World’s first fault-tolerant quantum computer

This innovation ushers in the world's first commercial fault-tolerant quantum computer equipped with "logical qubits," expected to be operational before this year concludes.

Logical qubits, or physical quantum bits interconnected through quantum entanglement, enhance quantum computing's accuracy by duplicating data storage across several locations. This approach diversifies the points of failure during computations, mitigating error risks.

Scheduled for release in late 2024, QuEra's groundbreaking quantum computer, endowed with 256 physical and 10 logical qubits, represents a significant milestone, according to QuEra representatives.

Following a recent publication on 6 December 2023 in the journal 'Nature', a collaboration between Harvard, QuEra, and other institutions showcased a functioning quantum computer with 48 logical qubits — the most extensive assembly of logical qubits tested thus far.

"It is the first machine with quantum error correction," said study co-author Harry Zhou, a physicist at QuEra and Harvard University, in an email to Live Science.

While the quantum computer in question lacks the capacity for standalone utility, it lays the groundwork for software developers to begin experimenting with code for future quantum computing iterations, Zhou added.

Quantum computing's necessity for error correction stems from its use of qubits, which, unlike conventional computers that utilise bits with values strictly as 0 or 1, can exist in a superposition of states between 0 and 1, thanks to quantum mechanics.

Quantum entanglement allows qubits to be interconnected, enabling simultaneous existence in multiple states and thereby facilitating calculations at speeds surpassing classical computers.

However, qubits are prone to disturbances, leading to a high error rate. With approximately one in a thousand qubits failing, compared to the one in a billion billion failure rate of bits in traditional computers, the scalability of quantum computers is significantly hampered.

Error correction aims to counteract the propensity of qubits to fail, with the construction of logical qubits being one such method.

Logical qubits utilise data redundancy, where identical information is stored in multiple locations, significantly reducing error rates should any physical qubits fail. This redundancy ensures that calculations can proceed uninterrupted.

In creating logical qubits, error-correcting computer code is applied to regular qubits. Logical gates or circuits are then established among the qubits to entangle them. The quantum computer calculates the 'syndrome' — an indicator of potential errors — and corrects any detected errors before moving to the next operational phase.

Despite not altering its power for autonomous operation, the advancement in qubit technology marked by QuEra's developments represents a significant leap forward.

Looking ahead, QuEra plans to introduce a series of quantum computers, beginning with a 30-logical-qubit, 3,000 physical qubit machine in 2025, and culminating in a behemoth with over 10,000 physical qubits and 100 logical qubits in 2026. "At 100 logical qubits, the [2026] machine can perform correct calculations that exceed the capability of today’s supercomputers," Zhou elucidated.