Superconducting Qubits
Superconducting qubits are a leading approach to building a quantum computer.1 Recent work has demonstrated systems with 50-100 qubits. The key element of a superconducting qubit is the nonlinear, nondissipative Josephson junction that is usually made from aluminum/aluminum oxide/aluminum layers.
Recently our group has developed superconducting qubits where the Josephson junction element is made from semiconductor materials.1 This semiconductor approach results in voltage-controlled superconducting qubits - known as the gatemon - that have the potential to naturally interface with large scale control solutions based on ubiquitous CMOS technology. While first demonstrations were using nanowire-based superconductor-semiconductor materials, more recently we have focused on materials that simplify fabrication of larger qubit systems such as two-dimensional electron gases.3 We are also working on improving qubit quality, for example, using low loss silicon-based materials and novel superconductors.
The physics of semiconductor-based Josephson junctions in which there is near-ballistic transport of charge carriers may also allow new approaches to building superconducting qubits that are robust against sources of error and allow for novel control schemes. We are also exploring novel qubit designs that exploit this physics.4
The superconducting qubit group also studies fundamental aspects of experimental implementations of quantum algorithms and quantum protocols. In particular, we are studying efficient protocols for quantum verification and validation, gate-benchmarking, entanglement measurement and novel tomographic protocols, using both gatemons and more traditional superconducting qubit modalities.
1 M. Kjaergaard et al., Superconducting Qubits: Current State of Play, Ann. Rev. Cond. Mat. 11, 369 (2020)
2 T.W. Larsen et al., A Semiconductor Nanowire-based Superconducting Qubit, Phys. Rev. Lett. 115, 127001 (2015)
3 L. Casparis et al., Superconducting gatemon qubits based on a proximitized two-dimensional electron gas, Nature Nano., 13, 915 (2018)
4 T. W. Larsen et al., Parity-Protected Superconductor-Semiconductor Qubit, Phys. Rev. Lett. 125, 056801 (2020)