13 research outputs found
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
Robust excitation of C-band quantum dots for quantum communication
Building a quantum internet requires efficient and reliable quantum hardware,
from photonic sources to quantum repeaters and detectors, ideally operating at
telecommunication wavelengths. Thanks to their high brightness and
single-photon purity, quantum dot (QD) sources hold the promise to achieve high
communication rates for quantum-secured network applications. Furthermore, it
was recently shown that excitation schemes, such as longitudinal acoustic
phonon-assisted (LA) pumping, provide security benefits by scrambling the
coherence between the emitted photon-number states. In this work, we
investigate further advantages of LA-pumped quantum dots with emission in the
telecom C-band as a core hardware component of the quantum internet. We
experimentally demonstrate how varying the pump energy and spectral detuning
with respect to the excitonic transition can improve quantum-secured
communication rates and provide stable emission statistics regardless of
network-environment fluctuations. These findings have significant implications
for general implementations of QD single-photon sources in practical quantum
communication networks
Triggered telecom C-band single-photon source with high brightness, high indistinguishability and sub-GHz spectral linewidth
Long-range, terrestrial quantum networks will require high brightness
single-photon sources emitting in the telecom C-band for maximum transmission
rate. Many applications additionally demand triggered operation with high
indistinguishability and narrow spectral linewidth. This would enable the
efficient implementation of photonic gate operations and photon storage in
quantum memories, as for instance required for a quantum repeater. Especially,
semiconductor quantum dots (QDs) have shown these properties in the
near-infrared regime. However, the simultaneous demonstration of all these
properties in the telecom C-band has been elusive. Here, we present a
coherently (incoherently) optically-pumped narrow-band (0.8 GHz) triggered
single-photon source in the telecom C-band. The source shows simultaneously
high single-photon purity with (),
high two-photon interference visibility of 0.508 (0.664) and high
application-ready rates of 0.75 MHz (1.45 MHz) of polarized photons. The source
is based on a QD coupled to a circular Bragg grating cavity combined with
spectral filtering. Coherent (incoherent) operation is performed via the novel
SUPER scheme (phonon-assisted excitation)
Highly indistinguishable single photons from droplet-etched GaAs quantum dots integrated in single-mode waveguides and beamsplitters
The integration of on-demand quantum emitters into photonic integrated
circuits (PICs) has drawn much of attention in recent years, as it promises a
scalable implementation of quantum information schemes. A central property for
several applications is the indistinguishability of the emitted photons. In
this regard, GaAs quantum dots (QDs) obtained by droplet etching epitaxy show
excellent performances with visibilities close to one for both individual and
remote emitters. Therefore, the realization of these QDs into PICs is highly
appealing. Here, we show the first implementation in this direction, realizing
the key passive elements needed in PICs, i.e. single-mode waveguides (WGs) with
integrated GaAs-QDs, which can be coherently controlled, as well as
beamsplitters. We study both the statistical distribution of wavelength,
linewidth and decay times of the excitonic line of multiple QDs, as well as the
quantum optical properties of individual emitters under resonant excitation.
Here, we achieve single-photon purities as high as
as well as two-photon interference
visibilities of up to V for two consecutively
emitted photons
Novel Photonic Crystal Nanocavity Design with high Tolerance to Disorder
We propose and experimentally demonstrate a new approach to the design of Photonic Crystal cavities. Rather than simply maximizing the design Q-factor, we take the effects of disorder into account, and develop a design that provides superior Q factors in the presence of disorder relative to existing designs.</p
Planar photonic crystal cavities with far-field optimization for high coupling efficiency and quality factor
We have designed and experimentally probed different types of planar photonic crystal cavities aimed at optimizing the far-field emission pattern. We systematically investigate the interplay between achieving the highest possible quality (Q) factor and maximizing the in- and out-coupling efficiency into a narrow emission cone. Cavities operate at telecommunications wavelengths, i.e. around ~1.55 microns, and are realized in silicon membranes. A strong modification of the far-field emission pattern, and therefore a substantial increase of the coupling efficiency in the vertical direction, is obtained by properly modifying the holes around L3, L5 and L7 type PhC cavities, as we predict theoretically and show experimentally. An optimal compromise yielding simultaneously a high Q-factor and a large coupling to the fundamental cavity mode is found for a L7-type cavity with a measured Q~62000, whose resonant scattering efficiency is improved by about two orders of magnitude with respect to the unmodified structure. These results are especially useful for prospective applications in light emitting devices, such as nano-lasers or single-photon sources, in which vertical in- and out-coupling of the electromagnetic field is necessarily required
Nonlinear optics in silicon photonic crystal nanocavities
Second- and third-harmonic generation in silicon photonic crystal nanocavities using a low-power, continuous wave laser at telecommunication wavelengths is demonstrated. This is achieved by employing cavities that are optimized for high quality factor and efficient coupling to the incoming beam in the far field