In this talk, I will describe our discovery and understanding of a manifestation of macroscopic quantum tunneling: the anti-proximity effect in superconducting nanowires. Most studies of quantum tunneling use extensive mathematical modeling and fitting to separate quantum tunneling from thermally activated events. The anti-proximity effect in contrast, offers an experimental way to achieve this separation. In addition to being a new tool to study macroscopic quantum tunneling, the discovery is relevant to superconducting quantum computing applications.
Quantum computing is arguably the most well known application of quantum mechanics today. Donor spin based qubits are a particularly promising platform for quantum computing. Realization of multiple qubits using this approach requires precise control over the placement and number of donors. The figure shows the technology we have developed to address this twofold challenge. A diode detector next to our qubit (see left panel), in which we demonstrate single ion implant sensitivity (see right panel for detector functioning), allows us to count donor implants in- situ and deterministically control the number of donors. The use of a focused ion beam allows control of donor location. We have demonstrated successful sensing of the donor electron in transport measurements. Our demonstration has opened the door to immediate fabrication of two-donor devices, which has been a goal of the donor qubit community for over a decade.