Timing is Key for CERN

A new optical fibre link has been established between CERN and Paris, providing the Laboratory with a crucial and precise frequency reference for its groundbreaking experiments. In particular, this link is essential for CERN's investigations into matter and antimatter, where accuracy in timing is of utmost importance.

Experiments at CERN's Antimatter Factory delve into fundamental principles such as charge-parity-time (CPT) by studying the properties and behavior of antimatter in comparison to normal matter. The ALPHA experiment, for instance, conducts tests through spectroscopy of antihydrogen, measuring frequencies of transitions in the anti-atom using laser light or microwaves. Matching these frequencies with those of normal hydrogen is crucial for verifying CPT symmetry.

The frequencies measured in units of Hz are vital for understanding energy level intervals in atoms and the spectral lines that emerge during quantum transitions. To ensure precise comparisons between matter and antimatter, ultra-precise clocks are required. Recently, a caesium fountain clock was installed in ALPHA, complemented by the new optical fibre link connecting the experiment to the French National Metrological Institute in Paris.

Physicist Janko Nauta from the ALPHA collaboration highlights the significance of this advancement, stating, "For our previous measurement of the transition in antihydrogen, we utilized a simpler clock with a precision of two parts per trillion. However, to match the precision of hydrogen measurements, which stand at four parts per quadrillion, a more advanced clock was necessary to detect potential differences between matter and antimatter."

Both the optical fibre link and the caesium fountain clock are pivotal in enhancing the precision of antihydrogen measurements at ALPHA. Nauta emphasizes the roles of these technologies, explaining that while the clock ensures accuracy, the link reduces noise in measurements and aids in long-term evaluation. Furthermore, the link opens up possibilities for utilizing signals from optical quantum clocks in the future, surpassing the stability of current clocks that define the SI second.