arXiv subjects

Alexander Tartakovskii

Publications and source records attributed to Alexander Tartakovskii.

3 recordsLinked to original sources

arXiv2026

Twist-Reconfigurable van der Waals Moiré Photonic Crystals

Moiré photonics has emerged as a fascinating concept to design and in situ control of the optical bands. Moiré enabled light localisation arises from the relative twist between periodic layers, rather than from fixed, pre-fabricated cavity features. So far, however, the realisation of practical moiré photonic crystals in the visible range has been elusive, due to challenges in engineering nanoscale structures and twisting them dynamically post fabrication. Here, we realise a mechanically reconfigurable moiré photonic crystal, comprising from two patterned van der Waals crystals (tungsten di sulphide, WS$_2$) slabs separated by an optically active hexagonal boron nitride (hBN) spacer. We reconfigured the same pair of WS$_2$ slabs from a twist angle of 3.8° to 8.4° and reconstructed their three-dimensional dispersion using momentum-resolved reflectivity spectroscopy. Further, by reducing the twist angle between the slabs, we observe a denser manifold of folded and hybridised resonances that coincides with a 30-fold enhancement of emission from embedded colour centres. Our results open exciting opportunities for in-situ dispersion engineering and programmable light matter interactions employing van der Waals nanostructures.

physics.optics↗

arXiv2024

Nonlinear Rydberg exciton-polaritons in Cu$_2$O microcavities

Rydberg excitons (analogues of Rydberg atoms in condensed matter systems) are highly excited bound electron-hole states with large Bohr radii. The interaction between them as well as exciton coupling to light may lead to strong optical nonlinearity, with applications in sensing and quantum information processing. Here, we achieve strong effective photon-photon interactions (Kerr-like optical nonlinearity) via the Rydberg blockade phenomenon and the hybridisation of excitons and photons forming polaritons in a Cu$_2$O-filled microresonators. Under pulsed resonant excitation polariton resonance frequencies are renormalised due to the reduction of the photon-exciton coupling with increasing exciton density. Theoretical analysis shows that the Rydberg blockade plays a major role in the experimentally observed scaling of the polariton nonlinearity coefficient as $\propto n^{4.4 \pm 1.8}$ for principal quantum numbers up to n = 7. Such high principal quantum numbers studied in a polariton system for the first time are essential for realisation of high Rydberg optical nonlinearities, which paves the way towards quantum optical applications and fundamental studies of strongly-correlated photonic (polaritonic) states in a solid state system.

cond-mat.mes-hall↗

arXiv2014

Influence of Nuclear Quadrupole Moments on Electron Spin Coherence in Semiconductor Quantum Dots

We theoretically investigate the influence of the fluctuating Overhauser field on the spin of an electron confined to a quantum dot (QD). The fluctuations arise from nuclear angular momentum being exchanged between different nuclei via the nuclear magnetic dipole coupling. We focus on the role of the nuclear electric quadrupole moments (QPMs), which generally cause a reduction in internuclear spin transfer efficiency in the presence of electric field gradients. The effects on the electron spin coherence time are studied by modeling an electron spin echo experiment. We find that the QPMs cause an increase in the electron spin coherence time and that an inhomogeneous distribution of the quadrupolar shift, where different nuclei have different shifts in energy, causes an even larger increase in the electron coherence time than a homogeneous distribution. Furthermore, a partial polarization of the nuclear spin ensemble amplifies the effect of the inhomogeneous quadrupolar shifts, causing an additional increase in electron coherence time, and provides an alternative to the experimentally challenging suggestion of full dynamic nuclear spin polarization.

cond-mat.mes-hall↗