Optical lattice clocks with non-interacting bosons and fermions

Abstract

Quantum statistics fundamentally controls the way particles interact; bosons tend to bunch together, whereas fermions repulse each other. As a consequence, statistically different isotopes are found in different macroscopic quantum states at ultracold temperatures. This is related to the total atomic spin, which forces atoms to couple to ambient fields. In designing high-precision atomic clocks that operate at a fractional uncertainty of 10−15 or less, quantum statistics and therefore the spins of the interrogated atoms have an essential role in determining the clocks’ ultimate performance. Here, we discuss the design of optical lattice clocks in view of the quantum statistics and lattice geometries. We propose two configurations that both make the interrogated atoms non-interacting: spin-polarized fermions in a one-dimensional (1D) and bosons in a 3D lattice. A 3D clock with bosonic 88Sr is demonstrated for the first time, in addition to a 1D clock with fermionic 87Sr. The sequential operation of the two clocks enables us to evaluate the clock stability with an uncertainty below 1×10−15 and to determine the isotope shift with significant reduction of the uncertainty related to atomic collisions. Optical lattice clocks, in which trapped atoms serve as a frequency reference, are promising candidates for next-generation atomic clocks. Depending on whether bosons or fermions are loaded into the lattice, fundamentally different design principles apply, as has now been shown.