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Big Questions in Science
Big Questions in Science, fall 2012. SdH, AUC   2
Big Questions in Science, fall 2012. SdH, AUC   3
Stern-Gerlach experiment    http://www.upscale.utoronto.ca/PVB/Harrison/SternGerlach/SternGerlach.htmlBig Questions in Sci...
   Superpositions of electrons:              Big Questions in Science, fall 2012. SdH, AUC   5
   Radiatioactive decay is random.   Same true for photon emission by atom:    unpredictable.             Big Questions ...
Wave pulse          Traveling wave                                                        Position well-definedFrequency (...
   Planck’s constant:     The larger the object, the smaller the uncertainty.   For large objects, probabilities are sh...
   Quantum physics seem to have bearing on    music as well. Anyone whos ever played in a    blues band will confirm that...
• First bank transfer encoded via quantum  crypto for entangled photons• Information via glass fiber cable from  Vienna Ci...
“God does not play dice”Big Questions in Science, fall 2012. SdH, AUC                      11
   Determinism: “I would always be able to keep my    deterministic faith for fundamental phenomena” (Lorentz)   Causali...
Big Questions in Science, fall 2012. SdH, AUC   13
Big Questions in Science, fall 2012. SdH, AUC   14
Einstein:• No influences faster than light.• Particle must have velocity  before measurement.• Violation of• Quantum mecha...
   There is no faster-than-light interaction in    this experiment.   Experimental set-up defines the meaning of    ‘vel...
   Faster-than-light interaction is not needed.    We only have correlations.   Entanglement: particles correlated and  ...
Big Questions in Science, fall 2012. SdH, AUC   18
Big Questions in Science, fall 2012. SdH, AUC   20
• First bank transfer encoded via quantum  crypto for entangled photons• Information via glass fiber cable from  Vienna Ci...
   Record: 144 km in La Palma, Tenerife              Big Questions in Science, fall 2012. SdH, AUC   22
110100010                                        110100010      Share a randomly generated key Big Questions in Science, f...
Big Questions in Science, fall 2012. SdH, AUC   25
   Can be used for secure communication.   Eavesdropper destroys correlations.             Big Questions in Science, fal...
   Photons:               Big Questions in Science, fall 2012. SdH, AUC   27
Big Questions in Science, fall 2012. SdH, AUC   28
   Interference means change   No possible ‘unvisible’ eavesdropper   Applications:     Banking     Confident informa...
   Counter-intuitive aspects:     “If you are not confused by quantum physics then you      haven’t really understood it...
Big Questions in Science, fall 2012. SdH, AUC   32
   Complementarity: waves and particles   Interference, superpositions   Heisenberg’s uncertainty principle   Probabil...
Our cosmic origins         Time and relativity                                            Atoms, forces          Modern sc...
   Outline (or summarize in a diagram) EPR’s line of    argument against quantum mechanics.     What where they contendi...
 Download from BB: “Transgressing the Boundaries”. Skim through the paper. Have a quick look at the  introduction and fi...
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7 Quantum Universe. Quantum Communication

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Big Questions in Science series, (7 of 9). Class taught at AUC (University of Amsterdam) during the 2012-2013 fall semester.

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Transcript of "7 Quantum Universe. Quantum Communication"

