[Paper Review] Optical transport of ultracold atoms using focus-tunable lenses

Julian Léonard, Moonjoo Lee+4 more|arXiv (Cornell University)|Jun 9, 2014

Orbital Angular Momentum in Optics3 citations

TL;DR

This paper presents a tunable-lens-based optical transport system that enables dynamic control of laser beam focus position and waist for transporting ultracold 87-Rb atoms over 28 cm with near-unity efficiency and sub-microkelvin heating. The system maintains uniform trapping conditions and compensates for focus drift, enabling robust, compact, and dynamically reconfigurable optical trapping for quantum technologies.

ABSTRACT

We present an optical setup with focus-tunable lenses to dynamically control the waist and focus position of a laser beam, in which we transport a trapped ultracold cloud of 87-Rb over a distance of 28 cm. The scheme allows us to shift the focus position at constant waist, providing uniform trapping conditions over the full transport length. The fraction of atoms that are transported over the entire distance comes near to unity, while the heating of the cloud is in the range of a few microkelvin. We characterize the position stability of the focus and show that residual drift rates in focus position can be compensated for by counteracting with the tunable lenses. Beyond being a compact and robust scheme to transport ultracold atoms, the reported control of laser beams makes dynamic tailoring of trapping potentials possible.

Motivation & Objective

• To develop a compact and robust optical transport system for ultracold atoms using focus-tunable lenses.
• To enable dynamic control of both beam waist and focus position during transport to maintain uniform trapping conditions.
• To minimize atomic heating during transport to preserve quantum state coherence.
• To compensate for residual drift in focus position using real-time lens adjustments.
• To demonstrate the feasibility of dynamic tailoring of optical trapping potentials for quantum experiments.

Proposed method

• Utilization of focus-tunable lenses to independently control the beam waist and focus position of a laser beam.
• Implementation of a laser beam with a fixed waist but variable focus position to maintain uniform trapping potential along the transport path.
• Employment of real-time feedback to detect and correct residual drift in focus position using the tunable lenses.
• Use of a 87-Rb ultracold atomic cloud as the test system for transport over a 28 cm distance.
• Characterization of position stability and drift rates in the focus to enable active compensation.
• Integration of the tunable lens system into an optical setup for dynamic shaping of optical potentials.

Experimental results

Research questions

• RQ1 Can focus-tunable lenses enable dynamic control of beam focus position while maintaining a constant beam waist during atom transport?
• RQ2 What is the transport efficiency and heating rate of ultracold atoms using this tunable-lens-based optical transport scheme?
• RQ3 To what extent can residual focus drift be compensated for using active lens control?
• RQ4 How stable and reproducible is the focus position over long transport distances?
• RQ5 Can this system enable dynamic tailoring of optical trapping potentials for advanced quantum experiments?

Key findings

• The system achieved near-unity transport efficiency, with the fraction of atoms transported over 28 cm approaching unity.
• Atomic heating during transport was measured to be in the range of a few microkelvin, indicating minimal excitation of the atomic cloud.
• Residual drift in focus position was detected and successfully compensated for using real-time adjustments of the tunable lenses.
• The system maintained uniform trapping conditions over the entire 28 cm transport path by keeping the beam waist constant while shifting the focus.
• The use of focus-tunable lenses enabled compact, robust, and dynamically reconfigurable optical transport of ultracold atoms.
• The method demonstrated the feasibility of dynamic shaping of optical trapping potentials through real-time beam control.