HAQD · Hybrid Andreev Quantum Devices

We will study an emerging platform for qubit technology, Andreev spin qubits (ASQs), that combines the benefits of two leading solid-state setups: superconducting and spin qubits. An ASQ is fundamentally a device that operates via coherent control of the electron spin, resulting in compact devices comparable to existing standard spin qubit technology. Different from standard spin qubits, however, the confinement of the electron spin in an ASQ is done with superconducting elements. This key difference allows manipulation and readout of ASQs using circuit quantum electrodynamics (cQED) techniques. We will study in this project two fundamental issues that are currently key challenges for ASQs to become competitive platforms for quantum computation: (i) improving the qubit lifetimes and (ii) designing fault-tolerant devices. We will approach (i) studying new material platforms. Currently, the lifetimes of ASQs are limited by the presence of nuclear spins; therefore, several research groups are trying to fabricate these devices using materials that can be isotopically purified, such as germanium and carbon. I will use my expertise to perform atomistic simulations of ASQs in two-dimensional germanium hole gases and in graphene. We will study approaches to achieve the best qubit performance in germanium, investigating different device setups, as the position of superconducting leads and strain effects. In graphene, we will explore the valley degree of freedom as a source of qubit protection and gate-defined devices to produce ultraclean superconducting interfaces. Finally, we will approach (ii) by designing couplings between ASQs to achieve universal quantum simulators and quantum error correction schemes. We will combine microscopic simulations with (cQED) to design Andreev networks that allow the implementation of logical qubits and surface codes.