Stability of a trapped-atom clock on a chip

Abstract

We present a compact atomic clock interrogating ultracold 87 Rb magnetically trapped on an atom chip. Very long coherence times sustained by spin self-rephasing allow us to interrogate the atomic transition with 85% contrast at 5 s Ramsey time. The clock exhibits a fractional frequency stability of 5.8 × 10 −13 at 1 s and is likely to integrate into the 10 −15 range in less than a day. A detailed analysis of 7 noise sources explains the measured frequency stability. Fluctuations in the atom temperature (0.4 nK shot-to-shot) and in the offset magnetic field (5 × 10 −6 relative fluctuations shot-to-shot) are the main noise sources together with the local oscillator, which is degraded by the 30% duty cycle. The analysis suggests technical improvements to be implemented in a future second generation set-up. The results demonstrate the remarkable degree of technical control that can be reached in an atom chip experiment.

Spontaneous spin squeezing in a rubidium BEC

“…To estimate the effective nonlinearity for the different choices of the scattering lengths, we calculated the parameter χ of the one-axis twisting Hamiltonian at the stationary state in our geometry. We obtain χ=7.5×10 −5 s 1 with the scattering length values from [32] (red curve), χ=7.3×10 −5 s 1 with the values from [20] (green curve), and 24.6 10 s 5 1 c =´-for the combination [20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37] (blue curve).…”

“…We use the 1 2 ñ « ñ | | clock transition, which enables first-order cancellation of spatial inhomogeneity of the transition frequency in a magnetic trap [21,28]. The transition is driven by a two-photon, RF and MW pulse [22] with Rabi frequency Ω=2π×3.6 Hz. This Rabi frequency, which leads to a pulse duration longer than the vertical trap oscillation period, guarantees that field inhomogeneity from the on-chip microwave guide is averaged out [22].…”

“…The transition is driven by a two-photon, RF and MW pulse [22] with Rabi frequency Ω=2π×3.6 Hz. This Rabi frequency, which leads to a pulse duration longer than the vertical trap oscillation period, guarantees that field inhomogeneity from the on-chip microwave guide is averaged out [22]. The MW signal at 6.8 GHz is generated by a custom-built synthesizer [29], while the RF photon of ≈2 MHz comes from a commercial direct-digital synthesizer.…”

“…Apart from these fundamental contributions, technical noise such as phase noise can limit the measurement of the noise reduction induced by the squeezing process. In order to evaluate our system in terms of technical instabilities, a standard clock measurement, similar to the one conducted in [22], has been performed using the same experimental condition as for figure 5. This measurement yielded a fractional frequency stability of 9.7 10 12 1 2 t --…”

Optical and magnetic properties of a transparent garnet film for atomic physics experiments

“…8 Atoms trapped above the surface, so-called atom chips, [9][10][11] are now used as the basis for many experiments, such as atom interferometry, 12 atomic sensors, 13 and atomic clocks. 14 There are two main kinds of manipulation technique: magnetic and optical. Magnetic fields above the surface can be produced either by currentcarrying wires or patterned magnetic materials and are used to reflect or trap atoms in low-fieldseeking states, 15 as well as to induce velocity-selective magnetic transitions at the surface.…”