Microsoft quantum cryogenic CMOS chip controls thousands of qubits

Technology News | January 28, 2021

By Rich Pell

Memory & Data Storage Boards & Embedded Cards Digital Signal Processing Analog MPUs/MCUs Power Management Interconnect & cables Materials & processes

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, the cryo-compute core, one step up the quantum stack, operates at around 2 Kelvin (K) – a temperature that can be reached by immersing it in liquid helium.

Although this is still very cold, say the researchers, it is 20 times warmer than the temperatures at which Gooseberry operates and, therefore, 400 times as much cooling power is available. With the luxury of dissipating 400 times as much heat, the core is capable of general-purpose computing. Both pieces of hardware, say the researchers, are critical advances toward large-scale quantum computer processes and are the result of years of work.

“Both chips help manage communication between different parts of a large-scale quantum computer – and between the computer and its user,” says Nayak. “They are the key elements of a complex ‘nervous system’ of sorts to send and receive information to and from every qubit, but in a way that maintains a stable cold environment, which is a significant challenge for a large-scale commercial system with tens of thousands of qubits or more. The Microsoft team has navigated many hurdles to accomplish this feat.”

While both Gooseberry and the cryo-compute core represent big steps forward for quantum computing, say the researchers, there are still many more leaps needed by researchers before a meaningful quantum computer can be realized. For more, see “ A cryogenic CMOS chip for generating control signals for multiple qubits .”

Microsoft