A Magneto-Optical Trap for Erbium

Figure 1. Erbium MOT apparatus, showing Zeeman slower and MOT chamber. (Inset: CCD image of erbium MOT)

One of the possible applications of our deterministic atom source is the implantation of single optically active ions into nanostructures, which could then be used in a number of scenarios, ranging from single photon sources to highly sensitive nanoscale strain sensors. Rare earth atoms make excellent candidates for such implantation, because they retain atomic-like spectra with very narrow energy levels, even when implanted in a host material. Since our deterministic source requires magneto-optical trapping, we have been investigating the possibility of a magneto-optical trap (MOT) for rare earths atoms, in particular, erbium.

Our MOT makes use of the 401 nm transition, one of several that could in principle be used for laser cooling erbium. While this transition has the advantage of a very strong oscillator strength, it also has a potential problem with "optical leaks" to a large number of metastable states, which might cause severe trap losses. To our surprise, we found that our erbium MOT had a very robust population of over 10⁶ atoms, and a density as high as 10¹¹ cm^-3, despite these leaks. Making observations of the transient behavior of the MOT population as a function of laser intensity and detuning, we were able to determine that the high MOT population is attributable to a novel recycling process, in which the leaks do occur, but the metastable atoms are retained in the vicinity of the MOT by the interaction between their large magnetic moments and the quadrupole magnetic field of the MOT. Eventually, these metastable atoms decay to the ground state, but do so in the vicinity of the MOT, so they can be easily recaptured.

In addition to enabling us to proceed with a deterministic source of rare earth atoms, the demonstration of a robust erbium MOT opens a wide range of new possibilities for studies in diverse areas, for example, cold dipolar gases, ultracold, narrow-band laser cooling, and quantum optics at telecom wavelengths.

Figure 2. Recycling mechanism. Atoms in the MOT decay from the excited state to metastable levels, which are
held by the quadrupole magnetic field of the MOT. The metastables decay to a reservoir, from which atoms can reload into the MOT.

Laser Cooling Without Repumping: a Magneto-Optical Trap for Erbium Atoms

Jabez J. McClelland - NIST
James Hanssen - University of Maryland
Andrew Berglund - NIST

Online: September 2005
Last Updated: February 2008

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