Coherence and Majorana qubits in Josephson circuits featuring pi-periodic elements

A Josephson junction based on a π-periodic energy-phase relation has emerged as a novel element that can provide augmented freedom in engineering of superconducting circuits. In ordinary Josephson circuits, the dependence of the energy spectrum on the offset charges on different islands is 2e periodic through the Aharonov-Casher effect and resembles a crystal band structure. The employment of cos(2φ) Josephson junctions enables tailoring of the Josephson potential and designing spectra featuring multiplets of flat bands, providing us with noise-insensitive energy levels. Furthermore, the suppression of individual Cooper pair tunneling in π-periodic Josephson junctions results in parity-protected superconducting qubits. We propose to couple such a qubit to a Majorana qubit based on Majorana zero energy modes. By properly driving the system we can obtain a SWAP gate between the superconducting qubit and the Majorana qubit and employ the latter as a topologically protected memory. The system enables fast gates and long-lived quantum memories, a key requirement for high fidelity quantum information processing in a noisy quantum computing environment.

The seminar is realized in the framework of the funded projects:
-       TOPOCIRCUS - G.A. 841894, H2020-MSCA-IF-2018 Marie Sklodowska Curie
-       SPECTRUM - G.A. 101057977, HORIZON-EIC-2021-TRANSITIONOPEN-01

See the SLIDES of the colloquium.