Quantum Reality

1. Quantum Reality Avshalom C. Elitzur Outline • The Nature of Classical light • Light going Quantum • Universal Duality • Quantum Non-Locality • Mysteries and Potential Applications Copyleft – All Rights Reversed Permission is granted to everyone to copy and/or use this work or any part of it.

2. Determinism: An extremely Powerful Idea Philosophiae Naturalis Principia Mathematica (1687)

3. Philosophiae Naturalis Principia Mathematica (1687) In every physical state, given the relevant law and initial conditions, it is possible to predict other states at any time in the past or future. Earth’s gravitational constant initial height time

4. What’s light? It’s made of particles I. Newton, 1643-1727

6. What’s light? It’s made of waves C. Huygens, 1629-1695

8. Light, then, is… Waves!!! Waves!! Waves!! Waves! Particles!!! Particles!! Particles!! Particles!

9. Why does the light ray widen after passing a slit? diffraction!!! Diffraction!! dispersal!!! diffraction! dispersal! diffraction! dispersal! dispersal!

10. What’s light? It’s waves (I conducted a simple experiment) He’s right (I proved it’s electromagnetism) T. Young, 1773-1829 J. C. Maxwell, 1831-1879

11. crest trough “in phase” crest constructive interference trough Classical Interference crest trough destructive interference “out of phase” crest trough

12. The Double-Slit Experiment Water waves interference

13. Interference of Water Waves(Courtesy of Tel-Aviv Municipality) Constructive interference Destructive Constructive

14. The Double-Slit Experiment Light interference

15. Farewell Classical Physics

16. And Welcome… George Koch

17. The Father of Quantum Mechanics M. Planck 1858-1947 Energy comes in discrete units

18. What’s light? It’s particles (they gave me the Nobel for that)

19. What’s light?

20. What’s light? Waves, eh? Newton 1 Quantum 1 Quantum

21. What’s light? 1 Quantum

22. What’s light?

23. What’s light?

24. Confused? Don’t worry! It will soon become much worse…

25. What’s Matter? It’s waves (They gave me a Nobel too) L. de Broglie (1892-1987)

26. What’s Matter? In the solar system, planets can move in any orbit Why? In the atom, electrons can move only in certain orbits

27. What’s Matter? Electrons revolve only in orbits where waves can reside

28. What’s Matter? Hence, you can demonstrate interference with • Photons • Electrons • Protons • Neutrons (Zeilinger) • Atoms (Zeilinger) • Molecules (Zeilinger) • ... (Zeilinger?)

29. Le travail de Louis de Broglie a fait une grande impression sur moi; il a levé un coin du grand voile (he has lifted the corner of a great veil). O la la… Einstein Langevin

30. The Wave-Particle Duality

31. What’s light/matter?

32. What’s light/matter? ErwinSchrödinger (1887-1961)

33. The Famous Dialogue Niels Bohr (1885-1962)

34. A harmless thought experiment: Where’s the single photon before being detected? detector detector 50% 50% half-silvered mirror light source

35. The Mach-Zehnder Interferometer: detectors C D half-silvered mirrors solid mirrors light source

36. The Mach-Zehnder Interferometer: • Light-ray is emitted and split into two: The reflected half undergoes phase-reflection, while the transmitted half undergoes phase-shift. • Two halves reflected back (plus phase ) • One half split again • Second half split again (at the same time) • Destructive interference on detector D • Constructive interference on detector C • All light reaches detector C. C D

37. The Mach-Zehnder Interferometer: • Photon is emitted and split into two • Reflected back (notice phase shift upon reflection!) • One half split again • Second half split again (at the same time) • Destructive Interference on detector D • Constructive Interference on detector C • All light reaches detector C. C D

38. Confused? Don’t worry: It will soon get much worse. Interference occurs with single Can we outsmart the “which path” uncertainty? • Photons • Electrons • Neutrons • Atoms • Molecules • … Interference 0% 100% 1 0 1 0 50%

39. Can we outsmart the “which path” uncertainty? Interference 0% 100% 50%

40. Can we outsmart the “which path” uncertainty? 50% 50% 50%

41. Can we outsmart the “which path” uncertainty? 50% 50% 50%

42. Can we outsmart the “which path” uncertainty? Interference 0% 100%

43. Can we outsmart the “which path” uncertainty? No, but Nam et Ipsa Ignorantia Scientia Potestas Est

44. עיקרון אי-הוודאות: "דע מאין באת – או לאן אתה הולך"(אבל לא שניהם) 0% 100% 50% 0% 100% 50% אין התאבכות יש התאבכות 50% 50%

45. What if we place only one detector? • In 50% of the cases a click will sound, • I.e., the photon has taken the right path, • hence, by the uncertainty principle, interference must be destroyed. • But in 50% cases no click will occur, • hence the photon took left. • Will interference be destroyed too? (Clue: Elitzur hasn’t been awarded the Nobel for disproving the uncertainty principle ) • For comparison: Suppose the single detector’s battery is off: Will a click be sound? Will interference be destroyed? • We must therefore distinguish between two negative results: • The classical one (no battery, no click, interference remains intact) should be called Nothing. • Whereas the quantum one (battery present, no click, interference destroyed) should be called… • Gurnisht. ... Click!

47. Can we outsmart the uncertainty principle? Yes we can!

48. Aharonov’s “weak measurement

49. x x x The EPR – Bell experiment Spin Turning the magnets byan angle : Stern Gerlach P =Cos2(2) P =1-Cos2(2)

50. x x x x The EPR – Bell experiment • EPR system: • The two particles’ spin is always correlated (opposite) • Unless we rotate one of the magnets