Dispersive sensing of electron tunneling between quantum dots in proximitized InAs nanowires

Dispersive gate sensing (DGS) is a powerful technique that has enabled novel ways for probing condensed matter systems and reading out solid-state quantum bits, such as Josephson or spin qubits. DGS has also been proposed for the measurement of topological qubits based on Majorana zero-modes (MZMs). Such a measurement can be realized by detecting parity-dependent electron tunneling through a superconducting island hosting MZMs at its ends.
Here, we demonstrate tunneling between two quantum dots separated by a superconducting island realized in an InAs nanowire, partially proximitized by Al. Using multiplexed coplanar waveguide resonators with tailored circuit parameters we can simultaneously detect tunneling between multiple quantum dots with high SNR to correlate tunneling events with sub-microsecond resolution. The resonator response depends -via the tunneling rate between the quantum dots- on the superconducting spectrum, and in particular on the presence of MZMs in the island. Importantly, dispersive readout allows the system to be probed in the floating regime without transport channels. This will be crucial for fast, non-invasive detection of the topological state of superconducting islands and parity readout of topological qubits.