Showing 1–36 of 36 results for author: Wigger, D

Coherent dynamics of individual excitons in a quantum dot embedded in a nanopost

Authors: Maxime Gaignard, Karolina Ewa Polczynska, Niels Gregersen, Daniel Wigger, Jean-Philippe Poizat, Jean-Michel Gérard, Julien Claudon, Jacek Kasprzak

Abstract: We measured coherent ultrafast dynamics of exciton complexes in a single strongly-confined InAs quantum dot embedded in a GaAs nanopost. Such a photonic structure combines a wave guiding with a cavity effect and assures an enhanced light-matter coupling. Coherence properties of an exciton-biexciton system hosted by a quantum dot are assessed with four-wave mixing microscopy. Our results show that… ▽ More We measured coherent ultrafast dynamics of exciton complexes in a single strongly-confined InAs quantum dot embedded in a GaAs nanopost. Such a photonic structure combines a wave guiding with a cavity effect and assures an enhanced light-matter coupling. Coherence properties of an exciton-biexciton system hosted by a quantum dot are assessed with four-wave mixing microscopy. Our results show that this broad-band photonic structure is an excellent asset to probe coherent couplings in a small set of solid state quantum systems and to investigate the coherence dynamics within the level structure of their excited states. △ Less

Submitted 10 July, 2026; originally announced July 2026.

Phonon polariton confinement in isotopically pure MOVPE-grown BN triangles

Authors: Maximilian Scharpey, Oskar Schröer, Daniel Wigger, Lena Miler, Jakub Iwański, Andrzej Wysmołek, Johannes Binder, Iris Niehues

Abstract: Phonon polaritons, quasiparticles formed by the resonant hybridization of light and lattice vibrations, exhibit unique properties like the possibility of hyperbolic dispersions. In this context, exfoliated hexagonal boron nitride (hBN) has emerged as a promising material for phonon polariton-based research. However, to advance toward practical applications, it is essential to demonstrate efficient… ▽ More Phonon polaritons, quasiparticles formed by the resonant hybridization of light and lattice vibrations, exhibit unique properties like the possibility of hyperbolic dispersions. In this context, exfoliated hexagonal boron nitride (hBN) has emerged as a promising material for phonon polariton-based research. However, to advance toward practical applications, it is essential to demonstrate efficient phonon-polariton propagation and confinement in large-area epitaxial BN. To address this topic, we use metalorganic vapor phase epitaxy (MOVPE)-grown BN and investigate the phonon polariton properties using scattering-type scanning near-field optical microscopy (s-SNOM) and nanoscale Fourier transform infrared spectroscopy (nano-FTIR). We report remarkably long phonon polariton propagation lengths, indicating the high crystalline quality of the BN layer. By using epitaxially grown isotopically pure triangular islands, we further demonstrate efficient phonon-polariton confinement with mode patterns tunable by the incident light wavelength. Our results pave the way for implementing all-epitaxial, microscale, high-quality polariton resonators for nanophotonics and quantum optics. △ Less

Submitted 11 June, 2026; originally announced June 2026.

Phonon-induced Markovian and non-Markovian effects on absorption spectra of moiré excitons in twisted transition metal dichalcogenide bilayers

Authors: Daniel Groll, Anton Plonka, Kevin Jürgens, Daniel Wigger, Tilmann Kuhn

Abstract: The properties of moiré excitons in twisted bilayers of transition metal dichalcogenides (TMDCs) vary significantly with the twist angle, ranging from quasi localized excitons with flat dispersions for small twist angles to delocalized excitons for larger ones. This twist angle dependence directly impacts the exciton-phonon coupling, which plays a significant role for the optical properties of the… ▽ More The properties of moiré excitons in twisted bilayers of transition metal dichalcogenides (TMDCs) vary significantly with the twist angle, ranging from quasi localized excitons with flat dispersions for small twist angles to delocalized excitons for larger ones. This twist angle dependence directly impacts the exciton-phonon coupling, which plays a significant role for the optical properties of these materials. In this work we theoretically investigate the twist angle dependent influence of phonons on absorption spectra of intralayer moiré excitons in a twisted TMDC hetero-bilayer. For the lowest-lying intralayer moiré exciton we find that the exciton-phonon coupling interpolates between two physically distinct regimes when tuning the twist angle. At small twist angles non-Markovian polarization dynamics and phonon sidebands dominate the properties of absorption spectra for localized excitons. For larger twist angles Markovian processes become more important leading to additional line broadening. Furthermore, the absorption spectra here show a characteristic asymmetric peak similar to monolayer TMDCs. When taking into account multiple bright moiré exciton bands we find that intraband scattering due to optical phonons has a significant impact on absorption spectra, effectively suppressing absorption peaks of higher lying bands when their bandwidth surpasses the optical phonon energy. △ Less

Submitted 9 January, 2026; originally announced January 2026.

Topical review on acousto-optical Floquet engineering of single-photon emitters

Authors: Daniel Groll, Daniel Wigger, Matthias Weiß, Mingyun Yuan, Alexander Kuznetsov, Alberto Hernández-Mínguez, Hubert J. Krenner, Tilmann Kuhn, Paweł Machnikowski

Abstract: The combination of solid state single-photon emitters and mechanical excitations on a common platform is a promising approach for the development of hybrid quantum technologies. In this topical review we discuss state-of-the-art platforms for emitter-based acousto-optics and their feasibility for acousto-optical Floquet engineering. To this aim we investigate theoretically the resonance fluorescen… ▽ More The combination of solid state single-photon emitters and mechanical excitations on a common platform is a promising approach for the development of hybrid quantum technologies. In this topical review we discuss state-of-the-art platforms for emitter-based acousto-optics and their feasibility for acousto-optical Floquet engineering. To this aim we investigate theoretically the resonance fluorescence (RF) spectrum of an acoustically modulated single-photon emitter under arbitrarily strong optical driving. In the spectrum, the combination of Mollow triplet physics and phonon sidebands results in a complex structure of crossings, anti-crossings, and line suppressions. We apply Floquet theory to develop an analytical expression for the RF spectrum. Complemented with perturbative and non-perturbative techniques, this allows us to fully understand the underlying acousto-optical double dressing physics of the hybrid quantum system, explaining the observed spectral features. We use these insights to perform an experimental feasibility study of existing emitter-based acousto-optical platforms and come to the conclusion that surface and bulk acoustic waves interfaced with quantum dots as an established Mollow triplet platform represent particularly promising infrastructures for acousto-optical Floquet engineering. △ Less

Submitted 30 March, 2026; v1 submitted 11 September, 2025; originally announced September 2025.

Fundamentals of heterodyne wave mixing spectroscopy: a tutorial

Authors: Daniel Groll, Thilo Hahn, Paweł Machnikowski, Tilmann Kuhn, Jacek Kasprzak, Daniel Wigger

Abstract: This tutorial provides a joint theoretical and experimental overview of heterodyne wave mixing spectroscopy, focusing mainly on four-wave mixing (FWM). This powerful and versatile time-resolved nonlinear optical spectroscopy technique enables the investigation of individual localized single photon emitters, as well as microscopy of extended samples, e.g., two-dimensional transition metal dichalcog… ▽ More This tutorial provides a joint theoretical and experimental overview of heterodyne wave mixing spectroscopy, focusing mainly on four-wave mixing (FWM). This powerful and versatile time-resolved nonlinear optical spectroscopy technique enables the investigation of individual localized single photon emitters, as well as microscopy of extended samples, e.g., two-dimensional transition metal dichalcogenides. Starting with the fundamental theory of optically driven two-level systems, we motivate the utility of wave mixing spectroscopy via a discussion on homogeneous and inhomogeneous linewidths which can be independently measured using FWM. We then provide a detailed overview of the heterodyne wave mixing setup operated by one of the authors (JK) at Institut Néel in Grenoble, supported by theoretical modeling of the signal detection process. Throughout the paper we elaborate on important benefits of heterodyne wave mixing spectroscopy, e.g., background-free detection, measurement of the full signal field including amplitude and phase, and investigation of coupling mechanisms in few-level systems. Within the context of the latter point we discuss the significance of two-dimensional (2D) FWM spectra. This tutorial is dedicated to students, young researchers, as well as experts in the field of nonlinear spectroscopy in general and FWM in particular. It explains the fundamental concepts and building blocks required to operate a heterodyne wave mixing experiment both from the experimental and theoretical side. This joint approach is helpful for theoreticians who want to accurately and quantitatively model wave mixing signals, as well as for experimentalists who aim to interpret their recorded data. △ Less

Submitted 25 March, 2025; originally announced March 2025.

