Single Photon Interference

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Single Photon Interference

• Jeff, Jacob, Bryce, Edward, and Julie

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Youngs Double Slit Experiment

• YAY!

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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

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Particles vs. Waves

• Particle

• Wave

• If light acts as a particle, only two slits will
  appear on the screen

• The light will diffract and interfere, making
  many fringes

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Why is this important?

• This proves light acts not only as a particle,
  but also as a wave!

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Equations for the Fringes
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Many Photon Interference Acquisition Time .1
sec Attenuation 3 optical depths Amplification
x1
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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

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Energy of a Single Photon
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• Power of 1 photon per meter
• P9.42110-11W
• The power of our laser is
• P9.110-7W
• So we use 3 optical depths to attenuate the beam
  to single photon energy levels.

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Single Photon Interference Acquisition Time .1
sec Attenuation 3 optical depths Amplification
x100
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Single Photon Interference Acquisition Time .1
sec Attenuation 3 optical depths Amplification
x200
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Single Photon Interference Acquisition Time 1
sec Attenuation 3 optical depths Amplification
x100
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Interferometry
Mach-Zehnder Interferometer
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• Power of 1 photon per meter
• P9.42110-11W
• The power of our laser is
• P6.1710-5W
• So we use 5 optical depths to attenuate the beam
  to single photon energy levels.

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Strong field Acquisition Time .1sec Attenuation
5 optical depths Amplification x100
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Single Photon Acquisition Time .1
sec Attenuation 5 optical depths Amplification
x100
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Single Photon Horizontal Polarization
Blocked Acquisition Time .1 sec Attenuation 5
optical depths Amplification x100
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Single Photon Vertical Polarization
Blocked Acquisition Time .1 sec Attenuation 5
optical depths Amplification x100
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Important Observations

• When path of photon is unknown, fringes are
  observed
• When path of photon is known, fringes are not
  observed

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Summary

• Youngs 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.

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

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Sources

• http//www.studyphysics.ca/newnotes/20/unit04_ligh
  t/chp1719_light/lesson58.htm
• http//dev.physicslab.org/asp/applets/doubleslit/d
  efault.asp
• http//physics.about.com/od/lightoptics/a/doublesl
  it.htm
• http//www.physics.brown.edu/physics/demopages/Dem
  o/modern/demo/7a5520.htm
• The book Seeing the Light