A qubit is defined as

A qubit is defined as

• A. A classical bit that can be 0 or 1
• B. A quantum bit that can be 0, 1, or both at the same time due to superposition
• C. A memory cell in a DVD
• D. A digital signal

Answer: (B)

A qubit is a two-level quantum system that can exist in a superposition of the basic states 0 and 1. It’s described by a state a|0> + b|1> with complex amplitudes a and b, where |a|^2 + |b|^2 = 1. When you measure it, you get 0 with probability |a|^2 and 1 with probability |b|^2, and the state collapses to the measured outcome. This is fundamentally different from a classical bit, which is definitively 0 or 1 at all times. The other descriptions refer to classical storage or signals, not to a quantum state.

A qubit is a two-level quantum system that can exist in a superposition of the basic states 0 and 1. It’s described by a state a|0> + b|1> with complex amplitudes a and b, where |a|^2 + |b|^2 = 1. When you measure it, you get 0 with probability |a|^2 and 1 with probability |b|^2, and the state collapses to the measured outcome. This is fundamentally different from a classical bit, which is definitively 0 or 1 at all times. The other descriptions refer to classical storage or signals, not to a quantum state.