A vapor-cell clock with fractional frequency reaching $10^{-16}$ level stability

TL;DR

This paper reports a compact vapor-cell optical clock achieving fractional frequency instability of 6.6×10^{-16}, surpassing previous standards and demonstrating potential for portable high-precision timekeeping.

Contribution

The authors present a novel design for a vapor-cell optical clock that reaches unprecedented stability levels, combining a monolithic spectroscopic unit with active temperature control in a compact system.

Findings

Achieved 6.6×10^{-16} instability at 100-2000 s intervals.

System occupies only 25 liters, suitable for field deployment.

Maintains 10^{-16} level stability over hours.

Abstract

Compact optical clocks with high stability are essential for next-generation frequency standard field applications, from navigation to geodesy, yet existing vapor cell clock systems have remained confined to fractional instabilities over $10^{-15}$. Here we report the breaking of this long standing barrier by demonstrating a molecular iodine optical clock that reaches an instability of $6.6\times 10^{-16}$ and consistently operates at the $10^{-16}$ level throughout 100 s to 2000 s, surpassing all previous vapor-cell standards by nearly an order of magnitude. This achievement is enabled by a special design architecture that integrates a monolithic, drift immune spectroscopic unit bonded to an ultra low expansion glass substrate with active temperature control of key components. The whole system only occupies 25 L. The system achieves $5\times 10^{-15}$ instability at 1 s and sustains $10^{-16}$ level performance over hours, representing the first medium-term optical stability at this level from a compact, field ready package. Our work establishes that $10^{-16}$ fractional frequency instability can be engineered into robust, portable systems through holistic stability conscious design, opening a path towards high precision time keeping beyond the laboratory environment.