Probing sub-nanosecond timing properties of micron-scale transition edge sensors via a parallel SQUID-semiconductor readout scheme

The transition edge sensor (TES) is known for its superior energy resolution and utilized in diverse physics experiments. TESs with micrometer dimensions have photon-number-resolving capabilities in infrared wavelengths, serving as a key device particularly for non-Gaussian quantum state generation in optical quantum information processing. Although theoretical timing limits for these devices are expected to be sub-nanosecond, such fast responses have remained unobserved with conventional superconducting quantum interference device (SQUID) readouts alone. In this study, we probe the sub-nanosecond timing properties of a micron-scale TES under near-infrared laser irradiation via a proposed parallel SQUID-semiconductor readout scheme. In this scheme, the SQUID performs energy measurement, while the semiconductor readout, which is inductively decoupled from the SQUID, performs timing measurement. We employed a high electron mobility transistor (HEMT) for the timing measurement. Under high-photon-number irradiation that drove the TES into its normal state, we achieved a timing jitter below 200 ps, compared with several nanoseconds for conventional readouts. Note that this value does not represent the single-photon timing jitter since it was obtained under high-photon-number irradiation; single-photon timing measurement remains a key objective for future study. The findings of this study will broaden the future applications of TESs in various fields requiring high timing resolution with energy-resolving capabilities.