Physically a qubit could be realized using the polarization of a single photon, or electron spin, or currents in a superconductor.
For example, qubits3 — the quantum version of the classical bit — are not restricted to the pure 0 or 1 of binary digits. Physically a qubit could be realized using the polarization of a single photon, or electron spin, or currents in a superconductor. At the end of a calculation when the answer is read, each qubit will come out as either 0 or 1. But during the calculation the qubit represents both 0 and 1 simultaneously. This is called superposition. This core aspect of quantum computing enables quantum computers to outperform classical computers in some problems requiring intense computation. A second crucial aspect is entanglement, or the superposition of a pair of more than one qubits. This allows a quantum computer to explore a much larger computational space than any classical computer can explore.