Mesoscopic Spectroscopy with Josephson Junctions

Spectroscopy is a powerful tool to probe matter. By measuring the spectrum of excitations, one can reveal the symmetries and topological properties of a physical system. Mesoscopic devices offer a unique possibility to both engineer and investigate novel excitations.  Unfortunately, conventional spectroscopy techniques suffer several drawbacks for coupling radiation to mesoscopic systems and detecting their small absorption signals. 

We propose an on-chip, Josephson-junction based spectrometer which surpasses state-of-the-art instruments and is ideally suited for probing elementary excitations in mesoscopic systems. It has a SQUID-based design providing uniform wideband coupling from 2-2000 GHz, low background noise, high sensitivity, and narrow linewidth. We describe the operating principle and design of the spectrometer, show preliminary results demonstrating proof-of-concept, and outline experiments which exploit the spectrometer to investigate unconventional Andreev states.