What is a qubit?

Qubit explained

Just like a binary bit is the basic unit of information in classical (or traditional) computing, a qubit (or quantum bit) is the basic unit of information in quantum computing. Quantum computing is driving new discoveries in healthcare, energy, environmental systems, smart materials, and beyond.

Qubit vs bit

Qubits are represented by a superposition of multiple possible states

A qubit uses the quantum mechanical phenomena of superposition to achieve a linear combination of two states. A classical binary bit can only represent a single binary value, such as 0 or 1, meaning that it can only be in one of two possible states. A qubit, however, can represent a 0, a 1, or any proportion of 0 and 1 in superposition of both states, with a certain probability of being a 0 and a certain probability of being a 1.

Superposition gives quantum computers superior computing power

Superposition allows quantum algorithms to process information in a fraction of the time it would take even the fastest classical systems to solve certain problems.

• The amount of information a qubit system can represent grows exponentially. Information that 500 qubits can easily represent would not be possible with even more than 2⁵⁰⁰ classical bits.
• It would take a classical computer millions of years to find the prime factors of a 2,048-bit number. Qubits could perform the calculation in just minutes.

There are many physical implementations of qubits

Where classical computers use familiar silicon-based chips, qubits (sometimes called “quantum computer qubits”) can be made from trapped ions, photons, artificial or real atoms, or quasiparticles. Depending on the architecture and qubit systems, some implementations need their qubits to be kept at temperatures close to absolute zero.

Superposition, interference, and entanglement

Superposition enables quantum algorithms to utilize other quantum mechanical phenomena, such as interference and entanglement. Together, superposition, interference, and entanglement create computing power that can solve problems exponentially faster than classical computers.