271 research outputs found
Evidence of two-dimensional macroscopic quantum tunneling of a current-biased DC-SQUID
The escape probability out of the superconducting state of a hysteretic
DC-SQUID has been measured at different values of the applied magnetic flux. At
low temperature, the escape current and the width of the probability
distribution are temperature independent but they depend on flux. Experimental
results do not fit the usual one-dimensional (1D) Macroscopic Quantum Tunneling
(MQT) law but are perfectly accounted for by the two-dimensional (2D) MQT
behaviour as we propose here. Near zero flux, our data confirms the recent MQT
observation in a DC-SQUID \cite{Li02}.Comment: 4 pages, 4 figures Accepted to PR
Improving the performance of bright quantum dot single photon sources using amplitude modulation
Single epitaxially-grown semiconductor quantum dots have great potential as
single photon sources for photonic quantum technologies, though in practice
devices often exhibit non-ideal behavior. Here, we demonstrate that amplitude
modulation can improve the performance of quantum-dot-based sources. Starting
with a bright source consisting of a single quantum dot in a fiber-coupled
microdisk cavity, we use synchronized amplitude modulation to temporally filter
the emitted light. We observe that the single photon purity, temporal overlap
between successive emission events, and indistinguishability can be greatly
improved with this technique. As this method can be applied to any triggered
single photon source, independent of geometry and after device fabrication, it
is a flexible approach to improve the performance of solid-state systems, which
often suffer from excess dephasing and multi-photon background emission
Fast Purcell-enhanced single photon source in 1,550-nm telecom band from a resonant quantum dot-cavity coupling
High-bit-rate nanocavity-based single photon sources in the 1,550-nm telecom
band are challenges facing the development of fibre-based long-haul quantum
communication networks. Here we report a very fast single photon source in the
1,550-nm telecom band, which is achieved by a large Purcell enhancement that
results from the coupling of a single InAs quantum dot and an InP photonic
crystal nanocavity. At a resonance, the spontaneous emission rate was enhanced
by a factor of 5 resulting a record fast emission lifetime of 0.2 ns at 1,550
nm. We also demonstrate that this emission exhibits an enhanced anti-bunching
dip. This is the first realization of nanocavity-enhanced single photon
emitters in the 1,550-nm telecom band. This coupled quantum dot cavity system
in the telecom band thus provides a bright high-bit-rate non-classical single
photon source that offers appealing novel opportunities for the development of
a long-haul quantum telecommunication system via optical fibres.Comment: 16 pages, 4 figure
Integrin Activation Promotes Axon Growth on Inhibitory Chondroitin Sulfate Proteoglycans by Enhancing Integrin Signaling
We report on the enhancement of the spontaneous emission in the visible red
spectral range from site-controlled InP/GaInP quantum dots by resonant coupling
to Tammplasmon modes confined beneath gold disks in a hybrid
metal/semiconductor structure. The enhancement of the emission intensity is
confirmed by spatially resolved microphotoluminescence area scans and
temperature dependent measurements. Single photon emission from our coupled
system is verified via second order autocorrelation measurements. We observe
bright single quantum dot emission of up to ~173000 detected photons per second
at a repetition rate of the excitation source of 82 MHz, and calculate an
extraction efficiency of our device as high as 7%
In vitro activity of the ÎČ-lactamase inhibitor NXL104 against KPC-2 carbapenemase and Enterobacteriaceae expressing KPC carbapenemases
Engineering of quantum dot photon sources via electro-elastic fields
The possibility to generate and manipulate non-classical light using the
tools of mature semiconductor technology carries great promise for the
implementation of quantum communication science. This is indeed one of the main
driving forces behind ongoing research on the study of semiconductor quantum
dots. Often referred to as artificial atoms, quantum dots can generate single
and entangled photons on demand and, unlike their natural counterpart, can be
easily integrated into well-established optoelectronic devices. However, the
inherent random nature of the quantum dot growth processes results in a lack of
control of their emission properties. This represents a major roadblock towards
the exploitation of these quantum emitters in the foreseen applications. This
chapter describes a novel class of quantum dot devices that uses the combined
action of strain and electric fields to reshape the emission properties of
single quantum dots. The resulting electro-elastic fields allow for control of
emission and binding energies, charge states, and energy level splittings and
are suitable to correct for the quantum dot structural asymmetries that usually
prevent these semiconductor nanostructures from emitting polarization-entangled
photons. Key experiments in this field are presented and future directions are
discussed.Comment: to appear as a book chapter in a compilation "Engineering the
Atom-Photon Interaction" published by Springer in 2015, edited by A.
Predojevic and M. W. Mitchel
Effects of decoherence and errors on Bell-inequality violation
We study optimal conditions for violation of the Clauser-Horne-Shimony-Holt
form of the Bell inequality in the presence of decoherence and measurement
errors. We obtain all detector configurations providing the maximal Bell
inequality violation for a general (pure or mixed) state. We consider local
decoherence which includes energy relaxation at the zero temperature and
arbitrary dephasing. Conditions for the maximal Bell-inequality violation in
the presence of decoherence are analyzed both analytically and numerically for
the general case and for a number of important special cases. Combined effects
of measurement errors and decoherence are also discussed.Comment: 18 pages, 5 figure
Single-photon sources for quantum technologies - Results of the joint research project SIQUTE
Spin-photon interface and spin-controlled photon switching in a nanobeam waveguide
Access to the electron spin is at the heart of many protocols for integrated
and distributed quantum-information processing [1-4]. For instance, interfacing
the spin-state of an electron and a photon can be utilized to perform quantum
gates between photons [2,5] or to entangle remote spin states [6-9].
Ultimately, a quantum network of entangled spins constitutes a new paradigm in
quantum optics [1]. Towards this goal, an integrated spin-photon interface
would be a major leap forward. Here we demonstrate an efficient and optically
programmable interface between the spin of an electron in a quantum dot and
photons in a nanophotonic waveguide. The spin can be deterministically prepared
with a fidelity of 96\%. Subsequently the system is used to implement a
"single-spin photonic switch", where the spin state of the electron directs the
flow of photons through the waveguide. The spin-photon interface may enable
on-chip photon-photon gates [2], single-photon transistors [10], and efficient
photonic cluster state generation [11]
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