Stop Obsessing About Qubits. Their Number Alone Doesn’t Matter

By Katia Moskvitch

How good are your qubits?

It’s the ability to execute specific quantum circuits that defines just how powerful a quantum computer really is — not in terms of the number of qubits but in terms of how stable and interconnected they are. That’s what companies should pay attention to when choosing a quantum computer for their specific task. That’s the notion of ‘quantum volume’ — the quality, capacity, and variety of quantum circuits.

The 1981 Physics of Computation Conference — the event that kickstarted quantum computing. See if you can spot Richard Feynman! (Credit: IBM Fellow Charlie Bennett)

Keeping the ‘noise’ down

Researchers are constantly improving and calibrating the microwave pulses, making them ever more precise. They can be sent from anywhere in the world through the cloud, using the ever-improving software.

The future of error correction

Hardware will never be error-free, so we just need to make sure that errors that the hardware introduces are of the type that we can correct using error correction codes. And we have to make sure that the fridge — the cryostat — doesn’t collapse. That could happen, if we were to continue adding, by brute force, more and more superconducting circuits to the bottom of the fridge. A cryostat with even one logical qubit made of, say, 500 physical qubits would be a structure of half a ton — and that is simply unfeasible.

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