Experiments with Supersonic Beams as a Source of Cold Atoms

where v is the velocity of the beam and d is the grating spacing [66]. Similarly, for
an acceleration a perpendicular to the direction of atomic motion the phase shift is
φ = 2πaL2
v2 [66]. Reducing the velocity clearly leads to a larger phase shift, and greater
d
resolution. The rotor is an excellent candidate for providing a reduced velocity helium
beam for atom interfometry. In interfometry, the flux is also quite important as shot
noise may otherwise limit sensitivity. Methods for increasing the flux downstream of
the rotor are discussed in [33]. Finally, resolution can also be increased by reducing
the grating spacing. In fact, the periodic structure of a crystal lattice can provide
an extremely short grating which is well matched to the de Broglie wavelength of
the incoming helium beam. It may be possible to construct the atomic analog of
the perfect single crystal neutron interferometer [44, 66], where instead of using the
crystal as a transmission grating, it would instead act as a reflection grating.
55