Tunable valley splitting and bipolar operation in graphene quantum dots

TL;DR

This paper demonstrates tunable valley splitting and bipolar operation in bilayer graphene quantum dots, enabling control over quantum states for potential qubit applications.

Contribution

It introduces a method to tune valley g-factors over a wide range and achieves bipolar operation with simple gate adjustments in graphene quantum dots.

Findings

Valley g-factor tunable from 20 to 90

Larger dots have higher valley g-factors

Bipolar operation with controllable charge carriers

Abstract

Quantum states in graphene are four-fold degenerate: two fold in spins, and two fold in valleys.Both degrees of freedom can be utilized for qubit preparations. In our bilayer graphene quantumdots, we demonstrate that the valley g-factorgv, defined analogously as the spin g-factorgsforvalley splitting in perpendicular magnetic field, is tunable by over a factor of 4 from 20 to 90. Wefind that largergvresults from larger electronic dot sizes, determined from the charging energy.This control is achieved by adjusting voltages on merely two gates, which also allows for tuning ofthe dot-lead tunnel coupling. On our versatile device, bipolar operation, charging our quantum dotwith charge carriers of the same or the opposite polarity as the leads, can be performed. Dots ofboth polarity are tunable to the first charge carrier by action of the plunger gate, such that thetransition from an electron to a hole dot can be observed. By adding more gates, this system caneasily be extended to host double dots.