Mutually Synchronized Macroscopic Josephson Oscillations Demonstrated by Polarization Analysis of Superconducting Terahertz Emitters

We demonstrate mutual synchronization of Josephson oscillations in multiple stacks of intrinsic Josephson junctions of the cuprate superconductor ${\mathrm{Bi}}_2{\mathrm{Sr}}_2{\mathrm{Ca}\mathrm{Cu}}_2{\mathrm{O}}_{8+\delta }$. Detailed analysis of the full polarization parameters allows the determination of a phase correlation between the stacks: a simultaneous emission state is described by a linear combination of individual emission states with a phase retardation. This proves that the stacks are coupled via a Josephson plasma in a superconducting substrate and that the coupling matrices can be extracted from polarization analyses. Our findings suggest a route towards the realization of high-power terahertz sources based on the synchronization of a large number of intrinsic Josephson junctions.

Figure 1

(a) Optical microscopy image of the $\mathrm{Bi}$-2212 mesa array. (b) Schematic view of the synchronized array. (c) Schematic of the optical configuration for Stokes parameter measurement.

Figure 2

Polar plots of the maximum bolometer output as a function of the QWP angle $\theta$ for (a) A1 and (b) $\mathrm{A1}\parallel \mathrm{A2}$. The solid lines represent results calculated using the Stokes parameters. Polarization ellipses for (c) A1 (red) and A2 (blue), and (d) $\mathrm{A1}\parallel \mathrm{A2}$.

Figure 3

Calculation of the polarization ellipse for (a) a single mesa and (b) two arrayed mesas.

Figure 4

Calculation of the axial ratio as a function of $\arg (\beta /\alpha )$. Inset: schematic side view of the $\mathrm{Bi}$-2212 mesa array.