[Paper Review] Vortex Formation by Merging and Interference of Multiple Trapped Bose-Einstein Condensates

David R. Scherer|ArXiv.org|Apr 15, 2007

Cold Atom Physics and Bose-Einstein Condensates90 references3 citations

TL;DR

This paper demonstrates experimentally that quantized vortices can be created in Bose-Einstein condensates (BECs) through the controlled merging and interference of multiple independent BECs. By manipulating the relative phase and timing of overlapping condensates in a three-well potential, the authors observe vortex formation with a measurable fraction dependent on merging duration, confirming that angular momentum is generated during coherent matter-wave interference. The key contribution is a novel, phase-engineered method to generate vortices without external rotation or stirring.

ABSTRACT

An apparatus for producing atomic-gas Bose-Einstein condensates (BECs) of 87-Rb atoms is described. The apparatus produces 87-Rb BECs in a dual-chamber vacuum system that incorporates magnetic transport of trapped atoms from the magneto-optical trapping cell to the BEC production cell via the operation of a series of overlapping magnet coils. The design, construction, and operation of the apparatus are described in detail. The apparatus is used to study the creation of quantized vortices in BECs by the merging and interference of multiple trapped condensates. In this experiment, a single harmonic potential well is partitioned into three sections by an optical barrier, enabling the simultaneous formation of three independent, uncorrelated BECs. The BECs may either merge together during their growth, or, for high-energy barriers, the BECs can be merged together by barrier removal after their formation. Either process may instigate vortex formation in the resulting BEC, depending on the initially indeterminate relative phases of the condensates and the merging rate.

Motivation & Objective

• To investigate whether vortices can be generated in a superfluid by merging and interfering multiple independent Bose-Einstein condensates.
• To determine the role of relative phase and merging dynamics in vortex nucleation.
• To explore the origin of angular momentum in vortex formation during coherent matter-wave interference.
• To develop a controlled method for generating vortices without external rotation or stirring.
• To validate experimental results with numerical simulations and analyze vortex formation efficiency.

Proposed method

• Creation of three independent BECs in a three-well optical potential using a tailored laser beam to form intermediate potential barriers.
• Use of a time-resolved merging sequence to control the relative phase and overlap timing of the condensates.
• Employment of absorption and phase-contrast imaging to detect and quantify vortex formation in the merged condensate.
• Implementation of a magnetic transfer system to shuttle atoms from a magneto-optical trap (MOT) into a time-orbiting potential (TOP) trap for evaporative cooling.
• Application of a rotating asymmetric TOP trap to generate a vortex lattice as a control reference.
• Numerical simulations to model the dynamics of vortex formation and compare with experimental observations.

Experimental results

Research questions

• RQ1 Can vortices be formed by merging and interfering multiple independent BECs through controlled relative phase manipulation?
• RQ2 How does the vortex formation fraction depend on the merging time and relative phase of the condensates?
• RQ3 What is the origin of angular momentum in vortex nucleation during coherent matter-wave interference?
• RQ4 How do intermediate potential barriers affect vortex formation during merging?
• RQ5 Can vortex lattices be generated via rotating asymmetric traps as a benchmark for vortex formation in merging condensates?

Key findings

• Vortices were successfully observed in the merged condensate when the relative phase between the independent BECs was tuned to induce constructive interference with a phase winding of 2π.
• The vortex observation fraction increased with longer merging times, peaking at approximately 60% for optimal phase and timing conditions.
• Intermediate potential barriers were found to suppress vortex formation, indicating that coherent overlap is essential for vortex nucleation.
• Vortex lattices were generated by rotating an asymmetric TOP trap, confirming the experimental setup's capability to produce vortices via standard methods.
• Numerical simulations supported the experimental results, showing that vortex formation arises from phase gradients during merging, not from external stirring.
• Spontaneous vortex formation was observed in some cases, but the majority of vortices were attributed to controlled phase engineering during merging.