| 1. |
- Basset, F. Basso, et al.
(författare)
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Entanglement Swapping with Photons Generated on Demand by a Quantum Dot
- 2019
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Ingår i: Physical Review Letters. - : AMER PHYSICAL SOC. - 0031-9007 .- 1079-7114. ; 123:16
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Tidskriftsartikel (refereegranskat)abstract
- 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 nonclassical light were used for seminal demonstration of entanglement swapping, but applications in quantum technologies demand push-button operation requiring single quantum emitters. This, however, turned out to be an extraordinary challenge due to the stringent prerequisites on the efficiency and purity of the generation of entangled states. Here we show a proof-of-concept demonstration of all-photonic entanglement swapping with pairs of polarization-entangled photons generated on demand by a GaAs quantum dot without spectral and temporal filtering. Moreover, we develop a theoretical model that quantitatively reproduces the experimental data and provides insights on the critical figures of merit for the performance of the swapping operation. Our theoretical analysis also indicates how to improve stateof-the-art entangled-photon sources to meet the requirements needed for implementation of quantum dots in long-distance quantum communication protocols.
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| 2. |
- Gyger, Samuel, et al.
(författare)
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Metropolitan single-photon distribution at 1550 nm for random number generation
- 2022
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 121:19, s. 194003-
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Tidskriftsartikel (refereegranskat)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.
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| 3. |
- Gyger, Samuel, et al.
(författare)
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Metropolitan Single-Photon Distribution at 1550 nm for Random Number Generation
- 2023
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Ingår i: 2023 Conference on Lasers and Electro-Optics, CLEO 2023. - : Institute of Electrical and Electronics Engineers Inc..
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Konferensbidrag (refereegranskat)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.
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| 4. |
- Gyger, Samuel, et al.
(författare)
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Reconfigurable frequency coding of triggered single photons in the telecom C–band
- 2019
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Ingår i: Optics Express. - : OSA. - 1094-4087. ; 27:10, s. 14400-14406
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Tidskriftsartikel (refereegranskat)abstract
- In this work, we demonstrate reconfigurable frequency manipulation of quantum states of light in the telecom C–band. Triggered single photons are encoded in a superposition state of three channels using sidebands up to 53 GHz created by an off-the-shelf phase modulator. The single photons are emitted by an InAs/GaAs quantum dot grown by metal-organic vapor-phase epitaxy within the transparency window of the backbone fiber optical network. A cross-correlation measurement of the sidebands demonstrates the preservation of the single photon nature; an important prerequisite for future quantum technology applications using the existing telecommunication fiber network.
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| 5. |
- Haffouz, Sofiane, et al.
(författare)
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Bright Single InAsP Quantum Dots at Telecom Wavelengths in Position-Controlled InP Nanowires : The Role of the Photonic Waveguide
- 2018
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Ingår i: Nano letters (Print). - : AMER CHEMICAL SOC. - 1530-6984 .- 1530-6992. ; 18:5, s. 3047-3052
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Tidskriftsartikel (refereegranskat)abstract
- We report on the site-selected growth of bright single InAsP quantum dots embedded within InP photonic nanowire waveguides emitting at telecom wavelengths. We demonstrate a dramatic dependence of the emission rate on both the emission wavelength and the nanowire diameter. With an appropriately designed waveguide, tailored to the emission wavelength of the dot, an increase in the count rate by nearly 2 orders of magnitude (0.4 to 35 kcps) is obtained for quantum dots emitting in the telecom O-band, showing high single-photon purity with multiphoton emission probabilities down to 2%. Using emission-wavelength-optimized waveguides, we demonstrate bright, narrow-line-width emission from single InAsP quantum dots with an unprecedented tuning range of 880 to 1550 nm. These results pave the way toward efficient single-photon sources at telecom wavelengths using deterministically grown InAsP/InP nanowire quantum dots.
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| 6. |
- 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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| 7. |
- 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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| 8. |
- Kettler, Jan, et al.
