OPT 253 Quantum Optics and Quantum Information Laboratory

OPT 253: Quantum Optics and Quantum Information Laboratory Final Presentation R. A. Smith II 12/10/2008 Performed with C. Gettliffe M. Lahiri

Lab 3 -4: Single Photon Source

Experimental Setup

Fluorescence Lifetime Measurement • Diode-pumped solid state laser excited Di. I dyle molecules • λ=532 nm • Pulse Separation: 13. 2 ns • Di. I Dye Molecule Fluorescence Lifetime: τ=3. 44 ns • APD signal was used as a start trigger; Electric pulse from laser was used as a stop trigger

EM-CCD Capture of Fluorescing Quantum Dots Acquisition time: 300 ms Gain: 255 Widefield micrsocopy scan of Colloidal Quantum Dots hosted in a Cholesteric Liquid Crystal Quantum Dots illuminated with Diode-Pumped Solid State Laser

Spatial Scan of Colloidal QD’s Hosted in CLC • 5μm x 5μm spatial scan of Sample of QD’s in CLC • APD 1 (top left) and APD 2 (bottom left) show fluorescence of quantum dots when excited with pulsed laser • Confocal microscopy used to illuminate sample • One coordinate location of the sample was scanned temporally (above right) • Blinking confirms existence of single quantum dot

Coincidence Counts of Temporal Scans • Coincidence counts of 5 ms temporal scan of QD’s in CLC host • The nearly zero occurrences of zero interphoton time shows the antibunching of the photons being emitted by the QD • Antibunched photons shows single photon emission by QD

Possible Improvements to Lab 3 -4 • Quantum Dot Concentration

Lab 2: Single Photon Interference

Experiemental Setup M 1 Laser ND Filters Spatial Filter Glass with slits Young’s Double Slit Experiment EM-CCD Camera Polarizing B/S M 1 Laser ND Filters Spatial Filter 45° Polarizer M 2 Mach-Zehnder Interferometer Setup EM-CCD Camera Non-Polarizing B/S 45° Polarizer

Wave-Particle Duality • Photons exhibit both characteristics of waves and particles • Wave phenomenon is exhibited by photons when photons are not “observed” • In the presence of an observer, the photons behave as particles • Without a linear polarizer oriented at 45° at the exit of the Mach-Zehnder interferometer, the path of the photon is being observed by the system • As a result, the photons act as particles and interference is destroyed • With the polarizer in place, the photons act as waves

Photon Spacing Helium-Neon laser used λ=633 nm Φ = 0. 27μW 9 x 1011 photons/s Neutral Density Filters were used to space one photon every 100 meters • Transmission ≈ 10 -6 • All pictures have a photon separation of 100 m • • •

Young’s Double Slit Experiment • Gain: 0 • Acquisition time: 0. 3 s • Transmission: 1. 57 x 10 -1 • 4. 24 x 1010 photons • Gain: 255 • Acquisition time: 1. 0 s • Transmission: ≈1. 0 x 10 -6 • 9. 0 x 105 photons

Young’s Double Slit Experiment • Gain: 255 • Acquisition time: 20. 0 s • Transmission: ≈ 1. 0 x 10 -6 • 1. 80 x 107 photons • Gain: 255 • Acquisition time: 25. 0 s • Transmission: ≈ 1. 0 x 10 -6 • 2. 25 x 107 photons

Mach-Zehnder Interferometer Images • No Interference Fringes (Polarizer Removed) • Gain: 100 • Acquisition time: 0. 3 s • Transmission: ≈ 1. 0 x 10 -2 • 2. 70 x 102 photons • Interference Fringes (Polarizer Present) • Gain: 100 • Acquisition time: 0. 3 s • Transmission: ≈ 1. 0 x 10 -2 • 2. 70 x 109 photons

Mach-Zehnder Interferometer Images • Interference Fringes (Polarizer Present) • Gain: 255 • Acquisition time: 1. 0 s • Transmission: ≈ 1. 0 x 10 -2 • 9. 0 x 109 photons • Interference Fringes (Polarizer Present) • Gain: 255 • Acquisition time: 5. 0 s • Transmission: ≈ 1. 0 x 10 -6 • 4. 50 x 106 photons

