High performance CPT-based vapor cell atomic clock

This PhD thesis work aims to explore further the CPT (Coherent Population Trapping) approach for the demonstration of high-performance microwave Cesium vapor cell clocks.

We begin with a thorough metrological characterization of a first clock. This clock uses an optimized pumping scheme named push-pull optical pumping (PPOP) and an pulsed interrogation technic (Ramsey-CPT or SABR-CPT, Symmetric Auto-Balanced Ramsey). A frequency stability at 1 s of 1×10⁻¹³ in Ramsey-CPT mode and 2×10⁻¹³ in SABR-CPT mode was demonstrated. We then measured dependencies of the clock frequency to numerous experimental parameters and demonstrated that the SABR-CPT sequence induces a drastic reduction of numerous dependency coefficients. A stability budget of 3.5×10⁻¹⁴ at 1 day was established. The temperature of passive optical components, the laser frequency, the microwave power and the magnetic field are main contributions to date. A degradation of the clock’s performances for 𝜏 ≥ 100 s was also observed. Numerous investigations were conducted to understand its source.

The second research axis consisted in the design and development of a clock, with a comparable architecture but more compact (optical bench < 10 L). Following its design and its assembly, first characterizations of this clock were reported, such as the spectroscopy of the CPT resonance in both the continuous and the Ramsey-CPT regime. Some frequency shifts measurements are also reported. This clock also demonstrated a preliminary fractional frequency stability of 1.5×10⁻¹¹ at 1 s, and 2.5×10⁻¹² at 10⁵ s in Ramsey-CPT.

Allan deviation, atomic clock, frequency shift, frequency stability, vapor cell.

Full document (FR) : TEL-05411125