| 1. |
- Hanschke, Lukas, et al.
(författare)
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Coherent scattering: either sub-natural linewidth or anti-bunched light
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- 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 emission 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 single–photon characteristics, i.e. show antibunching as a signature of single-photon emission. Here, we demonstrate that this simultaneous observation of subnatural–linewidth and single photoncharacter 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, and can be explained by a fundamental model considering higher-order photon correlations.
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| 2. |
- Hanschke, Lukas, et al.
(författare)
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Origin of Antibunching in Resonance Fluorescence
- 2020
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Ingår i: Physical Review Letters. - : American Physical Society. - 0031-9007 .- 1079-7114. ; 125:17
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Tidskriftsartikel (refereegranskat)abstract
- 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 emission.
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| 3. |
- Lettner, Thomas, et al.
(författare)
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GaAs Quantum Dot in a Parabolic Microcavity Tuned to Rb-87 D-1
- 2020
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Ingår i: ACS Photonics. - : AMER CHEMICAL SOC. - 2330-4022. ; 7:1, s. 29-35
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Tidskriftsartikel (refereegranskat)abstract
- We develop a structure to efficiently extract photons emitted by a GaAs quantum dot tuned to rubidium. For this, we employ a broadband microcavity with a curved gold backside mirror that we fabricate by a combination of photoresist reflow, dry reactive ion etching in an inductively coupled plasma, and selective wet chemical etching. Precise reflow and etching control allows us to achieve a parabolic backside mirror with a short focal distance of 265 nm. The fabricated structures yield a predicted (measured) collection efficiency of 63% (12%), an improvement by more than 1 order of magnitude compared to unprocessed samples. We then integrate our quantum dot parabolic microcavities onto a piezoelectric substrate capable of inducing a large in-plane biaxial strain. With this approach, we tune the emission wavelength by 0.5 nm/kV, in a dynamic, reversible, and linear way, to the rubidium D-1 line (795 nm).
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| 4. |
- Schweickert, Lucas, et al.
(författare)
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On-demand generation of background-free single photons from a solid-state source
- 2018
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Ingår i: Applied Physics Letters. - : American Institute of Physics (AIP). - 0003-6951 .- 1077-3118. ; 112:9
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Tidskriftsartikel (refereegranskat)abstract
- 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 g((2)) (0) = (7.5 +/- 1.6) x 10(-5) without any background subtraction or data processing. To this date, this is the lowest value of g((2)) (0) Peported for any single-photon source even compared to the previously reported 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 (0.0056 +/- 0.0007) s(-1) and (0.017 +/- 0.001) s(-1), respectively. Re-excitation processes are dramatically suppressed by (i), while (ii) removes false coincidences resulting in a negligibly low noise floor.
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| 5. |
- Schöll, Eva, et al.
(författare)
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Crux of Using the Cascaded Emission of a Three-Level Quantum Ladder System to Generate Indistinguishable Photons
- 2020
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Ingår i: Physical Review Letters. - : American Physical Society. - 0031-9007 .- 1079-7114. ; 125:23
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Tidskriftsartikel (refereegranskat)abstract
- We investigate the degree of indistinguishability of cascaded photons emitted from a three-level quantum ladder system; in our case the biexciton-exciton cascade of semiconductor quantum dots. For the three-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 noncascaded emission and cascaded emission from the same semiconductor quantum dot. Quantum optical simulations produce very good agreement with the measurements and allow us 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 three-level quantum ladder system.
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| 6. |
- Schöll, Eva, et al.
(författare)
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Resonance Fluorescence of GaAs Quantum Dots with Near-Unity Photon Indistinguishability
- 2019
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Ingår i: Nano letters (Print). - : AMER CHEMICAL SOC. - 1530-6984 .- 1530-6992. ; 19:4, s. 2404-2410
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Tidskriftsartikel (refereegranskat)abstract
- 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 is strain free GaAs/A1GaAs quantum dots obtained by aluminum 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 and trions confined in the GaAs quantum dots, we show single photon indistinguishability with a raw visibility of V-raw = (95.0(-6.1)(+5.0))%, 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 quantum light sources for quantum repeater architectures.
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| 7. |
- Schöll, Eva, et al.
(författare)
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The crux of using the cascaded emission of a 3-level quantum ladder system to generate indistinguishable photons
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- 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 too ptimize the lifetime ratio and overcome the limited indistinguishability of cascaded photon emission from a 3–level quantum ladder system.
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