55,999 research outputs found
Modeling a Space-based Quantum Link
Quantum sources and single photon detectors have improved, allowing quantum algorithms for communication, encryption, computing, and sensing to transition from theory and small-scale laboratory experiments to field experiments. One such quantum algorithm, Quantum Key Distribution, uses optical pulses to generate shared random bit strings between two locations. These shared bit strings can be turned into encryption keys to be used as a one-time-pad or integrated with symmetric encryption techniques such as the Advanced Encryption Standard. This method of key generation and encryption is resistant to future advances in quantum computing which significantly degrade the effectiveness of current asymmetric key sharing techniques. This research first reviews previous and current efforts in free-space Quantum Key Distribution. Next, a derivation of the propagation and atmospheric simulation techniques used to model the propagation of an optical pulse from a LEO satellite to ground through turbulence is provided. An Adaptive Optics system, including both lower order tracking as well as higher order corrections using a Self-Referencing Interferometer, is modeled to correct for the aberrations caused by the atmosphere. The propagation, atmospheric, and adaptive optics models are then organized into a general optical propagation toolkit. Satellite positions are calculated using the Simplified General Perturbations model and are used with the optical propagation models to show the effects of using an adaptive optics system during a realistic satellite pass. Finally, the results from the models are compared to experimental data taken from a recent Japanese satellite experiment
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
Quantum Modelling of Electro-Optic Modulators
Many components that are employed in quantum information and communication
systems are well known photonic devices encountered in standard optical fiber
communication systems, such as optical beamsplitters, waveguide couplers and
junctions, electro-optic modulators and optical fiber links. The use of these
photonic devices is becoming increasingly important especially in the context
of their possible integration either in a specifically designed system or in an
already deployed end-to-end fiber link. Whereas the behavior of these devices
is well known under the classical regime, in some cases their operation under
quantum conditions is less well understood. This paper reviews the salient
features of the quantum scattering theory describing both the operation of the
electro-optic phase and amplitude modulators in discrete and continuous-mode
formalisms. This subject is timely and of importance in light of the increasing
utilization of these devices in a variety of systems, including quantum key
distribution and single-photon wavepacket measurement and conformation. In
addition, the paper includes a tutorial development of the use of these models
in selected but yet important applications, such as single and multi-tone
modulation of photons, two-photon interference with phase-modulated light or
the description of amplitude modulation as a quantum operation.Comment: 29 pages, 10 figures, Laser and Photonics Reviews (in press
High Speed and High Efficiency Travelling Wave Single-Photon Detectors Embedded in Nanophotonic Circuits
Ultrafast, high quantum efficiency single photon detectors are among the most
sought-after elements in modern quantum optics and quantum communication. High
photon detection efficiency is essential for scalable measurement-based quantum
computation, quantum key distribution, and loophole-free Bell experiments.
However, imperfect modal matching and finite photon absorption rates have
usually limited the maximum attainable detection efficiency of single photon
detectors. Here we demonstrate a superconducting nanowire detector atop
nanophotonic waveguides which allows us to drastically increase the absorption
length for incoming photons. When operating the detectors close to the critical
current we achieve high on-chip single photon detection efficiency up to 91% at
telecom wavelengths, with uncertainty dictated by the variation of the
waveguide photon flux. We also observe remarkably low dark count rates without
significant compromise of detection efficiency. Furthermore, our detectors are
fully embedded in a scalable silicon photonic circuit and provide ultrashort
timing jitter of 18ps. Exploiting this high temporal resolution we demonstrate
ballistic photon transport in silicon ring resonators. The direct
implementation of such a detector with high quantum efficiency, high detection
speed and low jitter time on chip overcomes a major barrier in integrated
quantum photonics
Integrated Generation of High-dimensional Entangled Photon States and Their Coherent Control
We demonstrate the generation of high-dimensional entangled photon pairs with a Hilbert-space dimensionality larger than 100 from an on-chip nonlinear microcavity, and introduce a coherent control scheme using standard telecommunications components
Integrated frequency comb source of heralded single photons
We report an integrated photon pair source based on a CMOS-compatible microring resonator that generates multiple, simultaneous, and independent photon pairs at different wavelengths in a frequency comb compatible with fiber communication wavelength division multiplexing channels (200 GHz channel separation) and with a linewidth that is compatible with quantum memories (110 MHz). It operates in a self-locked pump configuration, avoiding the need for active stabilization, making it extremely robust even at very low power levels
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