Showing 1–31 of 31 results for author: Weihs, G

Towards Stirling cooler operable single-photon sources based on low-noise GaAs quantum dots

Authors: Maximilian Aigner, Jana Schlücking, Eva Schöll, Christian Weidinger, Gabriel Undeutsch, Ievgen Brytavskyi, Thomas Oberleitner, Tobias Maria Krieger, Ailton Jose Garcia Junior, Melina Peter, Thomas K. Bracht, Michał Gawełczyk, Saimon Filipe Covre da Silva, Santanu Manna, Yusuf Karli, Gregor Weihs, Doris E. Reiter, Armando Rastelli

Abstract: For photonic quantum technology applications, sources capable of emitting photons with indistinguishability close to unity are essential. Ideally, these sources should not require demanding cooling systems. Here, we present temperature-dependent two-photon-interference measurements on photons produced by the radiative decay of the negative trion in a low-noise GaAs quantum dot, which are in quanti… ▽ More For photonic quantum technology applications, sources capable of emitting photons with indistinguishability close to unity are essential. Ideally, these sources should not require demanding cooling systems. Here, we present temperature-dependent two-photon-interference measurements on photons produced by the radiative decay of the negative trion in a low-noise GaAs quantum dot, which are in quantitative agreement with theoretical calculations accounting for carrier-phonon interactions and coupling to excited states. While at at the lowest explored temperatures the emission linewidth reaches values only 6(2) % above the Fourier limit and the indistinguishability I between subsequently emitted photons reaches 0.966(6), the latter drops to 0.05(4) at 55 K. We show that this loss can be explained with the coupling with energetically close excited trion states and suggest that the photon indistinguishability at elevated temperatures can be increased by employing Purcell enhancement of the emission rate or by increasing the energy separation of the excited states. Using cavity-enhanced emission, we experimentally verify the first route and demonstrate an improvement in photon indistinguishability from 0.314(25) to 0.80(3) at 32 K, which - to our knowledge - is the highest reported value at such temperature. △ Less

Submitted 25 August, 2026; originally announced August 2026.

How to measure laser chirp rate at single-emitter excitation energies

Authors: Timothée Mounier, Moritz Kaiser, Mert Tuncel, Iker Avila Arenas, René Schwarz, Ria G. Krämer, Stefan Nolte, Florian Kappe, Yusuf Karli, Gregor Weihs, Vikas Remesh

Abstract: We present a simple and direct method for measuring laser chirp rate, i.e., group delay dispersion (GDD) of ultrashort laser pulses at power levels compatible with single-quantum-emitter excitation. Traditional pulse characterization techniques rely on nonlinear optical processes that require high peak powers, making them unsuitable for the attojoule-to-femtojoule regime relevant to quantum photon… ▽ More We present a simple and direct method for measuring laser chirp rate, i.e., group delay dispersion (GDD) of ultrashort laser pulses at power levels compatible with single-quantum-emitter excitation. Traditional pulse characterization techniques rely on nonlinear optical processes that require high peak powers, making them unsuitable for the attojoule-to-femtojoule regime relevant to quantum photonics. Our approach utilizes a wavelength-to-time mapping method in which the arrival times of spectrally filtered components of a broadband pulse are recorded using a superconducting nanowire single-photon detector and correlated via a high-resolution time-tagging system. The resulting linear relationship between wavelength and arrival time directly yields the dispersion parameter and, subsequently, the GDD. Beyond single-emitter excitation, this technique can be applied in areas such as single-photon spectroscopy, ultralow-power optical communications, and time-domain quantum control, where linear and non-destructive dispersion characterization is essential. △ Less

Submitted 5 December, 2025; originally announced December 2025.

Comments: 9 pages, 5 figures

Exciton and biexciton preparation via coherent swing-up excitation in a GaAs quantum dot embedded in micropillar cavity

Authors: Claudia Piccinini, Aleksander Rodek, Abdulmalik A. Madigawa, Ailton Garcia Jr., Saimon F. Covre da Silva, Martin A. Jacobsen, Luca Vannucci, Gregor Weihs, Armando Rastelli, Vikas Remesh, Niels Gregersen, Battulga Munkhbat

Abstract: Coherent control of quantum emitters is essential for scalable quantum photonic technologies. The recently proposed swing-up of quantum emitter (SUPER) scheme allows efficient and coherent preparation of single photons via off-resonant, red-detuned laser pulses, simplifying laser suppression and enhancing photon collection. We present a systematic study of SUPER excitation applied to a single GaAs… ▽ More Coherent control of quantum emitters is essential for scalable quantum photonic technologies. The recently proposed swing-up of quantum emitter (SUPER) scheme allows efficient and coherent preparation of single photons via off-resonant, red-detuned laser pulses, simplifying laser suppression and enhancing photon collection. We present a systematic study of SUPER excitation applied to a single GaAs quantum dot in a low-Q micropillar cavity. We perform a comparison of the key figures of merit against the well-established two-photon excitation (TPE). Despite requiring higher excitation powers, SUPER achieves near-unity population inversion of the exciton state ($\sim$95%) and high single-photon purity ($g^{(2)}=0.03$) comparable to that under TPE, while also exhibiting a shortened decay time ($\sim$200 ps) reducing the time jitter in the exciton population. A polarization-resolved analysis reveals that when both excitation and collection are aligned with one of the exciton dipoles, SUPER results in polarized single-photon emission, exceeding the resonant TPE saturation by a factor of 1.45. Under optimized excitation conditions, we also observe biexciton preparation via a distinct SUPER resonance, confirmed by the appearance of the biexciton emission line, constituting the first experimental demonstration of biexciton preparation using SUPER. These findings are in good agreement with a proposed four-level theoretical model that incorporates the biexciton state. We also report that a slight misalignment of laser polarization induces an additional SUPER resonance that selectively populates the orthogonal exciton dipole, without altering the nominal excitation polarization. This unexpected behavior reveals a new degree of freedom for coherent state preparation. Our findings establish the SUPER scheme as a versatile tool for state-selective exciton and biexciton control. △ Less

Submitted 2 December, 2025; v1 submitted 24 October, 2025; originally announced October 2025.

