IBM has upgraded one of its 27-qubit quantum computers to achieve a quantum volume of 64 – twice the previous value. Quantum volume is a test IBM created to quantify and compare quantum computer performance. It’s an architecture-independent measure of a system’s effective number of qubits, because, in many cases, it takes (much) more than one physical qubit to construct a logical qubit. This is due to the inherent instability of qubits, requiring qubit-consuming error correction mechanisms.
The quantum volume is the number 2 raised to the power of the effective number of qubits. This means IBM needed 27 qubits to create 6 effective qubits. Earlier this year, Honeywell beat IBM to a quantum volume of 64 using only 6 qubits. The difference is explained by the underlying technology: IBM uses superconducting circuits, Honeywell ions trapped in an electromagnetic field.