Geodesy and metrology with a transportable optical clock (1705.04089v1)

Abstract: The advent of novel measurement instrumentation can lead to paradigm shifts in scientific research. Optical atomic clocks, due to their unprecedented stability and uncertainty, are already being used to test physical theories and herald a revision of the International System of units (SI). However, to unlock their potential for cross-disciplinary applications such as relativistic geodesy, a major challenge remains. This is their transformation from highly specialized instruments restricted to national metrology laboratories into flexible devices deployable in different locations. Here we report the first field measurement campaign performed with a ubiquitously applicable $^{87}$Sr optical lattice clock. We use it to determine the gravity potential difference between the middle of a mountain and a location 90 km apart, exploiting both local and remote clock comparisons to eliminate potential clock errors. A local comparison with a $^{171}$Yb lattice clock also serves as an important check on the international consistency of independently developed optical clocks. This campaign demonstrates the exciting prospects for transportable optical clocks.

• The paper demonstrates that a transportable 87Sr optical clock resolves gravitational potential differences with 10 cm height resolution in field conditions.
• The methodology uses a 150-km noise-compensated fiber link and chronometric levelling to measure relativistic redshift over a 1000 m height difference.
• The experiment validates clock performance against conventional geodetic methods, setting the stage for advances in redefined SI units and geodetic applications.

Overview of the Research on Transportable Optical Clocks in Geodesy and Metrology

This paper provides a comprehensive account of the deployment and implications of a transportable optical clock, specifically focusing on its application in geodesy and metrology. The research undertaken by the authors demonstrates the use of a ^87Sr optical lattice clock to measure the gravitational potential differences with remarkable precision between two geographically separated points. This field measurement campaign signifies a critical step toward realizing the potential of optical clocks beyond the confines of metrology laboratories.

Methodology and Technical Implementation

The central experiment took place between two sites: the Laboratoire Souterrain de Modane (LSM) in France and INRIM in Torino, Italy, with a height difference of approximately 1000 meters. This configuration enabled the determination of the relativistic redshift and the gravity potential difference using chronometric levelling. The optical clock functioned effectively across these challenging terrains, which included profound geological features and long-standing land uplift.

The methodology employed involved a 150-km noise-compensated optical fiber link to compare clock frequencies between the two sites. Local comparisons using a ^171Yb lattice clock were also undertaken, serving as validation for the international consistency of independently developed optical clocks. The data was systematically processed to account for potential shifts induced by environmental conditions or optical path variations.

Numerical Results and Claims

The transportable optical clock achieved a resolution of 10 cm in height for a fractional frequency accuracy of 1×10^-17. While traditional geodetic systems display discrepancies at decimetre levels, optical clocks like the one studied offer a promising utility for resolving such inconsistencies. The experimental verification involved high-stability measurements where systematic uncertainties were managed effectively, achieving a potential difference measurement that aligns closely with independent geodetic methods (10 034(174) m^2/s^2 compared to 10 032.1(16) m^2/s^2).

Implications and Future Prospects

The successful deployment of a transportable optical clock extends the limits of current measurement capabilities and poses implications for future technological and scientific developments. From a practical standpoint, chronometric levelling facilitated by such clocks could redefine height systems in geodesy, particularly in difficult-to-access regions. Theoretical advances are also anticipated, as this research contributes to ongoing discussions on redefining fundamental constants within the International System of Units (SI).

Further improvements in the accuracy and stability of transportable optical clocks could allow for even finer measurements of Earth’s gravitational potential, which is vital for a range of scientific inquiries. As optical fiber networks expand, the possibility of integrating chronometric levelling along existing paths becomes more tangible.

Conclusion

This paper underscores a pivotal advancement in optically-driven geodesy through the deployment of a transportable ^87Sr optical clock. The research not only illuminates the adaptability and precision of these clocks but also establishes foundational methodologies for future implementations. Further experimental refinements and the broader deployment of optical clocks in varying environments are key avenues for upcoming research, potentially facilitating a dramatic enhancement in both geodesy and fundamental physics explorations.