56 research outputs found
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
High-yield fabrication of entangled photon emitters for hybrid quantum networking using high-temperature droplet epitaxy
Several semiconductor quantum dot techniques have been investigated for the
generation of entangled photon pairs. Among the other techniques, droplet
epitaxy enables the control of the shape, size, density, and emission
wavelength of the quantum emitters. However, the fraction of the
entanglement-ready quantum dots that can be fabricated with this method is
still limited to around 5%, and matching the energy of the entangled photons to
atomic transitions (a promising route towards quantum networking) remains an
outstanding challenge.
Here, we overcome these obstacles by introducing a modified approach to
droplet epitaxy on a high symmetry (111)A substrate, where the fundamental
crystallization step is performed at a significantly higher temperature as
compared to previous reports. Our method drastically improves the yield of
entanglement-ready photon sources near the emission wavelength of interest,
which can be as high as 95% due to the low values of fine structure splitting
and radiative lifetime, together with the reduced exciton dephasing offered by
the choice of GaAs/AlGaAs materials. The quantum dots are designed to emit in
the operating spectral region of Rb-based slow-light media, providing a viable
technology for quantum repeater stations.Comment: 14 pages, 3 figure
Strain-Tunable GaAs Quantum dot: A Nearly Dephasing-Free Source of Entangled Photon Pairs on Demand
Entangled photon generation from semiconductor quantum dots via the
biexciton-exciton cascade underlies various decoherence mechanisms related to
the solid-state nature of the quantum emitters. So far, this has prevented the
demonstration of nearly-maximally entangled photons without the aid of
inefficient and complex post-selection techniques that are hardly suitable for
quantum communication technologies. Here, we tackle this challenge using
strain-tunable GaAs quantum dots driven under two-photon resonant excitation
and with strictly-degenerate exciton states. We demonstrate experimentally that
our on-demand source generates polarization-entangled photons with fidelity of
0.978(5) and concurrence of 0.97(1) without resorting to post-selection
techniques. Moreover, we show that the remaining decoherence mechanisms can be
overcome using a modest Purcell enhancement so as to achieve a degree of
entanglement >0.99. Our results highlight that GaAs quantum dots can be readily
used in advanced communication protocols relying on the non-local properties of
quantum entanglement
Highly indistinguishable single photons from incoherently and coherently excited GaAs quantum dots
Semiconductor quantum dots are converging towards the demanding requirements
of photonic quantum technologies. Among different systems, quantum dots with
dimensions exceeding the free-exciton Bohr radius are appealing because of
their high oscillator strengths. While this property has received much
attention in the context of cavity quantum electrodynamics, little is known
about the degree of indistinguishability of single photons consecutively
emitted by such dots and on the proper excitation schemes to achieve high
indistinguishability. A prominent example is represented by GaAs quantum dots
obtained by local droplet etching, which recently outperformed other systems as
triggered sources of entangled photon pairs. On these dots, we compare
different single-photon excitation mechanisms, and we find (i) a "phonon
bottleneck" and poor indistinguishability for conventional excitation via
excited states and (ii) photon indistinguishablilities above 90% for both
strictly resonant and for incoherent acoustic- and optical-phonon-assisted
excitation. Among the excitation schemes, optical phonon-assisted excitation
enables straightforward laser rejection without a compromise on the source
brightness together with a high photon indistinguishability
On-demand generation of background--free single photons from a solid-state source
True on--demand high--repetition--rate single--photon sources are highly
sought after for quantum information processing applications. However, any
coherently driven two-level quantum system suffers from a finite re-excitation
probability under pulsed excitation, causing undesirable multi--photon
emission. Here, we present a solid--state source of on--demand single photons
yielding a raw second--order coherence of
without any background subtraction nor data processing. To this date, this is
the lowest value of reported for any single--photon source even
compared to the previously best background subtracted values. We achieve this
result on GaAs/AlGaAs quantum dots embedded in a low--Q planar cavity by
employing (i) a two--photon excitation process and (ii) a filtering and
detection setup featuring two superconducting single--photon detectors with
ultralow dark-count rates of and , respectively. Re--excitation processes are dramatically suppressed by
(i), while (ii) removes false coincidences resulting in a negligibly low noise
floor
Entanglement swapping with photons generated on-demand by a quantum dot
Photonic entanglement swapping, the procedure of entangling photons without
any direct interaction, is a fundamental test of quantum mechanics and an
essential resource to the realization of quantum networks. Probabilistic
sources of non-classical light can be used for entanglement swapping, but
quantum communication technologies with device-independent functionalities
demand for push-button operation that, in principle, can be implemented using
single quantum emitters. This, however, turned out to be an extraordinary
challenge due to the stringent requirements on the efficiency and purity of
generation of entangled states. Here we tackle this challenge and show that
pairs of polarization-entangled photons generated on-demand by a GaAs quantum
dot can be used to successfully demonstrate all-photonic entanglement swapping.
Moreover, we develop a theoretical model that provides quantitative insight on
the critical figures of merit for the performance of the swapping procedure.
This work shows that solid-state quantum emitters are mature for quantum
networking and indicates a path for scaling up.Comment: The first four authors contributed equally to this work. 17 pages, 3
figure
An artificial Rb atom in a semiconductor with lifetime-limited linewidth
We report results important for the creation of a best-of-both-worlds quantum
hybrid system consisting of a solid-state source of single photons and an
atomic ensemble as quantum memory. We generate single photons from a GaAs
quantum dot (QD) frequency-matched to the Rb D2-transitions and then use the Rb
transitions to analyze spectrally the quantum dot photons. We demonstrate
lifetime-limited QD linewidths (1.48 GHz) with both resonant and non-resonant
excitation. The QD resonance fluorescence in the low power regime is dominated
by Rayleigh scattering, a route to match quantum dot and Rb atom linewidths and
to shape the temporal wave packet of the QD photons. Noise in the solid-state
environment is relatively benign: there is a blinking of the resonance
fluorescence at MHz rates but negligible upper state dephasing of the QD
transition. We therefore establish a close-to-ideal solid-state source of
single photons at a key wavelength for quantum technologies
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Phonon-Assisted Two-Photon Interference from Remote Quantum Emitters
Photonic quantum technologies are on the verge of finding applications in everyday life with quantum cryptography and quantum simulators on the horizon. Extensive research has been carried out to identify suitable quantum emitters and single epitaxial quantum dots have emerged as near-optimal sources of bright, on-demand, highly indistinguishable single photons and entangled photon-pairs. In order to build up quantum networks, it is essential to interface remote quantum emitters. However, this is still an outstanding challenge, as the quantum states of dissimilar “artificial atoms” have to be prepared on-demand with high fidelity and the generated photons have to be made indistinguishable in all possible degrees of freedom. Here, we overcome this major obstacle and show an unprecedented two-photon interference (visibility of 51 ± 5%) from remote strain-tunable GaAs quantum dots emitting on-demand photon-pairs. We achieve this result by exploiting for the first time the full potential of a novel phonon-assisted two-photon excitation scheme, which allows for the generation of highly indistinguishable (visibility of 71 ± 9%) entangled photon-pairs (fidelity of 90 ± 2%), enables push-button biexciton state preparation (fidelity of 80 ± 2%) and outperforms conventional resonant two-photon excitation schemes in terms of robustness against environmental decoherence. Our results mark an important milestone for the practical realization of quantum repeaters and complex multiphoton entanglement experiments involving dissimilar artificial atoms
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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