27 research outputs found
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Wavelength-tunable sources of entangled photons interfaced with atomic vapours
The prospect of using the quantum nature of light for secure communication keeps spurring
the search and investigation of suitable sources of entangled photons. A single semiconductor
quantum dot is one of the most attractive, as it can generate indistinguishable
entangled photons deterministically and is compatible with current photonic-integration
technologies. However, the lack of control over the energy of the entangled photons is
hampering the exploitation of dissimilar quantum dots in protocols requiring the teleportation
of quantum entanglement over remote locations. Here we introduce quantum dot-based
sources of polarization-entangled photons whose energy can be tuned via three-directional
strain engineering without degrading the degree of entanglement of the photon pairs. As a
test-bench for quantum communication, we interface quantum dots with clouds of atomic
vapours, and we demonstrate slow-entangled photons from a single quantum emitter. These
results pave the way towards the implementation of hybrid quantum networks where
entanglement is distributed among distant parties using optoelectronic devices
Experimental Multi-state Quantum Discrimination in the Frequency Domain with Quantum Dot Light
The quest for the realization of effective quantum state discrimination
strategies is of great interest for quantum information technology, as well as
for fundamental studies. Therefore, it is crucial to develop new and more
efficient methods to implement discrimination protocols for quantum states.
Among the others, single photon implementations are more advisable, because of
their inherent security advantage in quantum communication scenarios. In this
work, we present the experimental realization of a protocol employing a
time-multiplexing strategy to optimally discriminate among eight non-orthogonal
states, encoded in the four-dimensional Hilbert space spanning both the
polarization degree of freedom and photon energy. The experiment, built on a
custom-designed bulk optics analyser setup and single photons generated by a
nearly deterministic solid-state source, represents a benchmarking example of
minimum error discrimination with actual quantum states, requiring only linear
optics and two photodetectors to be realized. Our work paves the way for more
complex applications and delivers a novel approach towards high-dimensional
quantum encoding and decoding operations
Strain-Tuning of the Optical Properties of Semiconductor Nanomaterials by Integration onto Piezoelectric Actuators
The tailoring of the physical properties of semiconductor nanomaterials by
strain has been gaining increasing attention over the last years for a wide
range of applications such as electronics, optoelectronics and photonics. The
ability to introduce deliberate strain fields with controlled magnitude and in
a reversible manner is essential for fundamental studies of novel materials and
may lead to the realization of advanced multi-functional devices. A prominent
approach consists in the integration of active nanomaterials, in thin epitaxial
films or embedded within carrier nanomembranes, onto
Pb(Mg1/3Nb2/3)O3-PbTiO3-based piezoelectric actuators, which convert electrical
signals into mechanical deformation (strain). In this review, we mainly focus
on recent advances in strain-tunable properties of self-assembled InAs quantum
dots embedded in semiconductor nanomembranes and photonic structures.
Additionally, recent works on other nanomaterials like rare-earth and metal-ion
doped thin films, graphene and MoS2 or WSe2 semiconductor two-dimensional
materials are also reviewed. For the sake of completeness, a comprehensive
comparison between different procedures employed throughout the literature to
fabricate such hybrid piezoelectric-semiconductor devices is presented. Very
recently, a novel class of micro-machined piezoelectric actuators have been
demonstrated for a full control of in-plane stress fields in nanomembranes,
which enables producing energy-tunable sources of polarization-entangled
photons in arbitrary quantum dots. Future research directions and prospects are
discussed.Comment: review manuscript, 78 pages, 27 figure
Signatures of the Optical Stark Effect on Entangled Photon Pairs from Resonantly-Pumped Quantum Dots
Two-photon resonant excitation of the biexciton-exciton cascade in a quantum
dot generates highly polarization-entangled photon pairs in a
near-deterministic way. However, there are still open questions on the ultimate
level of achievable entanglement. Here, we observe the impact of the
laser-induced AC-Stark effect on the spectral emission features and on
entanglement. A shorter emission time, longer laser pulse duration, and higher
pump power all result in lower values of concurrence. Nonetheless, additional
contributions are still required to fully account for the observed below-unity
concurrence.Comment: 7 pages, 3 figure
Strain-induced dynamic control over the population of quantum emitters in two-dimensional materials
The discovery of quantum emitters in two-dimensional materials has triggered
a surge of research to assess their suitability for quantum photonics. While
their microscopic origin is still the subject of intense studies, ordered
arrays of quantum emitters are routinely fabricated using static
strain-gradients, which are used to drive excitons toward localized regions of
the 2D crystals where quantum-light-emission takes place. However, the
possibility of using strain in a dynamic fashion to control the appearance of
individual quantum emitters has never been explored so far. In this work, we
tackle this challenge by introducing a novel hybrid semiconductor-piezoelectric
device in which WSe2 monolayers are integrated onto piezoelectric pillars
delivering both static and dynamic strains. Static strains are first used to
induce the formation of quantum emitters, whose emission shows photon
anti-bunching. Their excitonic population and emission energy are then
reversibly controlled via the application of a voltage to the piezoelectric
pillar. Numerical simulations combined with drift-diffusion equations show that
these effects are due to a strain-induced modification of the
confining-potential landscape, which in turn leads to a net redistribution of
excitons among the different quantum emitters. Our work provides relevant
insights into the role of strain in the formation of quantum emitters in 2D
materials and suggests a method to switch them on and off on demand.Comment: 13 pages, 4 figure
A source of entangled photons based on a cavity-enhanced and strain-tuned GaAs quantum dot
A quantum-light source that delivers photons with a high brightness and a
high degree of entanglement is fundamental for the development of efficient
entanglement-based quantum-key distribution systems. Among all possible
candidates, epitaxial quantum dots are currently emerging as one of the
brightest sources of highly entangled photons. However, the optimization of
both brightness and entanglement currently requires different technologies that
are difficult to combine in a scalable manner. In this work, we overcome this
challenge by developing a novel device consisting of a quantum dot embedded in
a circular Bragg resonator, in turn, integrated onto a micromachined
piezoelectric actuator. The resonator engineers the light-matter interaction to
empower extraction efficiencies up to 0.69(4). Simultaneously, the actuator
manipulates strain fields that tune the quantum dot for the generation of
entangled photons with fidelities up to 0.96(1). This hybrid technology has the
potential to overcome the limitations of the key rates that plague current
approaches to entanglement-based quantum key distribution and
entanglement-based quantum networks. Introductio