Atomic clocks in the solid state

Mohit Verma, Hiromitsu Sawaoka, Amar C. Vutha

Kurt Gibble

Siminda Deng, Wei Ren, Jingfeng Xiang +9 more

Abstract Atomic clocks with higher frequency stability and accuracy than traditional space-borne atomic clocks are the cornerstone of long-term autonomous operation of space-time-frequency systems. We proposed a space cold atoms clock based on an intracavity cooling scheme, which captures cold atoms at the center of a microwave cavity and then executes in situ interactions between the cold atoms and microwaves. As a result of the microgravity environment in space, the cold atoms can interact with the microwaves for a longer time, which aids in realizing a high-precision atomic clock in space. This paper presents the overall design, operational characteristics, and reliability test results of the space atomic clock based on the intracavity cooling scheme designed for the operation onboard the China space station. In addition, the engineering prototype performance of the space cold atoms microwave clock is also presented. The ground test results for the clock show a fractional frequency stability of 1.1 × 10−12 τ−1/2 reaching 2.5 × 10−15 at 200,000 s, providing solid technical and data support for its future operation in orbit.

Konstantin Beyer, Niklas E. Önne, Shimon Kolkowitz +4 more

Atomic clocks achieve extraordinary precision through quantum control over large ensembles of atoms, with precision increasing and atom number advancing steadily. Emerging nuclear clock technology encodes clock states in nuclear rather than electronic transitions, offering a new frontier for precision measurement. Here we study whether a large ensemble of such clock nuclei could be used to observe their mutual gravitational interaction. We investigate the gravitational redshift induced by neighboring atoms, including nuclear energy superpositions as sources of gravity, giving rise to a genuinely quantum gravitational interaction between pairs of nuclei. We find that the resulting clock frequency shift due to mutual gravity may become non-negligible for a macroscopic number of nuclei, for instance in a solid-state thorium clock, and we propose approaches to mitigate electromagnetic field effects by exploiting spatial symmetry and high-precision spectroscopy. We further discuss how energy-induced mass superpositions could be directly probed using external gravitational field sensors. By contrast, observing gravity-induced entanglement involving clocks would require substantially greater experimental advances due to decoherence from spontaneous emission. Taken together, our results suggest that nuclear clocks, either alone or in combination with complementary sensors such as optomechanical systems, may offer a future route toward probing gravity at short distances and testing gravitating quantum source masses beyond the Newtonian limit.

Andrew D. Ludlow

Daniel C. Reed

Strontium optical lattice clocks represent the current state of the art in precise measurement of time. By trapping atoms at the antinodes of a one dimensional interference pattern of light, frequency shifts associated with the absorption and re-emission of photons used to probe the narrow linewidth clock transition can be avoided. In such a periodic system atoms develop a motional bandstructure analogous to electrons in condensed matter systems. By studying the behavior of atoms in the optical lattice we can, by analogy, gain understanding into the behavior of electrons in the solid state. Indeed, we can perform experiments which cannot be done in the real bulk material by controlling parameters which are impossible to change in macroscopic solids. \n \nIn this work we report on modifications to the existing strontium optical lattice clock experiment which have allowed the study of spin-orbit coupling. By dynamically ramping the intensity of one lattice beam during an experimental cycle we can study a regime in which the inter-site hopping rate J is sufficiently large that an atoms internal state can become coupled to its quasimomentum. The design requirements of the changes and the preliminary results are discussed.