142 research outputs found
Energy-tunable sources of entangled photons: a viable concept for solid-state-based quantum relays
We propose a new method of generating triggered entangled photon pairs with
wavelength on demand. The method uses a micro-structured
semiconductor-piezoelectric device capable of dynamically reshaping the
electronic properties of self-assembled quantum dots (QDs) via anisotropic
strain-engineering. Theoretical models based on kp theory in combination with
finite-element calculations show that the energy of the polarization-entangled
photons emitted by QDs can be tuned in a range larger than 100 meV without
affecting the degree of entanglement of the quantum source. These results pave
the way towards the deterministic implementation of QD entanglement resources
in all-electrically-controlled solid-state-based quantum relays
Highly entangled photons from hybrid piezoelectric-semiconductor quantum dot devices
Entanglement resources are key ingredients of future quantum technologies. If
they could be efficiently integrated into a semiconductor platform a new
generation of devices could be envisioned, whose quantum-mechanical
functionalities are controlled via the mature semiconductor technology.
Epitaxial quantum dots (QDs) embedded in diodes would embody such ideal quantum
devices, but QD structural asymmetries lower dramatically the degree of
entanglement of the sources and hamper severely their real exploitation in the
foreseen applications. In this work, we overcome this hurdle using
strain-tunable optoelectronic devices, where any QD can be tuned for the
emission of highly polarization-entangled photons. The electrically-controlled
sources violate Bell inequalities without the need of spectral or temporal
filtering and they feature the highest degree of entanglement ever reported for
QDs, with concurrence as high as 0.75(2). These quantum-devices are at present
the most promising candidates for the direct implementation of QD-based
entanglement-resources in quantum information science and technology
Phase Locking in Heisenberg Helimagnets
We consider a Heisenberg model with ferromagnetic nearest‐neighbor and competing further‐neighbor exchange interactions in a small applied magnetic field at low temperature T. As a function of the exchange constants, the modulation vector is shown to have devil’s staircase behavior. We consider the effects of nonzero temperature and quantum effects. We find a special modulation wave vector at which the incommensurability energy vanishes for the classical system at T=0
Locking of Commensurate Phases in the Planar Model in an External Magnetic Field
Commensurate configuration locking is known in models like the anisotropic next-nearest-neighbor Ising model and the Frenkel-Kontorova model. We find an analogous scenario in the planar model with competing interactions when an external magnetic field is applied in the plane in which the spins lie. This model falls in the same symmetry class of the Heisenberg model with planar anisotropy. We performed a low-field, low-temperature expansion for the free energy of the model and we find phase locking energy for states with wave vectors of the form G/p where p is an integer and G is a reciprocal-lattice vector. The helix characterized by p=3 is peculiar because the commensuration energy vanishes at zero temperature. The helix corresponding to p=4 is not stable against the switching of a magnetic field that forces the spins into an up-up-down-down configuration analogous to the spin-flop phase of an antiferromagnet. For a generic commensurate value of p\u3e4, we expect locking both at zero and finite temperature as we have verified for p=5 and 6. The consequences of our results are examined for the 3N model (a tetragonal spin lattice with in-plane competitive interactions up to third-nearest neighbors)
A hybrid (Al)GaAs-LiNbO3 surface acoustic wave resonator for cavity quantum dot optomechanics
A hybrid device comprising a (Al)GaAs quantum dot heterostructure and a
LiNbO surface acoustic wave resonator is fabricated by heterointegration.
High acoustic quality factors are demonstrated for an operation
frequency MHz. The measured large quality factor-frequency
products ensures the suppression of decoherence due to
thermal noise for temperatures exceeding . Frequency and
position dependent optomechanical coupling of single quantum dots and the
resonator modes is observed.Comment: Accepted manuscrip
Enhancing the optical excitation efficiency of a single self-assembled quantum dot with a plasmonic nanoantenna
We demonstrate how the controlled positioning of a plasmonic nanoparticle
modifies the photoluminescence of a single epitaxial GaAs quantum dot. The
antenna particle leads to an increase of the luminescence intensity by about a
factor of eight. Spectrally and temporally resolved photoluminescence
measurements prove an increase of the quantum dot's excitation rate. The
combination of stable epitaxial quantum emitters and plasmonic nanostructures
promises to be highly beneficial for nanoscience and quantum optics.Comment: 5 pages, 4 figure
Quantum dots for photonic quantum information technology
The generation, manipulation, storage, and detection of single photons play a
central role in emerging photonic quantum information technology. Individual
photons serve as flying qubits and transmit the quantum information at high
speed and with low losses, for example between individual nodes of quantum
networks. Due to the laws of quantum mechanics, quantum communication is
fundamentally tap-proof, which explains the enormous interest in this modern
information technology. On the other hand, stationary qubits or photonic states
in quantum computers can potentially lead to enormous increases in performance
through parallel data processing, to outperform classical computers in specific
tasks when quantum advantage is achieved. Here, we discuss in depth the great
potential of quantum dots (QDs) in photonic quantum information technology. In
this context, QDs form a key resource for the implementation of quantum
communication networks and photonic quantum computers because they can generate
single photons on-demand. Moreover, QDs are compatible with the mature
semiconductor technology, so that they can be integrated comparatively easily
into nanophotonic structures, which form the basis for quantum light sources
and integrated photonic quantum circuits. After a thematic introduction, we
present modern numerical methods and theoretical approaches to device design
and the physical description of quantum dot devices. We then present modern
methods and technical solutions for the epitaxial growth and for the
deterministic nanoprocessing of quantum devices based on QDs. Furthermore, we
present the most promising concepts for quantum light sources and photonic
quantum circuits that include single QDs as active elements and discuss
applications of these novel devices in photonic quantum information technology.
We close with an overview of open issues and an outlook on future developments.Comment: Copyright 2023 Optica Publishing Group. One print or electronic copy
may be made for personal use only. Systematic reproduction and distribution,
duplication of any material in this paper for a fee or for commercial
purposes, or modifications of the content of this paper are prohibite
Two-photon interference from two blinking quantum emitters
We investigate the effect of blinking on the two-photon interference
measurement from two independent quantum emitters. We find that blinking
significantly alters the statistics in the second-order intensity correlation
function g and the outcome of two-photon interference
measurements performed with independent quantum emitters. We theoretically
demonstrate that the presence of blinking can be experimentally recognized by a
deviation from the g value when distinguishable photons
impinge on a beam splitter. Our results show that blinking imposes a mandatory
cross-check measurement to correctly estimate the degree of
indistinguishablility of photons emitted by independent quantum emitters
Independent control of exciton and biexciton energies in single quantum dots via electroelastic fields
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Inversion of the exciton built-in dipole moment in In(Ga)As quantum dots via nonlinear piezoelectric effect
We show that anisotropic biaxial stress can be used to tune the built-in
dipole moment of excitons confined in In(Ga)As quantum dots up to complete
erasure of its magnitude and inversion of its sign. We demonstrate that this
phenomenon is due to piezoelectricity. We present a model to calculate the
applied stress, taking advantage of the so-called piezotronic effect, which
produces significant changes in the current-voltage characteristics of the
strained diode-membranes containing the quantum dots. Finally, self-consistent
k.p calculations reveal that the experimental findings can be only accounted
for by the nonlinear piezoelectric effect, whose importance in quantum dot
physics has been theoretically recognized although it has proven difficult to
single out experimentally.Comment: 6 pages, 4 figure
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