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Introduction to quantum mechanics Copyleft

Quantum Reality

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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.

Determinism: An extremely Powerful Idea

Philosophiae Naturalis Principia Mathematica (1687)

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

It’s made of particles

I. Newton, 1643-1727

It’s made of waves

C. Huygens, 1629-1695

Waves!!!

Waves!!

Waves!!

Waves!

Particles!!!

Particles!!

Particles!!

Particles!

Why does the light ray widen after passing a slit?

diffraction!!!

Diffraction!!

dispersal!!!

diffraction!

dispersal!

diffraction!

dispersal!

dispersal!

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

crest

trough

“in phase”

crest

constructive

interference

trough

Classical Interference

crest

trough

destructive

interference

“out of phase”

crest

trough

Water waves interference

Interference of Water Waves(Courtesy of Tel-Aviv Municipality)

Constructive interference

Destructive

Constructive

Light interference

Farewell Classical Physics

And Welcome…

George Koch

The Father of Quantum Mechanics

M. Planck

1858-1947

Energy comes in discrete units

It’s particles

(they gave me the Nobel for that)

Waves, eh?

Newton

1 Quantum

1 Quantum

1 Quantum

Confused? Don’t worry!

It will soon become much worse…

It’s waves

(They gave me a Nobel too)

L. de Broglie (1892-1987)

In the solar system, planets can move in any orbit

Why?

In the atom, electrons can move only in certain orbits

Electrons revolve only in orbits where waves can reside

Hence, you can demonstrate interference with

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

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

ErwinSchrödinger (1887-1961)

Niels Bohr (1885-1962)

A harmless thought experiment:

Where’s the single photon before being detected?

detector

detector

50%

50%

half-silvered mirror

light source

detectors

C

D

half-silvered mirrors

solid mirrors

light source

- 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

- 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

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%

Can we outsmart the “which path” uncertainty?

Interference

0%

100%

50%

Can we outsmart the “which path” uncertainty?

50%

50%

50%

Can we outsmart the “which path” uncertainty?

50%

50%

50%

Can we outsmart the “which path” uncertainty?

Interference

0%

100%

Can we outsmart the “which path” uncertainty? No, but

Nam et Ipsa

Ignorantia

Scientia

Potestas Est

0%

100%

50%

0%

100%

50%

אין התאבכות

יש התאבכות

50%

50%

- 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!

Can we outsmart the uncertainty principle?

Yes we can!

Aharonov’s “weak measurement

x

x

x

Spin

Turning the magnets byan angle :

Stern Gerlach

P =Cos2(2)

P =1-Cos2(2)

x

x

x

x

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

- 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

00

100%

00

100%

300

300

300-

300-

100%

75%

300

00

75%

300-

00

00

75%

300

300-

00

75%

300-

25%

300

25%

300-

300

YakirAharonov

Lev Vaidman

Benni Reznik

Sandu Popescu

AvshalomElitzur

Daniel Rohrlich

Jeff Tollaksen

David Albert

BoazTamir

OrSela

Shahar Dolev

Doron Grossman

Einav Friedman

ShayBen Moshe

EliahuCohen

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

- Copenhagen: Bohr, Heisenberg, Wheeler
- Hidden Variables: de Broglie, Bohm
- Consciousness: von Neumann, Wigner
- Many Worlds: Everett, Wheeler
- Retrocausal Models: Aharonov, Cramer

Scientific Alternatives

Spontaneous Collapse: Ghirardi, Rimini & Weber

Decoherence: Zurek

Gravity: Penrose

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

- Quantum Cosmology
- Quantum Biology?
- Quantum Mind?

Quo Vadis Quantum Mechanics?

A. C. Elitzur, S. Dolev & N. Kolenda, EdsSpringer Verlag, 2005