研究目的
To calculate the delay time and timing jitter in superconducting nanowire single-photon detectors (SNSPDs) using a theoretical model, and to understand how these parameters depend on factors like absorption position, current, and energy fluctuations.
研究成果
The delay time and timing jitter in SNSPDs decrease monotonically with increasing current and are smaller for higher photon energies. At currents near the depairing current, timing jitter can be as low as ?/kBTc (≈0.8 ps for Tc=10 K). The position-dependent response leads to non-Gaussian distributions in photon counts versus delay time, with a shoulder feature from edge absorption. Fano fluctuations contribute to jitter but do not prevent minimal values at high currents.
研究不足
The model assumes complete thermalization of electrons, which may not hold due to finite inelastic relaxation times, making the results semiquantitative. The time-dependent Ginzburg-Landau equation is quantitatively valid only near Tc, and the study does not consider fluctuation-assisted regimes or variations in material parameters beyond Fano fluctuations.
1：Experimental Design and Method Selection:
The study uses a theoretical model combining a two-temperature model with a modified time-dependent Ginzburg-Landau equation and current continuity equation to simulate the dynamics in SNSPDs. The model assumes thermalized electrons and phonons with local temperatures Te and Tp, and includes equations for heat conductance, energy balance, and order parameter evolution.
2：Sample Selection and Data Sources:
Numerical calculations are performed for a typical NbN superconducting strip with parameters: width w = 20ξc ≈ 130 nm (ξc = 6.4 nm), thickness d = 4 nm, critical temperature Tc = 10 K, length L = 4w = 80ξc, and other parameters like γ = 10, τ0 = 900 ps, τesc = 0.05τ0. The photon absorption is modeled as instant local heating in a 2ξc × 2ξc area.
3：4 nm), thickness d = 4 nm, critical temperature Tc = 10 K, length L = 4w = 80ξc, and other parameters like γ = 10, τ0 = 900 ps, τesc = 05τThe photon absorption is modeled as instant local heating in a 2ξc × 2ξc area.
List of Experimental Equipment and Materials:
3. List of Experimental Equipment and Materials: No specific experimental equipment is mentioned as this is a theoretical paper; the focus is on computational modeling.
4：Experimental Procedures and Operational Workflow:
The model solves coupled differential equations numerically to compute the delay time τd for photon absorption at different positions across the strip and under varying currents and deposited energies. The delay time is defined as the time for a growing normal domain to appear, detected when voltage exceeds a threshold Vth = 20kBTc/2e.
5：2e.
Data Analysis Methods:
5. Data Analysis Methods: Results are analyzed to derive dependencies of τd on current, position, and energy, and to compute probability distributions for timing jitter considering Fano fluctuations.
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