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Quantum Imaging - UMBC Objective • Study the physics of multi-photon imaging for entangled state, coherent state and chaotic thermal state: distinguish their quantum and classical nature, in particular, the necessary and/or unnecessary role of quantum entanglement in quantum imaging and lithography. • Study the “magic mirror” for “ghost” imaging. New type of ghost imaging experiment: a successful collaboration with ARL. • Muti-photon sources and measurement devices. Approach Accomplishments • Using entangled two-photon and three-photon states created via optical nonlinear interaction in spontaneous and stimulated modes for multiphoton spatial correlation study and imaging; *The physics: Y.H. Shih, “Quantum Imaging”, IEEE Journal of Selected Topics in Quantum Electronics, 13, 1016 (2007). *The experiment: R. Meyers, K.S. Deacon, and Y.H. Shih, “A new type of ghost imaging experiment”, submitted to Phys. Rev. Lett., (2007). *The photon source: J.M. Wen, P. Xu, M.H. Rubin, Y.H. Shih, “Transverse correlations in triphoton entanglement: geometrical and physical optics, Phys. Rev. A76, 023828 (2007). • Using chaotic light source, coherent light source for two-photon spatial correlation study and ghost imaging; • Using photon counting and classical currentcurrent correlation circuit to explore the nature of two-photon correlation. * The detector: High uniformity, stability, and reliability large-format InGaAs APD arrays. Papers published in peer-reviewed journals * J.M. Wen, S.W Du , and M.H. Rubin, Spontaneous Parametric Down-Conversion in a Three-Level SystemΣ, Phys. Rev. A 76 (2007). * S.W Du, E. Oh, J. Wen, and M.H. Rubin, our-Wave Mixing in Three -Level Systems: Interference and EntanglementΣ, Phys. Rev. A 76, 013803 (2007). * S.W. Du, J. Wen, M.H. Rubin, and GY. Yin, our-Wave Mixing and Biphoton Generation in a Two-Level SystemΣ, Phys. Rev. Lett. 98, 053601 (2007). * J.M. Wen, S.W. Du, and M.H. Rubin, Biphoton Generation in a Two-Level Atomic EnsembleΣ, Phys. Rev. A 75, 033809 (2007). * J.M. Wen, P. Xu, M.H. Rubin, and Y.H. Shih, Transverse Correlation in Triphoton Entanglement: Geometrical and Physical OpticsΣ, Phys. Rev. A 76, 023828 (2007). * Y.H. Shih, Quantum ImagingΣ, IEEE J. of Selected Topics in Quantum Electronics, 13, 1016 (2007). * Y.H. Shih, The Physics of 2 1+1Σ, Front. Phys., 2, 125 (2007). Papers published in non-peer-reviewed journals/conference proceedings * Y.H. Shih, Quantum ImagingΣ, Front. in Optics, OSA annual meeting, San Jose, CA, 2007. * Y.H. Shih, Quantum ImagingΣ, CLEO Pacifi c Rim 2007, Seoul, Korea, 2007. * R. Meyers, K.S. Deacon, and Y.H. Shih, new two-photon ghost im aging experim entΣ, SPIE Annual Meeting, San Diego, CA, 2007. * X. Wu, Y Gu, F. Yan, F.S. Choa, P. Shu, High Unif ormity, Stabil ity, and Reli abili ty Large-Format InGaAs APD ArraysΣ, CLEO/QELSΥ07, Baltimore, MD, 2007. * Y. Zhou, P. Xu, S.N. Zhu, and Y.H. Shih, The Generation and Temporal Correlation Measurement of TriphotonΣ, CLEO/QELSΥ07, Baltim ore, MD, 2007. * J. Wen, S.W. Du, and M.H. Rubin, Biphoton in a Two-Level Cooled Atomi c EnsembleΣ, CLEO/QELSΥ07, Baltim ore, MD, 2007. * Y.H. Shih, Quantum ImagingΣ, International Conference on Quantum Information, Rochester, NY, 2007. * J. Wen, M.H. Rubin, and S.W Du, New Beating Experim ent Using Biphotons Generated from a Two-Level SystemΣ, Slow Light and Fast Light Conference, Salt Lake City, Utah, 2007. Part I: The Physics