Buffer gas loading and magnetic trapping of atoms and molecules
A. Peters
Buffer gas loading of molecules into a cryogenic He-filled cell and subsequent magnetic trapping of the thermalized molecules has been proven to be a powerful method for the production of samples of trapped cold molecules; the largest samples and number densities of trapped molecules that have been obtained thus far have been produced via this method. The method is rather generally applicable to paramagnetic species, atoms as well as molecules. For atoms, this intrinsic universality has been demonstrated in experiments studying a variety of rare-earth atoms, magnetically trapped at mK temperatures.
We have set up a buffer gas loading and magnetic trapping project in our laboratory to be able to directly compare the performance of this method to that of Stark deceleration and AC/DC electric field trapping of molecules. Our present set-up uses a superconducting quadrupole magnet in combination with a 3He-4He dilution refrigerator. From the various methods available for introducing atoms and molecules into the buffer gas cell, we have focused for now on laser ablation of a solid precursor material. We have demonstrated the performance of the system by trapping large samples of atomic chromium with densities exceeding 1012 atoms per cm³ at a temperature of 350 mK and trap lifetimes > 20 seconds.
Although in principle a great variety of paramagnetic molecules offer the potential for magnetic trapping, technical constraints as well as intrinsic molecular properties in praxis limit the selection of candidate species. In particular, large Zeeman relaxation (inelastic) cross sections with the cryogenic helium buffer gas seem to severely curtail the universality of the method. Based on theoretical estimates for the inelastic collision rates, we chose CrH and MnH as promising species and proceeded to trapping experiments after first investigating the relevant spectroscopic properties in the presence of magnetic fields. While the limiting effect of inelastic collisions is clearly apparent, we succeeded in "trapping" both molecules, with 1/e lifetimes of 160 ms for CrH and 135 ms for MnH (preliminary results). Combined with already demonstrated methods for rapid extraction of the buffer gas, this should allow for the preparation of thermally isolated samples with then much longer lifetimes. Current experiments aim at the precise determination of the relevant collisional cross sections.
Buffer gas loading of molecules into a cryogenic He-filled cell and subsequent magnetic trapping of the thermalized molecules has been proven to be a powerful method for the production of samples of trapped cold molecules; the largest samples and number densities of trapped molecules that have been obtained thus far have been produced via this method. The method is rather generally applicable to paramagnetic species, atoms as well as molecules. For atoms, this intrinsic universality has been demonstrated in experiments studying a variety of rare-earth atoms, magnetically trapped at mK temperatures.
We have set up a buffer gas loading and magnetic trapping project in our laboratory to be able to directly compare the performance of this method to that of Stark deceleration and AC/DC electric field trapping of molecules. Our present set-up uses a superconducting quadrupole magnet in combination with a 3He-4He dilution refrigerator. From the various methods available for introducing atoms and molecules into the buffer gas cell, we have focused for now on laser ablation of a solid precursor material. We have demonstrated the performance of the system by trapping large samples of atomic chromium with densities exceeding 1012 atoms per cm³ at a temperature of 350 mK and trap lifetimes > 20 seconds.
Although in principle a great variety of paramagnetic molecules offer the potential for magnetic trapping, technical constraints as well as intrinsic molecular properties in praxis limit the selection of candidate species. In particular, large Zeeman relaxation (inelastic) cross sections with the cryogenic helium buffer gas seem to severely curtail the universality of the method. Based on theoretical estimates for the inelastic collision rates, we chose CrH and MnH as promising species and proceeded to trapping experiments after first investigating the relevant spectroscopic properties in the presence of magnetic fields. While the limiting effect of inelastic collisions is clearly apparent, we succeeded in "trapping" both molecules, with 1/e lifetimes of 160 ms for CrH and 135 ms for MnH (preliminary results). Combined with already demonstrated methods for rapid extraction of the buffer gas, this should allow for the preparation of thermally isolated samples with then much longer lifetimes. Current experiments aim at the precise determination of the relevant collisional cross sections.
