Realization of Quantum Pascal Using Natural Fundamental Physical Constants

The acceptance of the redefinition of SI units on 20 May 2019, based on fundamental physical constants of nature led to significant changes in the field of metrology. The National Institute of Standards and Technology (NIST), USA has developed a quantum pressure standard, i.e. optical interferometer manometer (OIM), which is based on the change in the refractive index/polarizability/density of gas molecule that measures the pressure by calculating the change in fractional frequencies of monochromatic laser light passing through the medium compared to the vacuum. Theoretically, as per the ideal gas equation, pressure may be derived from fundamental physical constants either by Boltzmann's constant or Avogadro number. The NIST, USA has developed fixed and variable-length optical cavity (FLOC and VLOC) OIM, which is based on the change in the resonance frequency of laser-molecule interaction depending on the pressure inside the cavity. Worldwide, most national metrology institutes (NMIs) have been working to realize the quantum Pascal based on the principle mentioned earlier; however, their design and configuration might differ. The national physical laboratory has also initiated the OIM project to realize the quantum Pascal in India. For that, we have reviewed the pressure standards based on the laser refractometer developed by NMIs.