Journal ref: Nano Futures 9, 042601 (2025)

Nanoscale resolved mapping of the dipole emission of hBN color centers with a scattering-type scanning near-field optical microscope

Authors: Iris Niehues, Daniel Wigger, Korbinian Kaltenecker, Annika Klein-Hitpass, Philippe Roelli, Aleksandra K. Dąbrowska, Katarzyna Ludwiczak, Piotr Tatarczak, Janne O. Becker, Robert Schmidt, Martin Schnell, Johannes Binder, Andrzej Wysmołek, Rainer Hillenbrand

Abstract: Color centers in hexagonal boron nitride (hBN) are promising candidates as quantum light sources for future technologies. In this work, we utilize a scattering-type near-field optical microscope (s-SNOM) to study the photoluminescence (PL) emission characteristics of such quantum emitters in metalorganic vapor phase epitaxy grown hBN. On the one hand, we demonstrate direct near-field optical excit… ▽ More Color centers in hexagonal boron nitride (hBN) are promising candidates as quantum light sources for future technologies. In this work, we utilize a scattering-type near-field optical microscope (s-SNOM) to study the photoluminescence (PL) emission characteristics of such quantum emitters in metalorganic vapor phase epitaxy grown hBN. On the one hand, we demonstrate direct near-field optical excitation and emission through interaction with the nanofocus of the tip resulting in a sub-diffraction limited tip-enhanced PL hotspot. On the other hand, we show that indirect excitation and emission via scattering from the tip significantly increases the recorded PL intensity. This demonstrates that the tip-assisted PL (TAPL) process efficiently guides the generated light to the detector. We apply the TAPL method to map the in-plane dipole orientations of the hBN color centers on the nanoscale. This work promotes the widely available s-SNOM approach to applications in the quantum domain including characterization and optical control. △ Less

Submitted 25 January, 2025; originally announced January 2025.

Journal ref: Nanophotonics 14 (3), 335-342 (2025)

Theory of phonon sidebands in the absorption spectra of moiré exciton-polaritons

Authors: Kevin Jürgens, Daniel Wigger, Tilmann Kuhn

Abstract: Excitons in twisted bilayers of transition metal dichalcogenides have strongly modified dispersion relations due to the formation of periodic moiré potentials. The strong coupling to a light field in an optical cavity leads to the appearance of moiré polaritons. In this paper, we derive a theoretical model for the linear absorption spectrum of the coupled moiré polariton-phonon system based on the… ▽ More Excitons in twisted bilayers of transition metal dichalcogenides have strongly modified dispersion relations due to the formation of periodic moiré potentials. The strong coupling to a light field in an optical cavity leads to the appearance of moiré polaritons. In this paper, we derive a theoretical model for the linear absorption spectrum of the coupled moiré polariton-phonon system based on the time-convolutionless (TCL) approach. Results obtained by numerically solving the TCL equation are compared to those obtained in the Markovian limit and from a perturbative treatment of non-Markovian corrections. A key quantity for the interpretation of the findings is the generalized phonon spectral density. We discuss the phonon impact on the spectrum for realistic moiré exciton dispersions by varying twist angle and temperature. Key features introduced by the coupling to phonons are broadenings and energy shifts of the upper and lower polariton peak and the appearance of phonon sidebands between them. We analyze these features with respect to the role of Markovian and non-Markovian effects and find that they strongly depend on the twist angle. We can distinguish between the regimes of large, small, and intermediate twist angles. In the latter phonon effects are particularly pronounced due to dominating phonon transitions into regions which are characterized by van Hove singularities in the density of states. △ Less

Submitted 10 June, 2024; originally announced June 2024.

Journal ref: 2D Mater. 11 035027 (2024)

High Harmonic Spectroscopy Probes Lattice Dynamics

Authors: Jicai Zhang, Ziwen Wang, Frank Lengers, Daniel Wigger, Doris E. Reiter, Tilmann Kuhn, Hans Jakob Wörner, Tran Trung Luu

Abstract: The probing of coherent lattice vibrations in solids has been conventionally carried out using time-resolved transient spectroscopy where only the relative oscillation amplitude can be obtained. Using time-resolved X-ray techniques, absolute electron-phonon coupling strength could be extracted. However, the complexity of such an experiment renders it impossible to be carried out in conventional la… ▽ More The probing of coherent lattice vibrations in solids has been conventionally carried out using time-resolved transient spectroscopy where only the relative oscillation amplitude can be obtained. Using time-resolved X-ray techniques, absolute electron-phonon coupling strength could be extracted. However, the complexity of such an experiment renders it impossible to be carried out in conventional laboratories. Here we demonstrate that the electron-phonon, anharmonic phonon-phonon coupling, and their relaxation dynamics can be probed in real-time using high-harmonic spectroscopy. Our technique is background-free and has extreme sensitivity directly in the energy domain. In combination with the optical deformation potential calculated from density functional perturbation theory and the absolute energy modulation depth, our measurement reveals the maximum displacement of neighboring oxygen atoms in α-quartz crystal to tens of picometers in real space. By employing a straightforward and robust time-windowed Gabor analysis for the phonon-modulated high-harmonic spectrum, we successfully observe channel-resolved four-phonon scattering processes in such highly nonlinear interactions. Our work opens a new realm for accurate measurement of coherent phonons and their scattering dynamics, which allows for potential benchmarking ab-initio calculations in solids △ Less

Submitted 21 March, 2024; originally announced March 2024.

Determining Strain Components in a Diamond Waveguide from Zero-Field ODMR Spectra of NV$^{-}$ Center Ensembles

Authors: M. Sahnawaz Alam, Federico Gorrini, Michał Gawełczyk, Daniel Wigger, Giulio Coccia, Yanzhao Guo, Sajedeh Shahbazi, Vibhav Bharadwaj, Alexander Kubanek, Roberta Ramponi, Paul E. Barclay, Anthony J. Bennett, John P. Hadden, Angelo Bifone, Shane M. Eaton, Paweł Machnikowski

Abstract: The negatively charged nitrogen-vacancy (NV$^{-}$) center in diamond has shown great potential in nanoscale sensing and quantum information processing due to its rich spin physics. An efficient coupling with light, providing strong luminescence, is crucial for realizing these applications. Laser-written waveguides in diamond promote NV$^{-}$ creation and improve their coupling to light but, at the… ▽ More The negatively charged nitrogen-vacancy (NV$^{-}$) center in diamond has shown great potential in nanoscale sensing and quantum information processing due to its rich spin physics. An efficient coupling with light, providing strong luminescence, is crucial for realizing these applications. Laser-written waveguides in diamond promote NV$^{-}$ creation and improve their coupling to light but, at the same time, induce strain in the crystal. The induced strain contributes to light guiding but also affects the energy levels of NV$^{-}$ centers. We probe NV$^{-}$ spin states experimentally with the commonly used continuous-wave zero-field optically detected magnetic resonance (ODMR). In our waveguides, the ODMR spectra are shifted, split, and consistently asymmetric, which we attribute to the impact of local strain. To understand these features, we model ensemble ODMR signals in the presence of strain. By fitting the model results to the experimentally collected ODMR data, we determine the strain tensor components at different positions, thus determining the strain profile across the waveguide. This shows that zero-field ODMR spectroscopy can be used as a strain imaging tool. The resulting strain within the waveguide is dominated by a compressive axial component transverse to the waveguide structure, with a smaller contribution from vertical and shear strain components. △ Less

Submitted 12 August, 2024; v1 submitted 9 February, 2024; originally announced February 2024.

