arXiv subjects

D. E. Reiter

Publications and source records attributed to D. E. Reiter.

At least 19 recordsLinked to original sources

arXiv2025

Quantum beats of exciton-polarons in CsPbI3 perovskite nanocrystals

Exciton-phonon interactions govern the energy level spectrum and thus the optical response in semiconductors. In this respect, lead-halide perovskite nanocrystals represent a unique system, for which the interaction with optical phonons is particularly strong, giving rise to a ladder of multiple exciton states which can be optically excited with femtosecond pulses. We establish a new regime of coherent exciton-polaron dynamics with exceptionally long coherence times (T2 ~300 ps) in an ensemble of CsPbI3 nanocrystals embedded in a glass matrix. Using transient two-pulse photon echo at 2 K temperature, we observe quantum beats between the exciton-polaron states. Within a four-level model, we directly quantify the exciton-phonon coupling strength through the Huang-Rhys factors of 0.05-0.1 and 0.02-0.04 for low-energy optical phonons with energies of 3.2 and 5.1 meV, respectively. The pronounced size dependence of both coupling strengths and phonon lifetimes offers a path to tune the optical transitions between polaron states and to tailor the coherent optical dynamics in perovskite semiconductors for solid-state quantum technologies.

cond-mat.mes-hall↗

arXiv2024

Experimental measurement of the reappearance of Rabi rotations in semiconductor quantum dots

Phonons in solid-state quantum emitters play a crucial role in their performance as photon sources in quantum technology. For resonant driving, phonons dampen the Rabi oscillations resulting in reduced preparation fidelities. The phonon spectral density, which quantifies the strength of the carrier-phonon interaction, is non-monotonous as a function of energy. As one of the most prominent consequences, this leads to the reappearance of Rabi rotations for increasing pulse power, which was theoretically predicted in Phys. Rev. Lett. 98, 227403 (2007). In this paper we present the experimental demonstration of the reappearance of Rabi rotations.

cond-mat.mes-hall↗

arXiv2022

Multiple Rabi rotations of trions in InGaAs quantum dots observed by photon echo spectroscopy with spatially shaped laser pulses

We study Rabi rotations arising in intensity-dependent photon echoes from an ensemble of self-assembled InGaAs quantum dots. To achieve a uniform distribution of intensities within the excited ensemble, we introduce flattop intensity profiles of picosecond laser pulses. This allows us to overcome the damping of Rabi rotations imposed by the spatial inhomogeneity of Rabi frequencies by a Gaussian laser profile. Using photon echo polarimetry, we distinguish between the coherent optical responses from exciton and trion ensembles. Here, we demonstrate that a photo-induced charging of the quantum dots leads to a significant reduction of the number of neutral quantum dots under resonant excitation with intensive optical pulses with areas exceeding $\fracπ{2}$. The trion ensemble shows robust Rabi rotations when the area of the refocussing pulse is increased up to 5.5$π$. We analyze the remaining attenuation of Rabi rotations by theoretical modeling of excitation induced dephasing, inhomogeneity of dipole moments, and coupling to acoustic phonons. The latter is identified as the dominating mechanism resulting in a loss of optical coherence during the action of the involved optical pulses.

cond-mat.mes-hall↗

arXiv2022

$N$-photon bundle statistics in different solid-state platforms

The term $N$-photon bundles has been coined for a specific type of photon emission, where light quanta are released from a cavity only in groups of $N$ particles. This emission leaves a characteristic number distribution of the cavity photons that may be taken as one of their fingerprints. We study this characteristic $N$-photon bundle statistics considering two solid-state cavity quantum electrodynamics (cQED) systems. As one example, we consider a semiconductor quantum-dot--microcavity system coupled to longitudinal acoustic phonons. There, we find the environmental influence to be detrimental to the bundle statistics. The other example is a superconducting qubit inside a microwave resonator. In these systems, pure dephasing is not important and an experimentally feasible parameter regime is found, where the bundle statistics prevails.