Passive Demultiplexed Two-photon State Generation from a Quantum Dot

Authors: Yusuf Karli, Iker Avila Arenas, Christian Schimpf, Ailton José Garcia Junior, Santanu Manna, Florian Kappe, René Schwarz, Gabriel Undeutsch, Maximilian Aigner, Melina Peter, Saimon F Covre da Silva, Armando Rastelli, Gregor Weihs, Vikas Remesh

Abstract: High-purity multi-photon states are essential for photonic quantum computing. Among existing platforms, semiconductor quantum dots offer a promising route to scalable and deterministic multi-photon state generation. However, to fully realize their potential we require a suitable optical excitation method. Current approaches of multi-photon generation rely on active polarization-switching elements… ▽ More High-purity multi-photon states are essential for photonic quantum computing. Among existing platforms, semiconductor quantum dots offer a promising route to scalable and deterministic multi-photon state generation. However, to fully realize their potential we require a suitable optical excitation method. Current approaches of multi-photon generation rely on active polarization-switching elements (e.g., electro-optic modulators, EOMs) to spatio-temporally demultiplex single photons. Yet, the achievable multi-photon rate is fundamentally limited by the switching speed of the EOM. Here, we introduce a fully passive demultiplexing technique that leverages a stimulated two-photon excitation process to achieve switching rates that are only limited by the quantum dot lifetime. We demonstrate this method by generating two-photon states from a single quantum dot without requiring any active switching elements. Our approach significantly reduces the cost of demultiplexing while shifting it to the excitation stage, enabling loss-free demultiplexing and effectively doubling the achievable multi-photon generation rate when combined with existing active demultiplexing techniques. △ Less

Submitted 20 February, 2025; originally announced February 2025.

Comments: 7 pages, 4 figures

Robust Single-Photon Generation for Quantum Information Enabled by Stimulated Adiabatic Rapid Passage

Authors: Yusuf Karli, René Schwarz, Florian Kappe, Daniel A. Vajner, Ria G. Krämer, Thomas K. Bracht, Saimon F. Covre da Silva, Daniel Richter, Stefan Nolte, Armando Rastelli, Doris E. Reiter, Gregor Weihs, Tobias Heindel, Vikas Remesh

Abstract: The generation of single photons using solid-state quantum emitters is pivotal for advancing photonic quantum technologies, particularly in quantum communication. As the field continuously advances towards practical use cases and beyond shielded laboratory environments, specific demands are placed on the robustness of quantum light sources during operation. In this context, the robustness of the q… ▽ More The generation of single photons using solid-state quantum emitters is pivotal for advancing photonic quantum technologies, particularly in quantum communication. As the field continuously advances towards practical use cases and beyond shielded laboratory environments, specific demands are placed on the robustness of quantum light sources during operation. In this context, the robustness of the quantum light generation process against intrinsic and extrinsic effects is a major challenge. Here, we present a robust scheme for the coherent generation of indistinguishable single-photon states with very low photon number coherence (PNC) using a three-level system in a semiconductor quantum dot. Our novel approach combines the advantages of adiabatic rapid passage (ARP) and stimulated two-photon excitation (sTPE). We demonstrate robust quantum light generation while maintaining the prime quantum-optical quality of the emitted light state. Moreover, we highlight the immediate advantages for the implementation of various quantum cryptographic protocols. △ Less

Submitted 20 September, 2024; originally announced September 2024.

Comments: 12 pages, 6 figures

Towards Photon-Number-Encoded High-dimensional Entanglement from a Sequentially Excited Quantum Three-Level System

Authors: Daniel A. Vajner, Nils D. Kewitz, Martin von Helversen, Stephen C. Wein, Yusuf Karli, Florian Kappe, Vikas Remesh, Saimon F. Covre da Silva, Armando Rastelli, Gregor Weihs, Carlos Anton-Solanas, Tobias Heindel

Abstract: The sequential resonant excitation of a 2-level quantum system results in the emission of a state of light showing time-entanglement encoded in the photon-number-basis - notions that can be extended to 3-level quantum systems as discussed in a recent proposal. Here, we report the experimental implementation of a sequential two-photon resonant excitation process of a solid-state 3-level system, con… ▽ More The sequential resonant excitation of a 2-level quantum system results in the emission of a state of light showing time-entanglement encoded in the photon-number-basis - notions that can be extended to 3-level quantum systems as discussed in a recent proposal. Here, we report the experimental implementation of a sequential two-photon resonant excitation process of a solid-state 3-level system, constituted by the biexciton-, exciton-, and ground-state of a semiconductor quantum dot. The resulting light state exhibits entanglement in time and energy, encoded in the photon-number basis, which could be used in quantum information applications, e.g., dense information encoding or quantum communication protocols. Performing energy- and time-resolved correlation experiments in combination with extensive theoretical modelling, we are able to partially retrieve the entanglement structure of the generated state. △ Less

Submitted 8 July, 2024; originally announced July 2024.

