The Uncertainty Principle
Some pairs of properties, such as position and momentum, cannot both have sharp values in the same state. Werner Heisenberg found this in 1927; the precise rule is that the spread in position times the spread in momentum is at least ħ/2. It is not just clumsy measuring. It is built into how quantum states work, and qubits show it with two clashing questions.
Why can't we know everything about a particle at once?
In everyday life you can know where a car is and how fast it's going, both at the same time. Quantum physics says that, for tiny things, some pairs of facts can't both be sharp. Know one very well and the other must be fuzzy.
This is the uncertainty principle. The German physicist Werner Heisenberg found it in 1927. He won the 1932 Nobel Prize in Physics "for the creation of quantum mechanics."
It matters for quantum computers because each qubit can be asked different questions. Some of those questions clash, just like position and speed. Knowing which questions clash is how you design and read out quantum circuits.
- What does a short beep teach us about uncertainty?
- Worked example: an electron inside an atom
- Worked example: a baseball
- How do polarizing sunglasses show clashing questions?
- Run it: three filters as a circuitINTERACTIVE
- Try this: take the middle filter outINTERACTIVE
- Try this: tilt the middle filter only 22.5 degreesINTERACTIVE
- Is uncertainty just clumsy measuring?
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