The El Capitan supercomputer uses enormous amounts of power – and some quantum computers might need even more

LLNL/Garry McLeod

Large quantum computers may be able to solve problems impossible for even the best traditional supercomputers – but in order to do so, some of them might need far more energy than those supercomputers.

Existing quantum computers are relatively small, with most having fewer than a thousand building blocks called qubits. They are also prone to making errors during operation because of how fragile those qubits are. This makes these computers incapable of solving the economically and industrially relevant problems they have been predicted to excel at, such as aiding drug discovery. Researchers largely agree that really useful quantum computers must have radically larger qubit counts and an ability to correct errors – making them fault-tolerant quantum computers (FTQCs). But getting there is still a formidable engineering challenge, partly because there are several competing designs.

Olivier Ezratty at the Quantum Energy Initiative (QEI), an international organisation, says that one overlooked concern of building utility-scale FTQCs is their potential energy consumption. At the Q2B Silicon Valley conference in Santa Clara, California, on 9 December, he presented preliminary estimates of it. Strikingly, several FTQC designs surpassed the energy footprint of the world’s largest supercomputers.

The world’s fastest supercomputer, El Capitan at the Lawrence Livermore National Laboratory in California, needs about 20 megawatts of electrical power, which is approximately triple the energy consumption of the nearby 88,000-resident city of Livermore. In Ezratty’s estimate, two designs for FTQCs, scaled up to 4000 logical, or error-corrected, qubits, would require even more. The most power-hungry among them might need as much as 200 megawatts of power.

Basing his estimates on publicly available data, proprietary information from quantum computing firms and theoretical models, Ezratty has identified a wide spectrum of possible energy footprints for future FTQCs, which ranges from 100 kilowatts to 200 megawatts. Notably, in Ezratty’s estimation, three FTQC designs that are currently being developed would ultimately require less than 1 megawatt of electricity, which is comparable to typical supercomputers used by research facilities. In his view, this spectrum could influence the evolution of the industry, for instance making the quantum computing market larger if the less power-hungry designs come to dominate.