Introduction to Quantum Physics

Key Points

• Quantum physics is often perceived as complicated.
• Richard Feynman:
  • Claimed if you feel you understand quantum physics, you don't.
  • This quote can be misleading; we do understand quantum physics quite well.

Importance of Quantum Physics

• Essential for technologies like computers, cameras, LED screens, lasers, nuclear power plants.
• Describes the smallest things in the universe: molecules, atoms, subatomic particles.
• Everything is fundamentally made from quantum physics.

Basic Concepts

Wave-Particle Duality

• Particles like electrons are described as waves (wave functions).
• Wave function: abstract mathematical description, not a physical wave.
• Probability distributions: Tell the likelihood of finding particles in certain positions or with certain momenta.
• Measurement collapses the wave function, showing the particle as a point.

Measurement Problem

• No physics to describe how wave function collapses upon measurement.
• This gap is called the measurement problem.

Double Slit Experiment

• Demonstrates wave-particle duality.
• Electrons fired one at a time through two slits create an interference pattern over time.
• Shows electrons act as waves when not measured, and as particles when measured.

Key Phenomena

Superposition

• Particles can exist in multiple states (positions, energies) simultaneously.
• Example: Electrons can have a probability of being in two places at once.

Entanglement

• When two particles become linked, their properties are interdependent, even over large distances.
• Nonlocality: A measurement on one particle affects the other instantly.
• Doesn’t allow faster-than-light communication due to randomness.

Quantum Tunneling

• Particles can pass through barriers they seemingly shouldn't be able to.
• Essential for processes like fusion in the Sun.

Heisenberg Uncertainty Principle

• Position and momentum of a particle cannot both be measured exactly simultaneously.
• More precision in one leads to more uncertainty in the other.
• Fundamental property of the universe.

Quantization

• Certain physical properties (like energy) exist only in discrete amounts (quanta).
• Atomic spectra show this clearly through distinct energy levels in atoms.

Summary

• Quantum objects described as wave functions; appear as particles when measured.
• Results in wave-particle duality and the measurement problem.
• Key phenomena: superposition, entanglement, quantum tunneling, uncertainty principle, energy quantization.
• Despite complexities, the basics of quantum physics can be understood by most people.