Spectroscopy is a powerful tool to probe matter. By measuring the spectrum of elementary excitations, one reveals the symmetries and interactions inherent in a physical system. Mesoscopic devices, which preserve quantum coherence over lengths larger than the atomic scale, offer a unique possibility to both engineer and investigate excitations at the single quanta level. Unfortunately, conventional spectroscopy techniques are inadequate for coupling radiation to mesoscopic systems and detecting their small absorption signals.

We are developing an on-chip spectrometer based on Josephson junctions which is ideally suited for probing elementary excitations in mesoscopic systems. The design provides uniform wideband coupling from 2-1500 GHz, low background noise, high sensitivity, and narrow linewidth.