Quantum computers need classical computing to be truly useful

A vital ingredient to making quantum computers truly useful may be conventional computers. That was the message from a group of researchers this month, who explained that classical computers are vital to controlling quantum computers, deciphering the results of their calculations, and even developing new methods for producing quantum computers in the future.

Quantum computers are made of qubits—quantum objects that can take the form of extremely cold atoms or tiny superconducting circuits. The more qubits a quantum computer has, the more computationally powerful it receives.

But qubits are fragile, so they need to be carefully calibrated, tracked and controlled. Otherwise, they could introduce errors into calculations performed on a quantum computer or render these devices ineffective. To control the qubits, the researchers are turning to classical computing technologies they discussed at AQC25 Conference in Boston, Massachusetts, November 14.

Organizer: Quantum machineswhich makes controllers for several different types of qubits, the AQC25 conference brought together more than 150 researchers, from quantum computing professors to artificial intelligence startup executives. In several dozen presentations, they elaborated on the role of traditional computing as a technology enabling—and sometimes limiting—the future of quantum computing.

According to Shane Caldwellscientist at Nvidia, expects that a fault-tolerant quantum computer for solving useful problems will only be possible if it is supported by classical computing infrastructure at the petascale—the scale at which the world's most powerful traditional supercomputers currently operate. While Nvidia doesn't make its own quantum computing hardware, the company recently launched a system to connect quantum computing processors (QPUs) with traditional graphics processing units—specialized computer components typically used in machine learning and high-performance scientific computing.

Even when a quantum computer operates efficiently, its output is a collection of the quantum properties of its qubits. To become useful, they need to be decoded into more traditional formats – again, this requires classical computing devices.

Puya Rhona Vancouver startup 1Qbit talked about this decoding and how it means that the speed of fault-tolerant quantum computers will be determined by the speed of their classical components, such as controllers and decoders. In other words, whether an expensive machine built with highly specialized quantum hardware should run for days or hours to solve a computational problem may depend on its non-quantum parts.

In another presentation Benjamin Lienhard at the Walter-Meissner Institute for Low Temperature Research in Germany discussed how using traditional machine learning algorithms can make reading the quantum states of superconducting qubits more efficient. Likewise, Mark Saffman at the University of Wisconsin-Madison reported using classical neural networks improve the readout of qubits made of extremely cold atoms. Regardless of the type of qubit they study, the researchers agreed that non-quantum devices will help these qubits become useful.

IBM Blake Johnson presented details of a classical computational decoder that his team is developing as part of plans to create quantum supercomputer by 2029. This supercomputer will use unconventional error correction schemeand efficient decoding is one of the biggest challenges.

“Over time we see that more classic [computing] We get closer to QPU, the more we can push integrated system performance to new limits,” said Jonathan Cohen in Quantum Machines.

Traditional computers even play a role in assessing the behavior of future quantum computers and how they will be built. For example, Izhar Medalsy Startup Quantum Elements said virtual versions of artificial intelligence-powered quantum computers—or “digital twins”—of quantum computers could serve as a basis for real-world hardware design.

Quantum Scaling Allianceunder the leadership 2025 Nobel Prize Winner John Martiniswas also presented at the conference. This illustrates the importance of quantum and classical theory working together. The alliance brings together qubit manufacturers, traditional computer companies such as Hewlett Packard Enterprise, and materials modeling experts such as software company Synopsys.

The consensus view at the conference was clear: the future of quantum computing is fast approaching, but part of that is thanks to experts who have spent their entire careers firmly grounded in the classical world.