Timing is everything for CERN
A new optical fibre link between CERN and Paris will provide the Laboratory with an accurate frequency reference
To investigate Matter and anti-Matter Cern needs a very accurate timing reference –
“Experiments at CERN’s Antimatter Factory test fundamental principles such as charge-parity-time (CPT) by studying the properties and behaviour of antimatter and comparing them with normal matter. The ALPHA experiment performs such tests through spectroscopy of antihydrogen – that is, by measuring the frequencies of transitions in the anti-atom using laser light or microwaves. If the results match those of normal hydrogen, the measurement is consistent with CPT symmetry. These frequencies, measured in units of Hz, equivalent to one per second, correspond to the energy level intervals in atoms and the spectral lines that arise when they make quantum transitions between levels. To accurately compare matter and antimatter, the frequencies must be determined incredibly precisely, requiring ultra-precise clocks. That’s why a caesium fountain clock was recently installed in ALPHA and a new optical fibre link between the experiment and the French National Metrological Institute in Paris is now online. Both the clock and the optical link will help improve the precision of ALPHA’s antihydrogen measurements by orders of magnitude.”
“For our previous measurement of the transition between the ground state and the first excited state of antihydrogen, we used a simpler clock made out of a quartz oscillator referenced via GPS satellite as a frequency reference, and we reached a precision on the transition frequency of two parts per trillion (2×10-12),” says physicist Janko Nauta from the ALPHA collaboration. “However, the equivalent measurement on hydrogen, performed a few years before our antihydrogen measurement, has an even higher precision, of four parts per quadrillion (4×10-15), calling for a better clock to look for potential differences between matter and antimatter.”
“For ALPHA, both the optical fibre link and the caesium fountain clock play important roles in making antihydrogen measurements with a precision that matches that of the hydrogen measurements,” continues Nauta. “While we rely on the clock, the link helps us to reduce noise in the measurement and to better evaluate the clock in the long term, to verify that it stays accurate. In addition, the link will make it possible to use signals from optical quantum clocks in the future, surpassing the stability of clocks that currently realise the SI second.”
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