Prof. Subhadeep De

The Precision and Quantum Measurement Laboratory (PQM-lab) at IUCAA is working towards experimental verifications of the fundamental aspects of science. For that, we are developing a nearly monochromatic and highly stable photonic system [1], which will receive absolute referencing from the highly forbidden electric octupole (E3) transition of the ytterbium-ion at the 467 nm wavelength (the clock transition). This particular transition is chosen due to its high sensitivity to the possible time variations of the fine-structure constant and electron-to-proton mass ratio as well as for the Lorentz symmetry violation. Optical clocks are one of the most sensitive quantum sensors since changes in their tick rates resulting from unimaginably tiny perturbations of the energy states associated with the clock transition can be measured with unprecedented accuracy. To measure such tiny frequency variations, the lab-based clocks have to be part of a geographically distributed “optical clock network”, which is expected to shape up in India in the coming years as few groups have started developing such clocks in the recent past [2]. Therefore, the ultra-stable, nearly monochromatic 1550 nm photons, that is the communication wavelength, have to be disseminated from one lab to another using phase-stabilized optical fibers. We developed the required hardware for that and demonstrated its performance up to a 72 km fiber link [3]. For complete indigenization, we are also developing a 1550 nm laser system, transportable optical resonator and servo electronics [4], to build a compact rack-mount ‘Reference Photon Dissemination System (RPDS1550)’ that has a wide range of applications including for the future gravitational wave detectors (Einstein Telescope). I shall discuss the development status and results in my lecture. References: [1] S. Banerjee, et al., Int. J. of Mech. Sciences 250, 108299 (2023) [2] S. De, A. Sharma, Atoms 11, 71 (2023) [3] S. Johnson, et al., Indian Patent App No – 202321045035 (2024) [4] S. Johnson, et al., communicated (2024)