Dispersive sensing is a powerful technique that enables scalable and
high-fidelity readout of solid-state quantum bits. In particular, gate-based
dispersive sensing has been proposed as the readout mechanism for future
topological qubits, which can be measured by single electrons tunneling through
zero-energy modes. The development of such a readout requires resolving the
coherent charge tunneling amplitude from a quantum dot in a Majorana-zero-mode
host system faithfully on short time scales. Here, we demonstrate rapid
single-shot detection of a coherent single-electron tunneling amplitude between
InAs nanowire quantum dots. We have realized a sensitive dispersive detection
circuit by connecting a sub-GHz, lumped element microwave resonator to a
high-lever arm gate on one of dots. The resulting large dot-resonator coupling
leads to an observed dispersive shift that is of the order of the resonator
linewidth at charge degeneracy. This shift enables us to differentiate between
Coulomb blockade and resonance, corresponding to the scenarios expected for
qubit state readout, with a signal to noise ratio exceeding 2 for an
integration time of 1 microsecond. Our result paves the way for single shot
measurements of fermion parity on microsecond timescales in topological qubits.Comment: 6 pages, 4 figure
