198 research outputs found
Design of polarization-insensitive superconducting single photon detectors with high-index dielectrics
In this paper, the design of superconducting-nanowire single-photon detectors
which are insensitive to the polarization of the incident light is
investigated. By using high-refractive-index dielectrics, the index mismatch
between the nanowire and the surrounding media is reduced. This enhances the
absorption of light with electric field vector perpendicular to the nanowire
segments, which is generally hindered in this kind of detectors. Building on
this principle and focusing on NbTiN nanowire devices, we present several
easy-to-realize cavity architectures which allow high absorption efficiency (in
excess of 90%) and polarization insensitivity simultaneously. Designs based on
ultranarrow nanowires, for which the polarization sensitivity is much more
marked, are also presented. Finally, we briefly discuss the specific advantages
of this approach in the case of WSi or MoSi nanowires
Measurement of g-factor tensor in a quantum dot and disentanglement of exciton spins
We perform polarization-resolved magneto-optical measurements on single InAsP
quantum dots embedded in an InP nanowire. In order to determine all elements of
the electron and hole -factor tensors, we measure in magnetic field with
different orientations. The results of these measurements are in good agreement
with a model based on exchange terms and Zeeman interaction. In our experiment,
polarization analysis delivers a powerful tool that not only significantly
increases the precision of the measurements, but also enables us to probe the
exciton spin state evolution in magnetic fields. We propose a disentangling
scheme of heavy-hole exciton spins enabling a measurement of the electron spin
time
Observation of strongly entangled photon pairs from a nanowire quantum dot
A bright photon source that combines high-fidelity entanglement, on-demand
generation, high extraction efficiency, directional and coherent emission, as
well as position control at the nanoscale is required for implementing
ambitious schemes in quantum information processing, such as that of a quantum
repeater. Still, all of these properties have not yet been achieved in a single
device. Semiconductor quantum dots embedded in nanowire waveguides potentially
satisfy all of these requirements; however, although theoretically predicted,
entanglement has not yet been demonstrated for a nanowire quantum dot. Here, we
demonstrate a bright and coherent source of strongly entangled photon pairs
from a position controlled nanowire quantum dot with a fidelity as high as
0.859 +/- 0.006 and concurrence of 0.80 +/- 0.02. The two-photon quantum state
is modified via the nanowire shape. Our new nanoscale entangled photon source
can be integrated at desired positions in a quantum photonic circuit, single
electron devices and light emitting diodes.Comment: Article and Supplementary Information with open access published at:
http://www.nature.com/ncomms/2014/141031/ncomms6298/full/ncomms6298.htm
Dynamic strain modulation of a nanowire quantum dot compatible with a thin-film lithium niobate photonic platform
The integration of on-demand single photon sources in photonic circuits is a
major prerequisite for on-chip quantum applications. Among the various
high-quality sources, nanowire quantum dots can be efficiently coupled to
optical waveguides because of their preferred emission direction along their
growth direction. However, local tuning of the emission properties remains
challenging. In this work, we transfer a nanowire quantum dot on a bulk lithium
niobate substrate and show that its emission can be dynamically tuned by
acousto-optical coupling with surface acoustic waves. The purity of the single
photon source is preserved during the strain modulation. We further demonstrate
that the transduction is maintained even with a SiO2 encapsulation layer
deposited on top of the nanowire acting as the cladding of a photonic circuit.
Based on these experimental findings and numerical simulations, we introduce a
device architecture consisting of a nanowire quantum dot efficiently coupled to
a thin film lithium niobate rib waveguide and strain-tunable by surface
acoustic waves
Resonance fluorescence of GaAs quantum dots with near-unity photon indistinguishability
Photonic quantum technologies call for scalable quantum light sources that
can be integrated, while providing the end user with single and entangled
photons on-demand. One promising candidate are strain free GaAs/AlGaAs quantum
dots obtained by droplet etching. Such quantum dots exhibit ultra low
multi-photon probability and an unprecedented degree of photon pair
entanglement. However, different to commonly studied InGaAs/GaAs quantum dots
obtained by the Stranski-Krastanow mode, photons with a near-unity
indistinguishability from these quantum emitters have proven to be elusive so
far. Here, we show on-demand generation of near-unity indistinguishable photons
from these quantum emitters by exploring pulsed resonance fluorescence. Given
the short intrinsic lifetime of excitons confined in the GaAs quantum dots, we
show single photon indistinguishability with a raw visibility of
, without the need for Purcell enhancement. Our
results represent a milestone in the advance of GaAs quantum dots by
demonstrating the final missing property standing in the way of using these
emitters as a key component in quantum communication applications, e.g. as an
entangled source for quantum repeater architectures
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