Comments: 12 pages, 7 figures + Supplementary Information (6 pages, 3 figures)

How to read out the phonon number statistics via resonance fluorescence spectroscopy of a single-photon emitter

Authors: Daniel Groll, Fabian Paschen, Paweł Machnikowski, Ortwin Hess, Daniel Wigger, Tilmann Kuhn

Abstract: In today's development of quantum technologies a hybrid integration of phononic excitations becomes increasingly attractive. As natural quasi-particle excitations in solid state systems, phonons couple to virtually any other excitation and therefore constitute a useful interaction channel between different building blocks in hybrid quantum systems. This work explores how the efficient light-scatte… ▽ More In today's development of quantum technologies a hybrid integration of phononic excitations becomes increasingly attractive. As natural quasi-particle excitations in solid state systems, phonons couple to virtually any other excitation and therefore constitute a useful interaction channel between different building blocks in hybrid quantum systems. This work explores how the efficient light-scattering properties of a single-photon emitter and the appearance of characteristic sidebands in resonance fluorescence spectra, when interfaced with an arbitrary phonon quantum state, can be utilized for acousto-optical transduction. Within reasonable approximations, an analytical description for the optical spectra in the low excitation limit is developed which can be used to read the number statistics of the initial phonon state from a given spectrum. It is shown that the readout is faulty in situations where relevant resonant transitions are forbidden due to vanishing Franck-Condon factors, especially when considering spectra with a noisy background. Two possible solutions to this problem are presented: (A) changing the detuning of the laser relative to the single-photon emitter which modifies the relevant resonant transitions, or (B) increasing dissipation of the single-photon emitter to promote off-resonant transitions. △ Less

Submitted 30 June, 2023; originally announced June 2023.

Journal ref: Adv. Quantum Technol. 8, 2300153 (2025)

Controlled Coherent Coupling in a Quantum Dot Molecule Revealed by Ultrafast Four-Wave Mixing Spectroscopy

Authors: Daniel Wigger, Johannes Schall, Marielle Deconinck, Nikolai Bart, Paweł Mrowiński, Mateusz Krzykowski, Krzysztof Gawarecki, Martin von Helversen, Ronny Schmidt, Lucas Bremer, Frederik Bopp, Dirk Reuter, Andreas D. Wieck, Sven Rodt, Julien Renard, Gilles Nogues, Arne Ludwig, Paweł Machnikowski, Jonathan J. Finley, Stephan Reitzenstein, Jacek Kasprzak

Abstract: Semiconductor quantum dot molecules are considered as promising candidates for quantum technological applications due to their wide tunability of optical properties and coverage of different energy scales associated with charge and spin physics. While previous works have studied the tunnel-coupling of the different excitonic charge complexes shared by the two quantum dots by conventional optical s… ▽ More Semiconductor quantum dot molecules are considered as promising candidates for quantum technological applications due to their wide tunability of optical properties and coverage of different energy scales associated with charge and spin physics. While previous works have studied the tunnel-coupling of the different excitonic charge complexes shared by the two quantum dots by conventional optical spectroscopy, we here report on the first demonstration of a coherently controlled inter-dot tunnel-coupling focusing on the quantum coherence of the optically active trion transitions. We employ ultrafast four-wave mixing spectroscopy to resonantly generate a quantum coherence in one trion complex, transfer it to and probe it in another trion configuration. With the help of theoretical modelling on different levels of complexity we give an instructive explanation of the underlying coupling mechanism and dynamical processes. △ Less

Submitted 20 April, 2023; originally announced April 2023.

Journal ref: ACS Photonics 10 (5), 1504-1511 (2023)

Controlled coherent-coupling and dynamics of exciton complexes in a MoSe$_2$ monolayer

Authors: Aleksander Rodek, Thilo Hahn, James Howarth, Takashi Taniguchi, Kenji Watanabe, Marek Potemski, Piotr Kossacki, Daniel Wigger, Jacek Kasprzak

Abstract: Quantifying and controlling the coherent dynamics and couplings of optically active excitations in solids is of paramount importance in fundamental research in condensed matter optics and for their prospective optoelectronic applications in quantum technologies. Here, we perform ultrafast coherent nonlinear spectroscopy of a charge-tunable MoSe$_2$ monolayer. The experiments show that the homogene… ▽ More Quantifying and controlling the coherent dynamics and couplings of optically active excitations in solids is of paramount importance in fundamental research in condensed matter optics and for their prospective optoelectronic applications in quantum technologies. Here, we perform ultrafast coherent nonlinear spectroscopy of a charge-tunable MoSe$_2$ monolayer. The experiments show that the homogeneous and inhomogeneous line width and the population decay of exciton complexes hosted by this material can be directly tuned by an applied gate bias, which governs the Fermi level and therefore the free carrier density. By performing two-dimensional spectroscopy, we also show that the same bias-tuning approach permits us to control the coherent coupling strength between charged and neutral exciton complexes. △ Less

Submitted 25 February, 2023; originally announced February 2023.

Resonant and phonon-assisted ultrafast coherent control of a single hBN color center

Authors: Johann A. Preuß, Daniel Groll, Robert Schmidt, Thilo Hahn, Paweł Machnikowski, Rudolf Bratschitsch, Tilmann Kuhn, Steffen Michaelis de Vasconcellos, Daniel Wigger

Abstract: Single-photon emitters in solid-state systems are important building blocks for scalable quantum technologies. Recently, quantum light emitters have been discovered in the wide-gap van der Waals insulator hBN. These color centers have attracted considerable attention due to their quantum performance at elevated temperatures and wide range of transition energies. Here, we demonstrate coherent state… ▽ More Single-photon emitters in solid-state systems are important building blocks for scalable quantum technologies. Recently, quantum light emitters have been discovered in the wide-gap van der Waals insulator hBN. These color centers have attracted considerable attention due to their quantum performance at elevated temperatures and wide range of transition energies. Here, we demonstrate coherent state manipulation of a single hBN color center with ultrafast laser pulses and investigate in our joint experiment-theory study the coupling between the electronic system and phonons. We demonstrate that coherent control can not only be performed resonantly on the optical transition giving access to the decoherence but also phonon-assisted, which reveals the internal phonon quantum dynamics. In the case of optical phonons we measure their decoherence, stemming in part from their anharmonic decay. Dephasing induced by the creation of acoustic phonons manifests as a rapid decrease of the coherent control signal when traveling phonon wave packets are emitted. Furthermore, we demonstrate that the quantum superposition between a phonon-assisted process and the resonant excitation causes ultrafast oscillations of the coherent control signal. Our results pave the way for ultrafast phonon quantum state control on the nanoscale and open up a new promising perspective for hybrid quantum technologies. △ Less

Submitted 10 May, 2022; originally announced May 2022.