Comments: 14 pages (including 5 figures, 56 citations)

Journal ref: Optica Quantum 3, 99-110 (2025)

Keeping the photon in the dark: Enabling full quantum dot control by chirped pulses and magnetic fields

Authors: Florian Kappe, René Schwarz, Yusuf Karli, Thomas Bracht, Vollrath M. Axt, Armando Rastelli, Vikas Remesh, Doris E. Reiter, Gregor Weihs

Abstract: Because dark excitons in quantum dots are not directly optically accessible, so far they have not played a significant role in using quantum dots for photon generation. They possess significantly longer lifetimes than their brighter counterparts and hence offer enormous potential for photon storage or manipulation. In this work, we demonstrate an all-optical storage and retrieval of the spin-forbi… ▽ More Because dark excitons in quantum dots are not directly optically accessible, so far they have not played a significant role in using quantum dots for photon generation. They possess significantly longer lifetimes than their brighter counterparts and hence offer enormous potential for photon storage or manipulation. In this work, we demonstrate an all-optical storage and retrieval of the spin-forbidden dark exciton in a quantum dot from the ground state employing chirped pulses and an in-plane magnetic field. Our experimental findings are in excellent agreement with theoretical predictions of the dynamics calculated using state-of-the-art product tensor methods. Our scheme enables an all-optical control of dark states without relying on any preceding decays. This opens up a new dimension for optimal quantum control and time-bin entangled photon pair generation from quantum dots. △ Less

Submitted 16 April, 2024; originally announced April 2024.

Compact Chirped Fiber Bragg Gratings for Single-Photon Generation from Quantum Dots

Authors: Vikas Remesh, Ria G. Krämer, René Schwarz, Florian Kappe, Yusuf Karli, Malte Per Siems, Thomas K. Bracht, Saimon Filipe Covre da Silva, Armando Rastelli, Doris E. Reiter, Daniel Richter, Stefan Nolte, Gregor Weihs

Abstract: A scalable source of single photons is a key constituent of an efficient quantum photonic architecture. To realize this, it is beneficial to have an ensemble of quantum emitters that can be collectively excited with high efficiency. Semiconductor quantum dots hold great potential in this context, due to their excellent photophysical properties. Spectral variability of quantum dots is commonly rega… ▽ More A scalable source of single photons is a key constituent of an efficient quantum photonic architecture. To realize this, it is beneficial to have an ensemble of quantum emitters that can be collectively excited with high efficiency. Semiconductor quantum dots hold great potential in this context, due to their excellent photophysical properties. Spectral variability of quantum dots is commonly regarded as a drawback introduced by the fabrication method. However, this is beneficial to realize a frequency-multiplexed single-photon platform. Chirped pulse excitation, relying on the so-called adiabatic rapid passage, is the most efficient scheme to excite a quantum dot ensemble due to its immunity to individual quantum dot parameters. Yet, the existing methods of generating chirped laser pulses to excite a quantum emitter are bulky, lossy, and mechanically unstable, which severely hampers the prospects of a quantum dot photon source. Here, we present a compact, robust, and high-efficiency alternative for chirped pulse excitation of solid-state quantum emitters. Our simple plug-and-play module consists of chirped fiber Bragg gratings (CFBGs), fabricated via femtosecond inscription, to provide high values of dispersion in the near-infrared spectral range, where the quantum dots emit. We characterize and benchmark the performance of our method via chirped excitation of a GaAs quantum dot, establishing high-fidelity single-photon generation. Our highly versatile chirping module coupled to a photon source is a significant milestone toward realizing practical quantum photonic devices. △ Less

Submitted 20 June, 2023; originally announced June 2023.

Journal ref: APL Photonics, 2023

Controlling the Photon Number Coherence of Solid-state Quantum Light Sources for Quantum Cryptography

Authors: Yusuf Karli, Daniel A. Vajner, Florian Kappe, Paul C. A. Hagen, Lena M. Hansen, René Schwarz, Thomas K. Bracht, Christian Schimpf, Saimon F. Covre da Silva, Philip Walther, Armando Rastelli, Vollrath Martin Axt, Juan C. Loredo, Vikas Remesh, Tobias Heindel, Doris E. Reiter, Gregor Weihs

Abstract: Quantum communication networks rely on quantum cryptographic protocols including quantum key distribution (QKD) using single photons. A critical element regarding the security of QKD protocols is the photon number coherence (PNC), i.e. the phase relation between the zero and one-photon Fock state, which critically depends on the excitation scheme. Thus, to obtain flying qubits with the desired pro… ▽ More Quantum communication networks rely on quantum cryptographic protocols including quantum key distribution (QKD) using single photons. A critical element regarding the security of QKD protocols is the photon number coherence (PNC), i.e. the phase relation between the zero and one-photon Fock state, which critically depends on the excitation scheme. Thus, to obtain flying qubits with the desired properties, optimal pumping schemes for quantum emitters need to be selected. Semiconductor quantum dots generate on-demand single photons with high purity and indistinguishability. Exploiting two-photon excitation of a quantum dot combined with a stimulation pulse, we demonstrate the generation of high-quality single photons with a controllable degree of PNC. Our approach provides a viable route toward secure communication in quantum networks. △ Less

Submitted 31 May, 2023; originally announced May 2023.

