115 research outputs found
Characterizing heralded single-photon sources with imperfect measurement devices
Any characterization of a single-photon source is not complete without
specifying its second-order degree of coherence, i.e., its function.
An accurate measurement of such coherence functions commonly requires
high-precision single-photon detectors, in whose absence, only time-averaged
measurements are possible. It is not clear, however, how the resulting
time-averaged quantities can be used to properly characterize the source. In
this paper, we investigate this issue for a heralded source of single photons
that relies on continuous-wave parametric down-conversion. By accounting for
major shortcomings of the source and the detectors--i.e., the multiple-photon
emissions of the source, the time resolution of photodetectors, and our chosen
width of coincidence window--our theory enables us to infer the true source
properties from imperfect measurements. Our theoretical results are
corroborated by an experimental demonstration using a PPKTP crystal pumped by a
blue laser, that results in a single-photon generation rate about 1.2 millions
per second per milliwatt of pump power. This work takes an important step
toward the standardization of such heralded single-photon sources.Comment: 18 pages, 9 figures; corrected Eq. (11) and the description follows
Eq. (22
Separation of neutral and charge modes in one dimensional chiral edge channels
Coulomb interactions have a major role in one-dimensional electronic
transport. They modify the nature of the elementary excitations from Landau
quasiparticles in higher dimensions to collective excitations in one dimension.
Here we report the direct observation of the collective neutral and charge
modes of the two chiral co-propagating edge channels of opposite spins of the
quantum Hall effect at filling factor 2. Generating a charge density wave at
frequency f in the outer channel, we measure the current induced by
inter-channel Coulomb interaction in the inner channel after a 3-mm propagation
length. Varying the driving frequency from 0.7 to 11 GHz, we observe damped
oscillations in the induced current that result from the phase shift between
the fast charge and slow neutral eigenmodes. We measure the dispersion relation
and dissipation of the neutral mode from which we deduce quantitative
information on the interaction range and parameters.Comment: 23 pages, 6 figure
Electron quantum optics : partitioning electrons one by one
We have realized a quantum optics like Hanbury Brown and Twiss (HBT)
experiment by partitioning, on an electronic beam-splitter, single elementary
electronic excitations produced one by one by an on-demand emitter. We show
that the measurement of the output currents correlations in the HBT geometry
provides a direct counting, at the single charge level, of the elementary
excitations (electron/hole pairs) generated by the emitter at each cycle. We
observe the antibunching of low energy excitations emitted by the source with
thermal excitations of the Fermi sea already present in the input leads of the
splitter, which suppresses their contribution to the partition noise. This
effect is used to probe the energy distribution of the emitted wave-packets.Comment: 5 pages, 4 figure
Coherence measures for heralded single-photon sources
Single-photon sources (SPSs) are mainly characterized by the minimum value of
their second-order coherence function, viz. their function. A precise
measurement of may, however, require high time-resolution devices, in
whose absence, only time-averaged measurements are accessible. These
time-averaged measures, standing alone, do not carry sufficient information for
proper characterization of SPSs. Here, we develop a theory, corroborated by an
experiment, that allows us to scrutinize the coherence properties of heralded
SPSs that rely on continuous-wave parametric down-conversion. Our proposed
measures and analysis enable proper standardization of such SPSs.Comment: 4 pages, 4 figures, corrected Eq. (10
Partitioning of on-demand electron pairs
We demonstrate the high fidelity splitting of electron pairs emitted on
demand from a dynamic quantum dot by an electronic beam splitter. The fidelity
of pair splitting is inferred from the coincidence of arrival in two detector
paths probed by a measurement of the partitioning noise. The emission
characteristic of the on-demand electron source is tunable from electrons being
partitioned equally and independently to electron pairs being split with a
fidelity of 90%. For low beam splitter transmittance we further find evidence
of pair bunching violating statistical expectations for independent fermions
Current correlations of an on-demand electron source as an evidence of single particle emission
In analogy with quantum optics, short time correlations of the current
fluctuations are used to characterize an on-demand electron source consisting
of a quantum dot connected to a conductor via a tunable tunnel barrier. We
observe a new fundamental noise for electrons associated with the quantum
fluctuations of the electron emission time, which we call quantum jitter. In
optimum operating conditions of the source, the noise reduces to the quantum
jitter limit, which demonstrates single particle emission. Combined with the
coherent manipulations of single electrons in a quantum conductor, this
electron quantum optics experiment opens the way to explore new problems
including quantum statistics and interactions at the single electron level
Single electron quantum tomography in quantum Hall edge channels
We propose a quantum tomography protocol to measure single electron coherence
in quantum Hall edge channels and therefore access for the first time the wave
function of single electron excitations propagating in ballistic quantum
conductors. Its implementation would open the way to quantitative studies of
single electron decoherence and would provide a quantitative tool for analyzing
single to few electron sources. We show how this protocol could be implemented
using ultrahigh sensitivity noise measurement schemes.Comment: Version 3: long version (7 figures): corrections performed and
references have been added. Figures reprocessed for better readabilit
A corner reflector of graphene Dirac fermions as a phonon-scattering sensor
Dirac fermion optics exploits the refraction of chiral fermions across
optics-inspired Klein-tunneling barriers defined by high-transparency p-n
junctions. We consider the corner reflector (CR) geometry introduced in optics
or radars. We fabricate Dirac fermion CRs using bottom-gate-defined barriers in
hBN-encapsulated graphene. By suppressing transmission upon multiple internal
reflections, CRs are sensitive to minute phonon scattering rates. We report on
doping-independent CR transmission in quantitative agreement with a simple
scattering model including thermal phonon scattering. As a new signature of
CRs, we observe Fabry-P\'erot oscillations at low temperature, consistent with
single-path reflections. Finally, we demonstrate high-frequency operation which
promotes CRs as fast phonon detectors. Our work establishes the relevance of
Dirac fermion optics in graphene and opens a route for its implementation in
topological Dirac matter.Comment: 11 pages, 4 figure
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