  The next generation of rare-event searches, such as those aimed at
determining the nature of particle dark matter or in measuring fundamental
neutrino properties, will benefit from particle detectors with thresholds at
the meV scale, 100-1000x lower than currently available. Quantum parity
detectors (QPDs) are a novel class of proposed quantum devices that use the
tremendous sensitivity of superconducting qubits to quasiparticle tunneling
events as their detection concept. As envisioned, phonons generated by particle
interactions within a crystalline substrate cause an eventual quasiparticle
cascade within a surface patterned superconducting qubit element. This process
alters the fundamental charge parity of the device in a binary manner, which
can be used to deduce the initial properties of the energy deposition. We lay
out the operating mechanism, noise sources, and expected sensitivity of QPDs
based on a spectrum of charge-qubit types and readout mechanisms and detail an
R&D pathway to demonstrating sensitivity to sub-eV energy deposits.