of Quantum Imaging Objective: “Study the physics of multi-photon imaging, distinguish their quantum and classical nature, in particular, the necessary and/or unnecessary role of quantum entanglement in quantum imaging.” Quantum imaging has demonstrated two peculiar features: (1) Enhancing the spatial resolution beyond diffraction limit; (2) Reproducing “ghost” images in a “nonlocal” manner. Either the nonlocal behavior observed in ghost imaging or the apparent violation of the uncertainty principle explored in the quantum lithography are due to the coherent superposition of two-photon amplitudes, a nonclassical entity corresponding to different yet indistinguishable alternative ways of triggering a joint-detection event. Classical Imaging - the concepts Idealized Classical Imaging 1 1 1 so si f Gaussian thin lens equation o F(i ) i d A( ) ( /m) o o o i m si /so object-plane and the image-plane Point-point relationship between the is the result of constructive interference of the fields. Diffraction-limited Classical Imaging 1 1 1 so si f Gaussian thin lens equation o F(i ) i d A( ) somb( /m) o o o i m si /so somb(x) = 2J1(x) / x Point-“spot” relationship between the object plane and the image plane is the result of constructive superposition: adiffraction pattern. Biphoton Ghost Imaging Biphoton “ghost” Imaging So Si 1 1 1 S0 Si f “Ghost” Image: an EPR Experiment in momentum and position correlation. PRA, 52, R3429 (1995); PRL, 74, 3600 (1995). What is so special about entangled two-photon state? “Can quantum mechanical physical reality be considered complete?” Einstein, Poldosky, Rosen, Phys. Rev. 47, 777 (1935). Proposed the entangled two-particle state according to the principle of quantum superposition: x1, x 2 p1, p2 dp p x 2 u p x1 (x1 x 2 x 0 ) dx x p2 v x p1 ( p1 p2 ) (x1 x2 ) 0 (p1 p2 ) 0 Although: x1 , x2 , p1 , p2 . What is so special about entangled two-photon states? ( s i p ) (k s k i k p ) aˆ s aˆ i 0 s,i A typical EPR state: (s i ) (s i ) In EPR’s language, the signal and the idler may come out from any point of the object plane; however, if the signal (idler) is found in a certain position, the idler (signal) must be found in the same position, with 100% certainty. Biphoton “ghost” Imaging (s i ) & (s i ) Photon #1 stop at a point on object plane (O I) Photon #2 stop at a unique point on image plane ?? Result of a constructive superposition of two-photon amplitudes, a nonclassical entity corresponding to different yet indistinguishable alternative ways of triggering a joint-detection event. Biphoton Ghost Imaging G ( O, I ) (O , I ) (2) RC ( I ) d O A( O ) (O , I ) 2 2 R 2 dO A(O ) somb( O I /m ) so /2 d O A(O ) ( O I /m) 2 2 Chaotic light Ghost Imaging Lens-less ghost Imaging D2 S.C X2 X2 Thermal light (Near-field) C.C D1 S.C X2 X2 Ghost Image with chaotic light Thermal light source Correlator Photon Counting Correlation Measurement Near-field 10 / d Recent Experiment In collaboration with ARL Ghost image of an Army soldier A photon counting detector, D1, is used to collect and to count all the photons that are randomly scattered-reflected from the soldier. A CCD array (2D) was facing the light source instead of the object. An image of the soldier was observed in the joint-detection of D1 and the CCD. Chaotic light Ghost Imaging RC (I ) dO A2 (O ) G(2) (O, I ) (1) 2 12 G ( O, I ) G G G (2) (1) 11 (1) 22 G0 (O I ) Constant Background Image Chaotic light ghost Imaging (1) 2 12 G ( O, I ) G G G (2) (1) 