quant-ph↗

arXiv2022

Deterministic photon storage and readout in a semimagnetic quantum-dot--cavity system doped with a single Mn ion

Light trapping is a crucial mechanism for synchronization in optical communication. Especially on the level of single photons, control of the exact emission time is desirable. In this paper, we theoretically propose a single-photon buffering device composed of a quantum dot doped with a single Mn atom in a cavity. We present a method to detain a single cavity photon as an excitation of the dot. The storage scheme is based on bright to dark exciton conversion performed with an off-resonant external optical field and mediated via a spin-flip with the magnetic ion. The induced Stark shift brings both exciton states to resonance and results in an excitation transfer to the optically inactive one. The stored photon can be read out on demand in the same manner by repopulating the bright state, which has a short lifetime. Our results indicate the possibility to suspend a photon for almost two orders of magnitude longer than the lifetime of the bright exciton.

quant-ph↗

arXiv2021

Accuracy of the quantum regression theorem for photon emission from a quantum dot

The quantum regression theorem (QRT) is the most-widely used tool for calculating multitime correlation functions for the assessment of quantum emitters. It is an approximate method based on a Markov assumption for the environmental coupling. In this work we quantify properties of photons emitted from a single quantum dot coupled to phonons. For the single-photon purity and the indistinguishability, we compare numerically exact path-integral results with those obtained from the QRT. It is demonstrated that the QRT systematically overestimates the influence of the environment for typical quantum dots used in quantum information technology.

quant-ph↗

arXiv2021

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

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.

cond-mat.mes-hall↗

arXiv2021

Schrödinger cats in quantum-dot--cavity systems

A Schrödinger-cat state is a coherent superposition of macroscopically distinguishable quantum states, in quantum optics usually realized as superposition of coherent states. Protocols to prepare photonic cats have been presented for atomic systems. Here, we investigate in what manner and how well the preparation protocols can be transferred to a solid state platform, namely a semiconductor quantum-dot--cavity system. In quantum-dot--cavity systems there are many disruptive influences like cavity losses, the radiative decay of the quantum dot, and the pure-dephasing type coupling to longitudinal acoustic phonons. We show that for one of the protocols these influences kill the quantum coherence between the states forming the cat, while for a second protocol a parameter regime can be identified where the essential characteristics of Schrödinger-cat states survive the environmental influences under realistic conditions.

cond-mat.mes-hall↗

arXiv2020

On-demand generation of higher-order Fock states in quantum-dot--cavity systems

The on-demand preparation of higher-order Fock states is of fundamental importance in quantum information sciences. We propose and compare different protocols to generate higher-order Fock states in solid state quantum-dot--cavity systems. The protocols make use of a series of laser pulses to excite the quantum dot exciton and off-resonant pulses to control the detuning between dot and cavity. Our theoretical studies include dot and cavity loss processes as well as the pure-dephasing type coupling to longitudinal acoustic phonons in a numerically complete fashion. By going beyond the two-level approximation for quantum dots, we study the impact of a finite exchange splitting, the impact of a higher energetic exciton state, and an excitation with linearly polarized laser pulses leading to detrimental occupations of the biexciton state. We predict that under realistic conditions, a protocol which keeps the cavity at resonance with the quantum dot until the desired target state is reached is able to deliver fidelities to the Fock state $| 5\rangle$ well above $40\,\%$.

cond-mat.mes-hall↗

arXiv2020

Phonon-mediated exciton capture in Mo-based transition metal dichalcogenides

Localized excitons play a vital role in the optical response of monolayers of transition metal dichalcogenides and can be exploited as single photon sources for quantum information technology. While the optical properties of such localized excitons are vastly studied, the ultrafast capture process of delocalized excitons into localized potentials is largely unexplored. We perform quantum kinetic calculations of exciton capture via acoustic and optical phonons showing that efficient capture takes place on an ultrafast time scale. The polaron formation in the low-temperature limit leads to higher-energy excitons which can then be efficiently trapped. We demonstrate that the interplay of acoustic and optical phonons leads to an efficient broadening of energy-selection rules. Our studies provide a deep understanding of the carrier trapping from two-dimensional materials into zero-dimensional potentials.

