What is a qubit, and how is it actually different from a regular bit?

[Lewis_43]

A classical bit, the basic unit of information in every normal computer, can only ever be a 0 or a 1 at any given moment. A qubit, short for quantum bit, is the equivalent basic unit in a quantum computer, and it can act like a bit storing a plain 0 or 1, but it can also exist as a weighted combination of both at the same time, a property called superposition. When you combine multiple qubits together, their superpositions can grow in complexity so that the whole system represents an enormous number of possible configurations simultaneously rather than just one

Physically, a qubit can be built from very different kinds of hardware, a single trapped ion, the spin of an electron, the polarization of a photon, or a microscopic superconducting circuit cooled to near absolute zero. What all of these approaches share is a two level quantum mechanical system capable of holding a superposition. Qubits can also become entangled with each other, meaning their states become so tightly linked that measuring one instantly tells you something about the state of the others, even though nothing was physically sent between them

None of this makes a single qubit useful on its own though. The real computational power comes from interference, where many qubits in a collective superposition behave like overlapping waves, with some outcomes reinforcing each other and others canceling out. When you finally measure the system, all of that superposition collapses down into an ordinary string of 0s and 1s, and a well designed quantum algorithm arranges the interference so that the correct answer is the one most likely to survive that collapse

What Is Quantum Computing? | IBMwww.ibm.com