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Single Photon Interference

Single Photon Interference. Jeff, Jacob, Bryce, Edward, and Julie. Young’s Double Slit Experiment. YAY!. What is it?. First conducted in 1801 by Thomas Young Light passed through a barrier with two slits (before it usually passed through a single slit to make the light coherent)

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Single Photon Interference

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  1. Single Photon Interference Jeff, Jacob, Bryce, Edward, and Julie

  2. Young’s Double Slit Experiment YAY!

  3. What is it? • First conducted in 1801 by Thomas Young • Light passed through a barrier with two slits (before it usually passed through a single slit to make the light coherent) • The light diffracted through each slit • Created interference pattern • In order to interfere the light that passes through the slit must be of the same frequency and polarization and it must be coherent

  4. Particles vs. Waves Particle Wave The light will diffract and interfere, making many fringes • If light acts as a particle, only two slits will appear on the screen

  5. Why is this important? • This proves light acts not only as a particle, but also as a wave!

  6. Equations for the Fringes

  7. Many Photon Interference Acquisition Time: .1 sec Attenuation: 3 optical depths Amplification: x1

  8. Single Photon • When a single photon is used, wave interference is still present • It is impossible for a photon to act as a wave as it is can only go through one slit • If one slit is blocked, there is no interference

  9. Energy of a Single Photon

  10. Power of 1 photon per meter • P=9.421∗10−11W • The power of our laser is • P=9.1∗10−7W • So we use 3 optical depths to attenuate the beam to single photon energy levels.

  11. Single Photon Interference Acquisition Time: .1 sec Attenuation: 3 optical depths Amplification: x100

  12. Single Photon Interference Acquisition Time: .1 sec Attenuation: 3 optical depths Amplification: x200

  13. Single Photon Interference Acquisition Time: 1 sec Attenuation: 3 optical depths Amplification: x100

  14. Interferometry Mach-Zehnder Interferometer

  15. Power of 1 photon per meter • P=9.421∗10−11W • The power of our laser is • P=6.17∗10−5W • So we use 5 optical depths to attenuate the beam to single photon energy levels.

  16. Strong field Acquisition Time: .1sec Attenuation: 5 optical depths Amplification: x100

  17. Single Photon Acquisition Time: .1 sec Attenuation: 5 optical depths Amplification: x100

  18. Single Photon – Horizontal Polarization Blocked Acquisition Time: .1 sec Attenuation: 5 optical depths Amplification: x100

  19. Single Photon – Vertical Polarization Blocked Acquisition Time: .1 sec Attenuation: 5 optical depths Amplification: x100

  20. Important Observations • When path of photon is unknown, fringes are observed • When path of photon is known, fringes are not observed

  21. Summary • Young’s Double Slit Experiment • Fringes were observed under high intensity, as well as with only a single photon. • Interferometer • Fringes were observed under high intensity as well as with only a single photon. • When either path of the interferometer was blocked, fringes were not observed.

  22. What Problems Did We Encounter? Single Photon Interference Acquisition Time: .1 sec Attenuation: 5 optical depths Amplification: x100

  23. Conclusion • Single photons behaved the same way as the high intensity beam. • In the double slit experiment, the single photon appeared to interfere with itself – going through both slit simultaneously. • In the interferometer the single photon appeared to take both paths simultaneously – blocking a path removed interference fringes.

  24. Sources • http://www.studyphysics.ca/newnotes/20/unit04_light/chp1719_light/lesson58.htm • http://dev.physicslab.org/asp/applets/doubleslit/default.asp • http://physics.about.com/od/lightoptics/a/doubleslit.htm • http://www.physics.brown.edu/physics/demopages/Demo/modern/demo/7a5520.htm • The book – Seeing the Light

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