| 1. |
- Elshaari, Ali W., et al.
(author)
-
Strain-Tunable Quantum Integrated Photonics
- 2018
-
In: Nano letters (Print). - : American Chemical Society (ACS). - 1530-6984 .- 1530-6992. ; 18:12, s. 7969-7976
-
Journal article (peer-reviewed)abstract
- Semiconductor quantum dots are crucial parts of the photonic quantum technology toolbox because they show excellent single-photon emission properties in addition to their potential as solid-state qubits. Recently, there has been an increasing effort to deterministically integrate single semiconductor quantum dots into complex photonic circuits. Despite rapid progress in the field, it remains challenging to manipulate the optical properties of waveguide-integrated quantum emitters in a deterministic, reversible, and nonintrusive manner. Here we demonstrate a new class of hybrid quantum photonic circuits combining III V semiconductors, silicon nitride, and piezoelectric crystals. Using a combination of bottom-up, top-down, and nanomanipulation techniques, we realize strain tuning of a selected, waveguide-integrated, quantum emitter and a planar integrated optical resonator. Our findings are an important step toward realizing reconfigurable quantum-integrated photonics, with full control over the quantum sources and the photonic circuit.
|
|
| 2. |
- Gutzat, Ruben, et al.
(author)
-
Arabidopsis shoot stem cells display dynamic transcription and DNA methylation patterns
- 2020
-
In: EMBO Journal. - : EMBO. - 0261-4189 .- 1460-2075. ; 39:20
-
Journal article (peer-reviewed)abstract
- In plants, aerial organs originate continuously from stem cells in the center of the shoot apical meristem. Descendants of stem cells in the subepidermal layer are progenitors of germ cells, giving rise to male and female gametes. In these cells, mutations, including insertions of transposable elements or viruses, must be avoided to preserve genome integrity across generations. To investigate the molecular characteristics of stem cells inArabidopsis, we isolated their nuclei and analyzed stage-specific gene expression andDNAmethylation in plants of different ages. Stem cell expression signatures are largely defined by developmental stage but include a core set of stem cell-specific genes, among which are genes implicated in epigenetic silencing. Transiently increased expression of transposable elements in meristems prior to flower induction correlates with increasingCHGmethylation during development and decreasedCHHmethylation, before stem cells enter the reproductive lineage. These results suggest that epigenetic reprogramming may occur at an early stage in this lineage and could contribute to genome protection in stem cells during germline development.
|
|
| 3. |
- Gyger, Samuel, et al.
(author)
-
Metropolitan single-photon distribution at 1550 nm for random number generation
- 2022
-
In: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 121:19, s. 194003-
-
Journal article (peer-reviewed)abstract
- Quantum communication networks will connect future generations of quantum processors, enable metrological applications, and provide security through quantum key distribution. We present a testbed that is part of the municipal fiber network in the greater Stockholm metropolitan area for quantum resource distribution through a 20 km long fiber based on semiconductor quantum dots emitting in the telecom C-band. We utilize the service to generate random numbers passing the NIST test suite SP800-22 at a subscriber 8 km outside of the city with a bit rate of 23.4 kbit/s.
|
|
| 4. |
- Gyger, Samuel, et al.
(author)
-
Metropolitan Single-Photon Distribution at 1550 nm for Random Number Generation
- 2023
-
In: 2023 Conference on Lasers and Electro-Optics, CLEO 2023. - : Institute of Electrical and Electronics Engineers Inc..
-
Conference paper (peer-reviewed)abstract
- Quantum communication networks are used for QKD and metrological applications. We present research connecting two nodes ≈ 20 kilometers apart over the municipal fiber network using semiconductor quantum dots emitting at 1550 nm.
|
|
| 5. |
- Hanschke, Lukas, et al.
(author)
-
Coherent scattering: either sub-natural linewidth or anti-bunched light
-
Other publication (other academic/artistic)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.
|
|
| 6. |
- Hanschke, Lukas, et al.
(author)
-
Origin of Antibunching in Resonance Fluorescence
- 2020
-
In: Physical Review Letters. - : American Physical Society. - 0031-9007 .- 1079-7114. ; 125:17
-
Journal article (peer-reviewed)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.