Journal ref: Optica 9(5), 522-531 (2022)

Photon scattering from a quantum acoustically modulated two-level system

Authors: Thilo Hahn, Daniel Groll, Hubert J. Krenner, Tilmann Kuhn, Paweł Machnikowski, Daniel Wigger

Abstract: We calculate the resonance fluorescence signal of a two-level system coupled to a quantized phonon mode. By treating the phonons in the independent boson model and not performing any approximations in their description, we also have access to the state evolution of the phonons. We confirm the validity of our model by simulating the limit of an initial quasi-classical coherent phonon state, which c… ▽ More We calculate the resonance fluorescence signal of a two-level system coupled to a quantized phonon mode. By treating the phonons in the independent boson model and not performing any approximations in their description, we also have access to the state evolution of the phonons. We confirm the validity of our model by simulating the limit of an initial quasi-classical coherent phonon state, which can be compared to experimentally confirmed results in the semiclassical limit. In addition we predict photon scattering spectra in the limit of purely quantum mechanical phonon states by approaching the phononic vacuum. Our method further allows us to simulate the impact of the light scattering process on the phonon state by calculating Wigner functions. We show that the phonon mode is brought into characteristic quantum states by the optical excitation process. △ Less

Submitted 20 January, 2022; originally announced January 2022.

Journal ref: AVS Quantum Sci. 4, 011403 (2022)

Coherent dynamics of a single Mn-doped quantum dot revealed by four-wave mixing spectroscopy

Authors: Jacek Kasprzak, Daniel Wigger, Thilo Hahn, Tomasz Jakubczyk, Łukasz Zinkiewicz, Paweł Machnikowski, Tilmann Kuhn, Jean-François Motte, Wojciech Pacuski

Abstract: For future quantum technologies the combination of a long quantum state lifetime and an efficient interface with external optical excitation are required. In solids, the former is for example achieved by individual spins, while the latter is found in semiconducting artificial atoms combined with modern photonic structures. One possible combination of the two aspects is reached by doping a single q… ▽ More For future quantum technologies the combination of a long quantum state lifetime and an efficient interface with external optical excitation are required. In solids, the former is for example achieved by individual spins, while the latter is found in semiconducting artificial atoms combined with modern photonic structures. One possible combination of the two aspects is reached by doping a single quantum dot, providing a strong excitonic dipole, with a magnetic ion, that incorporates a characteristic spin texture. Here, we perform four-wave mixing spectroscopy to study the system's quantum coherence properties. We characterize the optical properties of the undoped CdTe quantum dot and find a strong photon echo formation which demonstrates a significant inhomogeneous spectral broadening. Incorporating the Mn$^{2+}$ ion introduces its spin-5/2 texture to the optical spectra via the exchange interaction, manifesting as six individual spectral lines in the coherent response. The random flips of the Mn-spin result in a special type of spectral wandering between the six transition energies, which is fundamentally different from the quasi-continuous spectral wandering that results in the Gaussian inhomogeneous broadening. Here, the discrete spin-ensemble manifests in additional dephasing and oscillation dynamics. △ Less

Submitted 3 January, 2022; originally announced January 2022.

Journal ref: ACS Photonics 9 (3), 1033-1041 (2022)

Comparison of the semiclassical and quantum optical field dynamics in a pulse-excited optical cavity with a finite number of quantum emitters

Authors: K. Jürgens, F. Lengers, D. Groll, D. E. Reiter, D. Wigger, T. Kuhn

Abstract: The spectral and temporal response of a set of $N$ quantum emitters embedded in a photonic cavity is studied. Quantum mechanically, such systems can be described by the Tavis-Cummings (TC) model of $N$ two-level systems coupled to a single light mode. Here we compare the full quantum solution of the TC model for different numbers of quantum emitters with its semiclassical limit after a pulsed exci… ▽ More The spectral and temporal response of a set of $N$ quantum emitters embedded in a photonic cavity is studied. Quantum mechanically, such systems can be described by the Tavis-Cummings (TC) model of $N$ two-level systems coupled to a single light mode. Here we compare the full quantum solution of the TC model for different numbers of quantum emitters with its semiclassical limit after a pulsed excitation of the cavity mode. Considering different pulse amplitudes, we find that the spectra obtained from the TC model approach the semiclassical one for an increasing number of emitters $N$. Furthermore they match very well for small pulse amplitudes. While we observe a very good agreement in the temporal dynamics for photon numbers much smaller than $N$, considerable deviations occur in the regime of photon numbers similar to or larger than $N$, which are linked to collapse and revival phenomena. Wigner functions of the light mode are calculated for different scenarios to analyze the quantum state of the light field. We find strong deviations from a coherent state even if the dynamics of the expectation values are still well described by the semiclassical limit. For higher pulse amplitudes Wigner functions similar to those of Schrödinger cat states between two or more quasi-coherent contributions build up. △ Less

Submitted 11 November, 2021; originally announced November 2021.

Comments: accepted for publication in Physical Review B https://journals.aps.org/prb/

Journal ref: Phys. Rev. B 104, 205308 (2021)

Destructive photon echo formation in six-wave mixing signals of a MoSe$_2$ monolayer

Authors: Thilo Hahn, Diana Vaclavkova, Miroslav Bartos, Karol Nogajewski, Marek Potemski, Kenji Watanabe, Takashi Taniguchi, Paweł Machnikowski, Tilmann Kuhn, Jacek Kasprzak, Daniel Wigger

Abstract: Monolayers of transition metal dichalcogenides display a strong excitonic optical response. Additionally encapsulating the monolayer with hexagonal boron nitride allows to reach the limit of a purely homogeneously broadened exciton system. On such a MoSe$_{2}$-based system we perform ultrafast six-wave mixing spectroscopy and find a novel destructive photon echo effect. This process manifests as a… ▽ More Monolayers of transition metal dichalcogenides display a strong excitonic optical response. Additionally encapsulating the monolayer with hexagonal boron nitride allows to reach the limit of a purely homogeneously broadened exciton system. On such a MoSe$_{2}$-based system we perform ultrafast six-wave mixing spectroscopy and find a novel destructive photon echo effect. This process manifests as a characteristic depression of the nonlinear signal dynamics when scanning the delay between the applied laser pulses. By theoretically describing the process within a local field model we reach an excellent agreement with the experiment. We develop an effective Bloch vector representation and thereby demonstrate that the destructive photon echo stems from a destructive interference of successive repetitions of the heterodyning experiment. △ Less

Submitted 6 October, 2021; originally announced October 2021.

Journal ref: Adv. Sci. 9, 2103813 (2022)

Resonance fluorescence spectral dynamics of an acoustically modulated quantum dot

Authors: Daniel Wigger, Matthias Weiß, Michelle Lienhart, Kai Müller, Jonathan J. Finley, Tilmann Kuhn, Hubert J. Krenner, Paweł Machnikowski

Abstract: Quantum technologies that rely on photonic qubits require a precise controllability of their properties. For this purpose hybrid approaches are particularly attractive because they offer a large flexibility to address different aspects of the photonic degrees of freedom. When combining photonics with other quantum platforms like phonons, quantum transducers have to be realized that convert between… ▽ More Quantum technologies that rely on photonic qubits require a precise controllability of their properties. For this purpose hybrid approaches are particularly attractive because they offer a large flexibility to address different aspects of the photonic degrees of freedom. When combining photonics with other quantum platforms like phonons, quantum transducers have to be realized that convert between the mechanical and optical domain. Here, we realize this interface between phonons in the form of surface acoustic waves (SAWs) and single photons, mediated by a single semiconductor quantum dot exciton. In this combined theoretical and experimental study, we show that the different sidebands exhibit characteristic blinking dynamics that can be controlled by detuning the laser from the exciton transition. By developing analytical approximations we gain a better understanding of the involved internal dynamics. Our specific SAW approach allows us to reach the ideal frequency range of around 1 GHz that enables simultaneous temporal and spectral phonon sideband resolution close to the combined fundamental time-bandwidth limit. △ Less

Submitted 10 August, 2021; originally announced August 2021.

