I. D. Burkov | Searcharxiv

arXiv2026

Coherent states in quantum billiards constructed in the basis of the continued eigenfunctions

In the article a new approach to construction of generalized coherent states in quantum billiards is proposed. The coherent states are defined as the projections of a Gaussian wave function on the basis of the eigenstates of the quantum billiard, continued outside. The continuation is built as the solution of the equivalent Balian--Bloch equation, defined on the entire $\mathbb{R}^2$ and the projection operator is built using the resolvent of the Balian--Bloch equation. In the case of the one--dimensional potential well and billiards, belonging to the Coxeter group, the wave functions of the coherent states were expressed analytically via the Jacobi and Riemann theta functions.

nlin.CD↗

arXiv2026

4-Pixel NbN Hot-Electron Bolometer Integrated in a Si$_3$N$_4$ Planar Optical Waveguide with On-Chip Fiber-Alignment Trench

In this work, we design and characterize a 4-pixel superconducting hot-electron bolometer (HEB) based on niobium nitride (NbN), integrated with individual planar silicon nitride (Si$_3$N$_4$) waveguides. The implemented architecture enables simultaneous detection of an optical signal in four independent channels. To efficiently couple optical radiation under cryogenic conditions, we employ an edge (end-fire) coupling approach using dedicated U-shaped grooves that provide accurate and stable positioning of an optical fiber with respect to the on-chip waveguide facet. The device responsivity is measured as a function of the HEB operating point. The measured voltage responsivity reaches $3800~\mathrm{V/W}$ at a modulation frequency of $3~\mathrm{GHz}$. We demonstrate detection of optically modulated signals in the gigahertz range. The developed fabrication route is promising for compact integrated receiver systems and low-noise cryogenic microwave transducers, including superconducting nanowire single-photon detectors (SNSPDs).

cond-mat.supr-con↗