20 research outputs found
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
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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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
Atomic Clouds as Spectrally-Selective and Tunable Delay Lines for Single Photons from Quantum Dots
We demonstrate a compact, spectrally-selective, and tunable delay line for
single photons emitted by quantum dots. This is achieved by fine-tuning the
wavelength of the optical transitions of such "artificial atoms" into a
spectral window in which a cloud of natural atoms behaves as slow-light medium.
By employing the ground-state fine-structure-split exciton confined in an
InGaAs/GaAs quantum dot as a source of single photons at different frequencies
and the hyperfine-structure-split transition of Cs-vapors as a tunable
delay-medium, we achieve a differential delay of up 2.4 ns on a 7.5 cm long
path for photons that are only 60 \mu eV (14.5 GHz) apart. To quantitatively
explain the experimental data we develop a theoretical model that accounts for
both the inhomogeneously broadening of the quantum-dot emission lines and the
Doppler-broadening of the atomic lines. The concept we proposed here may be
used to implement time-reordering operations aimed at erasing the "which-path"
information that deteriorates entangled-photon emission from excitons with
finite fine-structure-splitting.Comment: 29 pages, 5 figure
Slow and fast single photons from a quantum dot interacting with the excited state hyperfine structure of the Cesium D1-line
Hybrid interfaces between distinct quantum systems play a major role in the implementation of quantum networks. Quantum states have to be stored in memories to synchronize the photon arrival times for entanglement swapping by projective measurements in quantum repeaters or for entanglement purification. Here, we analyze the distortion of a single-photon wave packet propagating through a dispersive and absorptive medium with high spectral resolution. Single photons are generated from a single In(Ga)As quantum dot with its excitonic transition precisely set relative to the Cesium D1 transition. The delay of spectral components of the single-photon wave packet with almost Fourier-limited width is investigated in detail with a 200 MHz narrow-band monolithic Fabry-PĂ©rot resonator. Reflecting the excited state hyperfine structure of Cesium, âslow lightâ and âfast lightâ behavior is observed. As a step towards room-temperature alkali vapor memories, quantum dot photons are delayed for 5 ns by strong dispersion between the two 1.17 GHz hyperfine-split excited state transitions. Based on optical pumping on the hyperfine-split ground states, we propose a simple, all-optically controllable delay for synchronization of heralded narrow-band photons in a quantum network.DFG, 43659573, SFB 787: Halbleiter - Nanophotonik: Materialien, Modelle, BauelementeEC/H2020/679183/EU/Entanglement distribution via Semiconductor-Piezoelectric Quantum-Dot Relays/SPQRe
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High yield and ultrafast sources of electrically triggered entangled-photon pairs based on strain-tunable quantum dots
Triggered sources of entangled photon pairs are key components in most quantum communication protocols. For practical quantum applications, electrical triggering would allow the realization of compact and deterministic sources of entangled photons. Entangled-light-emitting-diodes based on semiconductor quantum dots are among the most promising sources that can potentially address this task. However, entangled-light-emitting-diodes are plagued by a source of randomness, which results in a very low probability of finding quantum dots with sufficiently small fine structure splitting for entangled-photon generation (âŒ10â2). Here we introduce strain-tunable entangled-light-emitting-diodes that exploit piezoelectric-induced strains to tune quantum dots for entangled-photon generation. We demonstrate that up to 30% of the quantum dots in strain-tunable entangled-light-emitting-diodes emit polarization-entangled photons. An entanglement fidelity as high as 0.83 is achieved with fast temporal post selection. Driven at high speed, that is 400âMHz, strain-tunable entangled-light-emitting-diodes emerge as promising devices for high data-rate quantum applications
Strain-tunable entangled-light-emitting diodes with high yield and fast operation speed
Triggered sources of entangled photons play crucial roles in almost any
existing protocol of quantum information science. The possibility to generate
these non-classical states of light with high speed and using electrical pulses
could revolutionize the field. Entangled-light-emitting-diodes (ELEDs) based on
semiconductor quantum dots (QDs) are at present the only devices that can
address this task 5. However, ELEDs are plagued by a source of randomness that
hampers their practical exploitation in the foreseen applications: the very low
probability (~10-2) of finding QDs with sufficiently small
fine-structure-splitting for entangled-photon-generation. Here, we overcome
this hurdle by introducing the first strain-tunable ELEDs (S-ELEDs) that
exploit piezoelectric-induced strains to tune QDs for
entangled-photon-generation. We demonstrate that up to 30% of the QDs in
S-ELEDs emit polarization-entangled photon pairs with entanglement-fidelities
as high as f+ = 0.83(5). Driven at the highest operation speed of 400 MHz ever
reported so far, S-ELEDs emerge as unique devices for high-data rate
entangled-photon applications.Comment: 28 pages in total, including supplementary information. 5 figure
Electrically-Pumped Wavelength-Tunable GaAs Quantum Dots Interfaced with Rubidium Atoms
We demonstrate the first wavelength-tunable electrically-pumped source of
non-classical light that can emit photons with wavelength in resonance with the
D2 transitions of 87Rb atoms. The device is fabricated by integrating a novel
GaAs single-quantum-dot light-emitting-diode (LED) onto a piezoelectric
actuator. By feeding the emitted photons into a 75-mm-long cell containing warm
87Rb atom vapor, we observe slow-light with a temporal delay of up to 3.4 ns.
In view of the possibility of using 87Rb atomic vapors as quantum memories,
this work makes an important step towards the realization of hybrid-quantum
systems for future quantum networks
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