Journal ref: Phys. Rev. Research 3, 033197 (2021)

Local field effects in ultrafast light-matter interaction measured by pump-probe spectroscopy of monolayer MoSe$_{\boldsymbol 2}$

Authors: Aleksander Rodek, Thilo Hahn, Jacek Kasprzak, Tomasz Kazimierczuk, Karol Nogajewski, Karolina Połczyńska, Kenji Watanabe, Takashi Taniguchi, Tilmann Kuhn, Paweł Machnikowski, Marek Potemski, Daniel Wigger, Piotr Kossacki

Abstract: Using a novel approach to ultrafast resonant pump-probe spectroscopy we investigate the spectral shape and dynamics of absorption features related to the A exciton in an hBN/MoSe$_2$/hBN van der Waals heterostructure. While in a pure two-level system a pump-probe experiment measures the occupation or the polarization dynamics, depending on the time ordering of the pulse pair, in the transition met… ▽ More Using a novel approach to ultrafast resonant pump-probe spectroscopy we investigate the spectral shape and dynamics of absorption features related to the A exciton in an hBN/MoSe$_2$/hBN van der Waals heterostructure. While in a pure two-level system a pump-probe experiment measures the occupation or the polarization dynamics, depending on the time ordering of the pulse pair, in the transition metal dichalcogenide (TMD) system both quantities get thoroughly mixed by strong exciton-exciton interaction. We find that for short positive delays the spectral lines experience pronounced changes in their shape and energy and they relax to the original situation on a picosecond time scale. For negative delays distinctive spectral oscillations appear indicating the first-time observation of perturbed free induction decay for a TMD system. The comparison between co-circular and cross-circular excitation schemes further allows us to investigate the rapid inter-valley scattering. By considering a three-level system as a minimal model including the local field effect, excitation induced dephasing and scattering between the excited states we explain all phenomena observed in the experiment with excellent consistency. Our handy model can be even further reduced to two levels in the case of a co-circular excitation, for which we derive analytic expressions to describe the detected signals. This allows us to trace back the spectral shapes and shifts to the impact of local field effect and excitation induced dephasing thus fully reproducing the complex behavior of the observed effects. △ Less

Submitted 22 August, 2021; v1 submitted 9 March, 2021; originally announced March 2021.

Journal ref: Nanophotonics 10, 2717-2728 (2021)

Influence of local fields on the dynamics of four-wave mixing signals from 2D semiconductor systems

Authors: Thilo Hahn, Jacek Kasprzak, Paweł Machnikowski, Tilmann Kuhn, Daniel Wigger

Abstract: In recent years the physics of two-dimensional semiconductors was revived by the discovery of the class of transition metal dichalcogenides. In these systems excitons dominate the optical response in the visible range and open many perspectives for nonlinear spectroscopy. To describe the coherence and polarization dynamics of excitons after ultrafast excitation in these systems, we employ the Bloc… ▽ More In recent years the physics of two-dimensional semiconductors was revived by the discovery of the class of transition metal dichalcogenides. In these systems excitons dominate the optical response in the visible range and open many perspectives for nonlinear spectroscopy. To describe the coherence and polarization dynamics of excitons after ultrafast excitation in these systems, we employ the Bloch equation model of a two-level system extended by a local field describing the exciton-exciton interaction. We calculate four-wave mixing signals and analyze the dependence of the temporal and spectral signals as a function of the delay between the exciting pulses. Exact analytical results obtained for the case of ultrafast ($δ$-shaped) pulses are compared to numerical solutions obtained for finite pulse durations. If two pulses are used to generate the nonlinear signal, characteristic spectral line splittings are restricted to short delays. When considering a three-pulse excitation the line splittings, induced by the local field effect, persist for long delays. All of the found features are instructively explained within the Bloch vector picture and we show how the exciton occupation dynamics govern the different four-wave mixing signals. △ Less

Submitted 25 February, 2021; originally announced February 2021.

Journal ref: New J. Phys. 23 023036 (2021)

Controlling Photoluminescence Spectra of hBN Color Centers by Selective Phonon-Assisted Excitation: A Theoretical Proposal

Authors: Daniel Groll, Thilo Hahn, Paweł Machnikowski, Daniel Wigger, Tilmann Kuhn

Abstract: Color centers in hexagonal boron nitride (hBN) show stable single photon emission even at room temperature, making these systems a promising candidate for quantum information applications. Besides this remarkable property, also their interaction with longitudinal optical (LO) phonons is quite unique because they lead to dominant phonon sidebands (PSBs), well separated from the zero phonon line (ZP… ▽ More Color centers in hexagonal boron nitride (hBN) show stable single photon emission even at room temperature, making these systems a promising candidate for quantum information applications. Besides this remarkable property, also their interaction with longitudinal optical (LO) phonons is quite unique because they lead to dominant phonon sidebands (PSBs), well separated from the zero phonon line (ZPL). In this work we utilize this clear spectral separation to theoretically investigate the influence of phonon decay dynamics on time-dependent photoluminescence (PL) signals. Our simulations show, that by using tailored optical excitation schemes it is possible to create a superposition between the two LO modes, leading to a phonon quantum beat that manifests in the time-dependent PL signal. △ Less

Submitted 18 February, 2021; v1 submitted 19 November, 2020; originally announced November 2020.

Journal ref: Mater. Quantum. Technol. 1, 015004 (2021)

Four-wave mixing dynamics of a strongly coupled quantum-dot--microcavity system driven by up to 20 photons

Authors: Daniel Groll, Daniel Wigger, Kevin Jürgens, Thilo Hahn, Christian Schneider, Martin Kamp, Sven Höfling, Jacek Kasprzak, Tilmann Kuhn

Abstract: The Jaynes-Cummings (JC) model represents one of the simplest ways in which single qubits can interact with single photon modes, leading to profound quantum phenomena like superpositions of light and matter states. One system, that can be described with the JC model, is a single quantum dot embedded in a micropillar cavity. In this joint experimental and theoretical study we investigate such a sys… ▽ More The Jaynes-Cummings (JC) model represents one of the simplest ways in which single qubits can interact with single photon modes, leading to profound quantum phenomena like superpositions of light and matter states. One system, that can be described with the JC model, is a single quantum dot embedded in a micropillar cavity. In this joint experimental and theoretical study we investigate such a system using four-wave mixing (FWM) micro-spectroscopy. Special emphasis is laid on the dependence of the FWM signals on the number of photons injected into the microcavity. By comparing simulation and experiment, which are in excellent agreement with each other, we infer that up to ~20 photons take part in the observed FWM dynamics. Thus we verify the validity of the JC model for the system under consideration in this non-trivial regime. We find that the inevitable coupling between the quantum dot exciton and longitudinal acoustic phonons of the host lattice influences the real time FWM dynamics and has to be taken into account for a sufficient description of the quantum dot-microcavity system. Performing additional simulations in an idealized dissipation-less regime, we observe that the FWM signal exhibits quasi-periodic dynamics, analog to the collapse and revival phenomenon of the JC model. In these simulations we also see that the FWM spectrum has a triplet structure, if a large number of photons is injected into the cavity. △ Less

Submitted 12 June, 2020; originally announced June 2020.