Comments: 17 pages

Journal ref: npj Quantum Inf 10, 17 (2024)

Dressed-state analysis of two-color excitation schemes

Authors: Thomas K. Bracht, Tim Seidelmann, Yusuf Karli, Florian Kappe, Vikas Remesh, Gregor Weihs, Vollrath Martin Axt, Doris E. Reiter

Abstract: To coherently control a few-level quantum emitter, typically pulses with an energy resonant to the transition energy are applied making use of the Rabi mechanism, while a single off-resonant pulse does not result in a population inversion. Surprisingly, a two-color excitation with a combination of two off-resonant pulses making use of the Swing-UP of quantum EmitteR population (SUPER) mechanism is… ▽ More To coherently control a few-level quantum emitter, typically pulses with an energy resonant to the transition energy are applied making use of the Rabi mechanism, while a single off-resonant pulse does not result in a population inversion. Surprisingly, a two-color excitation with a combination of two off-resonant pulses making use of the Swing-UP of quantum EmitteR population (SUPER) mechanism is able to invert the system. In this paper, we provide an in-depth analysis of the SUPER scheme within the dressed-state picture. We show that the SUPER mechanism can be understood as a driving of the transition between the dressed states. In the two-level system this allows us to derive analytic expressions for the pulse parameters yielding a population inversion. We extend our considerations to the three-level system, where a strong mixing between the bare states takes place. The insights gained from these results help in finding accessible regimes for further experimental realizations of the SUPER scheme and similar two-color excitation schemes. △ Less

Submitted 15 November, 2022; originally announced November 2022.

Comments: 12 pages, 8 figures

Journal ref: Phys. Rev. B 107, 035425 (2023)

Collective Excitation of Spatio-Spectrally Distinct Quantum Dots Enabled by Chirped Pulses

Authors: Florian Kappe, Yusuf Karli, Thomas K. Bracht, Saimon Covre da Silva, Tim Seidelmann, Vollrath Martin Axt, Armando Rastelli, Gregor Weihs, Doris E. Reiter, Vikas Remesh

Abstract: For a scalable photonic device producing entangled photons, it is desirable to have multiple quantum emitters in an ensemble that can be collectively excited, despite their spectral variability. For quantum dots, Rabi rotation, the most popular method for resonant excitation, cannot assure a universal, highly efficient excited state preparation, because of its sensitivity to the excitation paramet… ▽ More For a scalable photonic device producing entangled photons, it is desirable to have multiple quantum emitters in an ensemble that can be collectively excited, despite their spectral variability. For quantum dots, Rabi rotation, the most popular method for resonant excitation, cannot assure a universal, highly efficient excited state preparation, because of its sensitivity to the excitation parameters. In contrast, Adiabatic Rapid Passage (ARP), relying on chirped optical pulses, is immune to quantum dot spectral inhomogeneity. Here, we advocate the robustness of ARP for simultaneous excitation of the biexciton states of multiple quantum dots. For positive chirps, we find that there is also regime of phonon advantage that widens the tolerance range of spectral detunings. Using the same laser pulse we demonstrate the simultaneous excitation of energetically and spatially distinct quantum dots. Being able to generate spatially multiplexed entangled photon pairs is a big step towards the scalability of photonic devices. △ Less

Submitted 19 September, 2022; originally announced September 2022.

Fast and efficient demultiplexing of single photons from a quantum dot with resonantly enhanced electro-optic modulators

Authors: Julian Münzberg, Franz Draxl, Saimon Filipe Covre da Silva, Yusuf Karli, Santanu Manna, Armando Rastelli, Gregor Weihs, Robert Keil

Abstract: We report on a multi-photon source based on active demultiplexing of single photons emitted from a resonantly excited GaAs quantum dot. Active temporal-to-spatial mode demultipexing is implemented via resonantly enhanced free-space electro-optic modulators, making it possible to route individual photons at high switching rates of 38 MHz. We demonstrate routing into four spatial modes with a high e… ▽ More We report on a multi-photon source based on active demultiplexing of single photons emitted from a resonantly excited GaAs quantum dot. Active temporal-to-spatial mode demultipexing is implemented via resonantly enhanced free-space electro-optic modulators, making it possible to route individual photons at high switching rates of 38 MHz. We demonstrate routing into four spatial modes with a high end-to-end efficiency of 79% and measure a four-photon coincidence rate of 0.17 Hz mostly limited by the single-photon source brightness and not by the efficiency of the demultiplexer itself. We use the demultiplexer to characterize the pairwise indistinguishability of consecutively emitted photons from the quantum dot with variable delay time. △ Less

Submitted 16 March, 2022; originally announced March 2022.

Comments: The supplementary material is included as ancillary file

Journal ref: APL Photonics 7, 070802 (2022)

SUPER Scheme in Action: Experimental Demonstration of Red-detuned Excitation of a Quantum Dot

Authors: Yusuf Karli, Florian Kappe, Vikas Remesh, Thomas K. Bracht, Julian Muenzberg, Saimon Covre da Silva, Tim Seidelmann, Vollrath Martin Axt, Armando Rastelli, Doris E. Reiter, Gregor Weihs

Abstract: The quest for the perfect single-photon source includes finding the optimal protocol for exciting the quantum emitter. Based on a recently proposed, so-called SUPER (swing-up of quantum emitter population) scheme, we demonstrate experimentally that two red-detuned laser pulses, neither of which could yield a significant upper-level population individually, lead to the coherent excitation of a semi… ▽ More The quest for the perfect single-photon source includes finding the optimal protocol for exciting the quantum emitter. Based on a recently proposed, so-called SUPER (swing-up of quantum emitter population) scheme, we demonstrate experimentally that two red-detuned laser pulses, neither of which could yield a significant upper-level population individually, lead to the coherent excitation of a semiconductor quantum dot. We characterize the emitted single photons and show that they have properties comparable to those achieved under resonant excitation schemes. △ Less

Submitted 1 March, 2022; originally announced March 2022.

