By default, every quantum computer is going to be a hybrid that combines quantum and classical compute. Microsoft estimates that a quantum computer that will be able to help solve some of the world’s most pressing questions will require at least a million stable qubits. It’ll take massive classical compute power — which is really only available in the cloud — to control a machine like this and handle the error correction algorithms needed to keep it stable. Indeed, Microsoft estimates that to achieve the necessary fault tolerance, a quantum computer will need to be integrated with a peta-scale compute platform that can manage between 10 to 100 terabits per second of data moving between the quantum and classical machine. At the American Physical Society March Meeting in Las Vegas, Microsoft today is showing off some of the work it has been doing on enabling this and launching what it calls the “Integrated Hybrid” feature in Azure Quantum.

“With this Integrated Hybrid feature, you can start to use — within your quantum applications — classical code right alongside quantum code,” Krysta Svore, Microsoft’s VP of Advanced Quantum Development, told me. “It’s mixing that classical and quantum code together that unlocks new types, new styles of quantum algorithms, prototypes, sub routines, if you will, where you can control what you do to qubits based on classical information. This is a first in the industry.”

Image Credits: Microsoft

This, she argued, is a step in bringing classical and quantum computing together, but also in enabling new error correction protocols. Without this massive amount of classical compute, it won’t be possible — at least in the foreseeable future — to effectively control a quantum machine.

“Arguably, the only place you will be able to have scaled-up quantum machines, scaled-up quantum computing will be in a public cloud because it’s that critical to have that level of scale of classical computing integrated with the quantum machine,” Svore explained. She describes the process as a dance, where the classical compute helps choreograph a million qubits to work together simultaneously, “all doing their little square dance — or hexagon dance, whatever it may be.” But to do that, you have to talk to all of these qubits simultaneously, which necessitates these massive compute and bandwidth requirements.

Svore also argues that it takes a lot of classical compute to build the algorithms that are then sent over to the quantum machine — which may then also take weeks to run a given computation (and that feedback loop may happen numerous times, too).

With this new Integrated Hybrid feature then, Microsoft is giving developers — and researchers — the tools to look at what this combination between quantum and classical looks like in practice. Specifically, Svore told me, it’ll enable them to run a version of the phase estimation algorithm, for example, which is a key algorithm in the quantum computing toolkit. Researchers will soon be able to use Quantinuum hardware available in Azure to test this and then have the classical computer react to data coming back from the quantum machine, for example. Until now, a lot of this was theoretical, but now it’ll be possible to do it in hardware.

Over time, the role of classical computing in enabling quantum computing has become more widely understood in the industry. Microsoft, of course, argues that its massive cloud will enable it to deliver the kind of classical compute power needed to control these machines. It’s obviously not the only player in the market, with Amazon, Google, IBM and others also being able to integrate quantum processors into their massive data centers as well.