Fast quantum non-demolition readout from longitudinal qubit-oscillator interaction

Understand

We show how to realize high-fidelity quantum non-demolition qubit readout using longitudinal qubit-oscillator interaction.

• This is realized by modulating the longitudinal coupling at the cavity frequency.
• The qubit-oscillator interaction then acts as a qubit-state dependent drive on the cavity, a situation that is fundamentally different from the standard dispersive case.
• Single-mode squeezing can be exploited to exponentially increase the signal-to-noise ratio of this readout protocol.