Journal ref: Phys. Rev. B 101, 245301 (2020)

Entropy Dynamics of Phonon Quantum States Generated by Optical Excitation of a Two-Level System

Authors: Thilo Hahn, Daniel Wigger, Tilmann Kuhn

Abstract: In quantum physics, two prototypical model systems stand out due to their wide range of applications. These are the two-level system (TLS) and the harmonic oscillator. The former is often an ideal model for confined charge or spin systems and the latter for lattice vibrations, i.e., phonons. Here, we couple these two systems, which leads to numerous fascinating physical phenomena. Practically, we… ▽ More In quantum physics, two prototypical model systems stand out due to their wide range of applications. These are the two-level system (TLS) and the harmonic oscillator. The former is often an ideal model for confined charge or spin systems and the latter for lattice vibrations, i.e., phonons. Here, we couple these two systems, which leads to numerous fascinating physical phenomena. Practically, we consider different optical excitations and decay scenarios of a TLS, focusing on the generated dynamics of a single phonon mode that couples to the TLS. Special emphasis is placed on the entropy of the different parts of the system, predominantly the phonons. While, without any decay, the entire system is always in a pure state, resulting in a vanishing entropy, the complex interplay between the single parts results in non-vanishing respective entanglement entropies and non-trivial dynamics of them. Taking a decay of the TLS into account leads to a non-vanishing entropy of the full system and additional aspects in its dynamics. We demonstrate that all aspects of the entropy's behavior can be traced back to the purity of the states and are illustrated by phonon Wigner functions in phase space. △ Less

Submitted 3 March, 2020; originally announced March 2020.

Journal ref: Entropy 2020, 22(3), 286

Acoustic Phonon Sideband Dynamics During Polaron Formation in a Single Quantum Dot

Authors: Daniel Wigger, Vage Karakhanyan, Christian Schneider, Martin Kamp, Sven Höfling, Paweł Machnikowski, Tilmann Kuhn, Jacek Kasprzak

Abstract: When an electron-hole pair is optically excited in a semiconductor quantum dot the host crystal lattice needs to adapt to the presence of the generated charge distribution. Therefore the coupled exciton-phonon system has to establish a new equilibrium, which is reached in the form of a quasiparticle called polaron. Especially, when the exciton is abruptly generated on a timescale faster than the t… ▽ More When an electron-hole pair is optically excited in a semiconductor quantum dot the host crystal lattice needs to adapt to the presence of the generated charge distribution. Therefore the coupled exciton-phonon system has to establish a new equilibrium, which is reached in the form of a quasiparticle called polaron. Especially, when the exciton is abruptly generated on a timescale faster than the typical lattice dynamics, the lattice displacement cannot follow adiabatically. Consequently, a rich dynamics on the picosecond timescale of the coupled system is expected. In this study we combine simulations and measurements of the ultrafast, coherent, nonlinear optical response, obtained by four-wave mixing spectroscopy, to resolve the formation of this polaron. By detecting and investigating the phonon sidebands in the four-wave mixing spectra for varying pulse delays and different temperatures we have access to the influence of phonon emission and absorption processes which finally result in the emission of an acoustic wave packet out from the quantum dot. △ Less

Submitted 9 January, 2020; originally announced January 2020.

Comments: accepted in Optics Letters

Journal ref: Opt. Lett. 45(4), 919-922 (2020)

Nonlinear quantum dot optomechanics

Authors: Matthias Weiß, Daniel Wigger, Maximilian Nägele, Kai Müller, Jonathan J. Finley, Tilmann Kuhn, Paweł Machnikowski, Hubert J. Krenner

Abstract: Wave mixing is an archetypical phenomenon in bosonic systems. In optomechanics, the bi-directional conversion between electromagnetic waves or photons at optical frequencies and elastic waves or phonons at radio frequencies is building on precisely this fundamental principle. Surface acoustic waves provide a versatile interconnect on a chip and, thus, enable the optomechanical control of remote sy… ▽ More Wave mixing is an archetypical phenomenon in bosonic systems. In optomechanics, the bi-directional conversion between electromagnetic waves or photons at optical frequencies and elastic waves or phonons at radio frequencies is building on precisely this fundamental principle. Surface acoustic waves provide a versatile interconnect on a chip and, thus, enable the optomechanical control of remote systems. Here, we report on the coherent nonlinear three-wave mixing between the coherent fields of two radio frequency surface acoustic waves and optical laser photons via the dipole transition of a single quantum dot exciton. In the resolved sideband regime, we demonstrate fundamental acoustic analogues of sum and difference frequency generation between the two SAWs and employ phase matching to deterministically enhance or suppress individual sidebands. This bi-directional transfer between the acoustic and optical domains is described by theory which fully takes into account direct and virtual multi-phonon processes. Finally, we show that the precision of the wave mixing is limited by the frequency accuracy of modern radio frequency electronics. △ Less

Submitted 18 June, 2020; v1 submitted 28 October, 2019; originally announced October 2019.

Comments: Submitted Manuscript

Journal ref: Optica 8, pp. 291-300 (2021)

Influence of excited state decay and dephasing on phonon quantum state preparation

Authors: Thilo Hahn, Daniel Groll, Tilmann Kuhn, Daniel Wigger

Abstract: The coupling between single-photon emitters and phonons opens many possibilities to store and transmit quantum properties. In this paper we apply the independent boson model to describe the coupling between an optically driven two-level system and a discrete phonon mode. Tailored optical driving allows not only to generate coherent phonon states, but also to generate coherent superpositions in the… ▽ More The coupling between single-photon emitters and phonons opens many possibilities to store and transmit quantum properties. In this paper we apply the independent boson model to describe the coupling between an optically driven two-level system and a discrete phonon mode. Tailored optical driving allows not only to generate coherent phonon states, but also to generate coherent superpositions in the form of Schrödinger cat states in the phonon system. We analyze the influence of decay and dephasing of the two-level system on these phonon preparation protocols. We find that the decay transforms the coherent phonon state into a circular distribution in phase space. Although the dephasing between two exciting laser pulses leads to a reduction of the interference ability in the phonon system, the decay conserves it during the transition into the ground state. This allows to store the phonon quantum state properties in the ground state of the single-photon emitter. △ Less

Submitted 17 July, 2019; originally announced July 2019.

Journal ref: Phys. Rev. B 100, 024306 (2019)

Phonon-assisted emission and absorption of individual color centers in hexagonal boron nitride

Authors: Daniel Wigger, Robert Schmidt, Osvaldo Del Pozo-Zamudio, Johann A. Preuß, Philipp Tonndorf, Robert Schneider, Paul Steeger, Johannes Kern, Yashar Khodaei, Jaroslaw Sperling, Steffen Michaelis de Vasconcellos, Rudolf Bratschitsch, Tilmann Kuhn

Abstract: Defect centers in hexagonal boron nitride represent room-temperature single-photon sources in a layered van der Waals material. These light emitters appear with a wide range of transition energies ranging over the entire visible spectrum, which renders the identification of the underlying atomic structure challenging. In addition to their eminent properties as quantum light emitters, the coupling… ▽ More Defect centers in hexagonal boron nitride represent room-temperature single-photon sources in a layered van der Waals material. These light emitters appear with a wide range of transition energies ranging over the entire visible spectrum, which renders the identification of the underlying atomic structure challenging. In addition to their eminent properties as quantum light emitters, the coupling to phonons is remarkable. Their photoluminescence exhibits significant side band emission well separated from the zero phonon line (ZPL) and an asymmetric broadening of the ZPL itself. In this combined theoretical and experimental study we show that the phonon side bands can be well described in terms of the coupling to bulk longitudinal optical (LO) phonons. To describe the ZPL asymmetry we show that in addition to the coupling to longitudinal acoustic (LA) phonons also the coupling to local mode oscillations of the defect center with respect to the entire host crystal has to be considered. By studying the influence of the emitter's wave function dimensions on the phonon side bands we find reasonable values for size of the wave function and the deformation potentials. We perform photoluminescence excitation measurements to demonstrate that the excitation of the emitters is most efficient by LO-phonon assisted absorption. △ Less

Submitted 27 March, 2019; originally announced March 2019.