11 (1) 22 G0 (O I ) N (1) G12 g1 j (O ) g2 j (I ) j1 (O I ) Superposition of two-photon amplitudes () () G ( x2 ; x1 ) 0 E ( x2 ) E ( x1 ) 1q ,1q ' ( 2) 2 q ,q ' g2 (x 2 ,q)g1(x1,q ') g2 (x 2,q ')g1 (x1,q) 2 q ,q ' 2 g1 (x1,q) 2 g2 (x 2,q) q 2 q g 1 (x1,q)g2 (x 2,q) q Source q' D1 q' q q D2 Superposition of classical fields? (1) 2 12 G G G (1) 11 (1) 22 N E j (1 ) j1 E k (2 ) 2 k1 N E 2 N j 2 N E j (1)E j (2 ) j1 (1 )E k (2 ) E j ( 2 )E k ( 1) 2 j,k1 Does it make any sense in Maxwell theory of light? HBT and Ghost Imaging k-k Momentum-Momentum Correlation Imaging x-x Position-Position Correlation 10 / d HBT Thermal light ghost imaging Far-field Near-field 1956 2006 50 years We cannot but stop to ask: What has been preventing this simple move for 50 years (1956-2006)? Something must be terribly misleading to give us such misled confidence not to even try the near-field measurement in half a century. Statistical correlation of intensity fluctuation ? I1 I2 I1 I2 I1 I2 ??? Mode 1 k1 Mode 2 k2 Far-field (Fourier transform Plane) Identical modes: I1 I2 I1 I2 I1 I2 Different modes: I1 I2 I1 I2 The HBT experiment was successfully interpreted as statistical correlation of intensity fluctuations. In HBT, the measurement is in far-field (Fouriertransform plane). The measured two intensities have the same fluctuations while the two photodetectors receive the same mode and thus yield maximum correlation. When the two photodetector receive different modes, however, the intensities have different fluctuations, and thus no correlation is observable. Statistical correlation of intensity fluctuation ??? It does not work for near field !!! Identical modes: Different modes: I1 I2 I1 I2 I1 I2 I1 I2 I1 I2 0 Near-field Chanceof receivingidentical mod es N 1 2 Chanceof receiving different mod es N N The physics of chaotic light ghost imaging? “Can Two-photon Correlation of Chaotic Light Be Considered as Correlation of Intensity Fluctuations?” PRL, 96, 063602 (2006) (G. Scarcelli,V. Berardi, and Y.H. Shih). “A New Type of Ghost Imaging Experiment”, submitted to Phys. Rev. Lett., (2007) (R. Meyers, K.S. Deacon, and Y.H. Shih). “Quantum Imaging”, IEEE J. of Selected Topic in Quantum Electronics, 13, 1016 (2007) (Y.H. Shih). The Physics * The nonlocal behavior observed in biphoton ghost imaging is due to the superposition of two-photon amplitudes, a nonclassical entity corresponding to different yet indistinguish-able alternative ways of triggering a joint-detection event. * The lens-less ghost imaging of thermal light is an interference phenomenon involving the superposition indistinguishable twophoton alternatives, rather than statistical correlation of intensity fluctuation. * Ghost imaging: a quantum phenomenon of light. Part II: The Theory Lensless imaging with a classical statistical source SPDC Klyshko Picture Incoherent source The current-current correlation is given by iA iB k constant+ d A C AB 2 2 where r r r r r r CAB d s d sg ( j , s )gA ( j , s )(s, s ) 2 2 * B This are derived using r r r E j d s g j ( j , s )S( s ) r r r r ( s, s ) S( s )S( s ) 2 In the paraxial approximation i eikd g A ( A , S ) AA dA r r ( , kP) e A r r r k A A t( A ) ( A S , ) dA 1 i kP 2 2 i eikd g B ( B , S ) AB dB r r B r r k A B ( B S , ) dB ik (d d ) r r r r r r i e C AB d 2 s d 2 sgB* ( j , s )gA ( j , s )( s , s ) A *B A A dA dB r r k r r k r r * 2 2 * r A B A A t( A ) d sd s ( B S , ) ( A S , )( S , S ) dB dA Let us assume the source is large so we can