Publications
Articles in Refereed Journals

L. Mertenskötter, M. Kantner, Frequency noise characterization of narrowlinewidth lasers: A Bayesian approach, IEEE Photonics Journal, 16 (2024), pp. 0601407/10601407/7, DOI 10.1109/JPHOT.2024.3385184 .
Abstract
We describe a Bayesian estimation approach to infer on the frequency noise characteristics of narrowlinewidth semiconductor lasers from delayed selfheterodyne beat note measurements. Our technique is grounded in a statistical model of the measurement process that accounts for both the impact of the interferometer and the detector noise. The approach yields accurate results, even in scenarios where the intrinsic linewidth plateau is obscured by detector noise. The analysis is carried out using a Markovchain Monte Carlo method in the frequency domain and exploits prior knowledge about the statistical distribution of the data. The method is validated using simulated time series data from a stochastic laser rate equation model incorporating 1/f type nonMarkovian noise. 
M. Kantner, L. Mertenskötter, Accurate evaluation of selfheterodyne laser linewidth measurements using Wiener filters, Optics Express, 31 (2023), pp. 1599416009, DOI 10.1364/OE.485866 .
Abstract
Selfheterodyne beat note measurements are widely used for the experimental characterization of the frequency noise power spectral density (FNPSD) and the spectral linewidth of lasers. The measured data, however, must be corrected for the transfer function of the experimental setup in a postprocessing routine. The standard approach disregards the detector noise and thereby induces reconstruction artifacts, i.e., spurious spikes, in the reconstructed FNPSD. We introduce an improved postprocessing routine based on a parametric Wiener filter that is free from reconstruction artifacts, provided a good estimate of the signaltonoise ratio is supplied. Building on this potentially exact reconstruction, we develop a new method for intrinsic laser linewidth estimation that is aimed at deliberate suppression of unphysical reconstruction artifacts. Our method yields excellent results even in the presence of strong detector noise, where the intrinsic linewidth plateau is not even visible using the standard method. The approach is demonstrated for simulated time series from a stochastic laser model including 1 / ftype noise. 
O. Marquardt, Simulating the electronic properties of semiconductor nanostructures using multiband $kcdot p$ models, Computational Materials Science, 194 (2021), pp. 110318/1110318/11, DOI 10.1016/j.commatsci.2021.110318 .
Abstract
The eightband $kcdot p$ formalism been successfully applied to compute the electronic properties of a wide range of semiconductor nanostructures in the past and can be considered the backbone of modern semiconductor heterostructure modelling. However, emerging novel material systems and heterostructure fabrication techniques raise questions that cannot be answered using this wellestablished formalism, due to its intrinsic limitations. The present article reviews recent studies on the calculation of electronic properties of semiconductor nanostructures using a generalized multiband $kcdot p$ approach that allows both the application of the eightband model as well as more sophisticated approaches for novel material systems and heterostructures. 
H. Wenzel, M. Kantner, M. Radziunas, U. Bandelow, Semiconductor laser linewidth theory revisited, APPS. Applied Sciences, 11 (2021), pp. 6004/16004/29, DOI 10.3390/app11136004 .
Abstract
More and more applications require semiconductor lasers distinguished not only by large modulation bandwidths or high output powers, but also by small spectral linewidths. The theoretical understanding of the root causes limiting the linewidth is therefore of great practical relevance. In this paper, we derive a general expression for the calculation of the spectral linewidth step by step in a selfcontained manner. We build on the linewidth theory developed in the 1980s and 1990s but look from a modern perspective, in the sense that we choose as our starting points the timedependent coupledwave equations for the forward and backward propagating fields and an expansion of the fields in terms of the stationary longitudinal modes of the open cavity. As a result, we obtain rather general expressions for the longitudinal excess factor of spontaneous emission (Kfactor) and the effective Alphafactor including the effects of nonlinear gain (gain compression) and refractive index (Kerr effect), gain dispersion and longitudinal spatial hole burning in multisection cavity structures. The effect of linewidth narrowing due to feedback from an external cavity often described by the socalled chirp reduction factor is also automatically included. We propose a new analytical formula for the dependence of the spontaneous emission on the carrier density avoiding the use of the population inversion factor. The presented theoretical framework is applied to a numerical study of a twosection distributed Bragg reflector laser.
Contributions to Collected Editions

L. Mertenskötter, M. Kantner, Bayesian estimation of laser linewidth from delayed selfheterodyne measurements, Conference on Structural Nonlinear Dynamics and Diagnosis (CSNDD 2023), Marrakesh, Morocco, May 15  17, 2024, M. Belhaq, ed., 301 of Springer Proceedings in Physics, Springer, Singapur, 2024, pp. 269279, DOI 10.1007/9789819979585_21 .
Abstract
We present a statistical inference approach to estimate the frequency noise characteristics of ultranarrow linewidth lasers from delayed selfheterodyne beat note measurements using Bayesian inference. Particular emphasis is on estimation of the intrinsic (Lorentzian) laser linewidth. The approach is based on a statistical model of the measurement process, taking into account the effects of the interferometer as well as the detector noise. Our method therefore yields accurate results even when the intrinsic linewidth plateau is obscured by detector noise. The regression is performed on periodogram data in the frequency domain using a Markovchain Monte Carlo method. By using explicit knowledge about the statistical distribution of the observed data, the method yields good results already from a single time series and does not rely on averaging over many realizations, since the information in the available data is evaluated very thoroughly. The approach is demonstrated for simulated time series data from a stochastic laser rate equation model with 1 / ftype nonMarkovian noise. 
L. Ermoneit, B. Schmidt, J. Fuhrmann, Th. Koprucki, L.R. Schreiber, M. Kantner, Simulation of singleelectron shuttling for spinqubit transport in a SiGe quantum bus, in: Book of Abstracts of the International Workshop on Computational Nanotechnology 2023 (IWCN 2023), X. Orios Plaedvall, G. Abadal Berini, X. Cartoixà Soler, A. Cummings, C.F. Destefani, D. Jiménez Jiménez, J. Mart'in Mart'inez, R. Rodr'iguez Mart'inez, A. Benali, eds., pp. 8889.

