Cesium atoms loaded from a two-dimensional (2D) MOT were trapped and laser cooled in a 3D MOT. We launched the atoms vertically at a velocity of 5.0 m s−1 using moving molasses with a (3D) cloud temperature of 1.2 μK. After the MOT and before the interrogation, the atoms were prepared in the |F = 4, mF = 0〉 state using a selection scheme based on the Stern-Gerlach effect (magnetic deflection of the atoms in mF ≠ 0 states). Light pulse interferometry is realized using two phase-locked Raman lasers that couple the cesium clock states (hyperfine splitting of 9.192 GHz). The Raman lasers have a wavelength close to the D2 line (wavelength λ ≃ 852 nm) and are detuned by 470 MHz from the excited state to reduce incoherent scattering. The impact of residual relative Raman laser phase noise has been estimated to 50 mrad per shot of atom interferometer phase. The Raman lasers were sent to the atoms through two optical windows separated by Embedded Image, with an interrogation time 2T = 801 ms. We used Gaussian Raman beams with 1/e2 diameter equal to 40 mm and about 120 mW of total power. The interferometer output signal was determined by the probability of transition, P, from the F = 4 to the F = 3 state, which is read out via fluorescence detection of the two levels’ populations after the atom interferometer light-pulse sequence. The probability of transition was modulated according to P = P0 + A sin Φ, where C = 2A is the interferometer contrast and Φ is the interferometer phase.

Our experiment uses retroreflected Raman beams, such as to form two pairs of Raman beams inducing two transitions: one in the Embedded Image direction and another in the Embedded Image direction. Selectivity of the Embedded Image transitions is provided by tilting the Raman beams by an angle θ ≃ 3.80° with respect to the horizontal to introduce a Doppler shift (± keffgT sin θ/2π ≃ ±611 kHz at the first and last π/2 pulses), which is much larger than the width of the atom Doppler distribution (~ 40 kHz). To follow the resonance condition at each Raman pulse, we stepwise changed the relative frequency between the two Raman lasers during the sequence, to match the values given by the underlying frequency chirp pattern (see details in fig. S2). To apply the frequency steps, we used a direct digital synthesizer driven by an FPGA (field-programmable gate array).

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