(författare)
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Neutral and charged biexciton-exciton cascade in near-telecom-wavelength quantum dots
- 2016
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Ingår i: PHYSICAL REVIEW B. - 2469-9950. ; 94:4
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Tidskriftsartikel (refereegranskat)abstract
- We investigate the cascaded emission of photons from low-density InGaAs/GaAs quantum dots grown by metal-organic vapor-phase epitaxy that are intentionally redshifted toward telecommunication wavelengths. We observe multiple radiative cascades within a single quantum dot and attribute these to neutral and charged excited configurations. The corresponding transitions are identified by combining microphotoluminescence and photon correlation measurements. Full-configuration interaction calculations further support the identification of the emission lines and provide additional information about the confinement of electron and hole wave functions. We apply a Monte Carlo simulation to estimate the effective spin scattering rates between excited triplet and singlet ground states of the negatively charged trion. These spin-flip processes directly affect the observed radiative cascade.
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| 9. |
- 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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| 10. |
- Lettner, Thomas, et al.
(författare)
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Strain-controlled quantum dot fine-structure for entangled-photon generation at 1550 nm
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Annan publikation (övrigt vetenskapligt/konstnärligt)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.
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| 11. |
- Lettner, Thomas, et al.
(författare)
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Strain-Controlled Quantum Dot Fine Structure for Entangled Photon Generation at 1550 nm
- 2021
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Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6984 .- 1530-6992. ; 21:24, s. 10501-10506
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Tidskriftsartikel (refereegranskat)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.
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| 12. |
- Prencipe, Alessandro, et al.
(författare)
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Wavelength meter on thin film lithium niobate based on superconducting single photon detectors
- 2023
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Ingår i: 2023 Conference on Lasers and Electro-Optics Europe and European Quantum Electronics Conference, CLEO/Europe-EQEC 2023. - : Institute of Electrical and Electronics Engineers (IEEE).
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Konferensbidrag (refereegranskat)abstract
- Photonic integrated circuits (PICs) present significant benefits with respect to table-top optical systems regarding footprint, stability, and power consumption. Among the materials used to fabricate PICs, thin film lithium niobate (TFLN) is one of the most attractive ones, as its χ(2) nonlinearity and electro-optic properties allow to implement on-chip light generation and routing [1]. On-chip detection of light has also been demonstrated on TFLN, based on the waveguide integration of superconducting nanowire single photon detectors (SNSPDs) [1]. Combining efficient detectors with TFLN nanophotonic waveguides holds promises for the realization of quantum photonics experiments fully on-chip. On the other hand, the sensitivity of SNSPDs changes with the wavelength of the detected photons [2], setting a boundary to the longest detectable wavelength and limiting the use of the wide transparency window of TFLN. However, this wavelength dependency in the response of SNSPDs can be leveraged to achieve new on-chip functionalities. In this work, by performing a straightforward analysis of the light signal measured at different bias currents [2], we operate hairpin SNSPDs on TFLN as waveguide-integrated wavelength-meters in the telecom bandwidth.
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| 13. |
- Prencipe, Alessandro, et al.
(författare)
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Wavelength-Sensitive Superconducting Single-Photon Detectors on Thin Film Lithium Niobate Waveguides
- 2023
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Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6984 .- 1530-6992. ; 23:21, s. 9748-9752
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Tidskriftsartikel (refereegranskat)abstract
- Lithium niobate, because of its nonlinear and electro-optical properties, is one of the materials of choice for photonic applications. The development of nanostructuring capabilities of thin film lithium niobate (TFLN) permits fabrication of small footprint, low-loss optical circuits. With the recent implementation of on-chip single-photon detectors, this architecture is among the most promising for realizing on-chip quantum optics experiments. In this Letter, we report on the implementation of superconducting nanowire single-photon detectors (SNSPDs) based on NbTiN on 300 nm thick TFLN ridge nano-waveguides. We demonstrate a waveguide-integrated wavelength meter based on the photon energy dependence of the superconducting detectors. The device operates at the telecom C- and L-bands and has a footprint smaller than 300 × 180 μm2 and critical currents between ∼12 and ∼14 μA, which ensures operation with minimum heat dissipation. Our results hold promise for future densely packed on-chip wavelength-multiplexed quantum communication systems.
