Krzysztof Sawicki, PhD || Postdoctoral Research Associate at Durham University

Krzysztof Sawicki

Durham University

My research concerns the intersection of nonlinear photonics and condensed matter physics with the main focus on topics related to experimental studies of Bose-Einstein condensation of polaritons, polariton lasing in single and coupled microcavities and dynamics of exciton-polaritons, as well as spectroscopy of single magnetic dopants in self-assembled quantum dots. I am currently a Postdoctoral Research Associate at Durham University.

From 2021 to 2025, I worked as a Postdoctoral Research Fellow in the Hybrid Optoelectronic Laboratory led by Prof. Pavlos Lagoudakis and Prof. Simone De Liberato at the University of Southampton. During this period, my research was focused on polariton trapping, ballistically coupled polariton condensates, liquid-crystal-based microcavities operating in the weak-coupling regime, and II–VI microcavity systems in the very strong coupling regime.

I obtained my PhD in 2021 from the University of Warsaw, where I investigated polariton lasing in single and coupled microcavities in the group of the Laboratory of Ultrafast Magneto-Spectroscopy.

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Paths of investigation

Magnetic control over trapped polariton condensates

AI for polaritonics

Ballistically coupled polariton condensates

New materials for organic polaritonics

Rydberg excitons and exciton-polaritons in cuprous oxide

Highlights

Cavity-enhanced second harmonic generation from Rydberg excitons in Cu2O

H. Q. X. Wong, K. Sawicki, M. Fisher, S. A. Lynch, W. Langbein, S. K. Rajendran, H. Ohadi, M. P. A. Jones, L. A. P. Gallagher

arXiv:2611.09705 (2026).

Here, we use second-harmonic generation (SHG) to study Rydberg excitons in a doubly resonant optical microcavity designed to enhance both the pump and second-harmonic fields. We observe even-parity exciton states in an optical cavity and extend cavity-based measurements of Rydberg excitons up to n=10. The SHG intensity depends strongly on pump cavity detuning, showing the dominant role of the microcavity is the enhancement of the intra-cavity pump field. Analysis reveals an additional enhancement from the resonant second-harmonic cavity giving an overall SHG enhancement factor of 21±2 inside the microcavity.

Electrically Reconfigurable Extended Lasing State in an Organic Liquid-Crystal Microcavity

D. Dovzhenko, L. S. Ricco, K. Sawicki, M. Muszyński, P. Kokhanchik, P. Kapuściński, P. Morawiak, W. Piecek, P. Nyga, P. Kula, D. Solnyshkov, G. Malpuech, H. Sigurðsson, J. Szczytko, S. De Liberato

Nature Communications 17, 5335 (2026).

Here we demonstrate electrically controlled in-plane interaction between optically reconfigurable spatially separated lasing states, operating at room temperature in the weak light-matter coupling regime. We show spatially extended coherent lasing state or "supermode" with wide-range micro-scale control of near-field, far-field and on-chip phase-locking tuning functionality.

Observation of 𝜎-𝜋 coupling and mode selection in optically trapped artificial polariton molecules

K. Sawicki, V. K. Daníelsson, D. Dovzhenko, P. G. Lagoudakis, S. De Liberato, H. Sigurðsson

Optica 13(1), 93-100 (2026).

Here, we explore this coupling mechanism between polariton condensates populating the first excited $p$-state manifold of coupled optically trapped condensates and show a rich structure of patterns based on excitation parameters. The optical reconfigurability of the laser excitation patterns enables the creation of an annular-shaped beam to confine polaritons in a tailored trapping potential, whilst the dissipative nature of the optical traps enables effective interaction with neighboring condensates.

A Fourier Neural Operator Approach for Modelling Exciton-Polariton Condensate Systems

Y. Wang, S. T. Sathujoda, K. Sawicki, K. Gandhi, A. I Aviles-Rivero, P. G. Lagoudakis

Communications Physics 8, 505 (2025).

In this work, we study the application of the FNO architecture to approximate solutions to the GPE. We are interested in this specific variant of Neural Operator as its mathematical formulation relates very closely to the SplitStep Fourier Method (SSFM), which is the numerical method used to solve the GPE in this instance.

Occupancy-driven Zeeman suppression and inversion in trapped polariton condensates

K. Sawicki, D. Dovzhenko, Y. Wang, T. Cookson, H. Sigurðsson, P. G. Lagoudakis

Physical Review B 109, 125307 (2024). [Editors' suggestion]

Extremely high coherence time and, thus, ultra-narrow spectral linewidths make it possible to resolve magnetically induced µeV fine-energy shifts in trapped exciton-polariton condensates. The continuous control over the polariton confinement enabled authors to explore two operation regimes: (1) the full parametric screening of the Zeeman splitting and (2) the Zeeman inversion regime. The transition from one range to the other occurs by adjusting the size of the optical trap, which controls the strength of the polariton-polariton and polariton-exciton reservoir interactions.

Polariton lasing and energy-degenerate parametric scattering in non-resonantly driven coupled planar microcavities

K. Sawicki, T. J. Sturges, M. Ściesiek, T. Kazimierczuk, K. Sobczak, A. Golnik, W. Pacuski J. Suffczyński

Nanophotonics 10(9) 2421-2429 (2021).

Here, we report non-equilibrium Bose–Einstein condensation of exciton-polaritons and low threshold, dual-wavelength polariton lasing in vertically coupled, double planar microcavities. Moreover, we find that the presence of the non-resonantly driven condensate triggers interbranch exciton-polariton transfer in the form of energy-degenerate parametric scattering.