Comments: Accepted, Including Supplementary Material, Licence: https://creativecommons.org/licenses/by/3.0/ (preprint published online: https://iopscience.iop.org/article/10.1088/2053-1583/ab1188)

Journal ref: 2D Mater. 6, 035006 (2019)

Rabi oscillations of a quantum dot exciton coupled to acoustic phonons: coherence and population readout

Authors: Daniel Wigger, Christian Schneider, Stefan Gerhardt, Martin Kamp, Sven Höfling, Tilmann Kuhn, Jacek Kasprzak

Abstract: While the advanced coherent control of qubits is now routinely carried out in low frequency (GHz) systems like single spins, it is far more challenging to achieve for two-level systems in the optical domain. This is because the latter evolve typically in the THz range, calling for tools of ultrafast, coherent, nonlinear optics. Using four-wave mixing micro-spectroscopy, we here measure the optical… ▽ More While the advanced coherent control of qubits is now routinely carried out in low frequency (GHz) systems like single spins, it is far more challenging to achieve for two-level systems in the optical domain. This is because the latter evolve typically in the THz range, calling for tools of ultrafast, coherent, nonlinear optics. Using four-wave mixing micro-spectroscopy, we here measure the optically driven dynamics of a single exciton quantum state confined in a semiconductor quantum dot. In a combined experimental and theoretical approach, we reveal the intrinsic Rabi oscillation dynamics by monitoring both central exciton quantities, i.e., its occupation and the microscopic coherence, as resolved by the four-wave mixing technique. In the frequency domain this oscillation generates the Autler-Townes splitting of the light-exciton dressed states, directly seen in the four-wave mixing spectra. We further demonstrate that the coupling to acoustic phonons strongly influences the FWM dynamics on the picosecond timescale, because it leads to transitions between the dressed states. △ Less

Submitted 27 September, 2018; originally announced September 2018.

Comments: accepted for publication in Optica

Journal ref: Optica 5(11), 1442-1450 (2018)

Exploring coherence of individual excitons in InAs quantum dots embedded in natural photonic defects: influence of the excitation intensity

Authors: Daniel Wigger, Valentin Delmonte, Quentin Mermillod, Tomasz Jakubczyk, François Fras, Simon Le-Denmat, Doris E. Reiter, Sven Höfling, Martin Kamp, Gilles Nogues, Christian Schneider, Tilmann Kuhn, Jacek Kasprzak

Abstract: The exact optical response of quantum few-level systems depends crucially on the exact choice of the incoming pulse areas. We use four-wave mixing (FWM) spectroscopy to infer the coherent response and dynamics of single InAs quantum dots (QDs) and study their pulse area dependence. By combining atomic force microscopy with FWM hyperspectral imaging, we show that the retrieved FWM signals originate… ▽ More The exact optical response of quantum few-level systems depends crucially on the exact choice of the incoming pulse areas. We use four-wave mixing (FWM) spectroscopy to infer the coherent response and dynamics of single InAs quantum dots (QDs) and study their pulse area dependence. By combining atomic force microscopy with FWM hyperspectral imaging, we show that the retrieved FWM signals originate from individual QDs enclosed in natural photonic defects. The optimized light-matter coupling in these defects allows us to perform our studies in a wide range of driving field amplitudes. When varying the pulse areas of the exciting laser pulses the so-called Rabi rotations can be resolved by the two-pulse FWM technique. We investigate these Rabi rotations within two- and three-level systems, both theoretically and experimentally, and explain their damping by the coupling to acoustic phonons. To highlight the importance of the pulse area influence, we show that the phonon-induced dephasing of QD excitons depends on the pulse intensity. △ Less

Submitted 11 April, 2017; originally announced April 2017.

Journal ref: Phys. Rev. B 96, 165311 (2017)

Systematic study of the influence of coherent phonon wave packets on the lasing properties of a quantum dot ensemble

Authors: D. Wigger, T. Czerniuk, D. E. Reiter, M. Bayer, T. Kuhn

Abstract: Coherent phonons can greatly vary light-matter interaction in semiconductor nanostructures placed inside an optical resonator on an ultrafast time scale. For an ensemble of quantum dots as active laser medium phonons are able to induce a large enhancement or attenuation of the emission intensity, as has been recently demonstrated. The physics of this coupled phonon-exciton-photon system consists o… ▽ More Coherent phonons can greatly vary light-matter interaction in semiconductor nanostructures placed inside an optical resonator on an ultrafast time scale. For an ensemble of quantum dots as active laser medium phonons are able to induce a large enhancement or attenuation of the emission intensity, as has been recently demonstrated. The physics of this coupled phonon-exciton-photon system consists of various effects, which in the experiment typically cannot be clearly separated, in particular because a rather complex strain pulse impinges on the quantum dot ensemble. Here we present a comprehensive theoretical study how the laser emission is affected by phonon pulses of various shapes as well as by ensembles with different spectral distributions of the quantum dots. This gives insight into the fundamental interaction dynamics of the coupled phonon-exciton-photon system, while it allows us to clearly discriminate between two prominent effects: the adiabatic shifting of the ensemble and the shaking effect. This paves the way to a tailored laser emission controlled by phonons. △ Less

Submitted 27 July, 2017; v1 submitted 16 January, 2017; originally announced January 2017.

Journal ref: New J. Phys. 19, 073001 (2017)

Picosecond control of quantum dot laser emission by coherent phonons

Authors: Thomas Czerniuk, Daniel Wigger, Andrey V. Akimov, Christian Schneider, Dmitri R. Yakovlev, Tilmann Kuhn, Doris E. Reiter, Manfred Bayer

Abstract: A picosecond acoustic pulse can be used to control the lasing emission from semiconductor nanostructures by shifting their electronic transitions. When the active medium, here an ensemble of (In,Ga)As quantum dots, is shifted into or out of resonance with the cavity mode, a large enhancement or suppression of the lasing emission can dynamically be achieved. Most interesting, even in the case when… ▽ More A picosecond acoustic pulse can be used to control the lasing emission from semiconductor nanostructures by shifting their electronic transitions. When the active medium, here an ensemble of (In,Ga)As quantum dots, is shifted into or out of resonance with the cavity mode, a large enhancement or suppression of the lasing emission can dynamically be achieved. Most interesting, even in the case when gain medium and cavity mode are in resonance, we observe an enhancement of the lasing due to shaking by coherent phonons. In order to understand the interactions of the non-linearly coupled photon-exciton-phonon subsystems, we develop a semiclassical model and find an excellent agreement between theory and experiment. △ Less

Submitted 16 January, 2017; v1 submitted 13 January, 2017; originally announced January 2017.

