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


What’s light?

It’s made of particles

I. Newton, 1643-1727


What’s light?

It’s made of waves

C. Huygens, 1629-1695


Light, then, is…

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!


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


crest

trough

“in phase”

crest

constructive

interference

trough

Classical Interference

crest

trough

destructive

interference

“out of phase”

crest

trough


The Double-Slit Experiment

Water waves interference


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

Constructive interference

Destructive

Constructive


The Double-Slit Experiment

Light interference


Farewell Classical Physics


And Welcome…

George Koch


The Father of Quantum Mechanics

M. Planck

1858-1947

Energy comes in discrete units


What’s light?

It’s particles

(they gave me the Nobel for that)


What’s light?


What’s light?

Waves, eh?

Newton

1 Quantum

1 Quantum


What’s light?

1 Quantum


What’s light?


What’s light?


Confused? Don’t worry!

It will soon become much worse…


What’s Matter?

It’s waves

(They gave me a Nobel too)

L. de Broglie (1892-1987)


What’s Matter?

In the solar system, planets can move in any orbit

Why?

In the atom, electrons can move only in certain orbits


What’s Matter?

Electrons revolve only in orbits where waves can reside


What’s Matter?

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


The Wave-Particle Duality


What’s light/matter?


What’s light/matter?

ErwinSchrödinger (1887-1961)


The Famous Dialogue

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


The Mach-Zehnder Interferometer:

detectors

C

D

half-silvered mirrors

solid mirrors

light source


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


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


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


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%


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!


Can we outsmart the uncertainty principle?

Yes we can!


Aharonov’s “weak measurement


x

x

x

The EPR – Bell experiment

Spin

Turning the magnets byan angle :

Stern Gerlach

P =Cos2(2)

P =1-Cos2(2)


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


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


EPR – Bell experiment

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


Quantum Paradoxes

  • The Wave-Particle Duality

  • The Quantum-Classical Limit

  • Quantum Non-Locality


Attempts at Resolution

  • 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 Technology

  • Quantum Chemistry

  • Quantum Optics

  • Transistors

  • Quantum Cryptography

  • Quantum Computation

  • Quantum Imaging

  • Quantum Teleportation


Broader Implications

  • Quantum Cosmology

  • Quantum Biology?

  • Quantum Mind?


Quo Vadis Quantum Mechanics?

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


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