cond-mat.mes-hall↗

arXiv2020

Dark Exciton Preparation in a Quantum Dot by a Longitudinal Light Field Tuned to Higher Exciton States

Several important proposals to use semiconductor quantum dots in quantum information technology rely on the control of the dark exciton ground states, such as dark exciton based qubits with a $μ$s life time. In this paper, we present an efficient way to occupy the dark exciton ground state by a single short laser pulse. The scheme is based on an optical excitation with a longitudinal field component featured by, e.g., radially polarized beams or certain Laguerre-Gauss or Bessel beams. Utilizing this component, we show within a configuration interaction approach that high-energy exciton states composed of light-hole excitons and higher dark heavy-hole excitons can be addressed. When the higher exciton relaxes, a dark exciton in its ground state is created.

cond-mat.mes-hall↗

arXiv2020

Semiclassical modeling of coupled quantum dot-cavity systems: From polariton-like dynamics to Rabi oscillations

Semiconductor quantum dots in photonic cavities are strongly coupled light-matter systems with prospective applications in optoelectronic devices and quantum information processing. Here we present a theoretical study of the coupled exciton--light field dynamics of a planar quantum dot ensemble, treated as two-level systems, embedded in a photonic cavity modeled by Maxwell's equations. When excited by coupling an external short laser pulse into the cavity, we find an exciton-polariton-like behavior for weak excitation and Rabi oscillations for strong excitation with a sharp transition between these regimes. In the transition region we find highly non-linear dynamics involving high harmonics of the fundamental oscillation. We perform a numerical study based on the Finite-Difference-Time-Domain method for the solution of Maxwell's equations coupled to Bloch equations for the quantum dots and also derive an analytical model to describe the coupled cavity-quantum dot system, which allows us to describe the light field dynamics in terms of a Newton-like dynamics in an effective anharmonic potential. From the shape of this potential combined with the initial conditions the transition can be well understood. The model is then extended to a broadened ensemble of quantum dots. For weak excitation the polariton spectrum broadens and the lines slightly shift, however, the sharp transition to the Rabi oscillation regime is still present. Furthermore, we find a second, lower threshold with additional lines in the spectra which can be traced back to Rabi oscillations driven by the polariton modes. Our approach provides new insights in the dynamics of both quantum dot and light field in the photonic structure.

cond-mat.mes-hall↗

arXiv2020

Selection rules for the excitation of quantum dots by spatially structured light beams -- Application to the reconstruction of higher excited exciton wave functions

Spatially structured light fields applied to semiconductor quantum dots yield fundamentally different absorption spectra than homogeneous beams. In this paper, we theoretically discuss the resulting spectra for different light beams using a cylindrical multipole expansion. For the description of the quantum dots we employ a model based on the effective mass approximation including Coulomb and valence band mixing. The combination of a single spatially structured light beam and state mixing allows all exciton states in the quantum dot to become optically addressable. Furthermore, we demonstrate that the beams can be tailored such that single states are selectively excited, without the need of spectral separation. Using this selectivity, we propose a method to measure the exciton wave function of the quantum dot eigenstate. The measurement goes beyond electron density measurements by revealing the spatial phase information of the exciton wave function. Thereby polarization sensitive measurements are generalized by including the infinitely large spatial degree of freedom.

