Multipolar blackbody radiation shifts for single-ion clocks.

Appraising the projected 10-18 fractional uncertainty in the optical frequency standards using singly ionized ions, we estimate the blackbody radiation (BBR) shifts due to the magnetic dipole (M1 ) and electric quadrupole (£2) multipoles of the applied external electromagnetic field. Multipolar scalar polarizabilities are determined for the singly ionized calcium (Ca+) and strontium (Sr+) ions using the relativistic coupled-cluster method, though the theory can be exercised for any single-ion clocks. The expected energy shifts for the respective clock transitions are estimated to be 4.38(3) x 10-4 Hz for Ca+ and 9.50(7) x 10-5 Hz for Sr+. These shifts are large enough and may be a prerequisite for the frequency standards to achieve the foreseen 10-18 precision goal. [ABSTRACT FROM AUTHOR]