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Physical Review Letters

First Observation of Magnetically Trapped Neutral Atoms

Alan L. Migdall, John V. Prodan, William D. Phillips, Thomas H. Bergeman, Harold J. Metcalf

Published Jun 17, 1985• 462 citations
Publisher

Abstract

We report the first observation of electromagnetically trapped neutral atoms. Laser cooled and stopped sodium atoms are confined in a magnetic quadrupole trap formed by two opposed, separated, coaxial current loops. The decay time constant for atoms in the trap is 0.83(7) s and is limited mainly by collisions with background gas atoms.
DOI
10.1103/physrevlett.54.2596

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A thermal atomic Na beam is opposed by a resonantly tuned laser beam. The radiation pressure decelerates and compresses the thermal velocity distribution, bringing the average velocity to zero and reducing the width from ~1000 m/s to a few tens of m/s or less.1 The density of stopped atoms is > 106/cm3 within a bandwidth of a few m/ s. These densities and velocities are suitable for trapping by a number of proposed optical and magnetic traps. Using these stopped atoms, we have demonstrated the first electromagnetic trapping of neutral atoms. The trap, a magnetic quadrupole formed by two separated, coaxial, opposed current loops, confines the atoms by virtue of the force exerted on the Na magnetic dipole moment by the inhomogeneous magnetic field. The time constant for exponential decay of the atomic population in the trap is 0.83(7) s and is limited mainly by collisions with fast background gas atoms. The maximum velocity of atoms contained in the trap is 3.5 m/s, corresponding to a maximum energy of 17 mK.
Neutral sodium atoms have been continuously loaded into a 0.1-K-deep superconducting magnetic trap with laser light used to slow and stop them. At least 1 \ifmmode\times\else\texttimes\fi{} 109{10}^{9}109 atoms were trapped with a decay time of 2\textonehalf{} min. The fluorescence of the trapped atoms was studied as a function of time; possible loss mechanisms from the trap are discussed.
We have continuously stopped thermal sodium atoms with laser light and loaded them into a 0.1-K deep superconducting magnetic trap. The trap is formed by a local minimum of the magnetic field produced by two superconducting coils and a radially confining octupole field. The atoms are slowed and stopped in two stages: The atoms are first slowed to ~200 m/s using a counterpropagating resonant laser beam and tapered magnetic field to compensate for the changing Doppler shift as the atoms are slowed.1 A second laser beam and tapered magnetic field, actually located within the trap, are used to stop the atoms in the trap. This continuous loading process has allowed us to accumulate up to 1 × 109 trapped atoms, and trapping times of several minutes have been achieved. Our trap has the feature of having a uniform magnetic field at its bottom, opening up the possibility of precision spectroscopy of the trapped atoms. The fluorescence from the trapped atoms has been studied, and they have been cooled to ~1 mK using 1-D optical molasses.