166 research outputs found
Tomography by noise
We present an efficient and robust method for the reconstruction of photon
number distributions by using solely thermal noise as a probe. The method uses
a minimal number of pre-calibrated quantum devices, only one on/off
single-photon detector is sufficient. Feasibility of the method is demonstrated
by the experimental inference of single-photon, thermal and two-photon states.
The method is stable to experimental imperfections and provides a direct,
user-friendly quantum diagnostics tool
Passive decoy state quantum key distribution: Closing the gap to perfect sources
We propose a quantum key distribution scheme which closely matches the
performance of a perfect single photon source. It nearly attains the physical
upper bound in terms of key generation rate and maximally achievable distance.
Our scheme relies on a practical setup based on a parametric downconversion
source and present-day, non-ideal photon-number detection. Arbitrary
experimental imperfections which lead to bit errors are included. We select
decoy states by classical post-processing. This allows to improve the effective
signal statistics and achievable distance.Comment: 4 pages, 3 figures. State preparation correcte
Two-Photon Polarization Interference for Pulsed SPDC in a PPKTP Waveguide
We study the spectral properties of Spontaneous Parametric Down Conversion in
a periodically poled waveguided structure of KTP crystal pumped by ultra-short
pulses. Our theoretical analysis reveals a strongly multimode and asymmetric
structure of the two-photon spectral amplitude for type-II SPDC. Experimental
evidence, based on Hong-Ou-Mandel polarization interference with narrowband
filtering, confirms this result.Comment: Submitted for publicatio
Efficient algorithm for optimizing data pattern tomography
We give a detailed account of an efficient search algorithm for the data
pattern tomography proposed by J. Rehacek, D. Mogilevtsev, and Z. Hradil [Phys.
Rev. Lett.~\textbf{105}, 010402 (2010)], where the quantum state of a system is
reconstructed without a priori knowledge about the measuring setup. The method
is especially suited for experiments involving complex detectors, which are
difficult to calibrate and characterize. We illustrate the approach with the
case study of the homodyne detection of a nonclassical photon state.Comment: 5 pages, 5 eps-color figure
Equivalent efficiency of a simulated photon-number detector
Homodyne detection is considered as a way to improve the efficiency of
communication near the single-photon level. The current lack of commercially
available {\it infrared} photon-number detectors significantly reduces the
mutual information accessible in such a communication channel. We consider
simulating direct detection via homodyne detection. We find that our particular
simulated direct detection strategy could provide limited improvement in the
classical information transfer. However, we argue that homodyne detectors (and
a polynomial number of linear optical elements) cannot simulate photocounters
arbitrarily well, since otherwise the exponential gap between quantum and
classical computers would vanish.Comment: 4 pages, 4 figure
Survey of vegetation and elevational relationships within coastal marsh transition zones in the central Atlantic coastal region : final report
This report contains the findings of a one-year botanical field study of the marsh to uplands vegetational transition zone at selected sites within the Central Atlantic Coastal Region of the United States. The latter region is herein defined to include the coasts of Delaware, Maryland, Virginia, and North Carolina. To obtain results representative of the various coastal environments and associated wetlands types found within this region, five primary sites and one to four secondary sites in the vicinity of each primary site were chosen for detailed investigations
Photon number resolving detection using time-multiplexing
Detectors that can resolve photon number are needed in many quantum
information technologies. In order to be useful in quantum information
processing, such detectors should be simple, easy to use, and be scalable to
resolve any number of photons, as the application may require great portability
such as in quantum cryptography. Here we describe the construction of a
time-multiplexed detector, which uses a pair of standard avalanche photodiodes
operated in Geiger mode. The detection technique is analysed theoretically and
tested experimentally using a pulsed source of weak coherent light.Comment: 20 pages, 14 figures, accepted to Journal of Modern Optic
Avalanche Photo-Detection for High Data Rate Applications
Avalanche photo detection is commonly used in applications which require
single photon sensitivity. We examine the limits of using avalanche photo
diodes (APD) for characterising photon statistics at high data rates. To
identify the regime of linear APD operation we employ a ps-pulsed diode laser
with variable repetition rates between 0.5MHz and 80MHz. We modify the mean
optical power of the coherent pulses by applying different levels of
well-calibrated attenuation. The linearity at high repetition rates is limited
by the APD dead time and a non-linear response arises at higher photon-numbers
due to multiphoton events. Assuming Poissonian input light statistics we
ascertain the effective mean photon-number of the incident light with high
accuracy. Time multiplexed detectors (TMD) allow to accomplish photon- number
resolution by photon chopping. This detection setup extends the linear response
function to higher photon-numbers and statistical methods may be used to
compensate for non-linearity. We investigated this effect, compare it to the
single APD case and show the validity of the convolution treatment in the TMD
data analysis.Comment: 16 pages, 5 figure
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