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Tuesday, April 19, 2016

Researchers from the Institute for Quantum Computing (IQC) and the Department of Applied Mathematics at the University of Waterloo have developed a universal method to manipulate quantum systems while minimizing their exposure to noise. Unlike related control methods that are designed for a particular physical setting, this new method is universal and can be applied regardless of the type of experimental set-up.

Performing a quantum computation or simulation involves quantum control – the ability to steer or manipulate a quantum system in a desired manner. Often, however, the process of controlling a quantum system exposes it to noise from its external environment, causing it to lose its quantum nature. The team of researchers found a novel method to steer a system while protecting it from noise, by steering it indirectly through an auxiliary quantum system called an actuator.

“We steer a system S, but instead of acting on it directly – for example, by addressing it with a laser – we act on an auxiliary system A, the actuator, which is coupled to S,” explained David Layden, a Master’s student in Applied Mathematics (Quantum Information). S is affected through its coupling with A, yet still remains protected from outside noise and therefore maintains its quantum behaviour. “The system S is steered indirectly. It’s as though we give it frequent gentle nudges with the actuator,” said Layden.

Collaborating with Layden were IQC research assistant professor Eduardo Martín-Martínez and Department of Applied Mathematics professor and IQC associate Achim Kempf, both also members of the Perimeter Institute for Theoretical Physics. “These nudges are strong enough to fully control the targeted quantum systems, but short enough to avoid destroying their quantum properties,” said Martín-Martínez.

This novel method of indirect quantum control is applicable to numerous quantum technologies, including metrology and computing. It can reduce the level of noise felt by a quantum system being steered which also reduces the amount of error-correction that’s required.

The results Universal scheme for indirect quantum control appeared in Physical Review A on April 1. 

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