A qubit, short for "quantum bit," is the fundamental unit of quantum information. It is the quantum analogue of a classical bit, which is the basic unit of classical information in classical computing. While classical bits can only exist in two distinct states, either 0 or 1, qubits can exist in a superposition of both 0 and 1 simultaneously.
The superposition property of qubits allows them to store and process information in a vastly different way compared to classical bits. A qubit can be represented as a linear combination of the two basis states, usually denoted as |0⟩ and |1⟩. This means that a qubit can exist in a coherent superposition of these two states, represented mathematically as α|0⟩ + β|1⟩, where α and β are complex numbers that define the probability amplitudes of the respective states.
The probability amplitudes α and β can be thought of as determining the likelihood of measuring the qubit in the states |0⟩ or |1⟩, respectively. When a measurement is made, the qubit "collapses" into one of the basis states with a probability determined by the squared magnitudes of the probability amplitudes.
So, while a qubit can represent two classical bit values, 0 and 1, it can also hold much more information due to its ability to exist in a superposition of these states. This property enables qubits to perform quantum computations and offer potential advantages in certain computational tasks, such as quantum parallelism and quantum algorithms like Shor's algorithm and Grover's algorithm.