Quantum Pascal Realization from Refractometry

After the redefinition of the International System of Units (SI), it has been realized that the pascal, the SI unit of pressure, can be calculated more accurately because, according to ideal gas law, the pressure depends on temperature, gas number density, and few fundamental constants like Boltzmann’s constant, the universal gas constant, and Avogadro’s number. Among those, the temperature is redefined by evaluating the thermal energy. The fundamental constants are already calculated using quantum electrodynamics (QED) with the utmost accuracy. Therefore, the precise measurement of pascal depends majorly on gas number density, which can be computed using optical techniques. Quantum calculations involve calculating pressure using optical methods, also known as the quantum realization of pascal. This chapter reviewed the optical techniques for measuring pressure using refractometry proposed by various national metrology institutes.