Imaging with entangled photons

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1 Imaging with entangled photons L. Gasparini 1, M. Perenzoni 1, H. Xu 1, L. Parmesan 1, M. Moreno Garcia 1, D. Stoppa 4, B. Bessire 2, M. Unternährer 2, A. Stefanov 2, V.Mitev 3 and D.L. Boiko 3 1 Fondazione Bruno Kessler, Italy 2 Institute of Applied Physics, University of Bern, Switzerland 3 Centre Suisse d Électronique et de Microtechnique CSEM, Switzerland 4 now at AMS-Heptagon, Switzerland;

2 Outline Motivation Requirements for imaging with entangled photons SuperEllen imager design and characterization G (2) correlations in SPDC with bi-photons G (2) -G (4) in thermal imaging Conclusions & future outlook 2

3 Outline Motivation Requirements for imaging with entangled photons SuperEllen imager design and characterization G (2) correlations in SPDC with bi-photons G (2) -G (4) in thermal imaging Conclusions & future outlook 3

$Conventional Optical Microscopy Limits Light as a wave: diffraction$ Object Image Expected size Actual size Limit is the wavelength With

4 Conventional Optical Microscopy Limits Light as a wave: diffraction limits resolution Large feature Light Object Small feature Light Object Image Expected size Actual size Limit is the wavelength With visible light: /2, about 25nm Cells: 1um Viruses: 1nm Image Rayleigh Limit 4

λ/n N measurements with N detectors give N times

5 Beyond Rayleigh: SUPERTWIN Concept Light as a particle N entangled photons de Broglie wavelength λ/n N measurements with N detectors give N times improvement SUPERTWIN N th entanglement :N diffraction N resolution 5

6 SUPERTWIN Concept & Goal Advanced All-Solid State Optical Microscope Imaging Beyond the Rayleigh Limit 6

7 Outline Motivation Requirements for imaging with entangled photons SuperEllen imager design and characterization G (2) correlations in SPDC with bi-photons G (2) -G (4) in thermal imaging Conclusions & future outlook 7

8 CMOS Single-Photon Imager Scattered entangled photons Spread in space (non-local) Simultaneous in time Single photon imager Position + Time (x,y) + Goal: extraction of N th order correlation function G (N) 8

9 Data processing flow 1. Data recording t

10 Data processing flow 1. Data recording Readout

11 Data processing flow Data recording 2. Readout 3. Compression ADDR (,1) (,3) (2,1) (2,2) (3,1) (3,3) TDC CODE 11

12 Data processing flow Data recording 2. Readout 3. Compression 4. Coincidence detection ADDR (,1) (,3) (2,1) (2,2) (3,1) (3,3) TDC CODE 12

13 Data processing flow Data recording 2. Readout Sensor G (3) Compression 4. Coincidence detection FPGA G (N) update PC ADDR (,1) (,3) (2,1) (2,2) (3,1) (3,3) TDC CODE 13

14 Memory requirements Full area correlations Correlation area G (k) k-dimensional space Histogram size = N pix! k! N pix k! Hypothesis: 2G memory N pix Feasible up to: array G (3) array G (2) 14

15 Memory requirements Reduced area correlations Correlation area G (k) k-dimensional space Histogram size = N pix! k! N pix k! N pix N corr Feasible up to: G (5) with N corr = 16 G (4) with N corr = 24 G (3) with N corr = 48 G (2) with N corr =

16 Outline Motivation Requirements for imaging with entangled photons SuperEllen imager design and characterization G (2) correlations in SPDC produced bi-photons G (2) -G (4) in thermal imaging Conclusions & future outlook 16

17 SuperEllen SPAD Imager Previous SPAD+TDC designs: Large pixel >5 m Small FF < 3% VDD Huge amount of data Reset Pixel array based on TDC, target: Low pitch FE Start Stop Δt Time/Digital Converter Out High FF Fast readout Vspad- 17

row/frame skip SPAD F-E Pixel array based on TDC, result: Low

18 SuperEllen SPAD Imager Previous CMOS SPAD+TDC 15nm tech designs: SPAD: p+/nwell Large pixel >6 m Sm all FF < 2% TDC: 8b, 25ps R-O: row/frame skip SPAD F-E Pixel array based on TDC, result: Low pitch High FF Fast readout 44.6 m 19.5% 8kfps RO 2T/bit 4 m 2 TDC 18

19 Pixel and TDC Concept Synchronous SPAD precharge with disable SRAM Edge-sensitive START and gated operation Ring-oscillator based TDC with 2b interpolation 19

20 Imager Readout Concept Row-wise empty row detection Current-based global threshold x1 gain in acq duty-cycle 2

21 SPAD Dark Count Rate (DCR) Mean = 6 khz Median = 47 Hz Density = 1.26 Hz/μm 2 SPAD 2 m square w/rounded corners p+/nwell (no sharing) Minimize xtalk 21

