“There are many issues to be resolved before we have a working large-scale quantum computer,” said team lead Fabio Sebastiano from QuTech and the Faculty of Electrical Engineering, Mathematics and Computer Science. “The quantum information stored in qubits can rapidly degrade and become unusable unless qubits are cooled down to temperatures very close to absolute zero (-273 degrees Celsius, or 0 Kelvin). For this reason, qubits typically operate inside special refrigerators at temperatures as low as 0.01 K, controlled by conventional electronics working at room temperature.”

One wire is required to connect each qubit to the control electronics. While this is feasible for the small number of qubits now in operation, the approach will become impractical for the millions of qubits required in useful quantum computers.



Horse Ridge mounted on the board ready to be installed

in the cryogenic refrigerator. Credit QuTech.



“It would be equivalent to taking the 12-megapixel camera on your mobile phone and trying to individually wire each of the million pixels to a separate electronic circuit,” explained Sebastiano. “A more viable solution is to operate the electronics controlling the qubits at extremely low (cryogenic) temperatures, so they can be placed as close as possible to the qubits.”

QuTech teamed up with Intel to address this precise challenge. The result is called Horse Ridge – an integrated circuit named after one of the coldest spots in Oregon.

“We have designed and fabricated a CMOS integrated circuit able to control up to 128 qubits, which can operate at 3 K (-270 °C) and can therefore be described as a cryo-CMOS circuit”, said Sebastiano. This is the same technology employed for standard microprocessors and such cryo-CMOS circuits could be used to create large-scale quantum computers.