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 Basic theory for high speed TES
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 Photonics 1, (2007) doi:
Highly secure communication tool
High speed and high capacity communication channels

4. Schrödinger's kitten state
Ti: Sapphire
fs laser
Gating
Squeezed light pulses
Schrödinger's kitten state
Beam splitter
SHG
OPA
Wigner function
2, 4, 6..
1, 3, 5.. 1
Photon number resolving detector (PNRD)
Phys. Rev. A 55, 3184 (1997).
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 %
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, , 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 ~ 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
n=2
Rbias=0.5 Rnormal
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 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) 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

22. Response to incident photons at 405 nm

23. Ti films by e-beam evaporation Nb electrodes by DC sputtering
Transition Temp. Tc
359 mK
Heat capacity* C
5.1fJ/K
Thermal conductance G
0.9 nW/K
Intrinsic time constant τ0
5.4 μs
Energy resolution* ∆EFWHM
0.21 eV
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 Film thickness d
45 nm
Transition Temp. Tc
359 mK
Heat capacity * C
2.1 fJ/K
Thermal conductance G
0.9 nW/K
Intrinsic time constant t0
2.3 ms
Energy resolution*DEFWHM
0.21 eV