Phonon-Trapping-Enhanced Energy Resolution in Superconducting Single-Photon Detectors

Abstract

A noiseless, photon-counting detector, which resolves the energy of each photon, could radically change astronomy, biophysics, and quantum optics. Superconducting detectors promise an intrinsic resolving power at visible wavelengths of R = E/δE ≈ 100 due to their low excitation energy. We study superconducting energy-resolving microwave kinetic inductance detectors (MKIDs), which hold particular promise for larger cameras. A visible and near-infrared photon absorbed in the superconductor creates a few thousand quasiparticles through several stages of electron-phonon interaction. Here we demonstrate experimentally that the resolving power of MKIDs at visible to near-infrared wavelengths is limited by the loss of hot phonons during this process. We measure the resolving power of our aluminum-based detector as a function of photon energy using four lasers with wavelengths between 1545-402 nm. For detectors on thick SiN/Si and sapphire substrates the resolving power is limited to 10-21 for the respective wavelengths, consistent with the loss of hot phonons. When we suspend the sensitive part of the detector on a 110-nm-thick SiN membrane, the measured resolving power improves to 19-52, respectively. The improvement is equivalent to a factor 8 ± 2 stronger phonon trapping on the membrane, which is consistent with a geometrical phonon propagation model for these hot phonons. We discuss a route towards the Fano limit by phonon engineering.

Strong reduction of quasiparticle fluctuations in a superconductor due to decoupling of the quasiparticle number and lifetime

“…However, for single-photon detection using microwave kinetic inductance detectors (MKIDs) [52,53], the quasiparticle trapping effects can be beneficial. The fluctuation level reduction results in a higher signal-to-noise ratio when generation-recombination noise is the dominant noise source and the responsivity L180506-4 stays the same, as we observe [26,29]. This means, somewhat counterintuitively, that single-photon detector performance can be improved at low temperatures, by introducing quasiparticle traps, compared to a quasiparticle number saturation [14].…”

“…( 4), where the fitted τ esc is used. A detailed analysis of the effects of the membrane on phonon statistics and energy resolution are published elsewhere [29].…”

Broadband solenoidal haloscope for terahertz axion detection

“…Photocounting is also possible using KIDs [128,129] and TESs [130][131][132], with the benefit of per-photon energy resolution. With e.g.…”

Improving the energy resolution of photon counting Microwave Kinetic Inductance Detectors using principal component analysis

“…Some suspected sources of these energy-independent shape changes are phonon loss into the substrate 22 and a position-dependent detector response. 23,24 Further improvements to the detectors themselves are likely required before the full benefits of using this analysis technique can be realized.…”