Single Photon Level Study of Microwave Properties of Lithium Niobate at milli-Kelvin Temperatures
Abstract
Properties of doped and natural impurities in Lithium Niobate single crystals are studied using the Whispering Gallery Mode method at low temperatures as a function of magnetic field. The study reveals considerable coupling of microwave photon modes to the Fe3+ spin ensemble in iron-doped and non-doped crystals. The S=5/2 structure of the Fe3+ impurities demonstrate Zero Field Splittings of 11.21 and 20.96 GHz, significant asymmetry of the Zeeman lines and additional lines with anomalous g-factors of 1.37 and 3.95. Also, interactions between different transitions of the Fe3+ ion is observed. An additional ion impurity ensemble with a splitting of about 1.7 GHz is shown to couple to the dominating Fe3+ spins and the effect on Q-factors of microwave photon modes due to the Fe3+ ion ensemble is also demonstrated. Measurements down to less than one photon level are made with a loss tangent of order 10-5 determined.