Superconducting Qubits and Gates
Superconducting Qubits and Devices
Superconducting qubits based on Josephson junctions are a promising platform for quantum computation, reachingquality factors of over one million. Such high quality factors enable the investigation of decoherence mechanisms withhigh accuracy. An intrinsic decoherence process originates from the coupling between the qubit degree of freedom andthe quasiparticles that tunnel across Josephson junctions. Interestingly, the quasiparticle-induced decoherence rate canbe modulated by a magnetic flux, due to the interference between processes involving electron-like and hole-likequasiparticles [1]. Theoretical predictions for quasiparticle effects have been verified in recent experiments with variousqubit designs, from the single-junction transmon [2] to the multi-junction fluxonium. Quasiparticles can also affect thebehavior of other devices, such as Cooper pair pumps and nanorefrigerators.
[1]. see, e.g., G. Catelani et al., Phys. Rev. Lett. 106, 077002 (2011)
[2]. H. Paik et al., Phys. Rev. Lett. 107, 240501 (2012)
Superconductivity – Fundamentals and Applications
The theoretical description of conventional superconductors has a long history, but there are still open questions, whoseanswer can also have important consequences for practical applications. For example, superconducting cavities forparticle accelerators are operated in a metastable Meissner state, and the fundamental limitations on such a state areunder investigation [1]. For metallic films in parallel magnetic fields, a detailed understanding of quantumsuperconducting fluctuations [2] has made possible the extension to high fields of techniques used to measure e.g.electron polarization in ferromagnetic metals and exchange fields induced by ferromagnetic insulators.
[1]. G. Catelani and J. P. Sethna, Phys. Rev. B 78, 224509 (2008)
[2]. M. Khodas, A. Levchenko, and G. Catelani, Phys. Rev. Lett. 108, 257004 (2012), and references therein
