A Superconducting 0-π Qubit Based on High Transmission Semiconductor-Superconductor Josephson Junctions*

The 0-π qubit has been proposed as the fundamental building block of topologically protected qubits [1] that feature topologically protected gates [2]. Recent experiments have measured non-cosinusoidal energy-phase relations in high-transmission, semiconductor-superconductor Josephson junctions (JJ) in gatemon qubits [3,4]. Here we present measurements on a superconducting circuit architecture exploiting this non-cosinusoidal energy-phase relation to form a protected 0-π qubit [5]. Voltage control of the semiconductor JJ’s creates a unique superconducting qubit system allowing in situ tuning between widely different qubit regimes: transmon, flux, and 0-π qubit. Close to the 0-π regime we observe enhanced lifetimes indicating protected qubit states.

[1] B. Douçot and L. B. Ioffe, Rep. Prog. Phys. 75, 072001 (2012).
[2] P. Brooks et al. Phys. Rev. A 87, 052306 (2013).
[3] G. de Lange et al. Phys. Rev. Lett. 115, 127002 (2015).
[4] A. Kringhøj et al. Submitted.
[5] M. T. Bell et al. Phys. Rev. Lett. 112, 167001 (2014).