Quantum Computing Hardware
Which statement about a qubit is correct?
- AIt is an analog storage element that holds a voltage between 0 and 1, and reading it returns that intermediate value
- BIt can be in a superposition of |0⟩ and |1⟩, and measuring it gives either 0 or 1 at random
- CBecause it holds 0 and 1 at the same time, a single measurement reads out both values, 0 and 1
Show answer and explanation
Answer: B. It can be in a superposition of |0⟩ and |1⟩, and measuring it gives either 0 or 1 at random
The state of a qubit can be written α|0⟩ + β|1⟩, where α and β are complex numbers (probability amplitudes) that satisfy |α|² + |β|² = 1. A measurement gives 0 with probability |α|² and 1 with probability |β|², and the state changes to match the result. A superposition is not a value halfway between 0 and 1: a measurement always gives either 0 or 1. A single measurement yields only one bit of information, and the values of α and β cannot be read out directly.
- A. A measurement gives either 0 or 1, never an intermediate value. Probability amplitudes cannot be read out like a continuous quantity such as a voltage.
- B. Correct. A measurement gives 0 with probability |α|² and 1 with probability |β|².
- C. A single measurement gives only one of 0 or 1. Thinking of a superposition as a state in which both values can be read at once is a common misconception.