Using commercially available technology and innovative methods, researchers at NBI have pushed the limits of how fast you can detect changes in the sensitive quantum states in the qubit. Their work allows researchers to follow rapid changes in qubit performance that were previously invisible. The study is published in the journal Physical Review X.

The workhorse of any quantum-based application aimed at the coveted, but not yet fully realized quantum computer is the qubit. It is, however, a rather fragile workhorse.

Qubits, and quantum processors in general, are highly sensitive to their environment. Typically, the materials in which they are embedded contain microscopic defects that are still not fully understood. These defects can spatially fluctuate extremely fast, sometimes hundreds of times per second. As they fluctuate, the rate at which a qubit loses energy, and therefore useful quantum information, also changes.

Researchers at the Niels Bohr Institute have significantly increased how quickly changes in delicate quantum states can be detected inside a qubit. By combining commercially available hardware with new adaptive measurement techniques, the team can now observe rapid shifts in qubit behavior that were previously impossible to see.

Qubits are the fundamental units of quantum computers, which scientists hope will one day outperform today’s most powerful machines. But qubits are extremely sensitive. The materials used to build them often contain tiny defects that scientists still do not fully understand. These microscopic imperfections can shift position hundreds of times per second. As they move, they alter how quickly a qubit loses energy and with it valuable quantum information.

Until recently, standard testing methods took up to a minute to measure qubit performance. That was far too slow to capture these rapid fluctuations. Instead, researchers could only determine an average energy loss rate, masking the true and often unstable behavior of the qubit.