Description
Ytterbium ion based Optical Clock: Possible way for Redefining SI Second
Speaker:
Prof Subhasis Panja
CSIR-National Physical laboratory
Academy of Scientific & Innovative Research
Abstract:
Present definition of time and frequency is based on a microwave transition of laser cooled Cesium atoms. The variance of the measurement “Allan Deviation” is inversely proportional to the resonance frequency, so an optical frequency standard at resonance frequency of few hundred THz is two to three orders of magnitude more accurate than a microwave frequency standard. It is expected that the definition of the SI unit of time will be redefined with an optical clock either based on the atomic transition of ultra-cold atoms confined within Optical lattices or a single ion trapped and laser cooled within a radio frequency ion trap.
At CSIR-NPL we are working towards building an optical frequency standard based on an quadrupole transition of single Ytterbium ion, stored in a Paul trap inside of an ultra-high vacuum. Ion confined within the rf trap will be cooled to micro-Kelvin temperature using laser cooling technique to restrict motion of the ions within the Lamb-Dicke regime.
A narrow bandwidth and high voltage radiofrequency (RF) is an essential requirement for trapping ions within a quadrupole ion trap, commonly known as Paul Trap. Delivery of high voltage RF to the trap electrodes is usually done through a helical resonator as it allows impedance matching for efficient power transfer with very high quality factor (Q). A simple and efficient method has been adopted for tracking the dynamic resonant frequency of the helical resonator by monitoring its reflected signal, as the strength of the reflected signal will be minimum at its resonance. The strong transition at 369.5 nm being used for laser cooling of 171Yb+ ions. However, in this case the excited state decays to the two different metastable states. So two repump laser at 935 nm and 760 nm will be utilized for depleting the long lived metastable states and to achieve close looped laser cooling. So we need three lasers at different frequencies for laser cooling itself. For the clock operation we need to measure the transition at 435 nm which has natural linewidth few Hz. For line narrowing of the laser we take help of a highly stabilized Fabry-Perrot cavity. The cavity of Finesse 50000 and free spectral range 1.5 GHz and made of ultra-low expansion progress towards developing the optical atomic clock based on the interrogation of 171Yb+ ion at CSIR-NPL, New Delhi.
- N. Batra, S. Panja, S. De, A. Roy, S. Majhi, S. Yadav, and A. Sen Gupta, “MAPAN – Journal of Metrology Society of India, 32, 3, September 2017, pp. 193-198, doi: 10.1007/s12647-017-0209-5.
- L Sharma, H. Rathore, S. Utreja, Neelam, A. Roy, S. De and S. Panja
MAPAN-Journal of Metrology Society of India 35 (2020) 531-540
doi: https://doi.org/10.1007/s12647-020-00397-y