Classical Silicon Fuels Quantum Calibration, Decoding

Quantum computers promise to one day solve problems beyond the most powerful supercomputers imaginable. But it’s often underappreciated how much classical computing it takes just to operate these machines. As qubit counts rise, innovations in this supporting infrastructure will be essential if they’re to live up to their promise.

To prepare for the scale of quantum computers the industry is working toward, many companies are also gearing up the classical hardware, and software, required to support them. In April, Nvidia announced new AI-based software to accelerate the classical tasks that enable quantum computers. Sydney-based quantum software company Q-CTRL has developed an automatic calibration algorithm for quantum computers, and is now leveraging Nvidia’s agent-based system. Other companies, including IBM Quantum, Cambridge, England–based Riverlane, which develops quantum-error correction, and Google Quantum AI, are developing similar tools.

The Role of Classical in Quantum

Digital computer chips are marvels of engineering, operating flawlessly out of the box and capable of trillions of operations without error. The quantum bits, or qubits, at the heart of a quantum computer, by contrast, are temperamental and unreliable, requiring regular calibration and complex error-correcting schemes to keep them on track.

Calibration and error-correction are fundamentally classical, not quantum, problems, and they require dedicated classical hardware to solve. As quantum computers get bigger, the scale of those resources will need to rise in lockstep. That means that for the foreseeable future, quantum computers are going to be hybrid devices with a healthy dose of classical computing on the side.

“The cheapest and fastest way to execute most computer programs is to run them on a classical computer—even if a quantum computer is available,” says Adam Zalcman, a quantum software engineer at Google Quantum AI. “This is true of most of the information processing involved in running a quantum computer itself…. Therefore, I expect that every practical and efficient quantum-computer architecture will incorporate fast classical devices.”

Tuning Quantum Hardware

While the transistor has cemented its place as the foundational component of classical chips, the qubits at the heart of a quantum computer come in many flavors—superconducting circuits, trapped ions, neutral atoms, even individual photons. Using them for computation requires a painstaking calibration process to turn the “bare metal” of the underlying hardware into a qubit that can be controlled to run quantum circuits, says Jay Guilmart, lead product manager at Q-CTRL.

Calibration has two stages. The first, known as “bring up,” determines the frequency at which each qubit resonates, how long it holds its quantum state, its sensitivity to control pulses, and the strength of its interactions with neighboring qubits. All of these factors determine its error propensity and…