Prof. Dr. Andrey S. Moskalenko

Mercator Fellow 2021-2024

The SFB 1432 hosts Prof. Dr. Andrey S. Moskalenko, Associate Professor at KAIST (Republic of Korea), as Mercator Fellow in Konstanz for 2 months every year of our funding period.

Prof. Moskalenko is one of the leading experts in the theory of ultrafast quantum phenomena. He made very important contributions to the theory of confined states in nanostructures, including quantum dots and rings, fullerenes, and graphene nanoribbons, as well as excitonic states, relaxation processes, and optically induced quantum tunnelling in nanostructures. He was one of the driving forces in the recent development of a new formulation of subcycle quantum electrodynamics and quantum optics for the understanding of electro-optic sampling in the ultrabroadband quantum regime. Prof. Moskalenko’s theoretical contribution as a junior research group leader in Prof. Dr. Guido Burkard’s group (A05) was instrumental in quantitatively understanding the first direct detection of the vacuum fluctuations in the electric field using subcycle electro-optic sampling, realised in the group of Prof. Dr. Alfred Leitenstorfer (A01, A06). This makes him a highly appreciated partner in intensive, ongoing dialog with the with the experimental and theoretical researchers in the A01, A05, and A06. In addition, a virtual dialogue has been established by the SFB 1432 with researchers in the projects A03 (Prof. Dr. W. Belzig) and C06 (Prof. Dr. M. Fuchs).

Research stays led Prof. Moskalenko to the Universities of Münster, Marburg, Halle, and Augsburg, a Max Planck Postdoctoral Research Fellowship to the Max Planck Institute for Microstructure Physics in Halle, and afterward a junior group leadership in Konstanz to his current position as assistant professor at KAIST. In 2012, Prof. Moskalenko was awarded the "Ioffe Institute Prize" by the Ioffe Physical-Technical Institute, in 2020, he won the "Best Paper Award" from the College
of Natural Sciences at KAIST, and recently a "Prestigious Midcareer Grant" from National Research Foundation of Korea (NRF).


Publications related to the fellowship in Konstanz

The 2023 terahertz science and technology roadmap (2023)

Abstract: Terahertz (THz) radiation encompasses a wide spectral range within the electromagnetic spectrum that extends from microwaves to the far infrared (100 GHz–∼30 THz). Within its frequency boundaries exist a broad variety of scientific disciplines that have presented, and continue to present, technical challenges to researchers. During the past 50 years, for instance, the demands of the scientific community have substantially evolved and with a need for advanced instrumentation to support radio astronomy, Earth observation, weather forecasting, security imaging, telecommunications, non-destructive device testing and much more. Furthermore, applications have required an emergence of technology from the laboratory environment to production-scale supply and in-the-field deployments ranging from harsh ground-based locations to deep space. In addressing these requirements, the research and development community has advanced related technology and bridged the transition between electronics and photonics that high frequency operation demands. The multidisciplinary nature of THz work was our stimulus for creating the 2017 THz Science and Technology Roadmap (Dhillon et al 2017 J. Phys. D: Appl. Phys. 50 043001). As one might envisage, though, there remains much to explore both scientifically and technically and the field has continued to develop and expand rapidly. It is timely, therefore, to revise our previous roadmap and in this 2023 version we both provide an update on key developments in established technical areas that have important scientific and public benefit, and highlight new and emerging areas that show particular promise. The developments that we describe thus span from fundamental scientific research, such as THz astronomy and the emergent area of THz quantum optics, to highly applied and commercially and societally impactful subjects that include 6G THz communications, medical imaging, and climate monitoring and prediction. Our Roadmap vision draws upon the expertise and perspective of multiple international specialists that together provide an overview of past developments and the likely challenges facing the field of THz science and technology in future decades. The document is written in a form that is accessible to policy makers who wish to gain an overview of the current state of the THz art, and for the non-specialist and curious who wish to understand available technology and challenges. A such, our experts deliver a 'snapshot' introduction to the current status of the field and provide suggestions for exciting future technical development directions. Ultimately, we intend the Roadmap to portray the advantages and benefits of the THz domain and to stimulate further exploration of the field in support of scientific research and commercial realisation.

A. Leitenstorfer, A. S. Moskalenko et al.
DOI: 10.1088/1361-6463/acbe4c
J. Phys. D: Appl. Phys. 56, 223001 - published 5 April 2023
related to project A06

Back action in quantum electro-optic sampling of electromagnetic vacuum fluctuations (2023)

Abstract: The influence of measurement back action on electro-optic sampling of electromagnetic quantum fluctuations is investigated. Based on a cascaded treatment of the nonlinear interaction between a near-infrared coherent probe and the mid-infrared vacuum, we account for the generated electric-field contributions that lead to detectable back action. Specifically, we theoretically address two realistic setups, exploiting one or two probe beams for the nonlinear interaction with the quantum vacuum, respectively. The setup parameters at which back action starts to considerably contaminate the measured noise profiles are determined. We find that back action starts to detrimentally affect the signal once the fluctuations due to the coupling to the mid-infrared vacuum become comparable to the base shot noise. Due to the vacuum fluctuations entering at the beam splitter, the shot noise of two incoming probe pulses in different channels is uncorrelated. Therefore, even when the base shot noise dominates the output of the experiment, it does not contribute to the correlation signal itself. However, we find that further contributions due to nonlinear shot-noise enhancement are still present. Ultimately, a regime in which electro-optic sampling of quantum fields can be considered as effectively back-action free is found.

