Design of a superconducting qubit array detector based on parity measurement.

Similar to quantum capacitance detectors, superconducting qubits based on parity measurement are highly sensitive to single quasiparticle tunneling events through the Josephson junction. This makes them promising candidates for detectors with an energy threshold on the order of 1 meV, potentially useful in detecting rare events such as weakly interacting massive dark matter particles. Based on this, we propose a superconducting qubit array detector using flipmon technology.

This detector places part of each qubit on a suspended absorber using an aluminum film with a long quasiparticle lifetime, while another part is placed on a substrate in good thermal contact with the sample box, using a tantalum film with a shorter quasiparticle lifetime. This setup enhances the conversion efficiency of phonons produced by rare events into quasiparticles and maximizes the quasiparticle density difference across the Josephson junction. Additionally, by employing "gap engineering," we facilitate quasiparticle accumulation near the Josephson junction, increasing the density of convertible quasiparticles. This design significantly improves the probability of quasiparticle tunneling triggered by rare events, thus enhancing the detector's response signal.