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An on-chip fully electronic molecular clock based on sub-terahertz rotational spectroscopy

Abstract

Mobile electronic devices require stable, portable and energy-efficient frequency references (or clocks). However, current approaches using quartz-crystal and microelectromechanical oscillators suffer from frequency drift. Recent advances in chip-scale atomic clocks, which probe the hyperfine transitions of evaporated alkali atoms, have led to devices that can overcome this issue, but their complex construction, cost and power consumption limit their broader deployment. Here we show that sub-terahertz rotational transitions of polar gaseous molecules can be used as frequency bases to create low-cost, low-power miniaturized clocks. We report two molecular clocks probing carbonyl sulfide (16O12C32S), which are based on laboratory-scale instruments and complementary metal–oxide–semiconductor chips. Compared with chip-scale atomic clocks, our approach is less sensitive to external influences and offers faster frequency error compensation, and, by eliminating the need for alkali metal evaporation, it offers faster start-up times and lower power consumption. Our work demonstrates the feasibility of monolithic integration of atomic-clock-grade frequency references in mainstream silicon-chip systems.

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Acknowledgements

The authors thank S. Coy (MIT, Department of Chemistry), R. Field (MIT, Department of Chemistry), D. Buss (Texas Instruments and MIT, Department of Electrical Engineering and Computer Science), B. Perkins (MIT Lincoln Labs), J. Muenter (University of Rochester, Department of Chemistry) and P. Nadeau (MIT, Department of Electrical Engineering and Computer Science) for helpful technical discussions. The authors also thank Y. Zhang and K. Nelson (MIT, Department of Chemistry) for help with OCS preparation and other technical support. This work was supported by an NSF CAREER award (ECCS-1653100), MIT Lincoln Laboratory, MIT Center of Integrated Circuits and Systems, and a Texas Instrument Fellowship.

Author information

C.W. and R.H. conceived and designed the research. C.W. constructed the two prototypes (including the laboratory-scale and chip-scale molecular clocks). X.Y. conducted the design of the VCXO and analysis of the clock-loop dynamics. C.W., M.K. and Z.W. conducted spectroscopy experiments. C.W. and J.M. conducted clock stability characterization. C.W. and R.H. analysed the data and wrote the manuscript. All authors reviewed the manuscript.

Correspondence to Ruonan Han.

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The authors declare no competing interests.

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Further reading

Fig. 1: Rotational spectrum of OCS in a WR-4.3 waveguide gas cell.
Fig. 2: Experimental results and analysis of the OCS spectral line at f0 = 267.530239 GHz.
Fig. 3: Laboratory-scale molecular clock.
Fig. 4: Measured stability of the laboratory-scale molecular clock.
Fig. 5: Chip-scale molecular clock on silicon and the measurement results.