cond-mat.mes-hall↗

arXiv2020

Theory of absorption lineshape in monolayers of transition metal dichalcogenides

The linear absorption spectra in monolayers of transition metal dichalcogenides show pronounced signatures of the exceptionally strong exciton-phonon interaction in these materials. To account for both exciton and phonon physics in such optical signals, we compare different theoretical methods to calculate the absorption spectra using the example of $\mathrm{MoSe_2}$. In this paper, we derive the equations of motion for the polarization either using a correlation expansion up to 4th Born approximation or a time convolutionless master equation. We show that the Born approximation might become problematic when not treated in high enough order, especially at high temperatures. In contrast, the time convolutionless formulation gives surprisingly good results despite its simplicity when compared to higher-order corrrelation expansion and therefore provides a powerful tool to calculate the lineshape of linear absorption spectra in the very popular monolayer materials.

cond-mat.mes-hall↗

arXiv2019

Spatiotemporal dynamics of Coulomb-correlated carriers in semiconductors

When the excitation of carriers in real space is focused down to the nanometer scale, the carrier system can no longer be viewed as homogeneous and ultrafast transport of the excited carrier wave packets occurs. In state-of-the-art semiconductor structures like low-dimensional heterostructures or monolayers of transition metal dichalcogenides, the Coulomb interaction between excited carriers becomes stronger due to confinement or reduced screening. This demands a fundamental understanding of strongly interacting electrons and holes and the influence of Coulomb correlations. To study the corresponding particle dynamics in a controlled way we consider a system of up to two electron-hole pairs exactly within a wave function approach. We show that the excited wave packets contain a non-trivial mixture of free particle and excitonic states. We further scrutinize the influence of Coulomb interaction on the wave packet dynamics revealing its different role for below and above band-gap excitation.

cond-mat.mes-hall↗

arXiv2018

Bessel beams revisited: a generalized scheme to derive optical vortices

The electromagnetic field of optical vortices is in most cases derived from vector and scalar potentials using either a procedure based on the Lorenz or the Coulomb gauge. The former procedure has been typically used to derive paraxial solutions with Laguerre-Gauss radial profiles, while the latter procedure has been used to derive full solutions of the wave equation with Bessel radial profiles. We investigate the differences in the derivation procedures applying each one to both Bessel and Laguerre-Gauss profiles. We show that the electromagnetic fields thus derived differ in the relative strength of electric and magnetic contributions. The new solution that arises from the Lorenz procedure in the case of Bessel beams restores a field symmetry that previous work failed to resolve. Our procedure is further generalized and we find a spectrum of fields beyond the Lorenz and Coulomb gauge types. Finally, we describe a possible experiment to test our findings.

physics.optics↗

arXiv2017

Phonon impact on optical control schemes of quantum dots: The role of quantum dot geometry and symmetry

Phonons strongly influence the optical control of semiconductor quantum dots. When modeling the electron-phonon interaction in several theoretical approaches the quantum dot geometry is approximated by a spherical structure, though typical self-assembled quantum dots are strongly lens-shaped. By explicitly comparing simulations of a spherical and a lens-shaped dot using a well-established correlation expansion approach we show that indeed lens-shaped dots can be exactly mapped to a spherical geometry when studying the phonon influence on the electronic system. We also give a recipe to reproduce spectral densities from more involved dots by rather simple spherical models. On the other hand, breaking the spherical symmetry has a pronounced impact on the spatio-temporal properties of the phonon dynamics. As an example we show that for a lens-shaped quantum dot the phonon emission is strongly concentrated along the direction of the smallest axis of the dot which is important for the use of phonons for the communication between different dots.

cond-mat.mes-hall↗

arXiv2017

Magnetic-optical transitions induced by twisted light in quantum dots

It has been theoretically predicted that light carrying orbital angular momentum, or twisted light, can be tuned to have a strong magnetic-field component at optical frequencies. We here consider the interaction of these peculiar fields with a semiconductor quantum dot and show that the magnetic interaction results in new types of optical transitions. In particular, a single pulse of such twisted light can drive light-hole-to-conduction band transitions that are cumbersome to produce using conventional Gaussian beams or even twisted light with dominant electric fields.

cond-mat.mes-hall↗