Most qubits in a quantum computer

The most usable qubits in a quantum computer is 1,180, achieved by Atom Computing (USA). The company's latest experimental prototype – which builds on technology developed for their 100-qubit Phoenix computer – was announced on 24 October 2023.

Quantum computing is a discipline that combines advances in physics with computer science. There are various different approaches currently being developed by different teams, but the basic feature they all share is the use of super-cooled and isolated atoms or subatomic particles (referred to as "qubits") to store and manipulate information.

Due to the peculiarities of quantum mechanics, these qubits can store information in far more complex states than the 1 or 0 used in traditional computer memory. The state of each qubit exists as a range of probability amplitudes, which can be simply described as the likelihood of the qubit being in any particular state. When the states of different qubits are compared, these amplitudes can strengthen each other, or cancel each other out.

This probability-based system can, in theory, allow a quantum computer to simultaneously calculate multiple potential answers to a question, arriving at the correct one almost instantaneously, rather than through repetition. This would be particularly useful in fields such as cryptography, as cracking modern encryption requires testing so many possible answers and takes a functionally infinite amount of time with conventional computer hardware.

The difficulty that developers face in making quantum computers is that it is very hard to isolate atoms from outside interference, and to manipulate them without introducing errors in the data they hold. As these errors are impossible to entirely eliminate, much of the cutting-edge research in this field is focused on making systems "fault tolerant". The most promising route to this goal is through machines with larger numbers of qubits, which can run processes in parallel.

The Atom Computing system uses what's called an optical lattice to hold a cloud of ytterbium atoms in a vacuum, perfectly still and separated from each other. Because this method allows for the use of neutral atoms, it avoids the problem of charged ions interacting with each other, which has complicated the efforts of other teams.