Scientists discover way to make quantum states 10,000 times longer

If we can take advantage of it, quantum technology promises fantastic new possibilities. But first, scientists need to coax quantum systems to stay jock longer than a few millionths of a second.

A team of scientists at the University of Chicago’s Pritzker School of Molecular Engineering announced the discovery of a simple modification that allows quantum systems to remain operational – or “coherent” – 10,000 times longer than before. Although scientists are testing their technique on a particular class of quantum systems called qubits of solid state, they think it should apply to many other types of quantum systems and could therefore revolutionize quantum communication, computing and censorship.

The study was published Aug. 13 in Science.

“This breakthrough lays the groundwork for exciting new avenues for research in quantum science,” said student-author David Awschalom, the Liew Family Professor in Molecular Engineering, senior scientist at Argonne National Laboratory and director of the Chicago Quantum Exchange. “The broad applicability of this discovery, coupled with a remarkably simple implementation, allows this robust coherence to influence many aspects of quantum technology. It enables new research possibilities that were previously thought impractical.”

Down to the atomic level, the world works according to the rules of quantum mechanics – very different from what we see around us in our daily lives. These different rules could translate into technology such as virtually unhackable networks or extremely powerful computers; the US Department of Energy published a blueprint for the future quantum internet at an event in UChicago on July 23. But fundamental technical challenges remain: Quantum states need an extremely quiet, stable space to operate, as they are easily disturbed by background noise vibrations, temperature changes or scattered electromagnetic fields.

So scientists are trying to find ways to keep the system coherent for as long as possible. One common approach is to physically isolate the system from the noisy environment, but this can be tricky and complex. Another technique involves making all materials as clean as possible, which can be costly. The scientists at UChicago took a different approach.

“With this approach, we are not trying to eliminate noise in the environment; instead, we ‘trick’ the system into thinking it does not experience the noise,” said postdoctoral researcher Kevin Miao, the paper’s first author.

In tandem with the usual electromagnetic pulses that were used to control quantum systems, the team applied an additional continuously alternating magnetic field. By setting this field precisely, the scientists were able to rotate the electron spins rapidly and allow the system to “emit” the rest of the sound.

“To get a sense of the principle, it’s like sitting on a merry-go-round with people screaming around you,” Miao explained. “When the ride is still quiet, you can hear them perfectly, but when you turn fast, the sound fades to a background.”

This small change left the system cohesive for up to 22 milliseconds, four orders of magnitude higher than without the modification – and much longer than any previously reported electron spin system. (For comparison, a blink of an eye takes about 350 milliseconds). The system is able to attenuate some forms of temperature fluctuations, physical vibrations, and electromagnetic noise almost completely, all of which usually destroy quantity coherence.

The simple fix could unlock discoveries in virtually any area of ​​quantum technology, the scientists said.

“This approach creates a path to scalability,” Awschalom said. “It could make storing quantum information in electron spin practical. Extended storage times would enable more complex operations in quantum computers and could allow quantum information transmitted from spin-based devices to travel longer distances in networks.”

Although their tests were performed in a solid state quantum system using silicon carbide, the scientists believe that the technique should have similar effects in other types of quantum systems, such as superconducting quantum bits and molecular quantum systems. This level of versatility is unusual for such a technical breakthrough.

“There are a lot of quantum technology candidates who were pushed aside because they could not maintain quantitative coherence for long periods of time,” Miao said. “They could be re-evaluated now that we have this way of completely improving cohesion.

“The best part is, it’s incredibly easy to do,” he added. “The science behind it is complicated, but the logistics of adding an alternating magnetic field are very simple.”