Portable atomic clocks are essential in a wide variety of applications, most notably in the operation of global navigation satellite systems. Existing portable atomic clocks utilizing microwave-based interrogation schemes are now routinely eclipsed by the next generation of atomic frequency standards based on optical interrogation. While optical frequency standards demonstrate greatly improved frequency stability, they have only recently reached a level of technical maturity required to demonstrate this improved performance outside of well curated laboratory environments. Here, we demonstrate a fully autonomous and portable optical frequency standard based on an efficient dual-color excitation of the
5S1/2→5D5/2 two-photon transition in
87Rb. The standard utilizes a combination of robust, highly developed commercial-off-the-shelf telecommunications technologies and a fully integrated portable optical frequency comb, providing the optical and microwave outputs vital for interfacing with existing electronic systems and infrastructure. The system demonstrates a fractional frequency stability of
1.9×10−13 at 1s of integration time, reaching
3.5×10−15 at 8000s of integration time without the need for drift removal. This portable demonstrator unit marks a significant achievement in the development of Rb optical atomic frequency standards, and for the deployment of optical atomic frequency standards outside of the laboratory.
Microgravity is expected to be a decisive ingredient for the next leap for experiments testing the fundamental physics of gravity, relativity and theories beyond the standard model. A promising technique for such tests in the quantum domain are matter-wave sensors based on cold atoms or atom lasers, which use atoms as unperturbed microscopic test bodies for measuring inertial forces or as frequency references. For matter-wave interferometers and experiments with quantum matter (Bose-Einstein Condensates or degenerate Fermi gases) microgravity allows the extension of the unperturbed free fall of these test particles in a low-noise environment.
This thesis investigates three novel architectures for compact and portable optical atomic clocks. Optical atomic clocks are known for their high accuracy and are some of the most precise instruments on Earth. Many applications of these instruments, such as space-based gravitational wave detection or tests of relativity, deep space navigation, or geodesy, require compact and portable systems. Creating compact clocks for field use, however, remains challenging as the equipment used to tightly control the motion and temperature of clock atoms is complex and adds to the size and weight of the system. The first two clock architectures described herein use two-photon transitions, with one system based on neutral rubidium (Rb) atoms and the other on neutral calcium (Ca) atoms. The third system uses samarium ions (Sm
2+) trapped in a crystal. Whereas using the two-photon transition in Rb and Ca eliminates the need for confinement of the atoms and for sub-Doppler cooling, the Sm
2+ concept embeds the clock atoms in an inherently rigid lattice. The Rb system was designed as a completely portable clock with a fractional frequency stability of 1 part in 10
13, which was compatible with a demonstration on a stratospheric balloon campaign. During the balloon campaign, the frequency standard was only able to reach a fractional frequency stability of $\delta\nu/\nu_0=6.4\times10^{-9}\persqrttau$ over the range 1-10000 s. The Ca and \sm systems target orders of magnitude higher precisions (greater than 1 part in 10
17 and 1 part in 10
20, respectively). The thesis reviews each system's design, details the experiments used to search for clock transition frequencies, and presents the results of these experiments along with other key measurements. Ultimately, this work provides new insights into the feasibility of these portable optical clock architectures.