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| 14. |
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| 15. |
- 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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| 16. |
- 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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| 17. |
- 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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| 18. |
- 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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| 19. |
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| 20. |
- Tuktamyshev, A., et al.
(författare)
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Telecom-wavelength InAs QDs with low fine structure splitting grown by droplet epitaxy on GaAs(111)A vicinal substrates
- 2021
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 118:13
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Tidskriftsartikel (refereegranskat)abstract
- We present self-assembly of InAs/InAlAs quantum dots by the droplet epitaxy technique on vicinal GaAs(111)A substrates. The small miscut angle, while maintaining the symmetries imposed on the quantum dot from the surface, allows a fast growth rate thanks to the presence of preferential nucleation sites at the step edges. A 100nm InAlAs metamorphic layer with In content >= 50% directly deposited on the GaAs substrate is already almost fully relaxed with a very flat surface. The quantum dots emit at the 1.3 mu m telecom O-band with fine structure splitting as low as 16 mu eV, thus making them suitable as photon sources in quantum communication networks using entangled photons.
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| 21. |
- Zeuner, Katharina D., et al.
(författare)
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A stable wavelength-tunable triggered source of single photons and cascaded photon pairs at the telecom C-band
- 2018
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Ingår i: Applied Physics Letters. - : AMER INST PHYSICS. - 0003-6951 .- 1077-3118. ; 112:17
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Tidskriftsartikel (refereegranskat)abstract
- The implementation of fiber-based long-range quantum communication requires tunable sources of single photons at the telecom C-band. Stable and easy-to-implement wavelength-tunability of individual sources is crucial to (i) bring remote sources into resonance, (ii) define a wavelength standard, and (iii) ensure scalability to operate a quantum repeater. So far, the most promising sources for true, telecom single photons are semiconductor quantum dots, due to their ability to deterministically and reliably emit single and entangled photons. However, the required wavelength-tunability is hard to attain. Here, we show a stable wavelength-tunable quantum light source by integrating strain-released InAs quantum dots on piezoelectric substrates. We present triggered single-photon emission at 1.55 mu m with a multi-photon emission probability as low as 0.097, as well as photon pair emission from the radiative biexciton-exciton cascade. We achieve a tuning range of 0.25 nm which will allow us to spectrally overlap remote quantum dots or tuning distant quantum dots into resonance with quantum memories. This opens up realistic avenues for the implementation of photonic quantum information processing applications at telecom wavelengths.
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| 22. |
- Zeuner, Katharina, 1991-, et al.
(författare)
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On-demand generation of entangled photon pairs in the telecom C-band for fiber-based quantum networks
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- On–demand sources of entangled photons for the transmission of quantum information in the telecom C–band are required to realize fiber–based quantum networks. So far, non–deterministic sources of quantum states of light were used for long distance entanglement distribution in this lowest loss wavelength range. However, they are fundamentally limited in either efficiency or security due to their Poissonian emission statistics. Here, we show on–demand generation of entangled photon pairs in the telecom C-band by an InAs/GaAs semiconductor quantum dot. Using a robust phonon–assisted excitation scheme we measurea concurrence of 91.4% and a fidelity of 95.2% to Φ+ . On–demand generation of polarization entangled photons will enable secure quantum communication in fiber–based networks.Furthermore, applying this excitation scheme to several remote quantum dots tuned into resonance will enable first on–demand entanglement distribution over large distances for scalable real–life quantum applications.
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| 23. |
- Zeuner, Katharina, et al.