T. L. M. Guedes, I. Vakulchyk, D. V. Seletskiy, A. Leitenstorfer, A. S. Moskalenko, and G. Burkard
DOI: 10.1103/PhysRevResearch.5.013151
Phys. Rev. Research 5, 013151 (2023) - published 27 February 2023
related to project A05 and A06

Realizing a rapidly switched Unruh-DeWitt detector through electro-optic sampling of the electromagnetic vacuum (2022)

A new theoretical framework to describe the experimental advances in electro-optic detection of broadband quantum states, specifically the quantum vacuum, is devised. Electro-optic sampling is a technique in ultrafast photonics which, when transferred into the quantum domain, can be utilized to resolve properties of a sampled quantum state via its interaction with a strong coherent probe pulse at ultrafast timescales. By making use of fundamental concepts from quantum field theory on spacetime metrics, the nonlinear interaction behind the electro-optic effect is shown to be equivalent to a stationary Unruh-DeWitt detector coupled to a conjugate field during a very short time interval. When the coupling lasts for a time interval comparable to the oscillation periods of the detected field mode (i.e., the subcycle regime), virtual particles inhabiting the field vacuum are transferred to the detector in the form of real excitation. We demonstrate that this behavior can be rigorously translated to the scenario of electro-optic sampling of the quantum vacuum, in which the (spectrally filtered) probe works as an Unruh-DeWitt detector, with its interaction-generated photons arising from virtual particles inhabiting the electromagnetic vacuum. Our analysis accurately encapsulates the quantum nature of the vacuum, and we propose the specific working regime in which we can experimentally verify the existence of virtual photons with quantum correlations in the electromagnetic ground state.


S. Onoe, T. L. M. Guedes, A.S. Moskalenko, A. Leitenstorfer, G. Burkard, and T.C. Ralph
Phys. Rev. D 105, 056023 - published 29 March 2022
DOI: 10.1103/PhysRevD.105.056023
related to projects A05 and A06

Quantum Susceptibilities in Time-Domain Sampling of Electric Field Fluctuations (2022)

Abstract: Electro-optic sampling has emerged as a new quantum technique enabling measurements of electric field fluctuations on subcycle time scales. In a second-order nonlinear material, the fluctuations of a terahertz field are imprinted onto the polarization properties of an ultrashort probe pulse in the near infrared. The statistics of this time-domain signal are calculated, incorporating the quantum nature of the involved electric fields right from the beginning. A microscopic quantum theory of the electro-optic process is developed adopting an ensemble of noninteracting three-level systems as a model for the nonlinear material. It is found that the response of the nonlinear medium can be separated into a conventional part, which is exploited also in sampling of coherent amplitudes, and quantum contributions, which are independent of the state of the terahertz input. Interactions between the three-level systems which are mediated by terahertz vacuum fluctuations are causing this quantum response. Conditions under which the classical response serves as a good approximation of the electro-optic process are also determined and how the statistics of the sampled terahertz field can be reconstructed from the electro-optic signal is demonstrated. In a complementary regime, electro-optic sampling can serve as a spectroscopic tool to study the pure quantum susceptibilities of matter.

M. Kizmann, Andrey S. Moskalenko, A. Leitenstorfer, G. Burkard, and S. Mukamel
Laser Photonics Rev. 2022, 2100423 - published 22 January 2022
DOI: https://doi.org/10.1002/lpor.202100423
related to projects A05 and A06

Quasiclassical theory of non-adiabatic tunneling in nanocontacts induced by phase-controlled ultrashort light pulses (2021)

Abstract: We theoretically investigate tunneling through free-space or dielectric nanogaps between metallic nanocontacts driven by ultrashort ultrabroadband light pulses. For this purpose we develop a time-dependent quasiclassical theory being especially suitable to describe the tunneling process in the non-adiabatic regime, when tunneling can be significantly influenced by photon absorption as the electron moves in the classically forbidden region. Firstly, the case of driving by an ideal half-cycle pulse is studied. For different distances between the contacts, we analyze the main solutions having the form of a quasiclassical wave packet of the tunneling electron and an evanescent wave of the electron density. For each of these solutions the resulting tunneling probability is determined with the exponential accuracy inherent to the method. We identify a crossover between two tunneling regimes corresponding to both solutions in dependence on the field strength and intercontact distance that can be observed in the corresponding behaviour of the tunneling probability. Secondly, considering realistic temporal profiles of few-femtosecond pulses, we demonstrate that the preferred direction of the electron transport through the nanogap can be controlled by changing the carrier-envelope phase of the pulse, in agreement with recent experimental findings and numerical simulations. We find analytical expressions for the tunneling probability, determining the resulting charge transfer in dependence on the pulse parameters. Further, we determine temporal shifts of the outgoing electron trajectories with respect to the peaks of the laser field as a function of the pulse phase and illustrate when the non-adiabatical character of the tunneling process is particularly important.

S. Kim, T. Schmude, Guido Burkard, and Andrey S. Moskalenko
New J. Phys. 23, 083006 - published 5 August 2021
DOI: 10.1088/1367-2630/ac1552
related to project A05