ISTITUTO NAZIONALE DI RICERCA METROLOGICA 1 M. Genovese Istituto Nazionale di Ricerca Metrologica (INRIM), Strada delle Cacce 91, Torino, Italy PDC correlations for Quantum Imaging

ISTITUTO NAZIONALE DI RICERCA METROLOGICA 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) ; R.Bennik et al., PRL 89 (02) ] -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) ] -Quantum Illumination [S. Tan et al., PRL 101 (08) ] -Sub-Rayleigh quantum imaging [V.Giovannetti et al., Phys. Rev. A 79, (2009)]. -Sub shot noise detection of weak objects [E. Brambilla et al., PRA 77, (08)]

ISTITUTO NAZIONALE DI RICERCA METROLOGICA 6 labs on quantum optics 4 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 program “Carlo Novero lab” Responsible: M. Genovese Our main sponsors: - Minister of Education - Piedmont Region - Bank Foundation San Paolo - ASP, Lagrange Found. - European Union - NATO,…

ISTITUTO NAZIONALE DI RICERCA METROLOGICA 4 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

ISTITUTO NAZIONALE DI RICERCA METROLOGICA Type-I PDC Type-II PDC

ISTITUTO NAZIONALE DI RICERCA METROLOGICA 6 Transverse phase matching condition q=0 q signal idler -q x -x-x Plane Wave Pump FAR FIELD Symmetrical point-to-point correlation in the far field Non classical correlation in the photon number registered by two symmetrically placed detectors ( if ) Spatial correlations in Parametric Down Conversion.....

ISTITUTO NAZIONALE DI RICERCA METROLOGICA 7 uncertainty in the propagation directions of twin photons Gaussian Pump Noisy Intensity Pattern, where the typical scale is the Coherence Area wpwp  (2 )‏ Spatial correlation in the real world..... Finite size of the pump waist w p 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, (2004)]. Transverse coherence length

ISTITUTO NAZIONALE DI RICERCA METROLOGICA 8 Experimental SET- UP T pulse =5 ns Rate=10Hz E pulse nm Q-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

ISTITUTO NAZIONALE DI RICERCA METROLOGICA Coherence Radius vs Pump Size (FIXED Pump Power but not the Intensity )‏ 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]

ISTITUTO NAZIONALE DI RICERCA METROLOGICA Pump Power range MW Coherence radius versus Photon Number The trend is almost linear for each fixed Pump Transverse Size w p. w p is smaller → R coh is bigger according to the relation R coh Coherence radius versus Parametric gain:

ISTITUTO NAZIONALE DI RICERCA METROLOGICA 11 Beam splitter 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 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, (09).]

ISTITUTO NAZIONALE DI RICERCA METROLOGICA 12 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, (2004)]. A single photon level demonstration was given in: [J. Blanchet el al. Phys Rev. Lett. 101, (2008)].

ISTITUTO NAZIONALE DI RICERCA METROLOGICA 13 R1R1 R2R2 R1R1 R2R2 Single shot images of SPDC emission collected by a CCD camera R1R1 R2R2 RsRs RiRi

ISTITUTO NAZIONALE DI RICERCA METROLOGICA 14 RsRs RiRi 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 R 1 belonging to the image of the signal branch, containing thousands of pixels. We move an equal region R 2 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

ISTITUTO NAZIONALE DI RICERCA METROLOGICA 15 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)

ISTITUTO NAZIONALE DI RICERCA METROLOGICA 16 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

ISTITUTO NAZIONALE DI RICERCA METROLOGICA 17 NRF Each point in the graph represents the value of NRF obtained in for one shot Fano factor No background subtraction (electronic noise of CCD, room light ecc.)! Good for sub shot noise imaging! G. Brida et al.,, Phys. Rev. Lett. 102, (2009).

ISTITUTO NAZIONALE DI RICERCA METROLOGICA 18 Some delicate experimental points.... 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.

ISTITUTO NAZIONALE DI RICERCA METROLOGICA 19 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]

ISTITUTO NAZIONALE DI RICERCA METROLOGICA 20 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. N i (-x) N s (x)

ISTITUTO NAZIONALE DI RICERCA METROLOGICA 21 Sub shot noise Imaging: Classical vs Quantum Classical differential measurement With PDC E. Brambilla et. al., Phys. Rev. A, 77, (2008).  = absorption

ISTITUTO NAZIONALE DI RICERCA METROLOGICA 22 Classical differential measurementWith PDC correlation some single shot (binning 12x12, NRF=0.7, R=1.2)

ISTITUTO NAZIONALE DI RICERCA METROLOGICA 23 Perform imaging of a weak absorbing object (binning 24x24, NRF=0.55, R=1.4) N s (x) Noise correlated N i (-x) N s (x)-N i (-x)

ISTITUTO NAZIONALE DI RICERCA METROLOGICA Preliminary !!