394 research outputs found
Direct measurement of spatial Wigner function with area-integrated detection
We demonstrate experimentally a novel technique for characterizing transverse
spatial coherence using the Wigner distribution function. The presented method
is based on measuring interference between a pair of rotated and displaced
replicas of the input beam with an area-integrating detector, and it can be
superior in regimes when array detectors are not available. We analyze the
quantum optical picture of the presented measurement for single-photon signals
and discuss possible applications in quantum information processing.Comment: 3 pages, REVTe
Fiber-assisted detection with photon number resolution
We report the development of a photon-number resolving detector based on a
fiber-optical setup and a pair of standard avalanche photodiodes. The detector
is capable of resolving individual photon numbers, and operates on the
well-known principle by which a single mode input state is split into a large
number (eight) of output modes. We reconstruct the photon statistics of weak
coherent input light from experimental data, and show that there is a high
probability of inferring the input photon number from a measurement of the
number of detection events on a single run.Comment: 4 pages, 2 figures; Submitted for publicatio
Photon engineering for quantum information processing
We study distinguishing information in the context of quantum interference
involving more than one parametric downconversion (PDC) source and in the
context of polarization-entangled photon pairs based on PDC. We arrive at
specific design criteria for two-photon sources so that when used as part of
complex optical systems, such as photon-based quantum information processing
schemes, distinguishing information between the photons is eliminated
guaranteeing high visibility interference. We propose practical techniques
which lead to suitably engineered two-photon states that can be realistically
implemented with available technology. Finally, we study an implementation of
the nonlinear-sign shift (NS) logic gate with PDC sources and show the effect
of distinguishing information on the performance of the gate.Comment: 23 pages, 13 figures. submitted to Quantum Information & Computatio
The usability of the optical parametric amplification of light for high-angular-resolution imaging and fast astrometry
High-angular-resolution imaging is crucial for many applications in modern
astronomy and astrophysics. The fundamental diffraction limit constrains the
resolving power of both ground-based and spaceborne telescopes. The recent idea
of a quantum telescope based on the optical parametric amplification (OPA) of
light aims to bypass this limit for the imaging of extended sources by an order
of magnitude or more. We present an updated scheme of an OPA-based device and a
more accurate model of the signal amplification by such a device. The
semiclassical model that we present predicts that the noise in such a system
will form so-called light speckles as a result of light interference in the
optical path. Based on this model, we analysed the efficiency of OPA in
increasing the angular resolution of the imaging of extended targets and the
precise localization of a distant point source. According to our new model, OPA
offers a gain in resolved imaging in comparison to classical optics. For a
given time-span, we found that OPA can be more efficient in localizing a single
distant point source than classical telescopes.Comment: Received: 11 November 2017, revision received: 31 January 2018,
accepted: 31 January 201
Photon counting with loop detector
We propose a design for a photon counting detector capable of resolving
multiphoton events. The basic element of the setup is a fiber loop, which traps
the input field with the help of a fast electrooptic switch. A single weakly
coupled avalanche photodiode is used to detect small portions of the signal
field extracted from the loop. We analyze the response of the loop detector to
an arbitrary input field, and discuss both the reconstruction of the photon
number distribution of an unknown field from the count statistics measured in
the setup, and the application of the detector in conditional state
preparation.Comment: 3 pages, REVTe
A measure of the non-Gaussian character of a quantum state
We address the issue of quantifying the non-Gaussian character of a bosonic
quantum state and introduce a non-Gaussianity measure based on the
Hilbert-Schmidt distance between the state under examination and a reference
Gaussian state. We analyze in details the properties of the proposed measure
and exploit it to evaluate the non-Gaussianity of some relevant single- and
multi-mode quantum states. The evolution of non-Gaussianity is also analyzed
for quantum states undergoing the processes of Gaussification by loss and
de-Gaussification by photon-subtraction. The suggested measure is easily
computable for any state of a bosonic system and allows to define a
corresponding measure for the non-Gaussian character of a quantum operation.Comment: revised and enlarged version, 7 pages, 4 figure
Direct measurement of the Wigner function by photon counting
We report a direct measurement of the Wigner function characterizing the
quantum state of a light mode. The experimental scheme is based on the
representation of the Wigner function as an expectation value of a displaced
photon number parity operator. This allowed us to scan the phase space
point-by-point, and obtain the complete Wigner function without using any
numerical reconstruction algorithms.Comment: 4 pages, REVTe
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