Hacking the Superconducting Nanowire: Detecting Single Photons, Resurrecting the Cryotron, and Pushing Current Around Corners

Condensed Matter Seminars

Speaker: Karl Berggren, MIT
Date & Time: March 31, 2016, 2:00 - 3:00
Location: Hennings 318
Local Contact: Sarah Burke
Intended Audience: Graduate

Superconducting nanowires have long been of interest for their unusual electrothermal behavior, and the exhibition of quantum phase slips–twists in the electron wavefunction that can occur spontaneously in the right environment. However, they have also demonstrated themselves recently to be of key importance to the field of photodetection, with important applications in communications and metrology. With these nanowires, individual infrared photons are readily detected with near-unity efficiency and sub-100-picosecond timing resolutions.

But photodetection is far from the only utility these nanowires can be put to. Because of the strange way that current flows in thin superconducting thin films, and the strong nonlinearities inherent in superconducting materials, geometric arrangements of these nanowires can be devised that act like digital comparators and current sensors, enabling complex electronic operations that in recent years have only been contemplated with circuits involving Josephson junctions. I say “in recent years” because there is a 50-year-old superconducting electronic device–the cryotron–which these devices share much in common with.

In this talk, I will present the latest developments in the field of supercondcuting nanowire single-photon detection, but I will also present various operations, amplification, digital circuits, and memories built with two variants of the nanowire-based cryotron. A simple three-terminal cryotron that can be used to amplify small signals based on electrothermal effects, and another that achieves the same function, but uses current crowding to effect these operations. These devices may be useful for signal amplification, digital signal processing, cryogenic low-power memories, and application as classical control and readout logic inside a quantum computer.