Comments: 11 pages, 9 figures

Journal ref: Nano Lett. 2022

The optical Stark shift to control the dark exciton occupation of a quantum dot in a tilted magnetic field

Authors: Miriam Neumann, Florian Kappe, Thomas K. Bracht, Michael Cosacchi, Tim Seidelmann, Vollrath Martin Axt, Gregor Weihs, Doris E. Reiter

Abstract: When a detuned and strong laser pulse acts on an optical transition, a Stark shift of the corresponding energies occurs. We analyze how this optical Stark effect can be used to prepare and control the dark exciton occupation in a semiconductor quantum dot. The coupling between the bright and dark exciton states is facilitated by an external magnetic field. Using sequences of laser pulses, we show… ▽ More When a detuned and strong laser pulse acts on an optical transition, a Stark shift of the corresponding energies occurs. We analyze how this optical Stark effect can be used to prepare and control the dark exciton occupation in a semiconductor quantum dot. The coupling between the bright and dark exciton states is facilitated by an external magnetic field. Using sequences of laser pulses, we show how the dark exciton and different superposition states can be prepared. We give simple analytic formulas, which yield a good estimate for optimal preparation parameters. The preparation scheme is quite robust against the influence of acoustic phonons. We further discuss the experimental feasibility of the used Stark pulses. Giving a clear physical picture our results will stimulate the usage of dark excitons in schemes to generate photons from quantum dots. △ Less

Submitted 25 May, 2021; originally announced May 2021.

Comments: 10 pages, 6 figures

Journal ref: Phys. Rev. B 104, 075428 (2021)

Polariton Lasing in Micropillars With One Micrometer Diameter and Position-Dependent Spectroscopy of Polaritonic Molecules

Authors: U. Czopak, M. Prilmüller, C. Schneider, S. Höfling, G. Weihs

Abstract: Microcavity polaritons are bosonic light-matter particles that can emit coherent radiation without electronic population inversion via bosonic scattering. This phenomenon, known as polariton lasing, strongly depends on the polaritons' confinement. Shrinking the polaritons' mode volume increases the interactions mediated by their excitonic part, and thereby the density-dependent blueshift of the po… ▽ More Microcavity polaritons are bosonic light-matter particles that can emit coherent radiation without electronic population inversion via bosonic scattering. This phenomenon, known as polariton lasing, strongly depends on the polaritons' confinement. Shrinking the polaritons' mode volume increases the interactions mediated by their excitonic part, and thereby the density-dependent blueshift of the polariton to a higher energy is enhanced. Previously, polariton lasing has been demonstrated in micropillars with diameters larger than three microns, in grating based cavities, fiber cavities and photonic crystal cavities. Here we show polariton lasing in a micropillar with one micron diameter operating in a single transverse mode that can be optimally coupled to a singlemode fiber. We geometrically decouple the excitation with an angle from the collection. From the number of collected photons we calculate the number of polaritons and observe a blueshift large enough to qualify our device for novel schemes of quantum light generation such as the unconventional photon blockade. To that end, we also apply angled excitation to polaritonic molecules and show site-selective excitation and collection of modes with various symmetries. △ Less

Submitted 8 February, 2021; originally announced February 2021.

Comments: Submission to SciPost

Quantum statistics of polariton parametric interactions

Authors: Mathias Sassermann, Zoltán Vörös, Mohsen Razavi, Wolfgang Langbein, Gregor Weihs

Abstract: Using a high-quality GaAs planar microcavity, we optically generate polariton pairs, and verify their correlations by means of time-resolved single-photon detection. We find that correlations between the different modes are consistently lower than identical mode correlations, which is attributed to the presence of uncorrelated background. We discuss a model to quantify the effects of such a backgr… ▽ More Using a high-quality GaAs planar microcavity, we optically generate polariton pairs, and verify their correlations by means of time-resolved single-photon detection. We find that correlations between the different modes are consistently lower than identical mode correlations, which is attributed to the presence of uncorrelated background. We discuss a model to quantify the effects of such a background on the observed correlations. Using spectral and temporal filtering, the background can be suppressed and a change in photon statistics towards non-classical correlations is observed. These results improve our understanding of the statistics of polariton-polariton scattering and background mechanisms, and pave the way to the generation of entangled polariton pairs. △ Less

Submitted 3 August, 2018; originally announced August 2018.

Time-bin Entanglement from Quantum Dots

Authors: Gregor Weihs, Tobias Huber, Ana Predojević

Abstract: The desire to have a source of single entangled photon pairs can be satisfied using single quantum dots as emitters. However, we are not bound to pursue only polarization entanglement, but can also exploit other degrees of freedom. In this chapter we focus on the time degree of freedom, to achieve so-called time-bin entanglement. This requires that we prepare the quantum dot coherently into the bi… ▽ More The desire to have a source of single entangled photon pairs can be satisfied using single quantum dots as emitters. However, we are not bound to pursue only polarization entanglement, but can also exploit other degrees of freedom. In this chapter we focus on the time degree of freedom, to achieve so-called time-bin entanglement. This requires that we prepare the quantum dot coherently into the biexciton state and also build special interferometers for analysis. Finally this technique can be extended to achieve time-bin and polarization hyper-entanglement from a suitable quantum dot. △ Less

Submitted 9 September, 2016; originally announced September 2016.

