High speed photon number resolving detector with titanium transition edge sensors

1. C03 High speed photon number resolving detector with titanium transition edge sensors Daiji Fukuda, Go Fujii, R.M.T. Damayanthi, Akio Yoshizawa, Hidemi Tsuchida, H. Takahashi, S. Inoue, and M. Ohkubo National Institute of Advanced Industrial Science and Technology(AIST) Nihon University The University of Tokyo The 12th workshop on Low Temperature Detectors, CNAM, Paris, France 23, July, 2007

2. Outline • Introduction • Schrödinger's kitten state • Basic theory for high speed TES • State of the art of our device • Speed • Energy resolution • Quantum efficiency(QE) • Summary

3. Introduction • There are strong demands to generate, operate, and detect “Single photons” in quantum information fields. • Quantum key distribution (QKD) • Quantum communication • Quantum teleportation • Quantum optical gate • Quantum decoding H.Takesue, S.W. Nam and et al.,Nature Photonics1, (2007) doi:10.1038 Highly secure communication tool High speed and high capacity communication channels

4. Schrödinger's kitten state Ti: Sapphire fs laser Gating Schrödinger's kitten state Squeezed light pulses • Requirements for the detectors • Work at an 1550 nm wavelength (0.8 eV) • Energy resolving (Photon number counting) • High speed courting rate ~ MHz. • No dark count • High quantum efficiency ~ 100 % Beam splitter SHG OPA Wigner function 2, 4, 6.. 1, 3, 5.. 1 Photon number resolving detector (PNRD) Phys. Rev. A 55, 3184 (1997). • Almost perfect detector..

5. Optical TES detectors • Stanford, NIST, and Albion group • Tungsten based TES (W-TES; Tc~90 mK) • Energy resolution 0.2 eV • (The energy of a single photon at 1550 nm is 0.8 eV.) • Quantum efficiency 88 % • Response speed 4 ms ( 50 kHz counting rate) • We need a higher speed TES with a MHz counting rate! B. Cabrera, R.M. Clarke, C. Colling et al., APL, Vol. 73, 735, 1998 A.J. Miller S.W. Nam, and M. Martinis, APL, Vol. 83, 791-793, 2003 D. Fukuda et al, IEEE trans. Appl. Supercon., Vol. 17, 2007 in printing

6. How to improve Speed ? Design of the TES detector • The ETF time constant dominated by electron-phonon conduction is described as: The ETF time constant is affected not by the TES volume, but by the operating temperature ! Thus, we have chosen a TITANIUM superconductor for TES, which has Tc at 390 mK in bulk. Optical reflectance Device picture • High vacuum EB evaporation on SiN(400nm) film • 10 and 20 mm device size • 46 nm thickness R ~ 80 % Nb lead Ti R ~ 65 % SiN(400nm) Si substrate

7. Optical coupling& Mount

8. Signal response to the incident photons at 405 nm wavelength Rbias=0.5 Rnormal • Very quick response time ! tfall = 300 ns trise = 60~70 ns (Thermal diffusion time ~70 ns) • Thermal sensitivity a ~ 80 • Theoretical res. DEFWHM= 0.22 eV • Saturation energy Esat= 42 eV • Energy collection efficiency 85 %

9. Energy spectrum of the incident photons at 405 nm wavelength l= 405 nm(3.1 eV) Incident photon number = 8.6 / pulse Measured, DENEP=0.60 eV Rbias=0.5 Rnormal Total noise DE=0.25 eV ? Phonon noise DEFWHM=0.76 eV SQ noise=5 pA/Hz1/2 DENEP =0.60 eV Johnson noise R=2.0 W • An incident photon number per pulse is dominated by the Poisson distribution. • Thermal healing length h ~ 26 mm • DENEP is dominated by the excess noise. • Quantum efficiency ~ 5.6 % @ 405 nm M. Ohkubo et al, IEEE trans. Appl. Supercon., 13, 634, (2003).

10. Energy spectrum of the incident photons at 1550 nm wavelength l= 1550 nm(0.8 eV) Incident photon number = 25.2 / pulse Rbias=0.5 Rnormal n=2 n=1 DEFWHM=0.68 eV n=3 QE~ 9.0 % n=4 n=5 DENEP =0.63 eV n=6 n=7

11. Energy spectrum over 100 kHz Energy spectrum at high counting rates Energy resolution vs counting rate l= 405 nm(3.1 eV) 10 kHz~400 kHz Rbias=0.5 Rnormal 500 kHz 700 kHz Sub-MHz counting rate! • No change up to 400 kHz counting rate. • Over 500 kHz, the energy resolution has rapidly degraded.

12. Effort to improve QE Optical absorption cavity D. Rosenberg et al, IEEE trans. Appl. Supercon., 15, 575, (2005). 65 % Optical absorption cavity drastically reduce the reflectance from 65 % to 20 % ! More details, see Poster B05 20 %

13. Conclusion • We have fabricated the Ti-TES operated at 354 mK. • The response speed of the device is 300 ns. • Maximum repetition frequency is 0.4 MHz. • The energy resolution is 0.68-0.76 eV. • The Quantum efficiency is 5-9%, however, can be improved by optical cavity soon !

17. Optical coupling& Mount The TES device is coupled to single- mode optical fiber Highly precise position aligner with 0.1 mm

18. Readout • The TES is electrically connected to the SQUID input coil with low inductance < 150 nH = 10 nH (SQUID) + 140 nH (Stray). • Maximum bandwidth of the readout is 5.1 MHz. • The incident photon number can be calculated as,

19. How to improve Speed ? Design of the TES detector • The optical TES is fabricated on the substrate (without SiN membrane structure). • In this case, Power flows is dominated by a hot-electron effect (n=5). • The ETF time constant is described as: The ETF time constant is not affected by the TES volume, but the operating temperature ! チタンを使うとか

20. Response to incident photons at 405 nm

21. Energy spectrum over 100 kHz 10 kHz 700 kHz 500 kHz 600 kHz

22. Response to incident photons at 405 nm

23. Ti films by e-beam evaporation Nb electrodes by DC sputtering

24. Hot electron effect in Ti-TES • IVとの関連

25. Read-out & mounting ADRの写真にする？

26. Optical coupling& Mount Housing Optical fiber TES chip Fiber tip

27. Device fabrication • EB evaporation Ti-TES on SiN films