# Presentation: 949720

## Absolute calibration of photo-detectors and applications of this technique at IENGF 

- MARCO GENOVESE
- Workshop on single photon: Detectors, Applications and Measurement Methods
- NIST Gaithersburg

## The IENGF Quantum Optics, Information and  Metrology group:

- Permanent staff:  G.Brida,S.Castelletto,M.G.,C.Novero,
-                              M.L.Rastello
- Students: E.Cagliero,I.Degiovanni,G.Falzetta,M.Gramegna,
-                M.Barbagallo, I.Ruo-Berchera

- This seminar is devoted to the memory of our friend and collaborator
-  Carlo Novero

## THE POSSIBILITY OF HAVING TWO CORRELATED 

- PHOTONS OF DEFINED WAVE LENGTH AND DIRECTION
- AT THE SAME INSTANT ALLOWS AN ABSOLUTE
- CALIBRATION OF DETECTORS.

- THE IDEA WAS ALREADY EXPLORED BY BURNHAM
- AND WEINBERG IN 1970.
- A MORE PRECISE METROLOGICAL PROPOSAL IN 70’s
- BY KLYSHKO AND COLLABORATORS
- TOWARD METROLOGICAL APPLICATION IN 90’s
- (Boston.Univ.,Moscow Univ.,NIST,IENGF,...)

## Slide 4

## Slide 5

## Nsignal=signal ·.N

- IEN optical lab

- Nsignal=signal ·.N
- Nidler=idler· N
- Nc=  signal  idler · N

-  signal = Nc/Ni
-  idler = Nc/Ns

## Corrections derive by the presence of spurious events and the loss of true coincidence events related to the acquisition systems. 

- In order to compare the effect of various acquisition systems for  preparing an uncertainty budget, we have implemented the coincidence systems in different ways, e.g. using two different Time to Amplitude Converter (TAC), with and without valid start output, an high resolution time interval counter and an AND logical gate
*[G.Brida,M.G.,C.Novero,JMO 47 (00) 2099]*

## Different acquisition systems

## LiIO3: 10x10x5 mm3

- LiIO3: 10x10x5 mm3
- pumping laser Ar+ at 100 mW
- pumping wavelength 351.2 nm
- Trigger channel 789.2 nm
- Signal  channel 632.8 nm
- I1, I2 (4 mm) iris
- F2 interference filter at 789.2 nm, 2.7 nm FWHM, transmittance 61.04%
- L1, L2 fibre optic coupling lenses (20x microscope objectives)
- NF neutral density filter
- LD laser diode 50 mW power
- parametric amplification of the LD used for alignment

- missed coincidence counts is given by (Wsignal(t) is the rate (counts/s) on the signal channel):

- A first correction is related to the presence of accidental coincindence
- counts, which can be estimated measuring coincidence  rate far from the
-  peak, this leads to:

## Furthermore, if a TAC without a valid start output is used, counting directly the trigger detector pulses, trigger counts are overestimated, with respect to the coincidence counts by a factor ( < TAC> is the mean value of the TAC dead time) :

-   We have also  to account for the signal counts loss due to the detector dead time.

## Slide 12

## OTHERS PHOTODETECTORS CALIBRATION WORKS REALISED IN OUR DEPARTMENT

- Comparison with a conventional radiometric technique
- Brida G.et al., (2000), *Metrologia*, **37, **625-628
- Brida G. et al. , (2000) *Metrologia*, **37, **629-632**.**
**Comparison with conventional techniques: agreement at 0.2%****.**** **
**Narrower confidence band for biphoton calibration.**
- Intercomparison with NIST
- Migdall A. et  al., (2002), *Appl. Opt*., **41,** 2914-2922** **
**Intercomparison with NIST for determining accuracy : qualitative consistency (overall uncertainty limited by spatial uniformity of detector)**
- Maximum Likelihood Estimator
- Castelletto S.et al.*,* (2000), *Metrologia*, **37, **613-616
- Castelletto S. et al.*,* (2002), *J. Opt. Soc. Am.*, **19, **1247-1258

