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Coherence of quantum system sustained 10,000 times longer

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University of Chicago engineers have demonstrated a simple modification which allows a particular quantum system to remain coherent 10,000 times longer than what was previously possible.

Quantum computing – which harnesses quantum phenomena such as superposition to perform tasks much faster than classical computers – remain in early stages of development. The main technical barrier is the difficulty in keeping quantum systems coherent (in this context, operational) for any substantial period of time. A quantum system can be thrown out of coherence with the slightest temperature change or external electromagnetic field.

While most efforts to keep the system coherent for longer involve physically isolating the system from its external environment, the University of Chicago researchers took a different approach.

“With this approach, we don’t try to eliminate noise in the surroundings; instead, we “trick” the system into thinking it doesn’t experience the noise,” said Kevin Miao, first author of the Science paper describing the technique.

The researchers applied this technique to a system of solid state qubits (the basic unit of quantum information). In addition to the usual electromagnetic pulses used to control quantum systems, they also applied a continuous alternating magnetic field.

By tuning this field, they were able to rapidly rotate the electron spins and allow the system to “tune out” the remaining noise. Miao compared this to a person tuning out distracting noise: “It’s like sitting on a merry-go-round with people yelling all around you. When the ride is still, you can hear them perfectly, but if you’re rapidly spinning, the noise blurs into a background.”

This addition allowed the system to remain coherent for up to 22ms: around 10,000 times higher than without the alternating magnetic field and far longer than any previously confirmed electron spin system. The system was able to almost entirely tune out some temperature fluctuations, vibrations, and electromagnetic noise.

Although the technique has only been applied to a solid-state system using silicon carbide, the researchers believe the technique should be applicable to superconducting quantum systems and molecular quantum systems.

Professor David Awschalom, lead author and director of the Chicago Quantum Exchange, commented: “This approach creates a pathway to scalability. It should make storing quantum information in electron spin practical. Extended storage times will enable more complex operations in quantum computers and allow quantum information transmitted from spin-based devices to travel longer distances in networks.”

“This breakthrough lays the groundwork for exciting new avenues of research in quantum science,” he added. “The broad applicability of this discovery, coupled with a remarkably simple implementation, allows this robust coherence to impact many aspects of quantum engineering. It enables new research opportunities previously thought impractical.”

Last year, Google researchers claimed in a paper that they had reached quantum supremacy: the point at which a quantum computer can perform tasks that would be impossible on a classical computer.

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