Microsoft quantum cryogenic CMOS chip controls thousands of qubits

January 28, 2021 // By Rich Pell
Microsoft quantum cryogenic CMOS chip controls thousands of qubits
Tech giant Microsoft, in collaboration with researchers at the University of Sydney, says it has developed a cryogenic quantum computing control platform using specialized CMOS circuitry to address the problem of qubit control and decoherence.

The platform, say the researchers, is designed to address the "achilles heel" of the qubits that enable quantum computing - their instability. Since quantum states are easily disturbed by the environment, researchers must go to extraordinary lengths to protect them, cooling them nearly down to absolute zero temperature and isolating them from outside disruptions, like electrical noise.

"Hence," says Chetan Nayak, Director of Station Q Condensed Matter Theory at Microsoft, "it is necessary to develop a full system, made up of many components, that maintains a regulated, stable environment. But all of this must be accomplished while enabling communication with the qubits. Until now, this has necessitated a bird’s nest-like tangle of cables, which could work for limited numbers of qubits (and, perhaps, even at an “intermediate scale”) but not for large-scale quantum computers."

Rather than employing a rack of room-temperature electronics to generate voltage pulses to control qubits in a special-purpose refrigerator whose base temperature is 20 times colder than interstellar space, say the researchers, they invented a control chip - dubbed Gooseberry - that sits next to the quantum device and operates in the extreme conditions prevalent at the base of the fridge. They also developed a first-of-its-kind general-purpose cryo-compute core that operates at the slightly warmer temperatures comparable to that of interstellar space, which can be achieved by immersion in liquid Helium.

This core, say the researchers, performs the classical computations needed to determine the instructions that are sent to Gooseberry which, in turn, feeds voltage pulses to the qubits. These novel classical computing technologies solve the I/O nightmares associated with controlling thousands of qubits.

Gooseberry resolves several issues with I/O in quantum computers by operating at 100 milliKelvin (mK) while dissipating sufficiently low power so that it does not exceed the cooling power of a standard commercially-available research refrigerator at these temperatures, sidestepping the otherwise insurmountable challenge of running thousands of wires into a fridge. Meanwhile,

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