Quantum Reality

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• Quantum Reality
• Avshalom C. Elitzur
• avshalom.elitzur_at_weizmann.ac.il
• Outline
• The Nature of Classical light
• Light going Quantum
• Universal Duality
• Quantum Non-Locality
• Mysteries and Potential Applications

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to everyone to copy and/or use this work or any
part of it.
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Determinism An extremely Powerful Idea
Philosophiae Naturalis Principia Mathematica
(1687)
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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.
Earths gravitational constant
initial height
time
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Whats light?
Its made of particles
I. Newton, 1643-1727
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Whats light?
Its made of waves
C. Huygens, 1629-1695
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Light, then, is
Waves!!!
Waves!!
Waves!!
Waves!
Particles!!!
Particles!!
Particles!!
Particles!
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Why does the light ray widen after passing a
slit?
diffraction!!!
Diffraction!!
dispersal!!!
diffraction!
dispersal!
diffraction!
dispersal!
dispersal!
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Whats light?
Its waves (I conducted a simple experiment)
Hes right (I proved its electromagnetism)
T. Young, 1773-1829
J. C. Maxwell, 1831-1879
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crest
trough
in phase
crest
constructive interference
trough
Classical Interference
crest
trough
destructive interference
out of phase
crest
trough
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The Double-Slit Experiment
Water waves interference
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The Double-Slit Experiment (Courtesy of
Tel-Aviv Municipality)
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The Double-Slit Experiment
Light interference
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The Father of Quantum Mechanics
M. Planck 1858-1947
Energy comes in discrete units
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Whats light?
Its particles (they gave me the Nobel for that)
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Whats light?
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Whats light?
Waves, eh?
1 Quantum
1 Quantum
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Whats light?
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Whats light?
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Whats light?
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Whats light?
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Confused? Dont worry!
It will soon become much worse
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Whats Matter?
Its waves (They gave me a Nobel too)
L. de Broglie (1892-1987)
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Whats Matter?
Why?
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Whats Matter?
Electrons revolve only in orbits where waves can
reside
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Whats Matter?
Hence, you can demonstrate interference with

• Photons
• Electrons
• Protons
• Neutrons (Zeilinger)
• Atoms (Zeilinger)
• Molecules (Zeilinger)
• ... (Zeilinger?)

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Your student has lifted the Margins of a great
veil
O la la
Einstein
Langevin
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The Wave-Particle Duality
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Whats light/matter?
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Whats light/matter?
Erwin Schrödinger (1887-1961)
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The Famous Dialogue
Niels Bohr (1885-1962)
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A harmless thought experiment Wheres the single
photon before being detected?
detector
detector
50
50
half-silvered mirror
light source
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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.

detectors
D
C
light source
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Confused? Dont worry
It will soon get much worse.
Interference occurs with single
Can we outsmart the which path uncertainty?

1. Photons
2. Electrons
3. Neutrons
4. Atoms
5. Molecules

Interference
0
100
1
0
1
0
50
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Can we outsmart the which path uncertainty?
Interference
0
100
50
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Can we outsmart the which path uncertainty?
50
50
50
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Can we outsmart the which path uncertainty?
50
50
50
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Can we outsmart the which path uncertainty?
Interference
0
100
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Can we outsmart the which path uncertainty? No,
but
Nam et Ipsa
Potestas Est
Ignorantia
Scientia
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?????? ??-??????? "?? ???? ??? ?? ??? ???
????"(??? ?? ?????)
50
50
100
0
100
0
?? ???????
??? ???????
50
50
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?? ???? ?? ???? ?? ???? ????

1. ?-50 ??????? ????? ????,
2. ?? ????? ??????? ??? ?????,
3. ????, ??-?? ?????? ??-???????, ???????? ?????.
4. ??? ?-50 ??????? ?? ????? ????
5. ??? ?????? ??? ?????.
6. ??? ???????? ????? ?? ????? (??? ?????? ??? ????
   ??? ???? ?? ????? ?????? ??-??????? ? )
7. ??? ?????? ???? ??????? ?? ????? ????? ?? ?????
   ??? ????? ????? ??? ????? ?????????
8. ?? ?????? ?? ?? ??? ??? ???? "????"
9. ?"????" ?????? (??? ?????, ??? ????, ????????
   ????? ?????) ????? ???? Nothing
10. ????? ????? ??????? (?? ?????, ???? ??? ?????
    ????, ??? ???, ???? ???????? ?????) ?????
    ????...
11. Gurnisht

...
????!
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????? ??????-?????? 1993
??? ??? ?? ????? "????" ??? ????? ?????

1. ????? ????
2. ???? ??????
3. "?????" ??? ?? ????? ?????
4. ???!

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????? ??????-?????? 1993

1. ????? ????
2. ???? ?????? ?????? ?????
3. ????? ??? ????? (Gurnisht)
4. ????? ?????? ????? ?????? ??????
5. ????? ?"????" ????? ????
6. ????? ????!

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Interaction-Free Measurement (Elitzur Vaidman,
1993)

• When a bomb is inserted, scenario 1

D
C

1. Photon emitted
2. Split
3. Collapse
4. Boom!

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Interaction-Free Measurement

• When a bomb is inserted, scenario 2

D
C

1. Photon emitted
2. Split
3. No Boom
4. Remaining wave split
5. Forbidden detector D might click
6. Zeilinger et al., 1995 Efficiency brought close
   to 100

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The EPR Bell experiment

• Spin
• Turning the magnets by an angle ?

Stern Gerlach
P Cos2(2?)
P 1-Cos2(2?)
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The EPR Bell experiment

• EPR system
• The two particles spin is always correlated
  (opposite)
• Unless we rotate one of the magnets

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EPR Bell experiment

• Rotate right hand magnet by 300 Spin
  correlations drop to 75
• Rotate left hand magnet by 300 Spin correlations
  drop to 75
• Rotating the two magnets in opposite directions
  Spin correlations drop to
• 25!
• No realist explanation without action at a
  distance

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EPR Bell experiment
Measured Directions Measured Directions Correlation









00
100
00
100
300
300
300-
300-
100
300
75
00
300-
75
00
00
300
75
300-
75
00
25
300-
300
300-
25
300
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Quantum Paradoxes

• The Wave-Particle Duality
• The Quantum-Classical Limit
• Quantum Non-Locality

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Attempts at Resolution

1. Copenhagen Bohr, Heisenberg, Wheeler
2. Hidden Variables de Broglie, Bohm
3. Consciousness von Neumann, Wigner
4. Many Worlds Everett, Wheeler
5. Retrocausal Models Aharonov, Cramer

Scientific Alternatives

1. Spontaneous Collapse Ghirardi, Rimini Weber
2. Decoherence Zurek
3. Gravity Penrose

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Quantum Technology

• Quantum Chemistry
• Quantum Optics
• Transistors
• Quantum Cryptography
• Quantum Computation
• Quantum Imaging
• Quantum Teleportation

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Broader Implications

• Quantum Cosmology
• Quantum Biology?
• Quantum Mind?

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Quo Vadis Quantum Mechanics? A. C. Elitzur, S.
Dolev N. Kolenda, EdsSpringer Verlag, 2005