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Single Photon Interference
Jeff, Jacob, Bryce, Edward, and Julie
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Young’s Double Slit ExperimentYAY!
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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 If light acts as a
particle, only two slits will appear on the screen
Wave 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 InterferenceAcquisition Time: .1 secAttenuation: 3 optical depthsAmplification: 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 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.
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Single Photon InterferenceAcquisition Time: .1 secAttenuation: 3 optical depthsAmplification: x100
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Single Photon InterferenceAcquisition Time: .1 secAttenuation: 3 optical depthsAmplification: x200
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Single Photon InterferenceAcquisition Time: 1 secAttenuation: 3 optical depthsAmplification: x100
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Interferometry
Mach-Zehnder Interferometer
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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.
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Strong fieldAcquisition Time: .1secAttenuation: 5 optical depthsAmplification: x100
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Single PhotonAcquisition Time: .1 secAttenuation: 5 optical depthsAmplification: x100
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Single Photon – Horizontal Polarization BlockedAcquisition Time: .1 secAttenuation: 5 optical depthsAmplification: x100
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Single Photon – Vertical Polarization BlockedAcquisition Time: .1 secAttenuation: 5 optical depthsAmplification: 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 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.
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What Problems Did We Encounter?
Single Photon InterferenceAcquisition Time: .1 secAttenuation: 5 optical depthsAmplification: 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_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