Comments: 20 pages, 10 figures, chapter of forthcoming Springer book edited by P. Michler

Effects of photo-neutralization on the emission properties of quantum dots

Authors: Tobias Huber, Ana Predojević, Glenn S. Solomon, Gregor Weihs

Abstract: In this paper we investigate the coherence properties of a quantum dot under two-photon resonant excitation in combination with an additional photo-neutralization laser. The photo-neutralization increases the efficiency of the excitation process and thus, the brightness of the source, by a factor of approximately 1.5 for biexciton-exciton pairs. This enhancement does not degrade the relevant coher… ▽ More In this paper we investigate the coherence properties of a quantum dot under two-photon resonant excitation in combination with an additional photo-neutralization laser. The photo-neutralization increases the efficiency of the excitation process and thus, the brightness of the source, by a factor of approximately 1.5 for biexciton-exciton pairs. This enhancement does not degrade the relevant coherences in the system; neither the single photon coherence time, nor the coherence of the excitation process. △ Less

Submitted 30 March, 2016; originally announced March 2016.

A solid state source of photon triplets based on quantum dot molecules

Authors: Milad Khoshnegar, Tobias Huber, Ana Predojević, Dan Dalacu, Maximilian Prilmüller, Jean Lapointe, Xiaohua Wu, Philippe Tamarat, Brahim Lounis, Philip Poole, Gregor Weihs, Hamed Majedi

Abstract: Producing advanced quantum states of light is a priority in quantum information technologies. While remarkable progress has been made on single photons and photon pairs, multipartite correlated photon states are usually produced in purely optical systems by post-selection or cascading, with extremely low efficiency and exponentially poor scaling. Multipartite states enable improved tests of the fo… ▽ More Producing advanced quantum states of light is a priority in quantum information technologies. While remarkable progress has been made on single photons and photon pairs, multipartite correlated photon states are usually produced in purely optical systems by post-selection or cascading, with extremely low efficiency and exponentially poor scaling. Multipartite states enable improved tests of the foundations of quantum mechanics as well as implementations of complex quantum optical networks and protocols. It would be favorable to directly generate these states using solid state systems, for better scaling, simpler handling, and the promise of reversible transfer of quantum information between stationary and flying qubits. Here we use the ground states of two optically active coupled quantum dots to directly produce photon triplets. The wavefunctions of photogenerated excitons localized in these ground states are correlated via molecular hybridization and Coulomb interactions. The formation of a triexciton leads to a triple cascade recombination and sequential emission of three photons with strong correlations. The quantum dot molecule is embedded in an epitaxially grown nanowire engineered for single-mode waveguiding and improved extraction efficiency at the emission wavelength. We record 65.62 photon triplets per minute, surpassing rates of all earlier reported sources, in spite of the moderate efficiency of our detectors. Our structure and data represent a breakthrough towards implementing multipartite photon entanglement and multi-qubit readout schemes in solid state devices, suitable for integrated quantum information processing. △ Less

Submitted 16 September, 2017; v1 submitted 20 October, 2015; originally announced October 2015.

Comments: 27 pages, 3 figures

Journal ref: Nature Communications 8 15716 (2017)

Optimal excitation conditions for indistinguishable photons from quantum dots

Authors: Tobias Huber, Ana Predojević, Daniel Föger, Glenn Solomon, Gregor Weihs

Abstract: In this letter, we present a detailed, all optical study of the influence of different excitation schemes on the indistinguishability of single photons from a single InAs quantum dot. For this study, we measure the Hong-Ou-Mandel interference of consecutive photons from the spontaneous emission of an InAs quantum dot state under various excitation schemes and different excitation conditions and gi… ▽ More In this letter, we present a detailed, all optical study of the influence of different excitation schemes on the indistinguishability of single photons from a single InAs quantum dot. For this study, we measure the Hong-Ou-Mandel interference of consecutive photons from the spontaneous emission of an InAs quantum dot state under various excitation schemes and different excitation conditions and give a comparison. △ Less

Submitted 26 November, 2015; v1 submitted 27 July, 2015; originally announced July 2015.

Comments: 7 pages, 3 figures

Polarization entangled photons from quantum dots embedded in nanowires

Authors: Tobias Huber, Ana Predojević, Milad Khoshnegar, Dan Dalacu, Philip J. Poole, Hamed Majedi, Gregor Weihs

Abstract: We present a first measurement of photon polarization entanglement from the biexciton to ground state cascade of a single InAsP quantum dot embedded in an InP nanowire. We observe a fidelity of 0.76(2) to a reference maximally entangled state as well as a concurrence of 0.57(6). We present a first measurement of photon polarization entanglement from the biexciton to ground state cascade of a single InAsP quantum dot embedded in an InP nanowire. We observe a fidelity of 0.76(2) to a reference maximally entangled state as well as a concurrence of 0.57(6). △ Less

Submitted 2 June, 2014; v1 submitted 15 May, 2014; originally announced May 2014.

Journal ref: Nano Lett. 14 (2014), 7107-7114

Rayleigh scattering in coupled microcavities: Experiment

Authors: Z. Vörös, P. Mai, M. Sassermann, G. Weihs, A. M. Andrews, H. Detz, G. Strasser

Abstract: We experimentally analyze Rayleigh scattering in coupled planar microcavities. We show that the correlations of the disorder in the two cavities lead to inter-branch scattering of polaritons, that would otherwise be forbidden by symmetry. These longitudinal correlations can be inferred from the strength of the inter-branch scattering. We experimentally analyze Rayleigh scattering in coupled planar microcavities. We show that the correlations of the disorder in the two cavities lead to inter-branch scattering of polaritons, that would otherwise be forbidden by symmetry. These longitudinal correlations can be inferred from the strength of the inter-branch scattering. △ Less

Submitted 29 April, 2014; originally announced April 2014.

