ISTITUTO NAZIONALE DI RICERCA METROLOGICA 1 M. Genovese Istituto Nazionale di Ricerca Metrologica...

1ISTITUTO

NAZIONALEDI RICERCAMETROLOGICA

M. Genovese

Istituto Nazionale di Ricerca Metrologica (INRIM), Strada delle Cacce 91, 10135 Torino, Italy

PDC correlations for Quantum Imaging

ISTITUTONAZIONALEDI RICERCAMETROLOGICA

Quantum Imaging: a new quantum technology addressed to exploit properties of quantum optical states for

overcoming limits of classical optics

[L. Lugiato et al., J.Opt.B 4 (2002) S176; ]

- Ghost imaging [A. Belinskii D.Klyshko Sov. P.JETP 78 (94) 259; T.Pittman et al., PRA 52 (95) R3429]

[A. Gatti PRA69 (04)133603; R.Bennik et al., PRL 89 (02) 113601 ]

- Quantum lithography [A. Boto et al, PRL 85 (00) 2733; M. D’Angelo et al., PRL 87 (01) 13602]

- Entangled Images [V.Boyer et al., Science 321 (08) 544]

- Image amplification by PDC [A. Gatti et al., PRL 83 (99) 1763 ; A.Mosset et al.; PRL 94 (05) 223603]

- Quantum Illumination [S. Tan et al., PRL 101 (08) 253601]

- Sub-Rayleigh quantum imaging [V.Giovannetti et al., Phys. Rev. A 79, 013827 (2009)].

- Sub shot noise detection of weak objects [E. Brambilla et al., PRA 77, 053807 (08)]


6 labs on quantum optics4 permanent researchers (M.G., G. Brida, I. Degiovanni, S. Castelletto)7 post docs (M. Gramegna, A. Meda, F. Piacentini, I. Ruo-Berchera, P.Traina,V. Schettini [now at Boston], A. Sherupukov) 2 External collaborators ( M. Chekhova, T. Ishkakov)2 PhD students (V. Caricato, A. Florio)various undergraduate students, ….

INRIM Quantum Optics Research programINRIM Quantum Optics Research program““Carlo Novero lab”Carlo Novero lab”

Responsible: M. GenoveseResponsible: M. Genovese

Our main sponsors:Our main sponsors:- Minister of EducationMinister of Education- Piedmont RegionPiedmont Region- Bank Foundation San PaoloBank Foundation San Paolo- ASP, Lagrange Found.ASP, Lagrange Found.- European UnionEuropean Union- NATO,…NATO,…

4ISTITUTO


Sub Shot Noise Imaging of Weak Objects

• Overview on spatial correlations in PDC and possible application to imaging of weak absorbing object

[see Lugiato talk for details and references]

• Tayloring PDC speckle structure

• Experimental achievement of sub shot noise spatial correlations without background subtraction

• Preliminary results of sub-shot-noise imaging


Type-I PDC

Type-II PDC

6ISTITUTO


0 is qq is xx

Transverse phase matching condition

q=0

qsignal

idler-q

x

-x

Plane Wave Pump

FAR FIELD

2

)(xN s

)( xN i

0)()( 1 xNxN s

Symmetrical point-to-point correlation in the far field

Non classical correlation in the photon number registered by two symmetrically placed detectors

is ( if )

Spatial correlations in Parametric Down Conversion.....

7ISTITUTO


uncertainty in the propagation directions of twin photons

qqq 021 xxx 021

Gaussian Pump

Noisy Intensity Pattern, where the typical scale is the Coherence Area

wp (2)

Spatial correlation in the real world.....

qq 0pump

)(xN s

)( xN i

Relaxation of the phase matching condition

To detect quantum correlation, the detector size d must be larger than the coherence area of the process [Brambilla, Gatti, Bache, Lugiato, Phys Rev A 69, 023802 (2004)].

pw

fd

2log2

2

x

Transverse coherence length

8ISTITUTO


Experimental SET- UP

Tpulse

=5 ns Rate=10Hz

Epulse

200 mJ @ 355 nmQ-switched Nd:Yag 355 nm

Spatial filter (f=50cm,

m)

Half wave plate

Third harmonic selection

UV mirror (T=98%) Red filter

(low pass)

(T=95%)

CCD array (1340X400) pixels

size 20 m

Type II BBO non-linear crystal ( L=7 mm )

Lens (f = 10 cm)

plates selecting orthogonal polarization

(T=97%)

w=1.25 mm


Coherence Radius vs Pump Size (FIXED Pump Power but not the Intensity )

pw

1

pw2

Only when the Pump diameter is large, i.e. the gain is low, the Coherence Radius goes as the inverse of the pump size.

