Whispering Vortices

Abstract

Experiments indicating the excitation of whispering gallery type electromagnetic modes by a vortex moving in an annular Josephson junction are reported. At relativistic velocities the Josephson vortex interacts with the modes of the superconducting stripline resonator giving rise to novel resonances on the current-voltage characteristic of the junction. The experimental data are in good agreement with analysis and numerical calculations based on the two-dimensional sine-Gordon model. 74.50.+r, 05.45.Yv, 85.25.Cp, 42.60.Da Whispering gallery modes are universal linear excitations of circular and annular resonators. They have first been observed in form of a sound wave traveling along the outer wall of a walkway in the circular dome of St. Paul's Cathedral in London and were investigated by Lord Rayleigh [1] and others [2]. In the 2 meter wide walkway, which forms a circular gallery of 38 meter diameter about 40 meters above the ground of the cathedral, the whispering of a person can be transmitted along the wall to another person listening to the sound on the other side of the dome. The investigations by Rayleigh led to the conclusion that the whisper of a person does excite acoustic eigenmodes of the circular dome which can be described using high order Bessel functions. This acoustic phenomenon lends its name "whispering gallery mode" to a number of similar, mostly electromagnetic excitations in circular resonators. Whispering gallery modes are of strong interest in micro-resonators used for ultra small lasers [3]. Most recently, circular resonators with small deformations, in which chaotic whispering gallery modes were observed, attracted a lot of attention [4]. Here we describe the experimental observation of electromagnetic whispering gallery modes excited by a vortex moving in an annular Josephson junction of diameter less than 100 µm.A long Josephson junction is an intriguing nonlinear wave propagation medium for the experimental study of the interaction between linear waves and solitons [5]. In this letter we report the excitation of whispering gallery type electromagnetic modes by a topological soliton (Josephson vortex) moving at relativistic velocities in a wide annular Josephson junction. We make use of the same Josephson vortex for both exciting and detecting the whispering gallery mode. These modes are manifested by their resonant interaction with the moving vortex, which results in a novel fine structure on the current-voltage characteristic of the junction. Our experiments are consistent with the recently published theory tion are described by the perturbed sine-Gordon equation (PSGE) for the superconducting phase difference φ between the top and bottom superconducting electrodes of the junction [5]. The Josephson vortex, often also called fluxon, corresponds to a twist over 2π in φ. It carries a magnetic flux equal to the magnetic flux quantum Φ 0 = h/2e = 2.07 10 −15 Vs. Physically, this flux is induced by a vortex of the screening current flowing across the junction barrier. Linear excitatio...

Vortex radiation in long narrow Josephson junctions: Theory and experiment

“…Such resonant steps have been predicted by numerical studies and been experimentally observed in parallel arrays of small Josephson junctions, 6,7 stacks of Josephson junctions, [8][9][10][11][12][13] and two-dimensional Josephson junctions. [14][15][16][17] In this paper, we will show that Cherenkov radiation also occurs in extremely narrow long Josephson junctions. The interest to study fluxon dynamics in long narrow junctions has been recently boosted by the fact that the effective mass of a fluxon, in such junctions, is small enough to observe macroscopic quantum effects.…”

Creation of classical and quantum fluxons by a current dipole in a long Josephson junction

“…The interest to annular long JJ's stems from the great potential they offer for fundamental studies of dynamical properties of solitons, such as, e.g., emission of the Cherenkov radiation. 5,6 A challenging problem for the theory is quantum soliton dynamics in long JJ's, which has been recently observed in experiment at ultralow temperatures. 7 On the other hand, annular JJ's offer applications in cryoelectronics, such as sources of highly coherent microwave radiation 4 and radiation detectors.…”

“…13 Other studies relied on fluxon trapping in the course of cooling the system below the critical temperature T c of the superconducting electrodes. [3][4][5][6]14,15 However, the latter technique does not provide for reproducible results, and requires heating of the junction to high temperatures. Moreover, trapped fluxons generated in such a manner get often pinned by Abrikosov vortices, which may be trapped in the electrodes in the course of cooling below T c .…”

Kink propagation and trapping in a two-dimensional curved Josephson junction

“…9, the excitation of whispering-gallery-type electromagnetic modes by a moving fluxon in an annular Josephson junction was found in Ref. 10. The fluxon dynamics in exponentially tapered Josephson flux-flow oscillator was studied in Ref.…”