Comments: 6 pages, 10 figures

Rayleigh scattering in coupled microcavities: Theory

Authors: Z. Vörös, G. Weihs

Abstract: In this paper we theoretically study how structural disorder in coupled semiconductor heterostructures influences single-particle scattering events that would otherwise be forbidden by symmetry. We extend the model of V. Savona to describe Rayleigh scattering in coupled planar microcavity structures, and answer the question, whether effective filter theories can be ruled out. They can. In this paper we theoretically study how structural disorder in coupled semiconductor heterostructures influences single-particle scattering events that would otherwise be forbidden by symmetry. We extend the model of V. Savona to describe Rayleigh scattering in coupled planar microcavity structures, and answer the question, whether effective filter theories can be ruled out. They can. △ Less

Submitted 29 April, 2014; originally announced April 2014.

Comments: 10 pages, 7 figures

Generation of hyper-entangled photon pairs in coupled microcavities

Authors: S. Portolan, L. Einkemmer, Z. Vörös, G. Weihs, P. Rabl

Abstract: We propose and theoretically analyze a new scheme for generating hyper-entangled photon pairs in a system of polaritons in coupled planar microcavities. Starting from a microscopic model, we evaluate the relevant parametric scattering processes and numerically simulate the phonon-induced noise background under continuous-wave excitation. Our results show that, compared to other polariton entanglem… ▽ More We propose and theoretically analyze a new scheme for generating hyper-entangled photon pairs in a system of polaritons in coupled planar microcavities. Starting from a microscopic model, we evaluate the relevant parametric scattering processes and numerically simulate the phonon-induced noise background under continuous-wave excitation. Our results show that, compared to other polariton entanglement proposals, our scheme enables the generation of photon pairs that are entangled in both path and polarization degrees of freedom, and simultaneously leads to a strong reduction of the photoluminesence noise background. This can significantly improve the fidelity of the entangled photon pairs under realistic experimental conditions. △ Less

Submitted 28 May, 2013; originally announced May 2013.

Comments: Main paper + Supplementary Material

Journal ref: New Journal of Physics 16 (2014) 063030

Time-bin entangled photons from a quantum dot

Authors: Harishankar Jayakumar, Ana Predojević, Thomas Kauten, Tobias Huber, Glenn S. Solomon, Gregor Weihs

Abstract: Long distance quantum communication is one of the prime goals in the field of quantum information science. With information encoded in the quantum state of photons, existing telecommunication fiber networks can be effectively used as a transport medium. To achieve this goal, a source of robust entangled single photon pairs is required. While time-bin entanglement offers the required robustness, cu… ▽ More Long distance quantum communication is one of the prime goals in the field of quantum information science. With information encoded in the quantum state of photons, existing telecommunication fiber networks can be effectively used as a transport medium. To achieve this goal, a source of robust entangled single photon pairs is required. While time-bin entanglement offers the required robustness, currently used parametric down-conversion sources have limited performance due to multi-pair contributions. We report the realization of a source of single time-bin entangled photon pairs utilizing the biexciton-exciton cascade in a III/V self-assembled quantum dot. We analyzed the generated photon pairs by an inherently phase-stable interferometry technique, facilitating uninterrupted long integration times. We confirmed the entanglement by performing a quantum state tomography of the emitted photons, which yielded a fidelity of 0.69(3) and a concurrence of 0.41(6). △ Less

Submitted 9 January, 2014; v1 submitted 9 May, 2013; originally announced May 2013.

Comments: 6 pages, 5 figures

Entanglement generation in microcavity polariton devices

Authors: L. Einkemmer, Z. Vörös, G. Weihs, S. Portolan

Abstract: Entanglement generation in microcavity exciton-polaritons is an interesting application of the peculiar properties of these half-light/half-matter quasiparticles. In this paper we theoretically investigate their luminescence dynamics and entanglement formation in single, double, and triple cavities. We derive general expressions and selection rules for polariton-polariton scattering. We evaluate a… ▽ More Entanglement generation in microcavity exciton-polaritons is an interesting application of the peculiar properties of these half-light/half-matter quasiparticles. In this paper we theoretically investigate their luminescence dynamics and entanglement formation in single, double, and triple cavities. We derive general expressions and selection rules for polariton-polariton scattering. We evaluate a number of possible parametric scattering schemes in terms of entanglement, and identify the ones that are experimentally most promising. △ Less

Submitted 29 August, 2013; v1 submitted 7 May, 2013; originally announced May 2013.

Comments: 25 pages, 8 figures

Journal ref: Physica status solidi (b), Volume 252, Issue 8, August 2015, Pages 1749-1756

Deterministic Photon Pairs via Coherent Optical Control of a Single Quantum Dot

Authors: Harishankar Jayakumar, Ana Predojević, Tobias Huber, Thomas Kauten, Glenn S. Solomon, Gregor Weihs

Abstract: The strong confinement of semiconductor excitons in a quantum dot gives rise to atom-like behavior. The full benefit of such a structure is best observed in resonant excitation where the excited state can be deterministically populated and coherently manipulated. Due to large refractive index and device geometry it remains challenging to observe resonantly excited emission that is free from laser… ▽ More The strong confinement of semiconductor excitons in a quantum dot gives rise to atom-like behavior. The full benefit of such a structure is best observed in resonant excitation where the excited state can be deterministically populated and coherently manipulated. Due to large refractive index and device geometry it remains challenging to observe resonantly excited emission that is free from laser scattering in III/V self-assembled quantum dots. Here we exploit the biexciton binding energy to create an extremely clean single photon source via two-photon resonant excitation of an InAs/GaAs quantum dot. We observe complete suppression of the excitation laser and multi-photon emissions. Additionally, we perform full coherent control of the ground-biexciton state qubit and observe an extended coherence time using an all-optical echo technique. The deterministic coherent photon pair creation makes this system suitable for the generation of time-bin entanglement and experiments on the interaction of photons from dissimilar sources. △ Less

Submitted 12 November, 2012; originally announced November 2012.

