Quantum Metrology and Sensing
A. Precision and Quantum Measurement lab (PQM-lab) (https://pqmlab.iucaa.in) is expeimenting on
- quantum metrology
- precision measurements
- developing quantum-phenomena based sensors/ technologies
The PQM-lab is dedicated to supporting India’s quantum mission, supporting mega-science projects (e.g., LIGO-India, TMT) and synergizing between precision atomic spectroscopy and astronomical studies to explore unanswered questions in fundamental science.
Indigenization of the quantum clock with unprecedented accuracy has national importance and also will be used for testing fundamental science and geodesy. In particular, our long-term interest is measuring the temporal constancy of the dimensionless fundamental constants and possible violation of fundamental symmetries. For that PQM-lab is working on three major inter-connecting areas,
- establishing a lab-based reference optical clock
- optical fiber-based quantum channel and
- developing a chip ion-trap.
The heart of our experiment is a ytterbium-ion-based quantum clock. For this, a single ytterbium-ion will be trapped in an indigenously developed precision ion trap. The ion will be cooled to sub-mK temperature using the laser cooling technique, which will then be used to probe its highly forbidden electric octupole (E3) clock transition at the 467 nm wavelength. An ultra-stable sub-Hz linewidth clock laser will be produced by referencing a commercial laser to an indigenously developed ultra-stable Fabry-Pérot cavity. Further, the optical clock referenced phase & frequency preserved photons need to be disseminated to geographically distributed locations for establishing a network among the quantum clocks and intercomparison. To meet the aforementioned requirement, active phase noise cancellation of the optical fiber by stabilizing its length will be implemented, a critical technology under development at the PQM-lab.
B. Quantum-enhanced techniques in Precision Interferometer (QuPI):
Precision interferometry is the basis for some of the most sensitive scientific instruments ever built, such as gravitational-wave detectors, atomic sensors, and optical clocks. At their core, gravitational-wave detectors measure extremely small changes in distance between test masses by exploiting interference of coherent laser light. However, the ultimate sensitivity of such devices is limited by fundamental sources of noise, especially quantum noise—comprising shot noise (photon counting uncertainty) and radiation-pressure noise (back-action from fluctuating photon momentum).
Quantum-enhanced techniques refer to the deliberate use of non-classical states of light and matter, as well as quantum measurement strategies, to overcome these limits. Key approaches include:
Squeezed Light Sources: By preparing light in a squeezed state, one can reduce fluctuations in one quadrature (phase or amplitude) at the expense of the other. This directly lowers shot noise or radiation-pressure noise, improving interferometer sensitivity beyond the standard quantum limit.
Quantum Non-Demolition (QND) Measurements: Design of measurement schemes that extract information without disturbing the observable of interest. Examples include variational readout or speed-meter interferometers.