Strontium Atoms Cooled with New ‘sawtooth’ Laser Technique Boost Sensor Potential

Researchers have successfully demonstrated sawtooth wave adiabatic passage (SWAP) within a grating magneto-optical trap, offering a novel approach to atomic cooling and manipulation. Peter K. Elgee, Ananya Sitaram, and Sara Ahanchi, all from the Joint Quantum Institute and the National Institute of Standards and Technology, alongside colleagues including Nikolai N. Klimov, Stephen P. Eckel, and Gretchen K. Campbell, report significantly enhanced transfer efficiency between strontium atomic states using SWAP. Their findings reveal that SWAP outperforms conventional triangle wave frequency modulation, even within the complex polarisation environment of a grating MOT, achieving a two-fold improvement in transfer efficiency and enabling the trapping of up to strontium atoms at 4.9 K. This advancement is particularly significant as it proves the efficacy of SWAP in non-orthogonal laser geometries, potentially facilitating increased duty cycles and higher atom numbers in narrow-line grating MOT-based sensors.

This breakthrough addresses a key challenge in manipulating neutral strontium atoms for applications in quantum technologies, specifically enhancing the performance of narrow-line grating MOTs.

The research details the successful implementation of SWAP within a grating magneto-optical trap operating on the 1S0 →3P1 transition of neutral 88Sr, demonstrating its effectiveness even within complex, non-orthogonal laser beam geometries. These parameters represent a significant advancement in the ability to confine and control strontium atoms for extended periods. Researchers overcame limitations inherent in tetrahedral laser beam geometries, where non-orthogonal beams and impure polarization typically reduce momentum transfer and adiabaticity.
The successful application of SWAP in this configuration opens avenues for increasing duty cycles and atom number in sensors reliant on narrow-line grating MOTs. This work extends prior investigations of SWAP, which were largely confined to one-dimensional or six-beam orthogonal laser arrangements, by adapting the technique to the specific geometry of a grating MOT.

Simulations incorporated the complex polarization environment and tetrahedral configuration, revealing that SWAP can generate stronger optical forces than traditional broadband MOT operation. The experimental setup involved upgrades to a previously established grating MOT apparatus, allowing for precise control and measurement of the SWAP process. Confirmation of the simulation results through experimental data underscores the potential of SWAP as a robust method for enhancing atom transfer and cooling in advanced strontium-based quantum systems.

Computational modelling of tetrahedral beam geometry and polarization effects

A 3D optical Bloch equation (OBE) model, implemented using the PyLCP python package, forms the basis of this work’s investigation into sawtooth wave adiabatic passage (SWAP) in a grating magneto-optical trap. This model accounts for the complex polarization and intensity gradients inherent in the tetrahedral laser beam geometry of the grating MOT, extending beyond previous one-dimensional simulations.

The simulation explores momentum transfer along the axial z-direction, aligned with the input beam wavevector, considering σ+, π, and σ− polarization components of the diffracted beams alongside the σ+ polarization of the input beam. The researchers addressed the challenges posed by non-orthogonal laser beams and impure polarization by focusing on adiabaticity requirements for transitions between Zeeman states.

To facilitate comprehensive exploration of adiabatic passages, spontaneous emission was initially neglected by setting the natural decay rate to a low value of 1s−1. The effectiveness of SWAP in improving atom transfer between broad-line and narrow-line MOTs was then demonstrated, revealing a factor of two improvement in transfer efficiency. These results confirm that SWAP remains effective even in non-orthogonal laser beam geometries, potentially enabling greater duty cycles or higher atom numbers in sensors utilizing narrow-line grating MOTs.

Enhanced strontium atom transfer via sawtooth wave adiabatic passage in a grating magneto-optical trap

Researchers demonstrated sawtooth wave adiabatic passage (SWAP) within a grating magneto-optical trap operating on the 1S0 →3P1 transition of neutral 88Sr. The study successfully trapped up to 3 × 106 88Sr atoms in the 1S0 →3P1 grating MOT. The work addresses challenges inherent in compact MOT geometries, specifically the reduced cooling forces and small capture volumes.

Simulations and experiments were conducted to optimize SWAP performance within the tetrahedral laser beam geometry of the grating MOT. The research explored how non-orthogonal beams and impure polarization affect the adiabaticity required for successful SWAP implementation. Results indicate that SWAP can enhance radiation pressure forces despite these geometric constraints, offering a pathway to improve transfer efficiency between broad-line and narrow-line MOTs. This technique utilizes coherent transitions with counter-propagating, frequency-swept laser beams to stimulate momentum transfer.

Enhanced strontium atom trapping via sawtooth wave adiabatic passage

Sawtooth wave adiabatic passage demonstrates enhanced cooling efficiency in a strontium grating magneto-optical trap. Numerical simulations and experimental results confirm that this technique surpasses traditional triangle wave frequency modulation for cooling atoms within the trap. These findings establish the effectiveness of sawtooth wave adiabatic passage even in complex, non-orthogonal laser beam geometries. This capability broadens the potential applications of narrow-line grating magneto-optical traps, enabling increased duty cycles or higher atom numbers in sensor technologies.

The authors acknowledge limitations related to the precision of magnetic field control and the influence of eddy currents, addressed through upgrades to the experimental apparatus including the replacement of permanent magnets with electromagnets and a change in mounting block material. Future research may focus on further optimisation of the magnetic field configuration and vacuum conditions to enhance trap performance and explore the limits of atom number and temperature achievable with this cooling method.