Measurement and Probability
How amplitudes become outcomes, and why quantum experiments are run repeatedly.
Quantum Measurement
What is quantum measurement?
Measurement extracts a definite classical outcome from a quantum system, with probabilities given by squared amplitudes.
Measurement generally disturbs the system, which is why quantum results are collected statistically over repeated runs.
The disturbance is also a resource: it is what makes eavesdropping detectable in quantum key distribution.
Recommended learning sequence
- Measurement and ProbabilityHow amplitudes become outcomes, and why quantum experiments are run repeatedly.
Frequently asked questions
- Does measurement require a conscious observer?
- No. Any sufficient interaction with the environment produces the same effect.
Lessons in this topic
Related subjects
Superposition
Superposition is a quantum state formed by combining other states, each carrying an amplitude.
Quantum Cryptography
Quantum cryptography uses quantum physics — chiefly the disturbance caused by measurement — to secure tasks such as key exchange.
Qubits
A qubit is a two-level quantum system used as the basic unit of quantum information.