take 2 r r r r d 2 q % r iqr g( r r ( S , S ) ( S S ) (q)e 2 (2 ) S S ) A B 2 d q iqr g( r A r B ) dB dA % r * 2 A B A A t( A ) d A d B e (q, )(q) 2 (2 ) k r r r * 2 A B A A d d t( A ) d A d B ( A B ) Point spread r A B function q dA S dB All the rays from the point at A coherently add at in the region centered at B . One can say the same thing in terms of the wave vectors. The correlation function is then given by r r d A C AB d A t 0 ( A )( A B ) r r r r 2 t 0 ( B ) if ( A B ) ( A B ) 2 2 2 2 If we change the detection scheme, we get a different result. In the paraxial approximation: Now each point of the detector A acts like the source of a spherical wave that illuminates the entire object; consequently, for dA=dB r r d A C AB d 0 t 0 ( O )( O B ) r r r r 2 t 0 ( B ) if ( A B ) ( A B ) 2 2 2 2 We see that although the two results are the same for completely incoherent sources, they differ in the more realistic case. When looked at in the Klyshko picture, allowing for the phase conjugate nature of the source, the last case looks like coherent imaging, while the previous case looks like incoherent imaging. Part III: The Detector Range Finder, Stand Off Detection, and 3-D Lidar (APD Arrays) Applications DIfferential SCattering/DIfferential Absorption Lidar (DISC/DIAL) IR LASER TRANSMITTER AND RECEIVER ... . . . .. High Performance Photon Counting Detectors and Arrays Space Optical Communications Quantum Communication & Image Applications Guard-Ring Mesa Mesa vs. Guard-Ring • Potential issues with mesa APDS for space applications: – Short lifetime from early breakdown (reliability) – Dark current increases over time (stability) Reliability of Guard-Ring APDS -6 Dark current at M~10 (A) 10 Mesa APDs* -7 10 -8 10 Goddard/AdTech guard ring APDs -9 10 0 10 1 10 2 10 3 10 4 10 5 10 Time (hour) Aging test condition: 200oC/I=100A Testing method: measure dark current at M~10 periodically * S. Tanaka et al on OFC 2003 Key Issues for Photon Counting (PC) 1. Low Dark Counts: Dark current is caused by surface leakage, tunneling, defects assisted tunneling. Can be reduced by decrease the electrical field in the active (absorption) region. 2. High Gain and High Differential Gain High gain can be obtained with high bias voltage. However, with high bias, a high dark current will also be produced. High differential gain relies on high rising slope of APD (dG/dV). An ideal PC APD will have a straight angle I-V curve, which can be achieved with better device designs. 3. Designing and Fabricating Materials with Reduced AfterPulse Dark Current (AFDC) Amplitude and Duration AFDC comes from traps in the avalanche regions and trapped carriers in the hetero-interface. Interstitial Zn atoms created during the diffusion processes are source of traps and can be activated and converted to substitutional dopants by appropriate annealing procedures. More steps of InGaAsP quaternary layers (1.1Q, 1.2Q, 1.3Q, 1.5Q, ..etc.) can added to the InP/InGaAs interface to reduce hole trapping. Geiger Mode Operations-I 1. Passive Quenching – Biased above breakdown voltage ( Vop-Vb< ~2V), rely on a series resistance to reduce voltage drop on the APD when avalanche is taking place. Advantages: simple circuits, disadvantages: long recovery time. I +Vop Iop Vout VB Vop V Geiger Mode Operations-II 2. Active Quenching – Normally biased above breakdown voltage ( VopVb< ~2V). Once sensed that an avalanche process is taking place, immediately reduce the bias below