Mach-Zehnder Interferometer Images • Interference Fringes (Polarizer Present) • Gain: 255 • Acquisition time: 10 s • Transmission: ≈ 1. 0 x 10 -2 • 9. 0 x 106 photons • Interference Fringes Visibility from picture at left, maximum: 80%, minimum: 67% • Definite peaks demonstrates interference at low photon levels

Possible Improvements to Lab 2 • Double Slit

Lab 1: Entanglement and Bell’s Inequalities

Entanglement Entangled Quantum State without Entanglement • When the wave functions of two particles are coupled, or the wave functions cannot be factored apart, the particles are said to be in an entangled quantum state. • If the wave function of one state is observed, then the wave function of the second state is known

Experimental Setup EM-CCD Camera Laser λ=363. 8 nm Neutral Density Thick BBO Crystal Filter Lens Setup for Photographing Down-converted Photons Mirror Laser Blue Filter Quartz Plate BBO Crystals Polarizer A APD A Setup for Testing Bell’s Inequalities Polarizer B Beam Stop APD B

Beta Barium Borate (BBO) Crystal Down-conversion of a horizontal polarization state to two vertical polarization states Down-conversion of a vertical polarization state to two horizontal polarization states When two BBO crystals are combined, the photons that exit the second BBO crystal are in a state of quantum entanglement

Cone of Down-Converted Photons after passing through a BBO Crystal

Quartz Plate Alignment Coincidence Counts as a Function of QP Horizontal Angle 1200 Coincidence Counts 1000 800 α=0 β=0 α=45 β=45 600 α=90 β=90 400 200 0 0 20 40 60 80 100 120 140 160 QP Horizontal Angle (Degrees) Graph coincidence counts as a function of horizontal quartz plate alignment, taken 8 December 2008.

Quartz Plate Alignment Graph coincidence counts as a function of vertical quartz plate alignment, taken 8 December 2008.

Cosine Squared Dependence on Polarizer Angle Rotation 250 Coincidence Counts With One Fixed Polarizer and One Rotating Polarizer Coincidence Counts 200 150 α=90 100 50 0 0 50 100 150 200 250 300 Angle of Rotating Polarizer (Degrees) 350 400 Coincidence counts as a function of Polarizer angle from quartz plate alignment made 1 December 2008

Cosine Squared Dependence on Polarizer Angle Rotation 180 Coincidence Counts With One Fixed Polarizer and One Rotating Polarizer 160 Coincidence Counts 140 120 100 α=45 80 α=135 60 40 20 0 0 50 100 150 200 250 300 Angle of Rotating Polarizer (Degrees) 350 400 Coincidence counts as a function of Polarizer angle from quartz plate alignment made 1 December 2008

Bell’s Inequality is calculated by the following: where And N(α, β) is the number of coincidence counts for Polarizer A at angle α and Polarizer B at angle β. • If S ≤ |2|, the correlation is classical • If S ≥ |2|, the correlation violates Bell’s Inequality, implying a quantum correlation

Results of Bell’s Inequality Coincidence Counts at Various Polarization Rotation Angles for quartz plate alignment from 8 December 2008 α Coincidence Counts β Average Calculation of Bell’s Inequality Net -45 -22. 5 754 716 704 724. 6666667 311. 6667 -45 22. 5 522 507 542 523. 6666667 110. 6667 -45 67. 5 469 484 465 472. 6666667 59. 66667 -45 112. 5 691 677 639 669 256 0 -22. 5 836 761 838 811. 6666667 398. 6667 0 22. 5 750 700 716 722 309 0 67. 5 426 389 402 405. 6666667 -7. 33333 0 112. 5 525 564 526 538. 3333333 125. 3333 45 -22. 5 553 529 616 566 153 45 22. 5 701 688 684 691 278 45 67. 5 767 750 776 764. 3333333 351. 3333 45 112. 5 619 591 613 607. 6666667 194. 6667 90 -22. 5 477 439 436 450. 6666667 37. 66667 90 22. 5 484 539 520 514. 3333333 101. 3333 90 67. 5 838 798 832 822. 6666667 409. 6667 90 112. 5 779 749 727 751. 6666667 338. 6667 N(0, 90)= S= 413 E(α, β): 0. 514274838 E(α, β'): -0. 272438443 E(α', β): 0. 927662957 E(α', β'): 0. 481509722 2. 19588596

Possible Improvements to Lab 1 • Quartz Plate Mounting • Lab. View Software • Stable Alignment