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 UniversityThe University of Tokyo

The 12th workshop on Low Temperature Detectors, CNAM, Paris, France

C03

23, July, 2007

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

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:10.1038

Highly secure communication tool

High speed and high capacity communication channels

Schrödinger's kitten state

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..

Ti: Sapphire fs laser

OPASHG

Beam splitter

GatingSchrödinger's kitten state

Photon number resolving detector (PNRD)

Squeezed light pulses

Phys. Rev. A 55, 3184 (1997).

Wigner function2, 4, 6.. 1, 3, 5..

1

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 s ( 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, 1998A.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

1. 0

0. 9

0. 8

0. 7

0. 6

0. 5

Refl

ecti

vity

1. 41. 21. 00. 80. 60. 40. 20. 0Photon energy (eV)

Ti W

I r Nb

Au

=1550 nm

R=0. 65

How to improve Speed ?

• The ETF time constant dominated by electron-phonon conduction is described as:

Design of the TES detector

LTAETF

11

5 3

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.

R ~ 80 %

R ~ 65 %

•High vacuum EB evaporation on SiN(400nm) film•10 and 20 m device size•46 nm thickness

Optical reflectance Device picture

Si substrateSiN(400nm)

TiNb lead

Optical coupling　 & Mount Housing

Optical

fiber

TES chip Fiber tip

Signal response to the incident photons at 405 nm wavelength

1.0x10- 6 1.5x10- 6 2.0x10- 6 2.5x10- 6 3.0x10- 6

0.0

1.0x10- 7

2.0x10- 7

3.0x10- 7

4.0x10- 7

5.0x10- 7

n=1

n=2

TES

curr

ent c

hang

e (A

)

time (s)

1 s

rise time 60 nsfall time 300 ns

Averaged pulse

n=3(exp(- x/ fall)- exp(- x/ rise))

Very quick response time !fall = 300 ns

rise = 60~70 ns

(Thermal diffusion time ~70 ns) Thermal sensitivity ~ 80

Theoretical res. EFWHM= 0.22 eVSaturation energy Esat= 42 eV Energy collection efficiency 85 %

Rbias=0.5 Rnormal

0 20 40 60 80 100 120 1400

50

100

150

200

250

300

350

400

n=4n=3

n=2

coun

ts/b

in

channel

n=1

Energy spectrum of the incident photons at 405 nm wavelength

An incident photon number per pulse is dominated by the Poisson distribution. Thermal healing length ~ 26 m

ENEP is dominated by the excess noise. Quantum efficiency ~ 5.6 % @ 405 nm

= 405 nm(3.1 eV)

2)(exp)(

21)(

!)(

max

2

2

ln

nl

n

lxlPxN

nlelP

Incident photon number = 8.6 / pulse

EFWHM=0.76 eV

ENEP

=0.60 eV

Measured, ENEP=0.60 eV

Ad

Rbias=0.5 Rnormal Total noise E=0.25 eV

Phonon noise

Johnson noiseR=2.0

SQ noise=5 pA/Hz1/2

?

M. Ohkubo et al, IEEE trans. Appl. Supercon., 13, 634, (2003).

Energy spectrum of the incident photons at 1550 nm wavelength

0 20 40 60 80 100 120 140 160 1800

20

40

60

80

100

120

140

160

180

200

Coun

ts/b

in

Channel

= 1550 nm(0.8 eV) Incident photon number = 25.2 / pulse

EFWHM=0.68 eVn=1 n=2

n=3

n=4

n=5

n=6n=7

ENEP

=0.63 eV

QE~ 9.0 %

Rbias=0.5 Rnormal

Energy spectrum over 100 kHz

10k 100k 1M0

1

2

3

Ener

gy re

solu

tion

(eV)

Counting rate (Hz)

400 kHz

0 20 40 60 80 100 1200

100

200

300

400

Coun

ts/b

in

Channel

10 kHz 500 kHz 700 kHz10 kHz~400 kHz

500 kHz

700 kHz

Energy resolution vs counting rateEnergy spectrum at high counting rates

No change up to 400 kHz counting rate.

Over 500 kHz, the energy resolution has rapidly degraded.Sub-MHz

counting rate!

= 405 nm(3.1 eV)

Rbias=0.5 Rnormal

Effort to improve QE

800 1000 1200 1400 1600 1800 2000 2200 24000

20

40

60

80

Refle

ctiv

ity (%

)

Wavelength (nm)

Landolt- Bornstein New series IV/ 5I

Experimental results

Simulation result

TH30SiO2(234 nm)/ T i(30 nm)/ SiO2(287 nm)/ Al(140 nm)/ Si

Optical absorption cavity drastically reduce the reflectance from 65 % to 20 % !

More details, see Poster B05

Optical absorption cavity

D. Rosenberg et al, IEEE trans. Appl. Supercon., 15, 575, (2005).

65 %

20 %

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 !

Optical coupling　 & Mount Housing

Optical

fiber

TES chip Fiber tip

The TES device is coupled to single- mode optical fiber

Highly precise position aligner with 0.1 m

Readout

103 104 105 106 1070.01

0.1

1

10

RTES = 4.8

f- 3dB= 5.1 MHz

RTES = 0

Ampli

tude

Frequency (Hz)

f- 3dB = 100 kHz

103 104 105 106 107- 20020406080100120140160180

Phas

e (d

egre

e)Frequency (Hz)

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,

How to improve Speed ?

• 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:

Design of the TES detector

LTAETF

11

5 3

The ETF time constant is not affected by the TES volume, but the operating temperature !

チタンを使うとか

Response to incident photons at 405 nm

800.0n 1.0μ 1.2μ 1.4μ 1.6μ 1.8μ 2.0μ 2.2μ 2.4μ 2.6μ 2.8μ 3.0μ- 50n

0

50n

100n

150n

200n

250n

300n

350n

400n

450n

500n

n=1

n=2

TES

curr

ent c

hang

e (A

)

time (s)

1 s

rise time 30- 60 nsfall time 300 ns

Averaged pulse

n=3

0 20 40 60 80 100 1200

100

200

300

400

Co

unts

/bin

Channel

10 kHz 500 kHz 600 kHz 700 kHz

Energy spectrum over 100 kHz

10 kHz700 kHz

500 kHz

600 kHz

Response to incident photons at 405 nm

1.0μ 1.5μ 2.0μ 2.5μ- 6.0x10- 3

- 4.0x10- 3

- 2.0x10- 3

0.0

2.0x10- 3

4.0x10- 3

6.0x10- 3

8.0x10- 3

1.0x10- 2

n=3

n=2

Pulse

hei

ght (

V)

time (s)

1 s

n=1

rise time 60 nsfall time 300 ns

Ti films by e-beam evaporationNb 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

Hot electron effect in Ti-TES

• IVとの関連

Read-out & mounting

103 104 105 106 1070.01

0.1

1

10

RTES = 4.8

f- 3dB= 5.1 MHz

RTES = 0

Ampli

tude

Frequency (Hz)

f- 3dB = 100 kHz

103 104 105 106 107- 20020406080100120140160180

Phas

e (d

egre

e)

Frequency (Hz)

ADRの写真にする？

Optical coupling　 & Mount Housing

Optical

fiber

TES chip Fiber tip

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 0 2.3 s

Energy resolution*EFWHM 0.21 eV

1.0

0.9

0.8

0.7

0.6

0.5

Refl

ecti

vity

1. 41.21.00.80.60. 40. 20.0Photon energy (eV)

Ti W

I r Nb

Au

=1550 nm

R=0. 65