What is a Basis?

Mission 2: The Art of Quantum Messages. Part of the Quantum Courier Service, a free course from the Oxford University Quantum Information Society.

In quantum mechanics, you can't just ask a qubit "What are you?" You have to explicitly choose a Basis; the specific philosophical lens or rigid framework you use to force the qubit to view the universe.

The Oxford Cocktail Party Analogy: Imagine you are profiling eccentric academics at a stuffy Oxford cocktail party. You have two entirely different social filters (bases) you can use to interrogate the guests:

• The Political Basis (+): You demand, "Are you a Tory or a Labour supporter?"
• The Aesthetic Basis (×): You casually ask, "Do you prefer Punting on the River Cherwell or Hiking in Shotover Woods?"