arXiv subjects

Kirill Shulga

Publications and source records attributed to Kirill Shulga.

4 recordsLinked to original sources

arXiv2026

Internal cyclotron probe of the vertical polarizability of a surface-state electron on helium

We study a surface-state electron on liquid helium in a tilted magnetic field. The tilt couples the cyclotron ladder to the vertical Rydberg-like subbands of the same electron and thereby realizes a self-coupled Landau-subband Hamiltonian. In the far-detuned regime, the cyclotron line acquires a state-dependent shift described by standard second-order perturbation theory. The resulting expression identifies the cyclotron resonance as a direct probe of the dynamical polarizability of the vertical ladder. The theory is intrinsically multilevel. Exact diagonalization confirms a broad microwave window in which sizable state-dependent cyclotron shifts are expected while the system remains dispersive.

cond-mat.supr-con↗

arXiv2026

Charged-Lepton Koide Geometry from a Green-Dressed Compact Family Cycle

Koide's charged-lepton relation suggests that $(\sqrt{m_e},\sqrt{m_μ},\sqrt{m_τ})$ is the natural family vector. We construct an effective compact-cycle model in which this vector is sampled from one real amplitude $Z(ϕ)$ on an internal circle, while the masses are quadratic overlaps, $m_a\propto |Z(2πa/3)|^2$. The amplitude is built from the two lowest antiperiodic modes on the circle; their symmetric square is periodic and gives the minimal three-harmonic family space $e^{iϕ},1,e^{-iϕ}$. A reality condition together with the requirement that the amplitude comes from the square of one two-component spinor fixes the relative weights required by Koide's $45^\circ$ geometry. The remaining orientation angle is fixed by matching one $C_3$ family shift to transport on the full circle: integrating out the higher Fourier harmonics gives the Berry dressing that enters the determinant term and selects $θ_\ell=-2/9$. Using $m_e$ and $m_μ$ as inputs, the model predicts $m_τ=1776.97\,\mathrm{MeV}$.

hep-ph↗

arXiv2025

Observation of individual vortex penetration in a coplanar superconducting resonator

We demonstrate the detection and control of individual Abrikosov vortices in superconducting microwave resonators. $\lambda/4$ resonators with a narrowed region near the grounded end acting as a vortex trap were fabricated and studied using microwave transmission spectroscopy at millikelvin temperatures. Sharp stepwise drops in resonance frequency are detected as a function of increasing external magnetic field, attributed to the entry of individual Abrikosov vortices in the narrow region. This interpretation is confirmed by NV center magnetometry revealing discrete vortex entry events on increasing field. Our results establish a method to investigate and manipulate the states of Abrikosov vortices with microwaves.

cond-mat.supr-con↗

arXiv2023

Dissipative Stability and Dynamical Phase Transition in Two Driven Interacting Qubits

We examine a two-qubit system influenced by a time-periodic external field while interacting with a Markovian bath. This scenario significantly impacts the temporal coherence characteristics of the system. By solving the evolution equation for the density matrix operator, we determine the characteristic equilibration time and analyze the concurrence parameter - a key metric for quantifying entanglement. Our findings reveal the system's ability to navigate through a dynamic phase transition. These results pave the way to designing systems of interacting qubits demonstrating robust entanglement under realistic conditions of interaction with the environment.

quant-ph↗