New possibilities in the search for dark matter

Metrological institutions around the world manage our time. They are based on atomic clocks, which use the natural vibrations of atoms as clock generators. These clocks, which are central to applications such as satellite navigation or data transmission, have recently been improved by the use of increasingly higher vibrational frequencies in optical atomic clocks.

Scientists from the University of Innsbruck and the Institute for Quantum Optics and Quantum Information (IQOQI) of the Austrian Academy of Sciences led by Christian Roos are now showing how a special type of entanglement generation can further improve the accuracy of measurements used by optical atomic clocks .

Ions entangled with lasers
Observations of quantum systems are always subject to a certain statistical fluctuation range. “This is in the nature of the quantum world,” explains Johannes Franke of Christian Roos’ team. “Entanglement can help us reduce these errors.” With the support of theorist Ana Maria Rey from JILA in Boulder, USA, the Innsbruck physicists tested measurement accuracy on an entangled ensemble of particles in the lab. Ions arranged in a vacuum chamber were interacted and entangled using lasers.

Measurement errors in the experiment halved
“The interaction between neighboring particles decreases with the distance between the particles. We use exchange interactions to make the system behave more collectively,” explains Raphael Kaubrügger from the Institute for Theoretical Physics at the University of Innsbruck. In this way, all particles in the chain became entangled and a so-called squeezed-out quantum state was created. With this, the physicists were able to demonstrate that the measurement error can be roughly halved by entanglement of 51 ions with respect to individual particles.

Until now, entanglement-based sensing has mainly relied on interactions over an infinite range, limiting its applicability to specific quantum platforms.

Even more accurate clocks
With their experiments, the quantum physicists from Innsbruck were able to prove that entanglement makes quantum sensors even more sensitive. ‘For our experiments we used an optical transition that is also used in atomic clocks,’ says Christian Roos. “This technology could lead to improvements in areas where atomic clocks are currently used, such as satellite navigation or data transmission. In addition, these advanced clocks can open up new possibilities in areas such as the search for dark matter or the detection of deviations from natural constants.”

Christian Roos and his team now want to test the new method in two-dimensional ion ensembles. The latest results have been published in the journal Nature.