Far-Infrared Optical Spectroscopy of Quantum Matter at Millikelvin Temperatures*

Many interesting quantum phenomena are associated with strongly correlated gaps at the energy scale in the far-infrared regime, and their observations are often optimized at ultra-low temperatures. They include integer and fractional quantum Hall effects, superconductivity in 2D materials and correlated states in moiré systems. Optical spectroscopy is a useful probe in determining the nature of these low energy states and excitations especially because light-matter interactions can couple to neutral excitations that are normally invisible to electronic probes. In this talk, we describe our efforts in developing a novel instrumental platform for implementing far-infrared optical spectroscopy on high quality 2D samples at milli-Kelvin temperatures.