Superconducting spin qubits: Spin qubits interacting through supercurrent
Abstract
This proposal addresses the goal, stated within the program Next New and Emerging Qubit Science & Technology, of developing a new qubit based on "superconductor-semiconductor" nanostructures. Specifically, the new type of qubit that the project proposes to realize is the Andreev spin qubit, a novel solid-state system that combines the advantages of both superconducting electrodynamic qubits and semiconducting spin qubits. The long term goal is to obtain a footprint-efficient device that naturally exhibits strong near-field electrodynamical interactions with other devices, with as little cross-talk as possible, and at the same time benefits from the long lifetimes of spin qubits from the mature semiconductor technology. The means to the goal are based on the discrete fermionic levels in a Josephson weak link known as Andreev levels. A crucial effect that will be employed is that Andreev levels develop a spin-dependent energy-phase relation when spin-orbit coupling is present in the semiconductor. Thus, Andreev spins inherently exhibit spin-dependent supercurrents -- in a sense, the "orbit" degree-of-freedom in spin-orbit coupling becomes macroscopic. This important feature offers significant advantages for both the typical energy of spin-splitting and the coupling of spin to electrodynamical modes of transmission lines that would mediate an interaction between different qubits. Because the wavefunction of the Andreev level is not extended like the plasmonic mode of Josephson junctions and because the direct spin transition matrix element is naturally weak, the Andreev spin qubit is much less sensitive to dielectric losses than conventional superconducting qubits like the transmon. The Andreev spin qubit can also be manipulated by Raman-like transitions involving higher levels in a way that is reminiscent of the manipulation of hyperfine doublets in trapped ions. These single-spin gates will be combined with a superconducting bus to achieve gates between spatially distant spin qubits, a long-standing goal in the spin qubit community. Preliminary results of our team on the Andreev spin qubit, which will soon appear in Science, validate the proposed approach, as far as the magnitude of the expected coupling and the possibility of Raman gates is concerned. The combination of fermionic solid-state physics and microwave quantum optics in the proposed experiments is valuable training-wise for many other branches of quantum information physics. If the project is successful, a completely new avenue for solid-state qubits with potentially high coherence and alternative material opportunities will be opened.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Mar 31, 2022
- Source ID
- W911NF2210053
Entities
People
- Michel Devoret
Organizations
- Army Contracting Command
- National Security Agency
- Yale University