Joel E. Moore

SWAP gate between a Majorana qubit and a parity-protected superconducting qubit

  1. Luca Chirolli,
  2. Norman Y. Yao,
  3. and Joel E. Moore
High fidelity quantum information processing requires a combination of fast gates and long-lived quantum memories. In this work, we propose a hybrid architecture, where a parity-protected
superconducting qubit is directly coupled to a Majorana qubit, which plays the role of a quantum memory. The superconducting qubit is based upon a π-periodic Josephson junction realized with gate-tunable semiconducting wires, where the tunneling of individual Cooper pairs is suppressed. One of the wires additionally contains four Majorana zero modes that define a qubit. We demonstrate that this enables the implementation of a SWAP gate, allowing for the transduction of quantum information between the topological and conventional qubit. This architecture combines fast gates, which can be realized with the superconducting qubit, with a topologically protected Majorana memory.
arxiv pdf

Enhanced coherence in superconducting circuits via band engineering

  1. Luca Chirolli,
  2. and Joel E. Moore
In superconducting circuits interrupted by Josephson junctions, the dependence of the energy spectrum on offset charges on different islands is 2e periodic through the Aharonov-Casher
effect and resembles a crystal band structure that reflects the symmetries of the Josephson potential. We show that higher-harmonic Josephson elements described by a cos(2φ) energy-phase relation provide an increased freedom to tailor the shape of the Josephson potential and design spectra featuring multiplets of flat bands and Dirac points in the charge Brillouin zone. Flat bands provide noise-insensitive quantum states, and band engineering can help improve the coherence of the system. We discuss a modified version of a flux qubit that achieves in principle no decoherence from charge noise and introduce a flux qutrit that shows a spin-one Dirac spectrum and is simultaneously quote robust to both charge and flux noise.
arxiv pdf