Competition effects of multiple quantum paths in an atom interferometer

We present an observation of competition effect among multiple quantum paths in a Raman-type Mach-Zehnder atom interferometer. The contrast of interference fringes is studied in a co-propagating three-Raman-pulse atom interferometer. By measuring the contrast of fringes, the competition effect among multiple interference paths is experimentally investigated. Due to the phase competition, the contrast periodically oscillates when modulating either the phase or the interrogation time between Raman pulses. The multiple quantum paths form because of the imperfect population transfer efficiency in stimulated Raman transitions, and are verified by modulating the duration of Raman pulses. The contrast could be optimized by suppressing the phase competition.