Majorana bound state in a coupled quantum-dot hybrid-nanowire system

Watching Majorana bound states form Majorana bound states (MBSs) are peculiar quasiparticles that may one day become the cornerstone of topological quantum computing. To engineer these states, physicists have used semiconductor nanowires in contact with a superconductor. Although many of the observed properties align with theoretical predictions, a closer look into the creation of MBSs is desirable. Deng et al. fabricated nanowires with a quantum dot at one end that served as a spectrometer for the states that formed inside the superconducting gap of the nanowire. Using this setup, topologically trivial bound states were seen to coalesce into MBSs as the magnetic field was varied. Science, this issue p. 1557 Tunneling spectroscopy gives insights into the formation of Majorana bound states in a proximitized indium arsenide nanowire. Hybrid nanowires combining semiconductor and superconductor materials appear well suited for the creation, detection, and control of Majorana bound states (MBSs). We demonstrate the emergence of MBSs from coalescing Andreev bound states (ABSs) in a hybrid InAs nanowire with epitaxial Al, using a quantum dot at the end of the nanowire as a spectrometer. Electrostatic gating tuned the nanowire density to a regime of one or a few ABSs. In an applied axial magnetic field, a topological phase emerges in which ABSs move to zero energy and remain there, forming MBSs. We observed hybridization of the MBS with the end-dot bound state, which is in agreement with a numerical model. The ABS/MBS spectra provide parameters that are useful for understanding topological superconductivity in this system.