Comments: 8 pages, 6 figures

Journal ref: Phys. Rev. Lett. 110, 135505, 2013

Multi-dimensional laser spectroscopy of exciton-polaritons with spatial light modulators

Authors: P. Mai, B. Pressl, M. Sassermann, Z. Vörös, G. Weihs, C. Schneider, A. Löffler, S. Höfling, A. Forchel

Abstract: We describe an experimental system that allows one to easily access the dispersion curve of exciton-polaritons in a microcavity. Our approach is based on two spatial light modulators (SLM), one for changing the excitation angles (momenta), and the other for tuning the excitation wavelength. We show that with this setup, an arbitrary number of states can be excited accurately and that re-configurat… ▽ More We describe an experimental system that allows one to easily access the dispersion curve of exciton-polaritons in a microcavity. Our approach is based on two spatial light modulators (SLM), one for changing the excitation angles (momenta), and the other for tuning the excitation wavelength. We show that with this setup, an arbitrary number of states can be excited accurately and that re-configuration of the excitation scheme can be done at high speed. △ Less

Submitted 31 December, 2011; originally announced January 2012.

Comments: 4 pages, 5 figures

Growth and characterization of GaAs nanowires on carbon nanotubes composite films: toward flexible nanodevices

Authors: P. K. Mohseni, G. Lawson, C. Couteau, G. Weihs, A. Adronov, R. R. LaPierre

Abstract: Poly(ethylene imine) functionalized carbon nanotube thin films, prepared using the vacuum filtration method, were decorated with Au nanoparticles by in situ reduction of HAuCl4 under mild conditions. These Au nanoparticles were subsequently employed for the growth of GaAs nanowires (NWs) by the vapor-liquid-solid process in a gas source molecular beam epitaxy system. The process resulted in the… ▽ More Poly(ethylene imine) functionalized carbon nanotube thin films, prepared using the vacuum filtration method, were decorated with Au nanoparticles by in situ reduction of HAuCl4 under mild conditions. These Au nanoparticles were subsequently employed for the growth of GaAs nanowires (NWs) by the vapor-liquid-solid process in a gas source molecular beam epitaxy system. The process resulted in the dense growth of GaAs NWs across the entire surface of the single-walled nanotube (SWNT) films. The NWs, which were orientated in a variety of angles with respect to the SWNT films, ranged in diameter between 20 to 200 nm, with heights up to 2.5 um. Transmission electron microscopy analysis of the NW-SWNT interface indicated that NW growth was initiated upon the surface of the nanotube composite films. Photoluminescence characterization of a single NW specimen showed high optical quality. Rectifying asymmetric current-voltage behavior was observed from contacted NW ensembles and attributed to the core-shell pn-junction within the NWs. Potential applications of such novel hybrid architectures include flexible solar cells, displays, and sensors. △ Less

Submitted 15 December, 2008; originally announced December 2008.

Journal ref: NanoLett., 2008, 8(11) pp 4075-4080

Multiple Quantum Well AlGaAs Nanowires

Authors: C. Chen, N. Braidy, C. Couteau, C. Fradin, G. Weihs, R. LaPierre

Abstract: This letter reports on the growth, structure and luminescent properties of individual multiple quantum well (MQW) AlGaAs nanowires (NWs). The composition modulations (MQWs) are obtained by alternating the elemental flux of Al and Ga during the molecular beam epitaxy growth of the AlGaAs wire on GaAs (111)B substrates. Transmission electron microscopy and energy dispersive X-ray spectroscopy perf… ▽ More This letter reports on the growth, structure and luminescent properties of individual multiple quantum well (MQW) AlGaAs nanowires (NWs). The composition modulations (MQWs) are obtained by alternating the elemental flux of Al and Ga during the molecular beam epitaxy growth of the AlGaAs wire on GaAs (111)B substrates. Transmission electron microscopy and energy dispersive X-ray spectroscopy performed on individual NWs are consistent with a configuration composed of conical segments stacked along the NW axis. Micro-photoluminescence measurements and confocal microscopy showed enhanced light emission from the MQW NWs as compared to non-segmented NWs due to carrier confinement and sidewall passivation. △ Less

Submitted 6 March, 2008; originally announced March 2008.

Journal ref: Nano Lett.; (Letter); 2008; 8(2); 495-499

Self-directed growth of AlGaAs core-shell nanowires for visible light applications

Authors: C. Chen, S. Shehata, C. Fradin, R. LaPierre, C. Couteau, G. Weihs

Abstract: Al(0.37)Ga(0.63)As nanowires (NWs) were grown in a molecular beam epitaxy system on GaAs(111)B substrates. Micro-photoluminescence measurements and energy dispersive X-ray spectroscopy indicated a core-shell structure and Al composition gradient along the NW axis, producing a potential minimum for carrier confinement. The core-shell structure formed during the growth as a consequence of the diff… ▽ More Al(0.37)Ga(0.63)As nanowires (NWs) were grown in a molecular beam epitaxy system on GaAs(111)B substrates. Micro-photoluminescence measurements and energy dispersive X-ray spectroscopy indicated a core-shell structure and Al composition gradient along the NW axis, producing a potential minimum for carrier confinement. The core-shell structure formed during the growth as a consequence of the different Al and Ga adatom diffusion lengths. △ Less

Submitted 2 October, 2007; originally announced October 2007.

Comments: 20 pages, 7 figures

Journal ref: Nano Lett.; (Letter); 2007; 7(9); 2584-2589