Metrological institutions around the world administer our time, using atomic clocks based on the natural oscillations of atoms. These clocks, pivotal for appli­cations like satellite navigation or data transfer, have recently been improved by using ever higher oscilla­tion frequencies in optical atomic clocks. Now, scientists at the University of Innsbruck and the Institute of Quantum Optics and Quantum Information (IQOQI) of the Austrian Academy of Sciences led by Christian Roos show how a particular way of creating entanglement can be used to further improve the accuracy of measure­ments integral to an optical atomic clock’s function.

Observations of quantum systems are always subject to a certain statistical uncertainty. “This is due to the nature of the quantum world,” explains Johannes Franke from Christian Roos' team. “Entanglement can help us reduce these errors.” With the support of theorist Ana Maria Rey from JILA in Boulder, the Innsbruck physicists tested the measurement accuracy on an entangled ensemble of particles in the labora­tory. The researchers used lasers to tune the interaction of ions lined up in a vacuum chamber and entangled them. “The interaction between neighboring particles decreases with the distance between the particles. Therefore, we used spin-exchange interactions to allow the system to behave more collec­tively,” explains Raphael Kaubrügger from the Department of Theoretical Physics at the University of Innsbruck.

Thus, all particles in the chain were entangled with each other and produced a squeezed quantum state. Using this, the physicists were able to show that measurement errors can be roughly halved by entangling 51 ions in relation to individual particles. Previously, entanglement-enhanced sensing mainly relied on infinite inter­actions, limiting its applicability to only certain quantum platforms. With their experiments, the Innsbruck quantum physicists were able to show that quantum entanglement makes sensors even more sensitive.

“We used an optical transition in our experiments that is also employed in atomic clocks,” says Christian Roos. This techno­logy could improve areas where atomic clocks are currently used, such as satellite-based navigation or data transfer. Moreover, these advanced clocks could open new possibilities in pursuits like the search for dark matter or the determination of time-variations of fundamental constants. Christian Roos and his team now want to test the new method in two-dimensional ion ensembles. (Source: U. Innsbruck)

Reference: J. Franke et al.: Quantum-enhanced sensing on optical transitions through finite-range interactions, Nature, online 30 August 2023; DOI: 10.1038/s41586-023-06472-z

Link: Quantum Optics and Spectroscopy, Institute for Quantum Optics and Quantum Information (IQOQI), Austrian Academy of Sciences, Innsbruck, Austria