Researchers have developed algorithms called phantom codes to make quantum computers less error-prone, potentially allowing them to run complex simulations more efficiently. These codes enable entanglement of logical qubits without physical manipulations, cutting down on error risks. The approach shows promise for tasks requiring extensive entanglement, though it is not a complete solution to quantum computing challenges.
Quantum computers face significant hurdles due to errors that have long cast doubt on their practical usefulness. Early physicists questioned whether these devices could ever perform reliably, given the difficulty in correcting errors. Today, various types of quantum computers exist and have contributed to scientific discoveries, but the error problem remains unresolved.
Shayan Majidy at Harvard University and his colleagues have proposed phantom codes as a remedy. These algorithms address computations involving many steps, which are lengthy and prone to accumulating errors. Quantum computers operate using physical units called qubits, but error-resistant calculations rely on logical qubits—groups of physical qubits that share information to lower error rates.
Typically, manipulating logical qubits requires physical actions, such as applying lasers or microwaves to entangle them or alter their properties. Phantom codes, however, allow multiple logical qubits to become entangled without any such interventions, earning their name from this 'phantom' effect. This reduces the number of physical operations needed, enhancing efficiency and minimizing error opportunities.
In computer simulations, the team tested phantom codes on two tasks: preparing a special qubit state commonly used in computations and simulating a toy model of a quantum material. The results were up to 100 times more accurate than those from conventional error-correction methods.
Majidy notes that phantom codes are not universal; they perform best in scenarios already demanding high levels of entanglement. 'It’s not a free lunch. It’s just a lunch that was already there and we weren’t eating it,' he says.
Mark Howard at the University of Galway compares selecting error-correction codes to choosing armor: phantom codes offer flexibility like chain mail but demand more qubits and may not suit all applications. Dominic Williamson at the University of Sydney adds that their competitiveness depends on future hardware advances.
Majidy's team is collaborating with builders of quantum computers using ultracold atoms, aiming to tailor programs more precisely to specific tasks and hardware.
The research appears in an arXiv preprint with DOI: 10.48550/arXiv.2601.20927.