Mid-infrared spectroscopy with a broadly tunable thin-film lithium niobate optical parametric oscillator
Mid-infrared spectroscopy, an important and widespread technique for sensing
molecules, has encountered barriers stemming from sources either limited in
tuning range or excessively bulky for practical field use. We present a
compact, efficient, and broadly tunable optical parametric oscillator (OPO)
device surmounting these challenges. Leveraging a dispersion-engineered
singly-resonant OPO implemented in thin-film lithium niobate-on-sapphire, we
achieve broad and controlled tuning over an octave, from 1.5 to 3.3 microns by
combining laser and temperature tuning. The device generates > 25 mW of
mid-infrared light at 3.2 microns, offering a power conversion efficiency of
15% (45% quantum efficiency). We demonstrate the tuning and performance of the
device by successfully measuring the spectra of methane and ammonia, verifying
our approach's relevance for gas sensing. Our device signifies an important
advance in nonlinear photonics miniaturization and brings practical field
applications of high-speed and broadband mid-infrared spectroscopy closer to
reality.Comment: 19 pages, 11 figure
Integrated frequency-modulated optical parametric oscillator
Optical frequency combs have revolutionized precision measurement,
time-keeping, and molecular spectroscopy. A substantial effort has developed
around "microcombs": integrating comb-generating technologies into compact,
reliable photonic platforms. Current approaches for generating these microcombs
involve either the electro-optic (EO) or Kerr mechanisms. Despite rapid
progress, maintaining high efficiency and wide bandwidth remains challenging.
Here, we introduce a new class of microcomb -- an integrated optical frequency
comb generator that combines electro-optics and parametric amplification to
yield a frequency-modulated optical parametric oscillator (FM-OPO). In stark
contrast to EO and Kerr combs, the FM-OPO microcomb does not form pulses but
maintains operational simplicity and highly efficient pump power utilization
with an output resembling a frequency-modulated laser. We outline the working
principles of FM-OPO and demonstrate them by fabricating the complete optical
system in thin-film lithium niobate (LNOI). We measure pump to comb internal
conversion efficiency exceeding 93% (34% out-coupled) over a nearly flat-top
spectral distribution spanning approximately 1,000 modes (approximately 6 THz).
Compared to an EO comb, the cavity dispersion rather than loss determines the
FM-OPO bandwidth, enabling broadband combs with a smaller RF modulation power.
The FM-OPO microcomb, with its robust operational dynamics, high efficiency,
and large bandwidth, contributes a new approach to the field of microcombs and
promises to herald an era of miniaturized precision measurement, and
spectroscopy tools to accelerate advancements in metrology, spectroscopy,
telecommunications, sensing, and computing.Comment: 8 pages, 4 figures main text; another 19 pages and 9 figures in
methods and supplementar
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