Loredana Parlato

1. Intrinsic dark counts in superconducting nanostrip single-photon detectors: the role of multiple fluctuation events in NbN and NbTiN LoredanaParlato M. Ejrnaes, R. Cristiano, CNR-SPIN, Italy D. Salvoni, D. Massarotti, G. P. Pepe, F. Tafuri, University of Naples and CNR- SPIN, Italy R. Caruso, SeeQC-eu, Roma, Italy X. Y. Yang, Shanghai Institute of Microsystem and Information Technology (SIMIT), Chinese Academy of Sciences (CAS), P. R. China L. You, Z. Wang,Shanghai Institute of Microsystem and Information Technology (SIMIT), Chinese Academy of Sciences (CAS), and CENSE, P. R. China

2. SNSPD : principles SNSPD use the fast and temporary phase transition from the superconducting to the normal state produced by any type of radiation (photons, ions, neutral particles, electrons….) d≤10nm G. Gol’tsman et al., APL 79, 705, 2001. W~100nm Ibias~ Ic Ib ~ Ic T < Tc • the magneticpenetrationdepth • l length of the strip

3. SNSPD : advantages • Properties of SNSPD • Wide frequency range (X-ray to mid IR) • High efficiency at high wavelengths (90 % at 1550 nm) • Low timing jitter • Operate above 1 K • No gating required • Short recovery time • Extremely low dark counts

4. Ibias Dark counts and fluctuations in 2-D nanostrips Dark count rate (DCR) increasesasIb~Ic Phase Slip (PS) switching events havebeenconsideredaspossible source of DCR in 2D nanostrips PS event: anyprocessleading to a quantizedphasechange of the orderparameter by 2pisable to produce a finite voltageacross the strip VH Single Vortex crossing the edge VAP Vortex-AntivortexPair splitting Ibias • A superconductingnanostrip can be describedas a 2D-system d≈xGLw ≈10 xGL<L=2lL2/d (Pearl length)

5. 2-D NbN and NbTiN nanostrips w= 80 nm d=5 nm Nanostripmeandercirculargeometry Yang X, et al. IEEE Trans. on Appl. Supercond. 28 200106 (2018)

6. Switching measurements NbTiN Currentsweep rate of 845 mA/s 10000 switching events ISW NbN

7. Switching measurements: analysis NbTiN M. Ejrnaes, et al. Scientific Reports 9(1), 8053 (2019) NbN

8. Switching measurements: analysis NbN NbTiN

9. Switching measurements: analysis DI bin size uI= sweep speed=dI/dt NbTiN T. A. Fulton and L. N. Dunkleberger, Phys. Rev. B 9, 4760 (1974) Single phase slip event Multiple phase slip events Scientific Reports 9(1), 8053 (2019)

10. Switching measurements: analysis NbN

11. Analysis Thermal activation of vortices VAP where A(T) is the vortex interaction constant and ε is the averaged polarizability of a VAP within the entire VAP population. H. Bartlof et al,. Phys. Rev. B 81, 2010 L.N. Bulaweski et al. Phys. Rev. B 83, 2011 T/Tc=0.3 A(T)/e= 20 meVNbN A(T)/e= 47 meVNbTiN

12. Conclusions • Thereis a regionat high temperatureswhere the switching iscaused by MPS events. • In thisregion the width of the switching distributionisreduced down to valuesbelow the onesobservedat the lowest temperature itispossible to work in this range of temperatures. • Thisbehviourislessevident in NbNnanostrip. ItcouldexplainwhySNSPDsbased on NbTiNhaveshownlower dark countrates with respect to the NbN T/Tc=0.63 • The proposedexperimentalapproachmayresult in a powerful tool for the diagnostic of SNSPD operation mode

13. Matera (Italy) Tentative date: June or September 2020 Chair: Giampiero Pepe gpepe@na.infn.it 14th International Workshop on Low Temperature Electronics The biennial conference devoted to the most recent advances in low temperature electronics and applications. Topics • Low Temperature Devices and Detectors: • Operation, Performance, Physics • Analog and Digital Electronics • Detectors and Sensors • Hybrid Super + Semi + Opto • MEMS and NEMS • Cryogenic Systems, Apps and Packaging • Quantum Electronics: • Communication • Computation • Sensing • Metrology • Spintronics • Space Electronics: • Analog, Digital and Sensing •               CubeSat