M. V. Fistul

Frustration induced highly anisotropic magnetic patterns in classical $XY$ model on kagome lattice

A. Andreanov [1], M. V. Fistul [1,2]

Abstract

We predict and observed novel highly anisotropic magnetic patterns obtained in the model of frustrated planar interacting magnetic moments (the classical $X-Y$ model) on the regular kagome lattice. The frustration is provided by the presence of both ferromagnetic and anti-ferromagnetic interactions between adjacent magnetic moments defined on the lattice nodes. At the critical value of the frustration $f=f_{cr}=3/4$ such a systems displays the phase transition from the ordered ferromagnetic state to the disordered frustration regime characterized by the highly-degenerated ground state. In the frustrated regime, $f_{cr}< f \leq 1$, unexpected scaling of spatially averaged magnetization $\langle \vec{M} \rangle $ on the total number of nodes,$N$, i.e. $\langle \vec{M} \rangle \simeq N^{-1/4}$, has been obtained. Such scaling is provided by highly anisotropic magnetic patterns displaying the ferromagnetic ordering along the $y$-direction, and short-range correlations of magnetic moments along the $x$-direction. We conjecture that all these intriguing features are explained by the presence of the double-degenerated ground state in the basic cell, i.e. single triangle, of the kagome lattice accompanying a large amount of intrinsic constraints. We anticipate the implementation of the phase transition and anisotropic magnetic patterns in various systems, e.g. natural magnetic molecular clusters, artificially prepared Josephson junctions networks, trapped-ions and/or photonic crystals.

Josephson vortex interaction mediated by cavity modes: Tunable coupling for superconducting qubits

M. V. Fistul [1], A. V. Ustinov [1]

Abstract

A quantum-mechanical model for the interaction of Josephson vortices (fluxons) embedded in superconducting transmission line is presented. The vortices interact through emission and absorption of linear waves (electromagnetic cavity modes). We show that in a classical regime this peculiar type of interaction is determined by the product of instantaneous velocities of fluxons. In a quantum regime, this property provides tunable coupling between vortices which can be used for entanglement of vortex qubits. The physical mechanism of the vortex interaction is similar to that proposed for qubits based on trapped ions. Different types of transmission lines mediating the vortex interaction are proposed.