Figure 20

Quantum-eraser experiment from [31]) based on an atomic interferometer. (a) The atomic beam A was split into two beams: beam B was reflected by the first Bragg grating formed by a standing wave, and beam C was transmitted. The atomic beams freely propagated for a time duration of t sep and acquired a lateral separation d . The beams B and C were then split again by a second standing light wave grating. In the far field, complementary spatial interference patterns were observed in two regions. These interference patterns were due to superpositions of beams D and E ( F and G ). (b), (c) The spatial fringe patterns in the far field of the interferometer for t sep = 105 μ s with d = 1.3 μ m and t sep = 255 μ s with d = 3.1 μ m , respectively. The left and right complementary interference patterns were, respectively, generated by the atomic beams D and E , and F and G [shown in (a)]. The dashed lines indicate the sum of the intensities of two interference patterns obtained with a relative phase shift of π . (d) The simplified scheme of the internal atomic states, which were addressed using microwave (mw) radiation and light. (e) The principle of correlating the path the atoms took with their internal electronic states. The standing-wave grating produced a relative π phase shift of state | 2 ⟩ relative to | 3 ⟩ conditional on its path. A Ramsey interferometer employed two microwave π / 2 pulses and converted different relative phases into different final internal states | 2 ⟩ and | 3 ⟩ , respectively. (f) When the which-path information was stored in the internal atomic state, the interference patterns vanished. From [31].