Atomic interferometry using stimulated Raman transitions

TLDR

Stimulated Raman transitions between hyperfine ground states of sodium atoms are driven by two nearly resonant counter‑propagating laser beams, which impart a velocity kick of ~6 cm s⁻¹ and, when far detuned, suppress spontaneous emission so the atoms behave as a two‑level system. An atom interferometer is realized by a π/2–π–π/2 Raman pulse sequence that coherently splits, redirects, and recombines the atomic wave packet. Wave‑packet interference was observed with 2.4 mm separation, and the interferometer measured gravitational acceleration to a precision of 3 ppm.

Abstract

Sodium atoms prepared in hyperfine ground-state 11 > are driven to the other ground-state hyperfine level 12> when two laser beams nearly resonant with an optical transition have a frequency difference equal to the ground-state hyperfine splitting. When the two laser beams are counterpropagating, conservation of momentum between the atom and the light field requires that the atom acquire a velocity kick ~2 2 ħk/m during the 11> and 12> transition (~6 cm/sec in our experiment). When the lasers are detuned far from the optical transition, spontaneous emission from the intermediate optical level becomes negligible, and the atom behaves as a two-level system coupled to a resonant rf driving field. We have created an interferometer by applying a π/2-π-π/2 Raman pulse sequence: a first π/2 pulse coherently splits the atomic wave packet by putting it in a superposition of states 11> and 12>, a second π pulse occurring a time Δ t later redirects each wave packet and a final π/2 pulse recombines the wave packets at time 2Δ t . We have observed wave packet interference for wave packet separations of 2.4 mm and, by using the interferometer as an accelerometer, have measured the atom’s acceleration due to gravity to 3 parts in 10 6 .