When the the intensity becomes high, i.e. g> 2, Exp. Data do not follow this simple model as we expected from the reduction of the effective gain area.

low gain theor. curve

Step 1: Tayloring speckle size[G.Brida, A.Meda, M.G., E. Predazzi, I.Ruo-Berchera; Int. Journ Quant. Inf. 7 (2009) 139; JMO 56 (09) 201]


Pump Power range 0.5--3.5 MW

Coherence radius versus Photon Number

The trend is almost linear for each fixed Pump Transverse Size w

p.

wp is smaller → R

coh is bigger according to the relation

Rcoh

effw

1

Coherence radius versus Parametric gain:

11ISTITUTO


Beam splitter

sN

iN

is

is

NN

xNxNNRF

)()(2

For quantifying the level of correlation we use the Noise Reduction Factor, defined as the fluctuation of the difference N

s-N

i normalized to the Shot Noise

Level

1NRF

1NRF

1NRF

For PDC η is the overall transmission of the optical channel

For classical light (e.g. thermal)

For coherent states

Step 2: Achieving sub-shot-noise reduction without background subtraction [G.Brida, L. Caspani, A. Gatti,M.Genovese, A.Meda, I.Ruo-Berchera, Phys. Rev. Lett. 102, 213602 (09).]

12ISTITUTO


Work at INRIM:

Sub Shot Noise intensity correlations over large spatial portions of twin beams.Mesoscopic photon flux (hundreds or thousends of PDC photons per single laser pulse) .No correction of NRF for background (as required for detection of weak objects beyond the Standard Quantum Limit).

Previous works: proof of principle of spatial SSN with strong a posteriori correction for background noise:[O. Jedrkievicz et al., Phys. Rev. Lett. 93, 243601 (2004)] .

A single photon level demonstration was given in:[J. Blanchet el al. Phys Rev. Lett. 101, 233604 (2008)].

13ISTITUTO


R1

R2

R1 R

2

Single shot images of SPDC emission collected by a CCD camera

R1R2

Rs

Ri

14ISTITUTO


Rs

Ri

Measurement of the Spatial Quantum Correlation in a

single image for a single shot of the pump pulse (5 ns)

Estimation of the NRF

We select a large region R1

belonging to the image of the signal

branch, containing thousands of

pixels. We move an equal region R2

in the idler branch searching the

optimal position, that minimizes the

NRF spatially evaluated.

The quantum mean values are estimated by spatial averages over the ensemble of pixel pairs contained inside the region R

s R

i

n

xs

n

xs

s

s

xNxNn

xNxNn

NN

xNxNNRF

11

11

2

1

12

)()(1

)()(1

)()(

15ISTITUTO


8cohx pixels

Perfect intensity correlation, under the shot noise limit , only for detection areas broader than a “coherence area” In order to reach sub shot noise, the ratio between the coherence area and the pixel dimension is a crucial parameter that must be controlled

(1 pixel = 20 m)

1NRF

16ISTITUTO


Binning 8 x 8, superpixel of size 160 m

....Therefore we grouped the physical pixels into blocks called SUPERPIXEL The binning of the pixels is made ad the hardware level

Signature of sub-shot-noise correlations!!1NRF

17ISTITUTO


NRF

s

s

N

xNF

)(2

Each point in the graph represents the value of NRF obtained in for

one shot

Fano factor

82.0NRF

No background subtraction (electronic noise of CCD,

room light ecc.)! Good for sub shot noise imaging!

G. Brida et al .,, Phys. Rev. Lett. 102, 213602 (2009).

18ISTITUTO


Some delicate experimental points....

4.03.01 theoNRF

Overall transmittance of the optical path must be as high as possible No interference filter!! (in our case we have η=60-70% ).

At the same time pump must be blocked. Scattering of pump in the crystal, mirrors fluorescence, room light should be suppressed!!

Residual pump

Electronic noise (4 ph/pixel)

Unavoidable non-uniformity in the intensity pattern over large spatial region of Signal and Idler.

19ISTITUTO


By increasing the binning we obtain Noise Reduction Factor even better, up to NRF= 0.5 for a binning 24x24 (pixel size 480 m)

Step 3: Quantum Imaging of Weak object under shot noise [G.Brida, A. Gatti, M.G., I.Ruo-Berchera, work in progress]

20ISTITUTO


CCD array (1340X400) pixels

size 240 m

π

Titanium deposition ( thickness 80 nm).

Absorption coefficient α=5%

The image of an object in one branch, eventually hidden in the noise, can be restored by subtracting the spatial noise pattern measured in the other branch.

Ni(-x)

Ns(x)

21ISTITUTO


Sub shot noise Imaging: Classical vs Quantum

NRFEn 22

1

Classical differential measurement With PDC

11

NRF

R

)1(2

22 NRFESNR

SNRR

nSQL

PDC

E. Brambilla et. al., Phys. Rev. A, 77, 053807 (2008).

= absorption

22ISTITUTO


Classical differential measurement With PDC correlation

some single shot (binning 12x12, NRF=0.7, R=1.2)

23ISTITUTO


• Perform imaging of a weak absorbing object(binning 24x24, NRF=0.55, R=1.4)

Ns(x)

Noise correlatedN

i(-x)

Ns(x)-N

i(-x)


Preliminary !!

ISTITUTO NAZIONALE DI RICERCA METROLOGICA 1 M. Genovese Istituto Nazionale di Ricerca Metrologica...

Documents

Transcript of ISTITUTO NAZIONALE DI RICERCA METROLOGICA 1 M. Genovese Istituto Nazionale di Ricerca Metrologica...