Nonlinear graphene quantum capacitors for electro-optics

Abstract

Owing to its peculiar energy dispersion, the quantum capacitance property of graphene can be exploited in a two-dimensional layered capacitor configuration. Using graphene and boron nitride, respectively, as the electrodes and the insulating dielectric, a strongly nonlinear behavior at zero bias and small voltages is obtained. When the temperature is sufficiently low, the strong nonlinear interaction emerging from the quantum capacitance exhibits a diverse range of phenomena. The proposed structure could take over the functionalities of nonlinear elements in many cryogenic quantum systems, and in particular, quantum electro-optics. It is shown that ultrastrong coupling is easily reached with small number of pump photons at temperatures around 1 K and capacitor areas of the order of 1 μm². A measure of anharmonicity is defined and as potential applications, a qubit design as well as schemes for non-reciprocal devices such as an electromagnetic frequency circulator are discussed.

Quantum Technology: Graphene Capacitor Enhances Nonlinear Circuitry at Low Temperatures

Graphene capacitors, known to be strongly nonlinear at very low temperatures, now find novel applications in superconducting quantum circuits. A research carried out at Sharif University of Technology, Iran, and École Polytechnique Fédéral de Lausanne, Switzerland, reveals a whole new range of applications for quantum graphene capacitors. This is a three-layer device, made of two graphene layers separated by a two-dimensional dielectric. At reasonably small area, the capacitor exhibits strong nonlinearity leading to unprecedented applications in quantum technology. It could serve as the missing element in the toolbox of low temperature circuits, where nonlinear inductors and Josephson junctions mostly dominate. It also would enable a new and diverse range of quantum circuits, while easily providing access to ultrastrong coupling.