Nine of the chip’s 17 qubits are arranged in a square three-by-three lattice and together form what is known as a logical qubit: the computational unit of a quantum computer. The remaining eight qubits on the chip are offset from them; their task is to detect errors in the system.
If a disturbance occurring in the logical qubit distorts the information, the system recognises this disturbance as an error. The control electronics then correct the measurement signal accordingly. “Right now, we’re not correcting the errors directly in the qubits,” admits Sebastian Krinner, a scientist in Wallraff’s group and lead author of the study together with Nathan Lacroix. “But for most arithmetic operations, that’s not even necessary.”
The highly specialised electronics used to control the qubits on the chip were manufactured by ETH spin-off Zurich Instruments. The chip itself is located on the lowest level of a large cryostat – a special cooling device – and operates at a temperature of just 0.01 Kelvin, barely above absolute zero.
Competitive research field
Error correction is currently a hotly contested field in quantum research. In addition to technical universities such as ETH Zurich or TU Delft, competitors include large corporations such as Google and IBM. “Together with our colleagues from Germany and Canada, we were the first group to perform practical error correction with qubits. That’s an accomplishment that fills us with pride,” Wallraff says. “It confirms that we, at ETH Zurich, are truly in the premier league of quantum research.”
As their next step, the ETH researchers now want to build a chip with a five-by-five qubit lattice, which requires correspondingly more complex technology and will also feature more qubits for error correction.
