December 21, 2017 – A team of Dartmouth physicists has contributed essential work to research that could result in a new generation of ultra-sensitive quantum sensors. Dartmouth’s role in the study helps solve one of the more common problems in quantum sensing devices – cutting out false “chatter” signals.

Dartmouth’s Lorenza Viola and Leigh Norris, both from the Department of Physics and Astronomy, developed a theory to apply techniques for characterizing noise from medicine and earth science to the world of quantum sensors. Based on that theory, the Dartmouth team designed a measurement scheme for the research, guided experimental implementation and participated in data analysis.

The research, led by experimentalist professor Michael Biercuk at the University of Sydney, and also including control theorist Dennis Lucarelli at the Johns Hopkins University Applied Physics Laboratory, was published this week in Nature Communications.

Quantum sensing devices are used in a variety of fields including biomedicine and defense, but according to the University of Sydney team, while quantum devices have improved, the measurement protocols used to capture and interpret signals have lagged behind the hardware. 

Even the best quantum sensors can have difficulty separating usable data from false signals that can complicate interpretation – commonly referred to as “spectral leakage” in signal processing. 

This is where the Dartmouth team came in: Viola and Norris devised a way to identify the specific spectral properties of jittering microwave signals that are used to control the trapped ions – or qubits – in quantum systems used as sensors. Once the microwaves are isolated, researchers can look for ways to build targeted error suppression in future quantum devices, thereby optimally reducing unwanted noise in the system.

“Being able to accurately characterize the noise in quantum sensors is a prerequisite for devising optimal ways to cancel that noise out,” said Viola, a professor of physics at Dartmouth. “More generally, this advance can offer fundamental insight into noise in open quantum systems.” 

The University of Sydney research team reports that the new protocol reduces spectral leakage by many orders of magnitude over conventional methods. 

“Our approach is relevant to nearly any quantum sensing application and can also be applied to quantum computing as it provides a way to help identify sources of hardware error. This is a major advance in how we operate quantum sensors,” said Biercuk, a chief investigator at the ARC Centre of Excellence for Engineered Quantum Systems, to which Viola is also affiliated as a partner investigator.

According to Biercuk, in certain circumstances, the methods developed are up to 100 million times better at excluding unwanted noise in quantum sensors.