ISTITUTO NAZIONALE DI RICERCA METROLOGICA 1 M. Genovese Istituto Nazionale di Ricerca Metrologica...
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Transcript of 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)]
ISTITUTONAZIONALEDI RICERCAMETROLOGICA
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
NAZIONALEDI RICERCAMETROLOGICA
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
6ISTITUTO
NAZIONALEDI RICERCAMETROLOGICA
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
NAZIONALEDI RICERCAMETROLOGICA
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
NAZIONALEDI RICERCAMETROLOGICA
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
ISTITUTONAZIONALEDI RICERCAMETROLOGICA
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]
ISTITUTONAZIONALEDI RICERCAMETROLOGICA
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
NAZIONALEDI RICERCAMETROLOGICA
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
NAZIONALEDI RICERCAMETROLOGICA
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
NAZIONALEDI RICERCAMETROLOGICA
R1
R2
R1 R
2
Single shot images of SPDC emission collected by a CCD camera
R1R2
Rs
Ri
14ISTITUTO
NAZIONALEDI RICERCAMETROLOGICA
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
NAZIONALEDI RICERCAMETROLOGICA
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
NAZIONALEDI RICERCAMETROLOGICA
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
NAZIONALEDI RICERCAMETROLOGICA
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
NAZIONALEDI RICERCAMETROLOGICA
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
NAZIONALEDI RICERCAMETROLOGICA
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
NAZIONALEDI RICERCAMETROLOGICA
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
NAZIONALEDI RICERCAMETROLOGICA
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
NAZIONALEDI RICERCAMETROLOGICA
Classical differential measurement With PDC correlation
some single shot (binning 12x12, NRF=0.7, R=1.2)
23ISTITUTO
NAZIONALEDI RICERCAMETROLOGICA
• 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)