Abstract
The electronic circulator and its close relative the gyrator are invaluable tools for noise management and signal routing in the current generation of low-temperature microwave systems for the implementation of new quantum technologies. The current implementation of these devices using the Faraday effect is satisfactory but requires a bulky structure whose physical dimension is close to the microwave wavelength employed. The Hall effect is an alternative nonreciprocal effect that can also be used to produce desired device functionality. We review earlier efforts to use an Ohmically contacted four-terminal Hall bar, explaining why this approach leads to unacceptably high device loss. We find that capacitive coupling to such a Hall conductor has much greater promise for achieving good circulator and gyrator functionality. We formulate a classical Ohm-Hall analysis for calculating the properties of such a device, and show how this classical theory simplifies remarkably in the limiting case of the Hall angle approaching 90°. In this limit, we find that either a four-terminal or a three-terminal capacitive device can give excellent circulator behavior, with device dimensions far smaller than the ac wavelength. An experiment is proposed to achieve GHz-band gyration in millimeter (and smaller) scale structures employing either semiconductor heterostructure or graphene Hall conductors. An inductively coupled scheme for realizing a Hall gyrator is also analyzed.
- Received 20 December 2013
- Publisher error corrected 12 September 2014
DOI:https://doi.org/10.1103/PhysRevX.4.021019
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Published by the American Physical Society
Corrections
12 September 2014
Erratum
Publisher’s Note: Hall Effect Gyrators and Circulators [Phys. Rev. X 4, 021019 (2014)]
Giovanni Viola and David P. DiVincenzo
Phys. Rev. X 4, 039902 (2014)
Popular Summary
One-way microwave signal propagation is a crucial technological element in ultralow-temperature devices based on a broad range of platforms, including superconducting qubits. It is made possible by a microwave component called the circulator, a venerable element that uses interference and magnetic effects to prevent microwaves from retracing their path backwards in devices. The centimeter-long wavelength of the microwave radiation, however, sets the physical scale of the present-day circulator, making it unacceptably bulky for envisioned large-scale applications as in quantum computers. In this theoretical paper, we propose and investigate a physically different basis for the circulator action that promises strikingly better miniaturization of its action.
The physical basis for one-way signal propagation in the circulator, and its close relative the gyrator, must necessarily break time-reversal symmetry (or using a slightly different term, be “nonreciprocal”). The current circulators employ nonreciprocal electric susceptibility in ferromagnetic materials that results in the Faraday rotation of the microwave polarization. This technology was already perfected around 1960. Around the same time, another nonreciprocal phenomenon of electric conduction in a magnetic field—the Hall effect—was also considered as an alternative for circulation. But the direct use of Hall conduction resulted in devices with high loss due to the contacts, and the idea was discarded.
Our paper investigates a new possibility: By exciting Hall currents in a nongalvanic way based on capacitive rather than ohmic coupling, good circulator action is achievable without any accompanying loss. This points the way to useful device schemes within the emerging area of “chiral plasmonics.” In fact, we have provided a prescription for how to put to use the excitations that have now been extensively studied in this new field, namely, the edge magnetoplasmons that are characteristic of the quantum Hall effect. We have also proposed an experimental setup, whose core is a graphene flake encapsulated between two layers of insulating boron nitride, that permits a significant miniaturization of the device.
We hope that these low-temperature quantum phenomena will be further explored, and exploited, to give vital assistance to quantum technologies that rely on nonreciprocal propagation of microwave signals.
