High-Performance Coherent Population Trapping Clock with Polarization Modulation

Abstract

We demonstrate a vapor cell atomic clock prototype based on continuous-wave (CW) interrogation and double-modulation coherent population trapping (DM-CPT) technique. The DM-CPT technique uses a synchronous modulation of polarization and relative phase of a bi-chromatic laser beam in order to increase the number of atoms trapped in a dark state, i.e. a non-absorbing state. The narrow resonance, observed in transmission of a Cs vapor cell, is used as a narrow frequency discriminator in an atomic clock. A detailed characterization of the CPT resonance versus numerous parameters is reported. A short-term frequency stability of 3.2 × 10 −13 τ −1/2 up to 100 s averaging time is measured. These performances are more than one order of magnitude better than industrial Rb clocks and comparable to those of best laboratory-prototype vapor cell clocks. The noise budget analysis shows that the short and mid-term frequency stability is mainly limited by the power fluctuations of the microwave used to generate the bi-chromatic laser. These preliminary results demonstrate that the DM-CPT technique is well-suited for the development of a high-performance atomic clock, with potential compact and robust setup due to its linear architecture. This clock could find future applications in industry, telecommunications, instrumentation or global navigation satellite systems.

A high-performance Raman-Ramsey Cs vapor cell atomic clock

“…A significant reduction of the clock frequency sensitivity to laser power variations was measured in the pulsed case, especially for high values of the free-evolution time T R . We think that the use of a pulsed Ramsey-like interrogation, possibly combined with some extensions of Hyper-Ramsey spectroscopy and original synthetic frequency protocols [35,43,44] stability at τ = 1 s. The noise sources contributions are named and calculated as described in [18]. The local oscillator (LO) phase noise item describes the contribution of the LO phase noise to the clock Allan deviation through the intermodulation (CW case) or Dick effect (pulsed case) [25].…”

“…Table I resumes and compares main experimental conditions, clock resonance characteristics and noise contributions to the clock shortterm fractional frequency stability, in both CW and pulsed regimes. The definition and estimation of noise sources contributions, supported by experimental measurements, were performed following the methodology described in [18]. For sake of simplicity, we consider only white noise sources and we assume that the different noise contributions can independently add.…”

“…For sake of simplicity, we consider only white noise sources and we assume that the different noise contributions can independently add. The total expected Allan variance σ 2 y (τ ) is computed as the sum of σ 2 y,LO (contribution due to the phase noise of the local oscillator) and i σ 2 y,p i , with σ 2 y,p i the Allan variance of the clock frequency induced by the fluctuations of the parameter p i [18].…”

“…Moreover, the use of two phase-locked lasers degrades the microwave phase noise, enhancing the Dick effect contribution [15] to the clock short-term frequency stability. Another promising and simple-architecture CPT clock developed in LNE-SYRTE, based on an original constructive polarization modulation technique [16,17], has recently demonstrated an Allan deviation at the level of 3 × 10 −13 τ −1/2 up to 100 s in the continuous-regime [18].…”

Interfering pathways for photon blockade in cavity QED with one and two qubits

“…The phenomenon of quantum interference (QI) effect [1] occurs between different photon transmission pathways, leading to the inhibition/attenuation of absorption by the destructive interference [2]. With its fascinating physical mechanism, many novel quantum effects and corresponding applications have emerged, e.g., electromagnetically induced transparency (EIT) [3], coherent population trapping (CPT) [4], laser without inversion [5], light with ultraslow group velocity [6] and so on. Specifically, quantum interference between two photons has been observed in experiments [7,8].…”