Week 3 - my own writings

Discretness: Energy can only take certain values.

Superposition: Qubits being in a combination of two(?) states at the same time.

Interference: The state of objects adding up or cancelling out.

Entanglement: One object’s state depends on another object’s state.

Measurement: The outcome is often random and obeserving (measuring) you can change it.

• Why do quantum objects show superposition, interference, and entanglemenet?
• How should they be described (their behavior)?

• Classical physics: things are either waves or particles. Which one of them should I use to describe what I see in my experiments?

  Waves:

  • Waves travel at a certain velocity.
  • Different kinds of waves have different speeds.
  • Sound waves are slower than light waves.

  • Waves interact with each other, they show interference. Interference can be constructive: two waves add together, or destructive: two waves cancel out.

    

  Particles:

  • Particles have mass.
  • Particles have a well-defined postion or location - they are discrete.
  • They move with a velocity.

Double-slit experiment is used to decide if quantum objects behave like a wave or a particle.

• Particles would leave two lines on the wall behind the two slits (discrete spots and no interference)
• Waves would leave a pattern of bright and dark lines, some waves are amplifying one another, while other waves are canceling out (interference).

Throwing electrons:

• Each electron is a discrete spot on the wall.
• After a certain amount of electrons, you get an interference pattern.
• A nice example of particle-wave duality on my opinion.
• This happens to all quantum objects
• In quantum, waves can behave as particles and particles can behave as waves.

• Article: Wave-particle duality of C60 molecules - Markus Arndt, Olaf Naiz, Julian Vos-Andreae, Claudia Keller, Gerbrand van der Zouw & Anton Zeilinger.

  State:

  • A possible condition of the classical bit or qubit.

Superposition and interference are very similar: both involve overlapping waves.

In a guitar, a string can take only specific shapes when it vibrates.

Specific shapes are a result of confinement.

The idea of confinement also applys to quantum objects.

If you limit something’s movement, it will also show the same kind of discretization (either a 0 or 1), just like a guitar’s string.

What confines quantum objects?

• trapped ions quantum computers, AKA as some sort of artificial atoms.
• Superconductiing computers, confinements are virtually created.

• Entanglement: Why does it happen? Is there just a mysterious link between atoms or is it something most likely more tangible and physical that we can understand?
• Why does measurument change the state of the qubit?
• Why is quantum measurument random?

and many more…

• The Copenhangen Interpretation (Niels Bohr and colleagues). When a quantum state is measured, it collapses to one of the possible results of the measurument - the most accepted interpretation
• The Many Worlds Interpretation (Hugh Everett). There is no collapse going on, but when you measure it, you are splitting into a new universe.
• De Broglie-Bohm Interpretation, AKA Pilot wave theory. The wave and particle parts of the quantum object coexist, like a droplet bouncing on a puddle.