22 Pixel/Array Timing Performance TDC Uniformity correct full-scale Timing Jitter LSB [ps] 2ps RMS TDC code Goal: detect non-local correlations 22

sparsity of data Raw frame = 1kB; compressed frame < 3B (typ) 3% compression ratio

23 Demonstrator of Quantum Imager CMOS-SPAD array Controls FPGA Data compression USB 3. DLL LABview Data Frame rate in the 8-5 kfps range Real-time data compression exploiting sparsity of data Raw frame = 1kB; compressed frame < 3B (typ) 3% compression ratio Address assignment performed by the FPGA Software-based calculation of correlation functions G (N) 23

24 Outline Motivation Requirements for imaging with entangled photons SuperEllen fabrication and characterization G (2) correlations in SPDC with bi-photons G (2) -G (4) in thermal imaging Conclusions & future outlook 24

25 Generation of bi-photons PPKTP: phase matching in type- SPDC Energy conservation: 1 nm 2 nm Momentum conservation 45 nm pump Non-Linear Crystal Different patterns wrt temperature (with T C critical temperature) Photon pair k 2 k 1 Non-collinear, degenerate: Wavevectors of bi-photons on a cone, anticorrelated Collinear, non-degenerate: Transversal wavevectors of bi-photons, correlated k signal k idler k signal k idler k pump T<T C k pump ω signal = ω idler T>T C ω signal ω idler 25

26 SPDC Laboratory Setup Lens f=15mm PPKTP in oven SuperEllen Lens f=45 mm 81 nm 2x BP filters Opt. Isolator 45 nm VBG stabilized ECDL 26

27 Effects of DCR and Crosstalk Source OFF Intensity: just accumulation of hits G (2) : linearized index on x and y axis of coincidences Integrated Intensity Glauber correlations G (2) (Pixel x1y1,pixel x2y2 ) Crosstalk effect Nearby cols: +1,-1 Nearby rows: +32,-32 DCR pattern 27

Anticorrelated Bi-photons (T<T C ) Integrated Intensity Integrated anticorrelations G (2) (Δ+k, Δ+-k)dk Integrated correlations G (2) (Δ+k, Δ+-k)dΔ Glauber correlations G (2) (Pixel

28 Anticorrelated Bi-photons (T<T C ) Integrated Intensity Integrated anticorrelations G (2) (Δ+k, Δ+-k)dk Integrated correlations G (2) (Δ+k, Δ+-k)dΔ Glauber correlations G (2) (Pixel x1y1,pixel x2y2 ) k s k pump Narrow correlation range around central position of spot Reproduces ring of constant distance, confirming correlations Anti-diagonal attests for anticorrelations k i 28

29 Matching Theory: SPDC Generation vs. Temperature Integrated intensity Integrated anticorrelations Integrated correlations G (2) (Pix x1y1,pix x2y2 ) 52.5 C<T C Anticorrelations 55. C=T C Degeneracy 57.5 C>T C Co-propagating bi-photons 29

30 Outline Motivation Requirements for imaging with entangled photons SuperEllen fabrication and characterization G (2) correlations in SPDC with bi-photons G (2) -G (4) in thermal imaging Conclusions & future outlook 3

31 Higher Order G (N) : Pseudo-Thermal Light Source Setup for thermal near-field imaging Rotating ground glass disk produces pseudothermal statistics D SuperEllen sensor Pseudothermal statistics Reduced aperture 31

32 G (2) Measurement with Pseudothermal Light D = 12 mm D =.8 mm D =.6 mm Thermal G (2) Coherent 2 improvement 32

33 G (3) Measurement with Pseudothermal Light D = 12 mm D =.8 mm D =.6 mm Thermal G (3) Thermal G (2) no improvement! 33

34 Improvement Without Processing Intensity Thermal G (2) 5pix Thermal G (3) 3pix Thermal G (4) G (N) (, ) diagonal terms 34

35 Applying Reconstruction Algorithm Limit: 9x D=.3mm Intensity Limit: 5x D=.5mm Thermal G (2) Limit: 5x D=.5mm Thermal G (3) Limit: 7x D=.4mm Thermal G (4) Limit:9x G (N) (, ) diagonal terms Limit:5x Limit:5x Limit:7x G (N) ( 1, N ) full correlation 35

36 Outline Motivation Requirements for imaging with entangled photons SuperEllen fabrication and characterization G (2) correlations in SPDC with bi-photons G (2) -G (4) in thermal imaging Conclusions & future outlook 36

37 Conclusions & Outlook Superresolution concept addressed by entangled photon detection Efficient detection of simultaneously impinging photons needs TDC-based architecture Thresholding mechanism Efficient readout 32x32 SPAD array demonstrator with per-pixel TDC and row/frame skipping 2ps timing resolution 2% fill-factor 8 kfps max Advantages are demonstrated in G (2) measurements of entangled photon pairs and G (2) -G (4) measurements with quasi-thermal light. Future step: 256x256 detector for G (5) measurements 37

38 S U P E R T W I N All Solid-State Super-Twinning Photon Microscope We thankfully acknowledge the support of the European Commission through the SUPERTWIN project, id

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