Vb. Advantages: relatively short recovery time (still limited by afterpulse dark counts). Disadvantages: more complex circuits. +Vop I Control Voltage supplier Iop Avalanche Sensing And trigger circuits Vout VB Vop V Geiger Mode Operations-III 3. Gated Operations – Normally biased below or around Vb. A short electrical pulse is applied to the APD terminal to raise the bias voltage above Vb and gain when photons are coming. Advantages : simpler ckt and very high gain. Disadvantages: can only work with periodic signals and synchronization is an issue. +Vop I Vout Vac Idc VB Vdc V Optimize Design To Achieve High Differential Gain and Low Dark Current Vp 10000 1000 Dark current 10 Gain 100 10 1 1 0.1 -100 Electrical Field (kV/cm) Gain 0 Dark Current (nA) 100 -200 -300 -400 -500 0.1 0 10 20 30 Voltage (V) 40 50 VB -600 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 Distant from Front (micrometer) Reducing the distance between the punch through voltage and the breakdown voltage will help to reduce the voltage drop falling on the small bandgap absorption region Dark Current I-V Characteristics Changing with Temperature Dark Current variation with Temperature * The dark current is reduced • The gain is increased • A sharp rising gain with the bias voltage will help to choose good operating points. -7 10 -9 10 -11 10 -13 10 Current (A) @ 294 K Current (A) @ 260 K Current (A) @ 230 K Current (A) @ 200 K Current (A) @ 140 K -15 10 -17 10 -10 0 10 20 Voltage (V) 30 40 50 16x16 Arrays and Vbr Color Map 55 52.5 50 47.5 45 42.5 40 37.5 14 12 10 8 6 4 2 0 0 2 4 6 14 12 10 8 55 44 54 43 53 42 52 41 51 40 50 39 49 38 48 37 47 36 46 35 45 44 64x64 Arrays and Vbr Breakdown Voltage Distribution Innovative Current Bias Scheme Current bias mode resolves several common difficult problems from conventional voltage biasing mode in arrays. • • • • • No need to know the breakdown voltage Less sensitive to the temperature fluctuation Much easier to control the bias point. Ideal for APD arrays operations Partially solved the after-pulsing problem. Photon Counting Testing Setup Operating temperature Dependence II 0 10 Dark Count Probability (b) -1 10 I =100 nA, V =1 V I =100 nA, V =1.5V I =100 nA, V =2 V DC DC -2 10 -100 -90 f a = 1k Hz, FWHM=20 ns -80 -70 -60 o Operating Temperature ( C) DC -50 ac ac ac -40 -30 Dark Count Probability Versus Vac at Different Temperatures 1 o at -70 C, I o 0.8 at -90 C, I o =100 nA DC at -100 C, I Dark Count Probability (c) =100 nA DC =100 nA DC 0.6 0.4 0.2 0 1 1.5 2 V ac (V) 2.5 3 Dark Count Probability Versus the Combination of IDC and Vac at Fixed Temperatures 1 1 o o at -90 C, V =1 V 0.9 at -90 C, I =100 nA ac o at -90 C, V =2 V ac o o 0.9 o at -90 C, V =3 V DC 0.8 0.8 0.7 0.7 Dark Count Probability Dark Count Probability DC at -90 C, I =500 nA ac 0.6 0.5 0.4 0.3 0.2 0.6 0.5 0.4 0.3 0.2 0.1 0 100 DC at -90 C, I =300 nA 0.1 200 300 400 500 600 I (nA) DC 700 800 900 1000 0 1 1.2 1.4 1.6 1.8 2 V (V) ac 2.2 2.4 2.6 2.8 3 Detection Efficiency ~25% Achieved Under Gated Mode Operations 30 25 o at -70 C, I =100 nA 20 o 25 at -70 C, I =300 nA o o DC DC 15 10 5 1.5 DC at -50 C, I =500 nA DC at -70 C, I =500 nA 0 1 DC at -50 C, I =300 nA DC Single Photon Detection Efficiency (%) Single Photon Detection Efficiency (%) o (b) at -50 C, I =100 nA (b) o 2 VB-VP=22V V (V) ac 2.5 3 20 15 10 5 0 1 1.2 1.4 2.2 2 1.8 VB-V =14V (V) V P 1.6 p 2.4 2.6 2.8 3 After Pulsing Problems 1. NASA lidar group did studies on one of the best reported commercial InGaAs photon counting APD product and found that within the claimed 10% DE, the portion of total counts caused by after-pulsing is 600% of that of the light count. 