Dipole-dipole frequency shifts in multilevel atoms

Dipole-dipole interactions lead to frequency shifts that are expected to limit the performance of next-generation atomic clocks. In this work, we compute dipolar frequency shifts accounting for the intrinsic atomic multilevel structure in standard Ramsey spectroscopy. When interrogating the transitions featuring the smallest Clebsch-Gordan coefficients, we find that a simplified two-level treatment becomes inappropriate, even in the presence of large Zeeman shifts. For these cases, we show a net suppression of dipolar frequency shifts and the emergence of dominant non-classical effects for experimentally relevant parameters. Our findings are pertinent to current generations of optical lattice and optical tweezer clocks, opening a way to further increase their current accuracy, and thus their potential to probe fundamental and many-body physics.

Coherent suppression of tensor frequency shifts through magnetic field rotation

We introduce a scheme to coherently suppress second-rank tensor frequency shifts in atomic clocks, relying on the continuous rotation of an external magnetic field during the free atomic state evolution in a Ramsey sequence. The method retrieves the unperturbed frequency within a single interrogation cycle and is readily applicable to various atomic clock systems. For the frequency shift due to the electric quadrupole interaction, we experimentally demonstrate suppression by more than two orders of magnitude for the ${}^2S_{1/2} to {}^2D_{3/2}$ transition of a single trapped ${}^{171}text{Yb}^+$ ion. The scheme provides particular advantages in the case of the ${}^{171}text{Yb}^+$ ${}^2S_{1/2} to {}^2F_{7/2}$ electric octupole (E3) transition. For an improved estimate of the residual quadrupole shift for this transition, we measure the excited state electric quadrupole moments $Theta({}^2D_{3/2}) = 1.95(1)~ea_0^2$ and $Theta({}^2F_{7/2}) = -0.0297(5)~ea_0^2$ with $e$ the elementary charge and $a_0$ the Bohr radius, improving the measurement uncertainties by one order of magnitude.

Single-Ion Atomic Clock with $3times10^{-18}$ Systematic Uncertainty

We experimentally investigate an optical frequency standard based on the $^2S_{1/2} (F=0)to {}^2F_{7/2} (F=3)$ electric octupole (textit{E}3) transition of a single trapped $^{171}$Yb$^+$ ion. For the spectroscopy of this strongly forbidden transition, we utilize a Ramsey-type excitation scheme that provides immunity to probe-induced frequency shifts. The cancellation of these shifts is controlled by interleaved single-pulse Rabi spectroscopy which reduces the related relative frequency uncertainty to $1.1times 10^{-18}$. To determine the frequency shift due to thermal radiation emitted by the ions environment, we measure the static scalar differential polarizability of the textit{E}3 transition as $0.888(16)times 10^{-40}$ J m$^2$/V$^2$ and a dynamic correction $eta(300~text{K})=-0.0015(7)$. This reduces the uncertainty due to thermal radiation to $1.8times 10^{-18}$. The residual motion of the ion yields the largest contribution $(2.1times 10^{-18})$ to the total systematic relative uncertainty of the clock of $3.2times 10^{-18}$.

Interference of Bose-Einstein Condensates on an Atom Chip

We have used a microfabricated atom chip to split a single Bose-Einstein condensate of sodium atoms into two spatially separated condensates. Dynamical splitting was achieved by deforming the trap along the tightly confining direction into a purely magnetic double-well potential. We observed the matter wave interference pattern formed upon releasing the condensates from the microtraps. The intrinsic features of the quartic potential at the merge point, such as zero trap frequency and extremely high field-sensitivity, caused random variations of the relative phase between the two split condensates. Moreover, the perturbation from the abrupt change of the trapping potential during the splitting was observed to induce vortices.