Time-resolved synchronization analysis of stacked intrinsic Josephson junctions of a cuprate superconductor with frequency-modulated terahertz radiation spectra

Abstract

Terahertz radiation from ${\text{Bi}}_2{\text{Sr}}_2{\text{CaCu}}_2{\text{O}}_{8+\hat{I}´}$ intrinsic Josephson junctions (IJJs) provides an ideal platform to study the synchronization of a macroscopic quantum system. Here, we present a spectral analysis of a frequency-modulated Josephson plasma emitter coupled with patch antennas. In the unmodulated intensity distribution as a function of radiation frequency $I_{\mathrm{UM}}(\ddot{I}‰)$, we observe a double Gaussian peak structure. Crucially, double-peak spectra obtained at a constant bias voltage imply either a rapid temporal distribution of resonances or their simultaneous excitation, driven by the mutual electromagnetic coupling between the IJJ mesa and the antennas. At low modulation frequencies $f_m$, the spectra are well reproduced by the products of $I_{\mathrm{UM}}(\ddot{I}‰)$ and frequency combs, yielding a synchronized relaxation time $\ddot{I}{„}_s\simeq 0.28\text{ ns}$. Incorporating $\ddot{I}{„}_s$ quantitatively reproduces a drastic spectral transformation observed around $f_m\sim 1\text{ GHz}$, unveiling the sub-nanosecond non-equilibrium dynamics of coupled Josephson plasma.

22 pages, 5 figures