Optical analogue for phase-sensitive measurements in quantum-transport experiments

The Aharonov-Bohm effect has recently been employed to measure the quantum-mechanical phase of an electron propagating ballistically through a quantum dot (QD) contained in one arm of the interferometer [Schuster et al., Nature (London) 385, 417 (1997)]. Jauho and Wingreen [Phys. Rev. B 58, 9619 (1998)] have analyzed this geometry under conditions where the QD is modulated harmonically in time as a way to distinguish unambiguously between coherent [e.g., photon-assisted transport] and incoherent processes [e.g., sequential resonant tunneling]. We show that an optical analogue of this experiment exists, namely, the propagation of light through a quantum well in the vicinity of an excitonic resonance subjected to a THz electric field. By carrying out an interferometric experiment, the phase of a transmitted (or reflected) optical beam at a sideband frequency-analogous to the electron's phase-can be measured. These phase shifts can be understood in terms of specific multi-THz-photon processes. The optical experiment affords fundamental insight not ordinarily accessible in transport experiments. [S0163-1829(99)16931-5].