Quantum detection at millimeter wavelengths

TLDR

Photon‑assisted tunneling of electrons through an insulating barrier may be used to detect long‑wavelength radiation with a sensitivity approaching the limit imposed by the Heisenberg uncertainty principle. The authors develop ultra‑low‑noise millimeter‑wave receivers that exploit the sharp nonlinearity of single‑electron tunneling in SIS junctions, where a photon’s quantum energy can exceed the tunneling onset voltage and trigger an extra electron to tunnel, and they review the experimental progress and quantum mixing theory that predicts the receivers’ performance. The regime enables quantum effects such as power amplification during frequency down‑conversion in heterodyne receivers.

Abstract

Photon-assisted tunneling of electrons through an insulating barrier may be used to detect long-wavelength radiation with a sensitivity approaching the limit imposed by the Heisenberg uncertainty principle. A new generation of ultra-low-noise millimeter-wave receivers, currently being developed for astronomical observation, utilizes the extremely sharp nonlinearity produced by single-electron quasiparticle tunneling between two superconductors in a superconductor-insulator-superconductor (SIS) tunnel junction. At millimeter wavelengths, the quantum energy $\frac{\ensuremath{\hbar}\ensuremath{\omega}}{e}$ may be larger than the voltage width for onset of quasiparticle tunneling in a SIS junction; and under these conditions the absorption of a single photon can cause one additional electron to tunnel through the barrier. Several newly discovered quantum effects become possible in this regime, including power amplification of an incoming signal during the process of frequency down-conversion in a heterodyne receiver. The experimental development of SIS millimeter-wave receivers is reviewed, along with the quantum theory of mixing which predicts their performance.