# Theme 2. Development of a new generation of optical sensors with enhanced detection limit for the variations in alpha and other fundamental constants.

### Theme 2 will be divided in to two work packages:

• Task 2.1: Development of new optical technologies for sensing the variations in the fine-structure constant (Months 1-24)
• Task 2.2: Development of new methodology for enhancing the sensitivity to variations in different fundamental constants (Months 13-36)

In the first research task of this theme we will build a new ultra-stable and low noise optical resonator. We will build a new optical cavity with 30-40 cm long spacer made of ULE glass and with passive thermal shielding to improve cavity temperature stability. Cavity will have a finesse greater than 200000, short therm linewidth below 1 Hz, and active thermal stabilisation and passive thermal shielding designed for thermal time constant of the order of days. We will explore Sr atoms coupled to an optical cavity in the bad cavity regime to reduce dominant clock laser frequency noise arising from reference cavity length fluctuations and to make it possible to operate an active optical clock.
The founding for most of the scientific equipments’ development for this task is already secured by the governmental grant.

In the second research task of this theme we will consider alternative approaches to sensing variations in fundamental constants. In particular, we will combine the cavity-enhanced molecular spectroscopy setups (already operating in our group) with the ultra-stable optical cavity to develop a sensor of variations in the electron-to-proton mass ratio. We will also estimate experimentally feasibility of using relativistic effects in atoms, molecules, ions and cavities to increase the sensitivity of such sensors. We will calculate the response of the usual (passive) optical atomic clock to short variations in $\alpha$, which is pivotal for a proper estimations of the sensitivity with our present approach. Finally, with our Hg trap set-up, we will broaden the range of sensitivity of our quantum sensors to other possible fundamental constants.