Currently IBM are at 62 cubits and want 1123 in 2023. If they can get 1123 they are confident of 1 million by 2030. But there is hope that 1 million won’t be needed if they can reduce error. Most of the 1 million qubits are used in error correction. I gather that 1 million qubits is a scale up issue more than anything else. How many refrigerators will they need? Will 12cq be the chip that is used to overcome much of the current problems with solving error correction and reducing the number of qubits?
Researchers think they can sidestep that problem if they can initialize all the qubits in their computer in particular “magic states” that, more or less, do half the work of the problematic gates. Unfortunately, still more qubits may be needed to produce those magic states. “If you want to perform something like Shor’s algorithm, probably 90% of the qubits would have to be dedicated to preparing these magic states,” Roffe says. So a full-fledged quantum computer, with 1000 logical qubits, might end up containing many millions of physical qubits.
Google has a plan to build just such a machine within 10 years. At first blush, that sounds preposterous. Superconducting qubits need to be cooled to near absolute zero, in a device called a cryostat that fills a small room. A million-qubit machine conjures visions of a thousand cryostats in a huge factory. But Google researchers think they can keep their device compact. “I don’t want to tip my hand, but we believe we figured this out,” Neven says.
Others are taking different tacks. Google’s scheme would require 1000 physical qubits to encode a single logical qubit because its chip allows only neighboring qubits to interact. If more distant qubits can be made to interact, too, the number of physical qubits could be much smaller, Gambetta says. “If I can achieve that, then these ridiculously scary numbers for the overhead of error correction can come crashing down,” he says. So IBM researchers are exploring a scheme with more distant interconnections among the qubits.
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