2. A test of after-pulsing duration can be done by increasing the gating pulse repetition rate (reducing time duration between gating pulse) and observe the increase of DCR. 3. As long as a few micro-seconds after-pulsing duration (equivalently the blind period) can usually be observed and that can put show stoppers to many timing sensitive applications. 4. After –pulsing is a material problem and need long term plan of improvement. However, it can be dealt with short term methods. Suppression of After-Pulsing 1. The “Current Mode” operation will only allow one avalanche event to take place and prevent any possible after-pulsing for each gating period. This is achieved by limiting the DC supply current and the value of the gating capacitor. 2. During the avalanche process, the APD is switching on and the gating capacitor is discharged. The APD bias drops below the breakdown voltage. Limited by the set current of the DC current source and the capacitance value of the gating capacitor, the charging time to reach breakdown can never happen until the gating period is passed. 3. On the other hand using the voltage mode to operate the APD, the gating capacitor is quickly charged up to above breakdown and the APD is not soon ready to be fired again. At that moment if there still plenty residue carriers in the avalanche region, after-pulses will be generated. Increasing The DC Source Current Can Reduce The Charging Time. 1 Dark Count Probability (%) 0.8 0.6 0.4 I =100 nA, V I =100 nA, V I =500 nA, V I =500 nA, V DC 0.2 DC DC DC 0 2 10 ac ac ac ac =2 V at -30 C =2 V at room temperature =2 V at -30 C =2 V at room temperature 3 4 10 10 Frequency (Hz) 5 10 More on Bias Current Effects 1 Dark Count Probability (%) 0.8 0.6 I =10 nA I =50 nA I =100 nA I =200 nA I =300 nA I =400 nA I =500 nA DC 0.4 DC DC DC 0.2 DC DC DC 0 2 10 3 4 10 10 Frequency (Hz) 5 10 Quantum Imaging - UMBC Objective • Study the physics of multi-photon imaging for entangled state, coherent state and chaotic thermal state: distinguish their quantum and classical nature, in particular, the necessary and/or unnecessary role of quantum entanglement in quantum imaging and lithography. • Study the “magic mirror” for “ghost” imaging. New type of ghost imaging experiment: a successful collaboration with ARL. • Muti-photon sources and measurement devices. Approach Accomplishments • Using entangled two-photon and three-photon states created via optical nonlinear interaction in spontaneous and stimulated modes for multiphoton spatial correlation study and imaging; *The physics: Y.H. Shih, “Quantum Imaging”, IEEE Journal of Selected Topics in Quantum Electronics, (2007). *The experiment: R. Meyers, K.S. Deacon, and Y.H. Shih, “A new type of ghost imaging experiment”, submitted to Phys. Rev. Lett., (2007). *The photon source: J.M. Wen, P. Xu, M.H. Rubin, Y.H. Shih, “Transverse correlations in triphoton entanglement: geometrical and physical optics, Phys. Rev. A76, 023828 (2007). • Using chaotic light source, coherent light source for two-photon spatial correlation study and ghost imaging; • Using photon counting and classical currentcurrent correlation circuit to explore the nature of two-photon correlation. * The detector: High uniformity, stability, and reliability large-format InGaAs APD arrays.