Citation: Placke, Benedikt, Stefano Bosco, and David P. DiVincenzo. "A model study of present-day Hall-effect circulators." EPJ Quantum Technology 4.1 (2017): 1-14.
Web: https://epjquantumtechnology.springeropen.com/articles/10.1140/epjqt/s40507-017-0057-9
Tags: Physical, Hardware
This paper considers the feasibility of a recent a recent proposal to make a microwave circulator using a two dimensional electron gas in its quantum Hall regime. Circulators are important components of modern low-temperature microwave engineering. They have three ports, each of which can carry a signal. The device takes in a signal coming in from one port and cyclically rotates it to the next port.
The conventional way of implementing these circulators uses the classical Faraday effect. These devices are very efficient in the sense that there is no loss on the signal, but they are very bulky. Microwave devices are expected to be large on the scale of tens of micrometers, but these circulators are large on the scale of centimeters. By the nature of the Faraday effect, these devices cannot be made any smaller. A proposal of Viola and DiVincenzo is to make a circulator using two dimensional electron gasses, which can in principle be made arbitrarily small:
> Viola, Giovanni, and David P. DiVincenzo. "Hall effect gyrators and circulators." Physical Review X 4.2 (2014): 021019.
Two years after this initial proposal, an experimental group successfully made an on-chip quantum Hall circulator, 1/1000th the size of the Faraday circulators, which is 10 times smaller than the original paper had predicted:
> Mahoney, A. C., et al. "On-chip microwave quantum hall circulator." Physical Review X 7.1 (2017): 011007.
The Hall effect had been known for a long time before this paper, and people had even proposed circulators based on it, but there were foundational issues in the way. Thus, researchers dropped the approach. The more modern discovery of two dimensional electron gasses is what allowed for a resurgence of the idea, as explained in the proposal.