  Most, if not all, photonic quantum computing (PQC) relies upon
superconducting nanowire single-photon detectors (SNSPDs) based on Nb operated
at a temperature < 4 K. This paper proposes and analyzes 300 K
Si-waveguide-integrated GeSi single-photon avalanche diodes (SPADs) based on
the recently demonstrated normal-incidence GeSi SPADs operated at room
temperature, and shows that their performance is competitive against that of
SNSPDs in a series of metrics for PQC with a reasonable time-gating window to
resolve the issue of dark-count rate (DCR). These GeSi SPADs become
photon-number-resolving avalanche diodes (PNRADs) by deploying a spatially
multiplexed M-fold-waveguide array of M SPADs. Using on-chip waveguided
spontaneous four-wave mixing (SFWM) sources and waveguided field-programmable
interferometer mesh (FPIM) circuits, together with the high-metric SPADs and
PNRADs, high-performance quantum computing at room temperature is predicted for
this PQC architecture.
