14,863 research outputs found
MHz rate and efficient synchronous heralding of single photons at telecom wavelengths
We report on the realization of a synchronous source of heralded single
photons at telecom wavelengths with MHz heralding rates and high heralding
efficiency. This source is based on the generation of photon pairs at 810 and
1550 nm via Spontaneous Parametric Down Conversion (SPDC) in a 1 cm
periodically poled lithium niobate (PPLN) crystal pumped by a 532 nm pulsed
laser. As high rates are fundamental for multi-photon experiments, we show that
single telecom photons can be announced at 4.4MHz rate with 45% heralding
efficiency. When we focus only on the optimization of the coupling of the
heralded photon, the heralding efficiency can be increased up to 80%.
Furthermore, we experimentally observe that group velocity mismatch inside long
crystals pumped in a pulsed mode affects the spectrum of the emitted photons
and their fibre coupling efficiency. The length of the crystal in this source
has been chosen as a trade off between high brightness and high coupling
efficiency.Comment: 10 pages, 2 figure
High quality asynchronous heralded single photon source at telecom wavelength
We report on the experimental realization and characterization of an
asynchronous heralded single photon source based on spontaneous parametric down
conversion. Photons at 1550nm are heralded as being inside a single-mode fiber
with more than 60% probability, and the multi-photon emission probability is
reduced by up to a factor 600 compared to poissonian light sources. These
figures of merit, together with the choice of telecom wavelength for the
heralded photons are compatible with practical applications needing very
efficient and robust single photon sources.Comment: 7 pages, 8 figure
Low-resource synchronous coincidence processor for positron emission tomography
We developed a new FPGA-based method for coincidence detection in positronemissiontomography. The method requires low device resources and no specific peripherals in order to resolve coincident digital pulses within a time window of a few nanoseconds. This method has been validated with a low-end Xilinx Spartan-3E and provided coincidence resolutions lower than 6 ns. This resolution depends directly on the signal propagation properties of the target device and the maximum available clock frequency, therefore it is expected to improve considerably on higher-end FPGAs
Dead Time Compensation for High-Flux Ranging
Dead time effects have been considered a major limitation for fast data
acquisition in various time-correlated single photon counting applications,
since a commonly adopted approach for dead time mitigation is to operate in the
low-flux regime where dead time effects can be ignored. Through the application
of lidar ranging, this work explores the empirical distribution of detection
times in the presence of dead time and demonstrates that an accurate
statistical model can result in reduced ranging error with shorter data
acquisition time when operating in the high-flux regime. Specifically, we show
that the empirical distribution of detection times converges to the stationary
distribution of a Markov chain. Depth estimation can then be performed by
passing the empirical distribution through a filter matched to the stationary
distribution. Moreover, based on the Markov chain model, we formulate the
recovery of arrival distribution from detection distribution as a nonlinear
inverse problem and solve it via provably convergent mathematical optimization.
By comparing per-detection Fisher information for depth estimation from high-
and low-flux detection time distributions, we provide an analytical basis for
possible improvement of ranging performance resulting from the presence of dead
time. Finally, we demonstrate the effectiveness of our formulation and
algorithm via simulations of lidar ranging.Comment: Revision with added estimation results, references, and figures, and
modified appendice
Experimental Free-Space Distribution of Entangled Photon Pairs over a Noisy Ground Atmosphere of 13km
We report free-space distribution of entangled photon pairs over a noisy
ground atmosphere of 13km. It is shown that the desired entanglement can still
survive after the two entangled photons have passed through the noisy ground
atmosphere. This is confirmed by observing a space-like separated violation of
Bell inequality of . On this basis, we exploit the distributed
entangled photon source to demonstrate the BB84 quantum cryptography scheme.
The distribution distance of entangled photon pairs achieved in the experiment
is for the first time well beyond the effective thickness of the aerosphere,
hence presenting a significant step towards satellite-based global quantum
communication.Comment: 4 pages, 3 figure
Ultrasensitive force and displacement detection using trapped ions
The ability to detect extremely small forces is vital for a variety of
disciplines including precision spin-resonance imaging, microscopy, and tests
of fundamental physical phenomena. Current force-detection sensitivity limits
have surpassed 1 (atto ) through coupling of micro or
nanofabricated mechanical resonators to a variety of physical systems including
single-electron transistors, superconducting microwave cavities, and individual
spins. These experiments have allowed for probing studies of a variety of
phenomena, but sensitivity requirements are ever-increasing as new regimes of
physical interactions are considered. Here we show that trapped atomic ions are
exquisitely sensitive force detectors, with a measured sensitivity more than
three orders of magnitude better than existing reports. We demonstrate
detection of forces as small as 174 (yocto ), with a
sensitivity 390 using crystals of Be
ions in a Penning trap. Our technique is based on the excitation of normal
motional modes in an ion trap by externally applied electric fields, detection
via and phase-coherent Doppler velocimetry, which allows for the discrimination
of ion motion with amplitudes on the scale of nanometers. These experimental
results and extracted force-detection sensitivities in the single-ion limit
validate proposals suggesting that trapped atomic ions are capable of detecting
of forces with sensitivity approaching 1 . We anticipate that
this demonstration will be strongly motivational for the development of a new
class of deployable trapped-ion-based sensors, and will permit scientists to
access new regimes in materials science.Comment: Expanded introduction and analysis. Methods section added. Subject to
press embarg
- …