the highest number of qubits achieved in a quantum computer is constantly evolving due to the rapid advancements in the field. At that time, quantum computers with around 50 to 100 qubits were being developed by several companies and research institutions.
IBM, for instance, had released a 65-qubit quantum computer called IBM Quantum Hummingbird. Google's quantum computer, called Sycamore, had 54 qubits. Other companies such as Rigetti, IonQ, and Honeywell were also making progress in developing quantum computers with tens of qubits.
It's important to note that the number of qubits alone does not determine the overall capability or performance of a quantum computer. Factors such as qubit quality, coherence times, error rates, and the level of control and connectivity between qubits also play crucial roles in assessing the power and usefulness of a quantum computer.
Since my knowledge is and the field of quantum computing is rapidly advancing, there may have been significant developments in the number of qubits in quantum computers. I would recommend referring to the latest research and announcements from quantum computing companies and research institutions to obtain the most up-to-date information on the highest qubit quantum computer available.