Paul Trap Crystal (image) Max-Planck-Gesellschaft Caption Frozen in the trap: In the Paul trap, which consists of four electrodes, cold helium ions stream in from back left. Collisions with particles of the ion crystal, which is suspended in the center of the trap, cause the noble gas atoms to slow down the rotation of the molecular ions and thus cool their rotational temperature. Credit J. R. Crespo/O. O. Versolato/MPI for Nuclear Physics Usage Restrictions None Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.