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M. Genovese Istituto Nazionale di Ricerca Metrologica (INRIM),

M. Genovese Istituto Nazionale di Ricerca Metrologica (INRIM), Strada delle Cacce 91, 10135 Torino, Italy. PDC correlations for Quantum Imaging. Quantum Imaging: a new quantum technology addressed to exploit properties of quantum optical states for overcoming limits of classical optics.

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M. Genovese Istituto Nazionale di Ricerca Metrologica (INRIM),

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  1. M. Genovese Istituto Nazionale di Ricerca Metrologica (INRIM), Strada delle Cacce 91, 10135 Torino, Italy • PDC correlations for Quantum Imaging

  2. 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)]

  3. INRIM Quantum Optics Research program “Carlo Novero lab” Responsible: M. Genovese 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, …. • Our main sponsors: • Minister of Education • Piedmont Region • Bank Foundation San Paolo • ASP, Lagrange Found. • European Union • NATO,…

  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

  5. PDC: a brief summary Type-I PDC Type-II PDC

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

  7. Spatial correlation in the real world..... Noisy Intensity Pattern, where the typical scale is the Coherence Area Gaussian Pump wp (2)‏ uncertainty in the propagation directions of twin photons 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)]. Transverse coherence length Finite size of the pump waist wp

  8. plates selecting orthogonal polarization (T=97%) CCD array (1340X400) pixels size 20 m Type II BBO non-linear crystal ( L=7 mm ) Spatial filter (f=50cm, m) w=1.25 mm UV mirror (T=98%) Half wave plate Red filter (low pass) (T=95%) Lens (f = 10 cm) Third harmonic selection Tpulse=5 ns Rate=10Hz Epulse 200 mJ @ 355 nm Q-switched Nd:Yag 355 nm Experimental SET- UP

  9. 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] low gain theor. curve 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.

  10. Coherence radius versus Photon Number Pump Power range 0.5--3.5 MW Coherence radius versus Parametric gain: The trend is almost linear for each fixed Pump Transverse Size wp. wp is smaller → Rcoh is bigger according to the relation Rcoh

  11. 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).] For quantifying the level of correlation we use the Noise Reduction Factor, defined as the fluctuation of the difference Ns-Ni normalized to the Shot Noise Level For PDC ηis the overall transmission of the optical channel Beam splitter For classical light (e.g. thermal) For coherent states

  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, 243601 (2004)] . A single photon level demonstration was given in: [J. Blanchet el al. Phys Rev. Lett. 101, 233604 (2008)].

  13. Single shot images of SPDC emission collected by a CCD camera R1 R1 R2 R2 Rs R1 Ri R2

  14. Measurement of the Spatial Quantum Correlation in a single image for a single shot of the pump pulse (5 ns)‏ Rs 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. Ri The quantum mean values are estimated by spatial averages over the ensemble of pixel pairs contained inside the region Rs R i

  15. (1 pixel = 20 m) 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

  16. ....Therefore we grouped the physical pixels into blocks called SUPERPIXEL The binning of the pixels is made ad the hardware level Binning 8 x 8, superpixel of size 160 m Signature of sub-shot-noise correlations

  17. Each point in the graph represents the value of NRF obtained in for one shot Fano factor NRF G. Brida et al .,, Phys. Rev. Lett. 102, 213602 (2009). No background subtraction (electronic noise of CCD, room light ecc.)! Good for sub shot noise imaging!

  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.

  19. Step 3: Quantum Imaging of Weak object under shot noise [G.Brida, A. Gatti, M.G., I.Ruo-Berchera, work in progress] By increasing the binning we obtain Noise Reduction Factor even better, up to NRF= 0.5 for a binning 24x24 (pixel size 480 m)

  20. CCD array (1340X400) pixels size 240 m Titanium deposition ( thickness 80 nm). Absorption coefficient α=5% Ns(x) π Ni(-x) 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.

  21. Sub shot noise Imaging: Classical vs Quantum Classical differential measurement With PDC  = absorption E. Brambilla et. al., Phys. Rev. A, 77, 053807 (2008).

  22. some single shot (binning 12x12, NRF=0.7, R=1.2) Classical differential measurement With PDC correlation

  23. Perform imaging of a weak absorbing object (binning 24x24, NRF=0.55, R=1.4) Ns(x) Noise correlated Ni(-x) Ns(x)-Ni(-x)

  24. Preliminary !!

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