PPubMed19 May 2015Cited 38×

Three Temperature Regimes in Superconducting Photon Detectors: Quantum, Thermal and Multiple Phase-Slips as Generators of Dark Counts

Andrew Murphy, Alexander Semenov, Alexander Korneev, Yulia Korneeva, Gregory Gol’tsman, Alexey Bezryadin

Abstract

'Gregory Gol’tsman' 'Alexey Bezryadin'] We perform measurements of the switching current distributions of three w ≈ 120 nm wide, 4 nm thick NbN superconducting strips which are used for single-photon detectors. These strips are much wider than the diameter of the vortex cores, so they are classified as quasi-two-dimensional (quasi-2D). We discover evidence of macroscopic quantum tunneling by observing the saturation of the standard deviation of the switching distributions at temperatures around 2 K. We analyze our results using the Kurkijärvi-Garg model and find that the escape temperature also saturates at low temperatures, confirming that at sufficiently low temperatures, macroscopic quantum tunneling is possible in quasi-2D strips and can contribute to dark counts observed in single photon detectors. At the highest temperatures the system enters a multiple phase-slip regime. In this range single phase-slips are unable to produce dark counts and the fluctuations in the switching current are reduced.

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Dark counts in NbN photon detectors switch from multiple thermal phase‑slips around 5 K to macroscopic quantum tunneling below ~2 K.

What’s new

i.Provided the first experimental evidence of macroscopic quantum tunneling in quasi‑2D NbN strips used for single‑photon detection.
ii.Identified three distinct temperature regimes—quantum, thermal, and multiple phase‑slip—that govern dark‑count generation.
iii.Applied the Kurkijärvi‑Garg model to switching‑current distributions, extracting quantum crossover temperatures (~2 K) for three samples.
iv.Demonstrated that multiple phase‑slips dominate dark counts at typical detector operating temperatures (~5 K).

How they did it

Switching‑current distributions of three ~120 nm wide, 4 nm thick NbN strips were measured in a He‑4 cryostat down to 1.45 K with extensive electromagnetic noise filtering. The distributions were transformed using the Kurkijärvi‑Fulton‑Dunkleberger method and fitted with the Kurkijärvi‑Garg model to extract escape rates and temperatures.

What they found

Standard deviation of switching currents saturates at low temperatures, indicating macroscopic quantum tunneling, with crossover temperatures Tq = 1.8 K, 1.9 K, and 2.4 K for the three samples.
Escape temperature also saturates around 2 K, confirming the quantum regime.
Critical temperatures of the strips are ~10 K, and switching rates fit the KG model across all temperature regimes.
Multiple phase‑slip regime observed at T > Tm, where Tm corresponds to the maximum in σ and σ decreases with increasing temperature.

Caveats

✕Only three commercially available detector samples were studied, limiting generality.
✕Measurements were confined to temperatures down to 1.45 K; behavior at even lower temperatures remains unexplored.
✕The analysis assumes the Kurkijärvi‑Garg model; alternative escape mechanisms may exist but were not investigated.
✕Multi‑phase‑slip switching events are identified but not fully characterized as dark‑count sources.

in plain words

When a superconducting strip in a photon detector suddenly becomes normal, it can happen because many tiny disturbances happen together at higher temperatures, or because the strip quantum‑tunnels at very low temperatures. The researchers measured these sudden switches and found that below about 2 K the quantum effect dominates, while around 5 K the switches are caused by multiple thermal events. This helps explain why detectors sometimes register false signals.

why it matters

Understanding the quantum and thermal origins of dark counts enables the design of more efficient superconducting photon detectors, which are crucial for quantum communication, imaging, and sensing technologies.

Follow the thread

macroscopic quantum tunneling superconducting photon detectors phase slips dark counts Kurkijärvi‑Garg model NbN strips

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