A surface-patterned chip as a strong source of ultra

A surface-patterned chip as a strong source of ultra-cold atoms for quantum
technologies: supplementary information
C. C. Nshii,1 M. Vangeleyn,1 J. P. Cotter,2 P. F. Griffin,1 E. A. Hinds,2
C. N. Ironside,3 P. See,4 A. G. Sinclair,4 E. Riis,1 and A. S. Arnold1
2
1
Dept. of Physics, SUPA, University of Strathclyde, Glasgow G4 0NG, UK
Centre for Cold Matter, Blackett Laboratory, Imperial College London, Prince Consort Road, London SW7 2BW, UK
3
Rankine Building, School of Engineering, University of Glasgow, Glasgow G12 8LT, UK and
4
National Physical Laboratory, Hampton Road, Teddington, Middlesex, TW11 0LW, UK
1 COMPARISON OF MAGNETO-OPTICAL TRAPS
Here we compare the standard, pyramidal and grating traps, with particular emphasis on the trapping volumes.
Fig. Ia shows a standard six-beam MOT1 consisting of three orthogonal pairs of counter-propagating laser beams of
appropriate circular polarisations. The four radial beams have the opposite helicity to the two axial beams, all of which
must be reversed if the direction of the current in the coils is reversed. Figure Ib shows how a 90◦ pyramidal reflector
can transform a single input beam into the equivalent of a 6-beam MOT2 . The helicity of the light is reversed on
each reflection. To generate the upward beam the downward input must undergo a double-reflection and pass through
the atomic cloud. Thus the light is susceptible to shadowing from atomic absorption and also to scattering from the
edges and corners of the pyramid. A standard 4-beam MOT3 is shown in Fig. Ic. It has a similar capture volume to
a 6-beam MOT when made using beams of the same radius. Because of the beam angles required, alignment can be
awkward using standard cubic vacuum chambers. This can be overcome using the triangular pyramid4 , as illustrated
in Fig. Id. This geometry has the benefit that, unlike the pyramid in Fig. Ib, the capture volume extends above the
opening allowing the atoms to be easily accessed for imaging. In Figs. I e & f we show the beam overlap volumes
for the grating traps of Chip B and D respectively, described in our Letter. These traps have the virtue of a larger
FIG. I: Comparison of magneto-optical traps. The k-vectors of laser beams are shown as red arrows, with circular
polarisations indicated by grey arrows. The black tori (shown in a, but only implied in b-f for clarity) are current carrying coils
used to generate the quadrupole magnetic field required by a MOT. The current directions are shown by black arrows. The
green zones with blue edges indicate the beam overlap regions. Standard 6- and 4-beam MOTs are shown in a and c, while
their pyramidal equivalents are shown in b and d. Two grating chip MOTs using Chip B and Chip D from Fig. 2 of our Letter
are shown in e and f. In e, outward diffraction orders are not shown.
2
trapping volume that is fully accessible.
[1] Raab, E. L., Prentiss, M., Cable, A., Chu, S. & Pritchard, D. E. Trapping of neutral sodium atoms with radiation pressure.
Phys. Rev. Lett. 59, 2631-2634 (1987).
[2] Lee, K. I., Kim, J. A., Noh, H. R. & Jhe, W. Single-beam atom trap in a pyramidal and conical hollow mirror. Opt. Lett.
21, 1177-1179 (1996).
[3] Shimizu, F., Shimizu, K. & Takuma, H. Four-beam laser trap of neutral atoms. Opt. Lett. 16, 339 (1991).
[4] Vangeleyn, M., Griffin, P. F., Riis, E. & Arnold, A. S. Single-laser, one beam, tetrahedral magneto-optical trap. Opt. Express
17, 13601-13608 (2009).