Abstract
The optical clock is a fundamental applications of the coherence of ultracold atoms. Most of the implementations with trapped ions are based on the single-ion optical clock by Dehmelt [1], and some of them have successfully achieved inaccuracies in the 10−18 level [2]. The idea has been extended to systems consisting of many neutral atoms by Katori with proper engineering on light shift associated with the optical lattice [3]. The enhanced stability is the great advantage obtained by multiple atoms. Extension of the single-ion system to multi-ion systems requires considerations on the inhomogeneous electric quadrupole shift originating from non-uniform electric field gradient at the location of each ion. A straightforward approach is to use ion species with null quadrupole moment such as In+, Al+ [4]. We present another approach using ions with non-zero quadrupole moment. In the approach we use a planar surface trap to arrange the ions in an equally-spaced manner to vanish the inhomogeneous shift. We show that a clock with multiple Ca+ ions can be operated even without a reference cavity for the clock laser, and that superradiant clock is expected when the ions are coupled to a cavity.
© 2019 IEEE
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