Quantum Superposition Mark Van Raamsdonk. The Quantum World All matter made of elementary particles...
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Transcript of Quantum Superposition Mark Van Raamsdonk. The Quantum World All matter made of elementary particles...
![Page 1: Quantum Superposition Mark Van Raamsdonk. The Quantum World All matter made of elementary particles Modern physics: understand in detail how nature works.](https://reader035.fdocuments.us/reader035/viewer/2022070410/56649f065503460f94c1c917/html5/thumbnails/1.jpg)
Quantum Superposition
Mark Van Raamsdonk
![Page 2: Quantum Superposition Mark Van Raamsdonk. The Quantum World All matter made of elementary particles Modern physics: understand in detail how nature works.](https://reader035.fdocuments.us/reader035/viewer/2022070410/56649f065503460f94c1c917/html5/thumbnails/2.jpg)
The Quantum World
All matter made of elementary particles
Modern physics: understand in detail how nature works at distances 100,000,000,000,000 times smaller than we can see!
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Classical physics fails at these distance
scales
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Orbiting charge would produce EM radiation
This carries away energy
Electron losing energy spirals into nucleus
Atoms would be unstable by classical rules
All atoms would cease to exist in a nanosecond
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The double slit experiment
Bright line appears directly between the slits, with other bright lines to the sides
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Explain via wave interference
Recall: light is a wave of oscillating electric and magnetic fields
Oscillating electric field
Oscillating magnetic field
James Clerk Maxwell 1864
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Light waves from two slits add up to make bright central line
Constructive Interference
In this direction, light from two slits is “out of phase” and cancels
Destructive Interference
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CRUCIAL POINT:
Pattern on screen results from combination of light waves from the two different slits.
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Surprise: same result for electrons
XXXXELECTRON
XXXX
XXXX
more electrons
less electrons
Electrons behave like waves??
Interference between different electrons going through the two slits?? (No!)
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Bigger surprise: same pattern when we send in one at a time!
Each electron can “see” both slits!
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Explanation: quantum superpositionelectrons can be in two places at once!
Electron at a definite location
Single electron at a superpositionof two locations
Single electron at a superpositionof many locations
Electron in superposition has no definite location until we measure it
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The wavefunction
Mathematically, we describe a quantum superposition by a function x)
is larger/smaller in magnitude in places where we are more/less likely to find electron
largest here
zero here
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Schrodinger’s Equation
Determines how wavefunctionswill evolve with time
Correctly explains double slit experiment in terms of single electrons
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A model of atoms
Schrodinger’s equation shows that electrons can exist in stable configurations around nuclei
Wavefunctions and energies for these configurations determine most properties of matter
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Mysterious spectrum of light from atomsand all other puzzles completely explained
Hydrogen Helium Neon
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Key idea: quantum superposition
For any two allowed states of any quantum system, the system can exist in
a state which is the