Towards a temperature-insensitive composite diamond clock

TL;DR

This paper demonstrates a temperature-insensitive diamond-based frequency reference by combining electronic and nuclear spin measurements, achieving high stability and robustness suitable for compact quantum clocks.

Contribution

The authors develop a composite frequency reference using NV centers that overcomes temperature dependence, with a specially designed pulse sequence for enhanced stability.

Findings

Achieved fractional instability below 5×10⁻⁹ at 200 s

Demonstrated stability improvements by factors of 4 and 200 over single-frequency clocks

Temperature is no longer the main source of instability in the system

Abstract

Frequency references based on solid state spins promise simplicity, compactness, robustness, multifunctionality, ease of integration, and high densities of emitters. Nitrogen-vacancy (NV) centers in diamond are a natural candidate, but the electronic zero-field splitting exhibits a large fractional temperature dependence, which has precluded its use as a stable clock transition. Here we show that this limitation can be overcome by forming a composite frequency reference that combines measurements of the electronic splitting D with the nuclear quadrupole splitting of the $^{14}$N nuclear spin intrinsic to the NV center. We further benchmark this composite approach against alternative strategies for mitigating temperature sensitivity. By implementing a specially designed pulse sequence with an eight-phase control scheme that suppresses pulse imperfections, we interleave measurements of D and Q in a high-density NV ensemble and demonstrate a temperature-compensated composite frequency reference. The stability of this composite diamond clock is characterized over a 10-day period at room temperature through a comparison to a Rb vapor-cell clock, yielding a fractional instability below $5 \times 10^{-9}$ for an averaging time of $\tau = 200$ s and below $1 \times 10^{-8}$ at $\tau = 2 \times 10^5$ s, corresponding to measured improvements by a factor of 4 and 200, respectively, over a clock based purely on the single frequency D for the same periods. By characterizing the residual sensitivity to magnetic fields, optical power, and radio-frequency drive amplitudes, we find that temperature is no longer the dominant source of instability. These results establish complementary electron- and nuclear-spin transitions in diamond as a viable route to thermally robust frequency metrology, providing a pathway toward compact, multifunctional solid-state clocks and quantum sensors.