Phase-sensitive imaging of microwave currents in superconductive circuits

TL;DR

This paper introduces a phase-sensitive laser scanning microscopy technique that captures both amplitude and phase of microwave currents in superconductive circuits, enhancing diagnostic capabilities beyond traditional amplitude-only methods.

Contribution

The paper presents a novel LSM method that synchronizes laser modulation with microwave phase, enabling phase-resolved imaging of microwave currents in superconductive circuits.

Findings

Successfully demonstrated phase-sensitive imaging on superconductive resonators.

Enhanced understanding of RF current distributions in superconductive circuits.

Provides a new diagnostic tool for complex superconductive electronic systems.

Abstract

The contemporary superconductive electronics is widely using planar circuits with micrometer-scale elements for a variety of applications. With the rise of complexity of a circuit and increased number of its components, a simple impedance measurement are often not efficient for diagnostics of problems, nor for clarifying the physics underlying the circuit response. The established Scanning Laser Microscope (LSM) technique generates the micrometer-scale images of the amplitude of the microwave currents in a planar superconductive circuit, but not the phase of the oscillating currents. Here we present a novel, more powerful type of LSM imaging containing the signal phase information. We employ a fast optical modulator in order to synchronize the phase of the laser intensity oscillation with the phase of the probing microwave signal. The loss induced in laser illuminated area strongly depends on the phase difference between the RF probing signal and the laser beam modulation. We explain the detection principle of the phase sensitive LSM and experimentally demonstrate the capability of this method using superconductive microwave resonators. The described technique facilitates understanding of complex RF current distributions in superconductive circuits.