Low phase noise beams for Raman transitions with a phase modulator and a highly birefringent crystal

Optical frequency filtering for Raman beams

We present an optical filter that is appropriate for use with Raman beams in atomic interferometry. This is a filter that lets the light of the two frequencies of the Raman pair go through and rejects spurious frequencies that may be close to the atomic resonance and cause decoherence. We characterized the filter's performance optically and also by shining the light into atoms in a Ramsey sequence, to look for decoherence effects from photon scattering. We found that it is safe to use tapered amplifiers in single and double pass for light amplification in the Raman beams since the pedestal of emission has a negligible effect, which can be further reduced by the use of the filter we present.

Effect of an aperture in atomic gravimetry

There is a continuous interest in shrinking the dimensions of portable atomic gravimeters. This inevitably ends up truncating the Gaussian wings of the excitation laser beams whose effect has not been properly quantified yet. The diffraction pattern created from this aperture creates ripples in the wavefront in both the phase and the intensity. We calculate the shift in the measured value of an atomic gravimeter introduced by the phase variations in the wavefront. Fortunately, this shift has a Gaussian decay with the aperture size. For extended clouds, we observe a reduction of the effect thanks to an averaging over transverse positions with different values of the shift. Surprisingly, we found that the intensity variations also introduce an important correction to the photon recoil, which contributes at about the same level as the previous shift in the measurement of the gravitational acceleration. Our results should help decide how small an apparatus can be to guarantee a particular accuracy.

Compact laser modulation system for a transportable atomic gravimeter

Nowadays, atom-based quantum sensors are leaving the laboratory towards field applications requiring compact and robust laser systems. Here we describe the realization of a compact laser system for atomic gravimetry. Starting with a single diode laser operating at 780 nm and adding only one fiber electro-optical modulator, one acousto-optical modulator and one laser amplifier we produce laser beams at all the frequencies required for a Rb-87 atomic gravimeter. Furthermore, we demonstrate that an atomic fountain configuration can also be implemented with our laser system. The modulated system reported here represents a substantial advance in the simplification of the laser source for transportable atom-based quantum sensors that can be adapted to other sensors such as atomic clocks, accelerometers, gyroscopes or magnetometers with minor modifications.

Robust single-sideband-modulated Raman light generation for atom interferometry by FBG-based optical rectangular filtration

Low-phase-noise and pure-spectrum Raman light is vital for high-precision atom interferometry by two-photon Raman transition. A preferred and prevalent solution for Raman light generation is electro-optic phase modulation. However, phase modulation inherently brings in double sidebands, resulting in residual sideband effects of multiple laser pairs beside Raman light in atom interferometry. Based on a well-designed rectangular fiber Bragg grating and a plain electro-optic modulator, optical single-sideband modulation has been realized at 1560 nm with a stable suppression ratio better than -25 dB despite of intense temperature variations. After optical filtration and frequency doubling, a robust phase-coherent Raman light at 780 nm is generated with a stable SNR of better than -19 dB and facilitates measuring the local gravity successfully. This FBG-based all-fiber single-sideband-modulated Raman light source, proposed for the first time and characterized as robust, compact and low-priced, is practical and potential for field applications of portable atom interferometry.

Soliton Interferometry with Very Narrow Barriers Obtained from Spatially Dependent Dressed States

Bright solitons in atomic Bose-Einstein condensates are strong candidates for high precision matter-wave interferometry, as their inherent stability against dispersion supports long interrogation times. An analog to a beam splitter is then a narrow potential barrier. A very narrow barrier is desirable for interferometric purposes, but in a typical realization using a blue-detuned optical dipole potential, the width is limited by the laser wavelength. We investigate a soliton interferometry scheme using the geometric scalar potential experienced by atoms in a spatially dependent dark state to overcome this limit. We propose a possible implementation and numerically probe the effects of deviations from the ideal configuration.

High-frequency broadband laser phase noise cancellation using a delay line

Laser phase noise remains a limiting factor in many experimental settings, including metrology, time-keeping, as well as quantum optics. Hitherto this issue was addressed at low frequencies ranging from well below 1 Hz to maximally 100 kHz. However, a wide range of experiments, such as, e.g., those involving nanomechanical membrane resonators, are highly sensitive to noise at higher frequencies in the range of 100 kHz to 10 MHz, such as nanomechanical membrane resonators. Here we employ a fiber-loop delay line interferometer optimized to cancel laser phase noise at frequencies around 1.5 MHz. We achieve noise reduction in 300 kHz-wide bands with a peak reduction of more than 10 dB at desired frequencies, reaching phase noise of less than -160 dB(rad²/Hz) with a Ti:Al₂O₃ laser. These results provide a convenient noise reduction technique to achieve deep ground-state cooling of mechanical motion.