|
|
| 7. |
- Lettner, Thomas
(author)
-
Bright and strain-tunable semiconductor quantum dot devices
- 2021
-
Doctoral thesis (other academic/artistic)abstract
- Optically active semiconductor quantum dots have proven to be excellent single- and entangled-photon sources, with applications in quantum optics and quantum photonics. These sources are considered crucial in the development of future photonic quantum technology, such as quantum communication, quantum computation and quantum metrology. In future quantum networks, they allow to share quantum information through optical fiber links and implement secure communication protocols based on quantum key distribution.However, there are several challenges when developing quantum dot devices in order to unlock the full potential of these quantum emitters. The ideal quantum dot source efficiently generates triggered single- and entangled-photons on-demand. It provides further high collection-efficiency, low multi-photon probability, near-unity indistinguishability and high entanglement fidelity. Finally, it also offers compatibility with other systems by providing photons with the desired spectral properties and enabling efficient photon coupling.In this thesis the development and fabrication of bright and strain-tunable quantum dot devices for single- and entangled-photon generation has been studied. It covers highly-symmetric GaAs quantum dots emitting in the near-infrared, InAs quantum dots generating photons in the telecom C-band and InAsP quantum dots embedded in InP nanowires enabling deterministic integration into photonic circuits. The main aspects of operating these quantum dots in cryogenic micro-photoluminescence experiments are described, with focus on enhancing the collection efficiency using solid immersion lenses. For strain-tunability, the focus lies on the fabrication of piezoelectric actuators as substrates for the integration of quantum dot samples by polymer-based bonding. Finally, this thesis describes the simulation, fabrication and measurement of a novel device featuring quantum dots embedded in broad-band parabolic mirror microcavities for enhanced light collection.Experimental results obtained with a variety of quantum dot devices are included: GaAs quantum dot devices featuring solid immersion lenses demonstrate record-low multi-photon probability and near-unity photon indistinguishability. Piezoelectric strain-tunable devices with InAs quantum dots emitting in the telecom C-band allow for on-demand generation of single- and entangled-photons with tunable quantum dot emission properties and high entanglement fidelity. Piezoelectric strain-tuning actuators enable further the realization of reconfigurable quantum photonic circuits featuring waveguide-integrated InAsP/InP nanowire quantum dots with tunable emission wavelength. Finally, GaAs quantum dots in microcavities with parabolic mirror integrated on piezoelectric actuators achieve an increase in brightness by one order of magnitude over planar structures while allowing to tune the emission wavelength to the atomic transition 87Rb D1 relevant for quantum memory applications.
|
|
| 8. |
- Lettner, Thomas, et al.
(author)
-
GaAs Quantum Dot in a Parabolic Microcavity Tuned to Rb-87 D-1
- 2020
-
In: ACS Photonics. - : AMER CHEMICAL SOC. - 2330-4022. ; 7:1, s. 29-35
-
Journal article (peer-reviewed)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).
|
|
| 9. |
- Lettner, Thomas, et al.
(author)
-
Strain-controlled quantum dot fine-structure for entangled-photon generation at 1550 nm
-
Other publication (other academic/artistic)abstract
- Entangled-photon generation at 1550nm in the telecom C-band is of critical importance, since it enables the realization of quantum communication protocols over long distance using deployed telecommunication infrastructure. InAs epitaxial quantum dots have recently enabled on-demand generation of entangled pairs of photons in this wavelength range. However, time-dependent state evolution, caused by the fine-structure splitting, currently limits the fidelity to a specific entangled state. Here, we show suppression of the fine-structure for InAs quantum dots using micromachined piezoelectric actuators and demonstrate generation of highly entangled photons in the telecom C-band. At the lowest fine-structure setting, we obtain a maximum fidelity of (90.0 ± 2.7)% (concurrence of (87.5 ± 3.1)%). The concurrence remains high also for moderate (weak) temporal-filtering, with values close to 80% (50%), corresponding to 30% (80%) of collected photons, respectively. The presented fine-structure control opens the way for the exploitation of entangled photons from quantum dots in fiber-based quantum communication protocols.
|
|
| 10. |
- Lettner, Thomas, et al.
(author)
-
Strain-Controlled Quantum Dot Fine Structure for Entangled Photon Generation at 1550 nm
- 2021
-
In: Nano Letters. - : American Chemical Society (ACS). - 1530-6984 .- 1530-6992. ; 21:24, s. 10501-10506
-
Journal article (peer-reviewed)abstract
- Entangled photon generation at 1550 nm in the telecom C-band is of critical importance as it enables the realization of quantum communication protocols over long distance using deployed telecommunication infrastructure. InAs epitaxial quantum dots have recently enabled on-demand generation of entangled photons in this wavelength range. However, time-dependent state evolution, caused by the fine-structure splitting, currently limits the fidelity to a specific entangled state. Here, we show fine-structure suppression for InAs quantum dots using micromachined piezoelectric actuators and demonstrate generation of highly entangled photons at 1550 nm. At the lowest fine-structure setting, we obtain a maximum fidelity of 90.0 +/- 2.7% (concurrence of 87.5 +/- 3.1%). The concurrence remains high also for moderate (weak) temporal filtering, with values close to 80% (50%), corresponding to 30% (80%) of collected photons, respectively. The presented fine-structure control opens the way for exploiting entangled photons from quantum dots in fiber-based quantum communication protocols.
|
|