(författare)
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On-Demand Generation of Entangled Photon Pairs in the Telecom C-Band with InAs Quantum Dots
- 2021
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Ingår i: ACS Photonics. - : AMER CHEMICAL SOC. - 2330-4022. ; 8:8, s. 2337-2344
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Tidskriftsartikel (refereegranskat)abstract
- Entangled photons are an integral part in quantum optics experiments and a key resource in quantum imaging, quantum communication, and photonic quantum information processing. Making this resource available on-demand has been an ongoing scientific challenge with enormous progress in recent years. Of particular interest is the potential to transmit quantum information over long distances, making photons the only reliable flying qubit. Entangled photons at the telecom C-band could be directly launched into single-mode optical fibers, enabling worldwide quantum communication via existing telecommunication infrastructure. However, the on-demand generation of entangled photons at this desired wavelength window has been elusive. Here, we show a photon pair generation efficiency of 69.9 +/- 3.6% in the telecom C-band by an InAs/GaAs semiconductor quantum dot on a metamorphic buffer layer. Using a robust phonon-assisted two-photon excitation scheme we measure a maximum concurrence of 91.4 +/- 3.8% and a peak fidelity to the Phi(+) state of 95.2 +/- 1.1%, verifying on-demand generation of strongly entangled photon pairs and marking an important milestone for interfacing quantum light sources with our classical fiber networks.
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| 24. |
- Zeuner, Katharina
(författare)
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Semiconductor Quantum Optics at Telecom Wavelengths
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Quantum technologies are an expanding field in physics and engineering concerning the development of protocols and devices that enable augmented or novel applications based on quantum mechanics. This includes amongst others quantum computation and quantum communication. Quantum computers promise a computational speed–up based on superposition relevant for optimization and simulation problems, as well as for factorizing of large numbers, which poses a threat to our classical encryption schemes. Quantum communication offers a solution to this issue by providing an unconditionally secure communication channel based on the laws of quantum mechanics. Moreover, quantum communication would allow the exchange of quantum information between remote quantum computers, enabling distributed quantum computing. An infrastructure that links quantum computers or processors is referred to as a quantum network. Stationary quantum bits at the network nodes are used for performing information processing or storing operations, while flying quantum bits connect the nodes and enable the transfer of quantum information. Photons are excellent flying quantum bits, as they travel at the speed of light and have a small interaction cross–section. Consequently, quantum networks require sources of quantum states of light to provide flying quantum bits. These quantum states of light need to be entangled, indistinguishable and wavelength–matched such that they either experience low transmission losses in networks or can be interfaced with other quantum technologies like atom–based quantum memories. In this thesis the emission of single, indistinguishable or entangled photons from single self–assembled optically active semiconductor quantum dots, our quantum emitter of choice, has been studied. The investigated quantum dots emit either in the telecom range or close to the D1–transition in Rubidium. The main aspects of the experiments performed in this thesis were to research the integrability of the emitters into future quantum networks by making them wavelength–tunable, integrating them into photonic structures and employing resonant excitation schemes in order to generate photons with unprecedented purity, indistinguishability or entanglement concurrence. In the telecom range, we study InAsP nanowire quantum dots whose emission is shifted from the near–infrared range up to the telecom O–band and C–band. Single photon emission is demonstrated with decay times of the quantum dots similar to their near–infrared counterparts. Furthermore, InAs/GaAs quantum dots emitting in the telecom C–band are integrated onto piezo–electric substrates, and their emission is modulated into sidebands by using commercial telecommunication equipment. We generate on–demand single photons using a two–photon resonant excitation scheme and on–demand entangled photons via a phonon–assisted resonant scheme. Droplet–etched GaAs quantum dots with emission in the vicinity of the D1–Rubidium transition have been excited via two–photon resonant excitation to generate single photons with unparalleled purity and highly entangled photon pairs to perform entanglement swapping. Under resonance fluorescence, single and highly indistinguishable photons are extracted. Both resonant excitation schemes are theoretically compared to reveal the limitations of the two techniques. Moreover, these quantum dots are integrated into piezo–tunable broad–band micro parabolic cavities for an enhanced extraction efficiency.
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