- OTHERS PHOTODETECTORS CALIBRATION WORKS REALISED IN OUR DEPARTMENT

## Vacuum fluctuations as a natural standard: absolute measurement of the number of photons per mode exploiting parametric amplification: radiometric application of QND measurements

- Castelletto S. et al., (1999), *Int. J. Mod. Phys. B*, **13**, 3383-3392
- Degiovanni I. et  al., (2001), *J. Opt. B: Quantum Semiclass. Opt.,* **3,** S60-S65
**Non destructive measurement based on parametric amplification: suited for high-radiance sources.**
- Applications to experiments on Quantum Information and Foundations of Quantum Mechanics
- Brida G. et al., (2000) Phys. Lett. A 268, 12; (2002) Phys.Lett.A. 299, 121.
- M.G., C. Novero, (2002) Eur. Phys. Journ. 21, 109.
- Brida G. et al., Journ of Phys B 35 (2002) 4751.
**Determination of quantum efficiencies as first step for experiments about Foundations of Quantum Mechanics (Bell inequalities etc.) and Quantum cryptography.**

## 
 portable source (400 nm diode laser)
European network:  Euromet  (IENGF,Univ.Geneva,NPL,BNM-CNAM,...)
Search for innovative schemes (analogic counters?).Collaboration with Moscow Univ. (S.Kulik, M. Chekova) 
Proposal for VI Framework programme EU

-  portable source (400 nm diode laser)
- European network:  Euromet  (IENGF,Univ.Geneva,NPL,BNM-CNAM,...)
- Search for innovative schemes (analogic counters?).Collaboration with Moscow Univ. (S.Kulik, M. Chekova)
- Proposal for VI Framework programme EU

- FUTURE DEVELOPEMENTS:

## SOME APPLICATIONS

- Test of Wigner function LHVT
- Double slit experiment
- Quantum logical gates
- ....

- Conclusions about detector calibration with PDC

- The use  of biphotons produced in PDC allows absolute calibration without the need of standard sources
- An uncertainty budget of this technique, including also acquisition systems contribution, has been realised
- A 0.1% uncertainty level can be reached making this scheme competitive for metrological purposes with conventional techniques

## Is possible to build a Local Realistic Theory reproducing all the results of Standard Quantum Mechanics?

- 1964 Bell: No  ->  Bell Inequalities
- Many experimental tests :
*A. Aspect et al., PRL. 49 (1982) 1804; J. P. Franson, PRL 62 (1989) 2205; J. G. Rarity and P. R. Tapster, PRL 64 (1990) 2495;** **J. Brendel et al., EPL 20 (1992) 275; P. G. Kwiat et al., PRA 41 (1990) 2910; T.E. Kiess et al., PRL 71 (1993) 3893; P.G. Kwiat et al., PRL 75 (1995) 4337; **G. Brida, M.G., C. Novero and E. Predazzi, PLA 268 (2000) 12**...*
- All confirm SQM: but low detection efficiency

- CH/N

## Specific LRM:

- One based on Wigner function formalism
- A. Casado et al., quant-ph 0202097; JOS A B 14 (1997) 494, PRA 55 (1997) 3879, PRA 56 (1997) 2477,  JOS A. B 15 (1998) 1572, EPJ D11 (2000) 465, D13 (2001) 109.

- There is a minimal light signal level which may be reliably detected:
- Single detection Rate  > ( R 2  F 2 2 L d 2 

- F = focal length of lens before detector,  R radius of active area of NLC, L active depth of detector, T photon absorbtion time;  = coherence time, d distance between NLC and detector

## EXPERIMENTAL TEST  

*G.Brida et al., PLA 299 (02) 121*

- 

- The former inequality is strongly violated (would require T > 1s), but:
- V = 0.98 
- CH =  513 

## Biphotons double slit experiment

*G.Brida et al., **J. Phys. B 35 (2002) 4751.** *

- 

## Quantum phase gate

- Work in progress...