M. Kantner, L. Mertenskötter, Estimation of frequency noise characteristics and datadriven modeling of narrowlinewidth semiconductor lasers, in: 23nd International Conference on Numerical Simulation of Optoelectronic Devices (NUSOD 2023), P. Bardella, A. Tibaldi, eds., IEEE, 2023, pp. 5556, DOI 10.1109/NUSOD59562.2023.10273522 .
Abstract
The design of narrowlinewidth lasers requires stochastic laser models providing a realistic description of the noise in the device. We present a statistical inference approach to extract the frequency noise characteristics and model parameters of narrowlinewidth lasers from delayed selfheterodyne beat note experiments. By exploiting prior knowledge about the statistical distribution of the measurement data, accurate estimates of the parameters of the free running laser can be achieved even in the presence of considerable detector noise. The approach is demonstrated for simulated time series data using a stochastic laser rate equation model including 1/ftype noise. 
M. Kantner, L. Mertenskötter, Wienerfilter enhanced estimation of the intrinsic laser linewidth from delayed selfheterodyne beat note measurements, in: 2023 Conference on Lasers and ElectroOptics Europe & European Quantum Electronics Conference (CLEO/EuropeEQEC), IEEE, 2023, pp. 8889, DOI 10.1109/CLEO/EuropeEQEC57999.2023.10232191 .
Abstract
Narrowlinewidth lasers exhibiting low phase noise are core elements of coherent optical communication systems, gravitational wave interferometers and emerging quantum technologies (e.g., optical atomic clocks, matterwave interferometers, iontrap quantumcomputers etc.). For many of these applications, the performance depends critically on the laser's intrinsic (Lorentzian) linewidth [1], which is typically obscured by additional 1/flike technical noise. Because of this socalled flicker noise, the laser linewidth alone is not a welldefined quantity and needs to be specified for a given measurement time. For a detailed characterization of the frequency noise exhibited by the laser, the measurement of the frequency noise power spectral density (FNPSD) is required. 
M. Kantner, L. Mertenskötter, Datadriven modeling of nonMarkovian noise in semiconductor lasers, in: 22nd International Conference on Numerical Simulation of Optoelectronic Devices (NUSOD), Turin, Italy, 2022, J. Piprek, P. Bardella, eds., IEEE, 2022, pp. 5758, DOI 10.1109/NUSOD54938.2022.9894788 .
Abstract
NonMarkovian noise degrades the coherence properties of semiconductor lasers and contributes significantly to broadening of the linewidth. Since modeling of such colored noise systems from first principles is not accessible, we aim for a datadriven modeling approach in which a system of stochastic rate equations shall be reconstructed from time series data.
Preprints, Reports, Technical Reports

L. Ermoneit, B. Schmidt, Th. Koprucki, J. Fuhrmann, T. Breiten, A. Sala, N. Ciroth, R. Xue, L.R. Schreiber, M. Kantner, Optimal control of conveyormode spinqubit shuttling in a Si/SiGe quantum bus in the presence of charged defects, Preprint no. 3082, WIAS, Berlin, 2023, DOI 10.20347/WIAS.PREPRINT.3082 .
PDF (9473 kByte)
Talks, Poster

L. Ermoneit, M. Kantner, Th. Koprucki, J. Fuhrmann, B. Schmidt, Optimal control of a Si/SiGe quantum bus for scalable quantum computing architectures, QUANTUM OPTIMAL CONTROL From Mathematical Foundations to Quantum Technologies, Berlin, May 21, 2024.

A. Thayil, Towards optimization of valley splitting in Si/SiGe quantum wells, Silicon Quantum Electronics Workshop 2024, Davos, Switzerland, September 4  6, 2024.
External Preprints

M. Kantner, L. Mertenskötter, Accurate evaluation of selfheterodyne laser linewidth measurements using Wiener filters, Preprint no. arXiv:2301.10645, Cornell University, 2023, DOI 10.48550/arXiv.2301.10645 .
Abstract
Selfheterodyne beat note measurements are widely used for the experimental characterization of the frequency noise power spectral density (FNPSD) and the spectral linewidth of lasers. The measured data, however, must be corrected for the transfer function of the experimental setup in a postprocessing routine. The standard approach disregards the detector noise and thereby induces reconstruction artifacts, i.e., spurious spikes, in the reconstructed FNPSD. We introduce an improved postprocessing routine based on a parametric Wiener filter that is free from reconstruction artifacts, provided a good estimate of the signaltonoise ratio is supplied. Building on this potentially exact reconstruction, we develop a new method for intrinsic laser linewidth estimation that is aimed at deliberate suppression of unphysical reconstruction artifacts. Our method yields excellent results even in the presence of strong detector noise, where the intrinsic linewidth plateau is not even visible using the standard method. The approach is demonstrated for simulated time series from a stochastic laser model including 1 / ftype noise.