Journal ref: Phys. Rev. Lett. 118, 133901 (2017)

Impact of phonons on dephasing of individual excitons in deterministic quantum dot microlenses

Authors: T. Jakubczyk, V. Delmonte, S. Fischbach, D. Wigger, D. E. Reiter, Q. Mermillod, P. Schnauber, A. Kaganskiy, J. -H. Schulze, A. Strittmatter, S. Rodt, W. Langbein, T. Kuhn, S. Reitzenstein, J. Kasprzak

Abstract: Optimized light-matter coupling in semiconductor nanostructures is a key to understand their optical properties and can be enabled by advanced fabrication techniques. Using in-situ electron beam lithography combined with a low-temperature cathodoluminescence imaging, we deterministically fabricate microlenses above selected InAs quantum dots (QDs) achieving their efficient coupling to the external… ▽ More Optimized light-matter coupling in semiconductor nanostructures is a key to understand their optical properties and can be enabled by advanced fabrication techniques. Using in-situ electron beam lithography combined with a low-temperature cathodoluminescence imaging, we deterministically fabricate microlenses above selected InAs quantum dots (QDs) achieving their efficient coupling to the external light field. This enables to perform four-wave mixing micro-spectroscopy of single QD excitons, revealing the exciton population and coherence dynamics. We infer the temperature dependence of the dephasing in order to address the impact of phonons on the decoherence of confined excitons. The loss of the coherence over the first picoseconds is associated with the emission of a phonon wave packet, also governing the phonon background in photoluminescence (PL) spectra. Using theory based on the independent boson model, we consistently explain the initial coherence decay, the zero-phonon line fraction, and the lineshape of the phonon-assisted PL using realistic quantum dot geometries. △ Less

Submitted 31 October, 2016; originally announced October 2016.

Quantum dynamics of optical phonons generated by optical excitation of a quantum dot

Authors: Daniel Wigger, Helge Gehring, V. Martin Axt, Doris E. Reiter, Tilmann Kuhn

Abstract: The study of the fundamental properties of phonons is crucial to understand their role in applica- tions in quantum information science, where the active use of phonons is currently highly debated. A genuine quantum phenomenon associated with the fluctuation properties of phonons is squeezing, which is achieved when the fluctuations of a certain variable drop below their respective vacuum value. W… ▽ More The study of the fundamental properties of phonons is crucial to understand their role in applica- tions in quantum information science, where the active use of phonons is currently highly debated. A genuine quantum phenomenon associated with the fluctuation properties of phonons is squeezing, which is achieved when the fluctuations of a certain variable drop below their respective vacuum value. We consider a semiconductor quantum dot in which the exciton is coupled to phonons. We review the fluctuation properties of the phonons, which are generated by optical manipulation of the quantum dot, in the limiting case of ultra short pulses. Then we discuss the phonon properties for an excitation with finite pulses. Within a generating function formalism we calculate the corre- sponding fluctuation properties of the phonons and show that phonon squeezing can be achieved by the optical manipulation of the quantum dot exciton for certain conditions even for a single pulse excitation where neither for short nor for long pulses squeezing occurs. To explain the occurrence of squeezing we employ a Wigner function picture providing a detailed understanding of the induced quantum dynamics. △ Less

Submitted 15 July, 2016; v1 submitted 15 June, 2016; originally announced June 2016.

Journal ref: Journal of Computational Electronics, 2016

Dynamics of excitons in individual InAs quantum dots revealed in four-wave mixing spectroscopy

Authors: Q. Mermillod, D. Wigger, V. Delmonte, D. E. Reiter, C. Schneider, M. Kamp, S. Höfling, W. Langbein, T. Kuhn, G. Nogues, J. Kasprzak

Abstract: A detailed understanding of the population and coherence dynamics in optically driven individual emitters in solids and their signatures in ultrafast nonlinear-optical signals is of prime importance for their applications in future quantum and optical technologies. In a combined experimental and theoretical study on exciton complexes in single semiconductor quantum dots we reveal a detailed pictur… ▽ More A detailed understanding of the population and coherence dynamics in optically driven individual emitters in solids and their signatures in ultrafast nonlinear-optical signals is of prime importance for their applications in future quantum and optical technologies. In a combined experimental and theoretical study on exciton complexes in single semiconductor quantum dots we reveal a detailed picture of the dynamics employing three-beam polarization-resolved four-wave mixing (FWM) micro-spectroscopy. The oscillatory dynamics of the FWM signals in the exciton-biexciton system is governed by the fine-structure splitting and the biexciton binding energy in an excellent quantitative agreement between measurement and analytical description. The analysis of the excitation conditions exhibits a dependence of the dynamics on the specific choice of polarization configuration, pulse areas and temporal ordering of driving fields. The interplay between the transitions in the four-level exciton system leads to rich evolution of coherence and population. Using two-dimensional FWM spectroscopy we elucidate the exciton-biexciton coupling and identify neutral and charged exciton complexes in a single quantum dot. Our investigations thus clearly reveal that FWM spectroscopy is a powerful tool to characterize spectral and dynamical properties of single quantum structures. △ Less

Submitted 8 April, 2016; originally announced April 2016.

Comments: 12 pages, 10 figures

Journal ref: Optica Vol. 3, Issue 4, pp. 377-384 (2016)

Energy transport and coherence properties of acoustic phonons generated by optical excitation of a quantum dot

Authors: D. Wigger, S. Lüker, D. E. Reiter, V. M. Axt, P. Machnikowski, T. Kuhn

Abstract: The energy transport of acoustic phonons generated by the optical excitation of a quantum dot as well as the coherence properties of these phonons are studied theoretically both for the case of a pulsed excitation and for a continuous wave (cw) excitation switched on instantaneously. For a pulsed excitation, depending on pulse area and pulse duration, a finite number of phonon wave packets is emit… ▽ More The energy transport of acoustic phonons generated by the optical excitation of a quantum dot as well as the coherence properties of these phonons are studied theoretically both for the case of a pulsed excitation and for a continuous wave (cw) excitation switched on instantaneously. For a pulsed excitation, depending on pulse area and pulse duration, a finite number of phonon wave packets is emitted, while for the case of a cw excitation a sequence of wave packets with decreasing amplitude is generated after the excitation has been switched on. We show that the energy flow associated with the generated phonons is partly related to coherent phonon oscillations and partly to incoherent phonon emission. The efficiency of the energy transfer to the phonons and the details of the energy flow depend strongly and in a non-monotonic way on the Rabi frequency exhibiting a resonance behavior. However, in the case of cw excitation it turns out that the total energy transferred to the phonons is directly linked in a monotonic way to the Rabi frequency. △ Less

Submitted 10 June, 2014; v1 submitted 13 December, 2013; originally announced December 2013.

Fluctuation properties of acoustic phonons generated by ultrafast optical excitation of a quantum dot

Authors: D. Wigger, D. E. Reiter, V. M. Axt, T. Kuhn

Abstract: We study theoretically the fluctuation properties of acoustic phonons created in a semiconductor quantum dot after ultrafast optical excitation. An excitation with a single ultrafast pulse creates an exciton confined to the quantum dot, which is coupled to longitudinal acoustic phonons. This leads to the formation of a polaron in the quantum dot accompanied by the emission of a phonon wave packet.… ▽ More We study theoretically the fluctuation properties of acoustic phonons created in a semiconductor quantum dot after ultrafast optical excitation. An excitation with a single ultrafast pulse creates an exciton confined to the quantum dot, which is coupled to longitudinal acoustic phonons. This leads to the formation of a polaron in the quantum dot accompanied by the emission of a phonon wave packet. We show that the fluctuations of the lattice displacement associated with the wave packet after a single laser pulse excitation in resonance with the exciton transition are always larger than their respective vacuum values. Manipulating the exciton with a second pulse can result in a reduction of the fluctuations below their vacuum limit, which means that the phonons are squeezed. We show that the squeezing properties of the wave packet strongly depend on the relative phase and the time delay between the two laser pulses. △ Less

Submitted 14 January, 2013; originally announced January 2013.