Photon-assisted tunneling of zero modes in a Majorana wire

Hybrid nanowires with proximity-induced superconductivity in the topological regime host Majorana zero modes at their ends. Networks of such structures can produce topologically protected qubits where the fundamental energy scale is given by the inter-pair coupling EM between the zero modes belonging to different wire segments.

Researchers have reported on the spectroscopic measurement of EM in an InAs/Al double-island device by tracking the position of the microwave-induced quasiparticle excitations using a radio-frequency charge sensor.

At zero magnetic field, photon-assisted tunneling of Cooper pairs allows to estimate the Josephson coupling between the islands. In the presence of a magnetic field aligned along the nanowire, the team has observed the 1e periodic excitation spectrum resulting from a zero-energy subgap state that emerges in a magnetic field. The discrete 1e periodic excitation spectrum is consistent with the coherent hybridization of single-electron states belonging to two opposite-parity branches.

The dependence of excitation frequency on detuning indicates a sizable (GHz-scale) and controllable hybridization of zero modes across the junction separating islands, a requirement for applications related to Majorana-based qubits.

The paper has been published in Nature Physics.