Readout scheme for superconducting qubits exploiting an in-situ tunable Purcell filter

State-of-the-art dispersive readout of transmon qubits has reached performance limits in speed, fidelity, and quantum non-demolition characteristics due to transmon ionisation [1] and Purcell decay when increasing measurement amplitudes and coupling rates. Here, we study an alternative readout scheme leveraging the frequency tunability of an on-chip Purcell filter to enable high-fidelity, rapid qubit readout while allowing concurrent gate and measurement operations. We implement this concept in a superconducting circuit device featuring a modified transmon acting as a frequency-tunable Purcell filter. This element enables fast control of the effective decay rate of the readout resonator, allowing suppression of Purcell loss during idle periods while maintaining efficient coupling during readout. We present initial experimental results on chip characterisation and qubit readout and analyse the potential of the scheme to improve measurement speed in quantum error-correction cycles.

Reference:

[1] Dumas et al. PRX 14.4 (2024): 041023