24 research outputs found
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
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
The crux of using the cascaded emission of a 3-level quantum ladder system to generate indistinguishable photons
We investigate the degree of indistinguishability of cascaded photons emitted
from a 3-level quantum ladder system; in our case the biexciton-exciton cascade
of semiconductor quantum dots. For the 3-level quantum ladder system we
theoretically demonstrate that the indistinguishability is inherently limited
for both emitted photons and determined by the ratio of the lifetimes of the
excited and intermediate states. We experimentally confirm this finding by
comparing the quantum interference visibility of non-cascaded emission and
cascaded emission from the same semiconductor quantum dot. Quantum optical
simulations produce very good agreement with the measurements and allow to
explore a large parameter space. Based on our model, we propose photonic
structures to optimize the lifetime ratio and overcome the limited
indistinguishability of cascaded photon emission from a 3-level quantum ladder
system.Comment: We moved the paragraph about asymmetric Purcell enhancement from page
4 bottom to page 5 first colum
The Origin of Antibunching in Resonance Fluorescence
Epitaxial quantum dots have emerged as one of the best single-photon sources,
not only for applications in photonic quantum technologies but also for testing
fundamental properties of quantum optics. One intriguing observation in this
area is the scattering of photons with subnatural linewidth from a two-level
system under resonant continuous wave excitation. In particular, an open
question is whether these subnatural linewidth photons exhibit simultaneously
antibunching as an evidence of single-photon emission. Here, we demonstrate
that this simultaneous observation of subnatural linewidth and antibunching is
not possible with simple resonant excitation. First, we independently confirm
single-photon character and subnatural linewidth by demonstrating antibunching
in a Hanbury Brown and Twiss type setup and using high-resolution spectroscopy,
respectively. However, when filtering the coherently scattered photons with
filter bandwidths on the order of the homogeneous linewidth of the excited
state of the two-level system, the antibunching dip vanishes in the correlation
measurement. Our experimental work is consistent with recent theoretical
findings, that explain antibunching from photon-interferences between the
coherent scattering and a weak incoherent signal in a skewed squeezed state.Comment: 8 pages, 4 figure
Origin of antibunching in resonance fluorescence
Resonance fluorescence has played a major role in quantum optics with predictions and later experimental confirmation of nonclassical features of its emitted light such as antibunching or squeezing. In the Rayleigh regime where most of the light originates from the scattering of photons with subnatural linewidth, antibunching would appear to coexist with sharp spectral lines. Here, we demonstrate that this simultaneous observation of subnatural linewidth and antibunching is not possible with simple resonant excitation. Using an epitaxial quantum dot for the two-level system, we independently confirm the single-photon character and subnatural linewidth by demonstrating antibunching in a Hanbury Brown and Twiss type setup and using high-resolution spectroscopy, respectively. However, when filtering the coherently scattered photons with filter bandwidths on the order of the homogeneous linewidth of the excited state of the two-level system, the antibunching dip vanishes in the correlation measurement. Our observation is explained by antibunching originating from photon-interferences between the coherent scattering and a weak incoherent signal in a skewed squeezed state. This prefigures schemes to achieve simultaneous subnatural linewidth and antibunched emissio