Demolition measurement of superconducting qubits

Qubit initialization, state preparation, and measurement are some of the core components of quantum computation using superconducting qubits. Traditional methods to initialize the state of the qubit rely on waiting a few T1 times for the qubit to decay into the ground state. But, with better qubit designs (increased coherence time) initialization by this method would lead to longer wait times. Additionally, algorithms like quantum error correction require the qubits to be re-initialized quickly. This necessitates the need for an active reset protocol.

Active reset of a qubit by performing a measurement (conditional reset protocol) has been developed but they require fast electronics for feedback and are prone to readout errors. Here we combine the reset and the readout pulses to perform an unconditional reset on the qubit. This leads to a demolition measurement, where we obtain the state of the qubit and also reset the qubit at the end. We achieve this by swapping the qubit excitation to the readout resonator and then performing a readout of the qubit. We use optimal control to optimize the swap and readout pulses. This does not require any additional dedicated hardware and can significantly increase the experimental data-taking rate.