Graphene-based superconducting Quantum circuits – GRAPHMON

Devices based on the control of quantum states will revolutionize information and communications technologies. It is now possible to fabricate and isolate individual quantum objects that can be prepared in any superposition of quantum states. Several implementations of the quantum bit (Qubit), i.e. the building block for systems targeting quantum-enabled functionalities, were already demonstrated. Approaches based on all-superconducting materials provide the most advanced solid-state platform to date but one of their drawbacks is that they must rely on magnetic effects for control and operation, which is not an industry standard for devices. This starts already to be an issue in large scale circuits. On the other hand, approaches fully based on semiconductors provide spin Qubits with long coherence times that are electrically tunable and addressable. They are very promising for large scale integration because they are based on mainstream industry technologies. But fast quantum state readout will require their co-integration with superconducting resonators.

To bridge the gap between these two approaches, I propose the integration of a gapless two-dimensional semiconductor, graphene, in the key element of superconducting quantum circuits: the Josephson junction, a weak link between two superconducting electrodes. It will create an electrically tunable Josephson element. The resulting quantum circuits will gain electrical tunability, a breakthrough for control and future integration. Assisted by a strong theoretical support, several pivotal elements of quantum technologies will be demonstrated during the project: an electrically tunable Qubit, an electrically pumped quantum limited Josephson parametric amplifier and an electrically controlled coupler between Qubits that will be a major step for future scaling. Beyond those demonstrations, the unique properties of a graphene based Josephson element will be used to build a topologically protected Qubit, i.e. a Qubit that is intrinsically immune to decoherence, an outstanding problem in quantum computation.

Graphene, which can now be grown on wafer scale while maintaining high electron mobilities, is only one atom thick and can be combined in a simple manner with mainstream technologies by using recently developed transfer techniques. This is a fundamental asset for future developments and a clear advantage compared to competing technologies based on III-V semiconductor nanowires or two-dimensional electron gas.