  1. 1. Big Questions in Science
  2. 2. Big Questions in Science, fall 2012. SdH, AUC 2
  3. 3. Big Questions in Science, fall 2012. SdH, AUC 3
  4. 4. Stern-Gerlach experiment http://www.upscale.utoronto.ca/PVB/Harrison/SternGerlach/SternGerlach.htmlBig Questions in Science, fall 2012. SdH, AUC 4
  5. 5.  Superpositions of electrons: Big Questions in Science, fall 2012. SdH, AUC 5
  6. 6.  Radiatioactive decay is random. Same true for photon emission by atom: unpredictable. Big Questions in Science, fall 2012. SdH, AUC 6
  7. 7. Wave pulse Traveling wave Position well-definedFrequency (and velocity) well-defined Frequency (and velocity) ill-defined Position ill-defined Planck’s constant: Big Questions in Science, fall 2012. SdH, AUC 7
  8. 8.  Planck’s constant:  The larger the object, the smaller the uncertainty. For large objects, probabilities are sharply peaked. Big Questions in Science, fall 2012. SdH, AUC 8
  9. 9.  Quantum physics seem to have bearing on music as well. Anyone whos ever played in a blues band will confirm that, while you know where the drummer is (in the pub), theres no way of knowing what time he will show up for rehearsal (or sound check, or whatever). This is known in quantum mechanics as Heisenbergs Uncertainty Principle : "The more precisely the POSITION is determined, the less precisely the MOMENTUM is known". Big Questions in Science, fall 2012. SdH, AUC 9
  10. 10. • First bank transfer encoded via quantum crypto for entangled photons• Information via glass fiber cable from Vienna City Hall to Bank Austria Creditanstalt branch office “Schottengasse” Big Questions in Science, fall 2012. SdH, AUC 10
  11. 11. “God does not play dice”Big Questions in Science, fall 2012. SdH, AUC 11
  12. 12.  Determinism: “I would always be able to keep my deterministic faith for fundamental phenomena” (Lorentz) Causality Can compute, but what does it mean? “If I am not satisfied with current state of problem it is because I do not understand yet physical meaning of its solution. What Heisenberg has said is mathematically unexceptionable, but the point in question is that of physical interpretation” (Schrödinger). “Anschaulichkeit”: “The way Dirac has formulated Schrödinger’s theory [leads to] a more advanced renunciation of Anschaulichkeit, a fact very characteristic of symbolic methods in quantum theory” (Bohr). Big Questions in Science, fall 2012. SdH, AUC 12
  13. 13. Big Questions in Science, fall 2012. SdH, AUC 13
  14. 14. Big Questions in Science, fall 2012. SdH, AUC 14
  15. 15. Einstein:• No influences faster than light.• Particle must have velocity before measurement.• Violation of• Quantum mechanics is incomplete. Big Questions in Science, fall 2012. SdH, AUC 15
  16. 16.  There is no faster-than-light interaction in this experiment. Experimental set-up defines the meaning of ‘velocity’. Change in position: from ‘to measure is to interact’ to ‘measurement context’. Big Questions in Science, fall 2012. SdH, AUC 16
  17. 17.  Faster-than-light interaction is not needed. We only have correlations. Entanglement: particles correlated and system behaves as a whole rather than sum of parts. Bell’s theorem (‘64): If velocities defined before measured, this implies certain inequality. QM violates this: experiment confirms quantum mechanics (Aspect ‘82). Big Questions in Science, fall 2012. SdH, AUC 17
  18. 18. Big Questions in Science, fall 2012. SdH, AUC 18
  19. 19. Big Questions in Science, fall 2012. SdH, AUC 20
  20. 20. • First bank transfer encoded via quantum crypto for entangled photons• Information via glass fiber cable from Vienna City Hall to Bank Austria Creditanstalt branch office “Schottengasse” 21
  21. 21.  Record: 144 km in La Palma, Tenerife Big Questions in Science, fall 2012. SdH, AUC 22
  22. 22. 110100010 110100010 Share a randomly generated key Big Questions in Science, fall 2012. SdH, AUC 24
  23. 23. Big Questions in Science, fall 2012. SdH, AUC 25
  24. 24.  Can be used for secure communication. Eavesdropper destroys correlations. Big Questions in Science, fall 2012. SdH, AUC 26
  25. 25.  Photons: Big Questions in Science, fall 2012. SdH, AUC 27
  26. 26. Big Questions in Science, fall 2012. SdH, AUC 28
  27. 27.  Interference means change No possible ‘unvisible’ eavesdropper Applications:  Banking  Confident information Collaboration fundamental research with industry (and government). Key feature: entanglement (“spooky action at a distance”) Big Questions in Science, fall 2012. SdH, AUC 29
  28. 28.  Counter-intuitive aspects:  “If you are not confused by quantum physics then you haven’t really understood it.” (Niels Bohr)  “I think I can safely say that nobody understands quantum mechanics.” (Richard Feynman).  After WWII: “Shut up and calculate”.  Imposed by increasing numbers of students: “Such classroom numbers, Berkeley’s department chair exclaimed to his dean, were ‘a disgrace and should not be tolerated at any respectable university’… The larger the class, the less time spent talking through the big issues.” (David Kaiser) Big Questions in Science, fall 2012. SdH, AUC 30
  29. 29. Big Questions in Science, fall 2012. SdH, AUC 32
  30. 30.  Complementarity: waves and particles Interference, superpositions Heisenberg’s uncertainty principle Probability No determinism Applications: cryptography, quantum computing Big Questions in Science, fall 2012. SdH, AUC 33
  31. 31. Our cosmic origins Time and relativity Atoms, forces Modern science Radiation and QM Classical physics fall 2012. SdH, AUCBig Questions in Science, spring 2012. SdH, AUC 34
  32. 32.  Outline (or summarize in a diagram) EPR’s line of argument against quantum mechanics.  What where they contending?  Describe the experiment in a few lines.  What were the key concepts and what do they mean?  What assumptions did they make?  How did they arrive at their conclusion? Can you reformulate the paradox in terms of spin? Big Questions in Science, fall 2012. SdH, AUC 35
  33. 33.  Download from BB: “Transgressing the Boundaries”. Skim through the paper. Have a quick look at the introduction and first section. Questions:1. What is, according to the introduction, the relation between physics and power?2. What is the announced aim of the paper?3. Do the sections have any particular structure (argumentative, logical, etc.)?4. Are any of the suggested arguments convincing?5. What, in your opinion, is the author trying to argue? Big Questions in Science, fall 2012. SdH, AUC 36
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