A Mesoscopic Quantum Eraser

– Motivated by a recent experiment by Buks et al. [Nature 391, 871 (1998)] we consider electron transport through an Aharonov–Bohm interferometer with a quantum dot in one of its arms. The quantum dot is coupled to a quantum system with a finite number of states acting as a which–path detector. The Aharonov–Bohm interference is calculated using a two–particle scattering approach for the joint transitions in detector and quantum dot. Tracing over the detector yields dephasing and a reduction of the interference amplitude. We show that the interference can be restored by a suitable measurement on the detector and propose a mesoscopic quantum eraser based on this principle. Recent progress in quantum and atom optics has made it possible to test basic tenets of quantum physics. Complementarity has been tested in various realizations [1] of the classical double–slit gedanken experiment using photon pairs created in parametric down–conversion. Related experiments [2] utilizing atomic beams instead of photons have been performed very recently. These experiments not only confirmed the destruction of multiple–path interference due to a which–path measurement. More importantly, they also demonstrated that the loss of interference need not be irreversible if the which-path detector is itself a quantum system. In fact, realizing Scully's [3] idea of a quantum eraser it was shown that the interference can be restored by erasing the which-path information from the detector in a subsequent measurement. Quantum detectors which have been used in practical implementation of quantum erasers include the photon polarization and internal degrees of freedom of atoms in an atomic beam. In this Letter, we address the measurement process and the concept of a quantum eraser in the domain of mesoscopic physics. Specifically, we propose a semiconductor microstructure which can act as a quantum eraser. Far from only duplicating and/or corroborating results in optics, such a device would be of considerable interest in its own right. First, it would test quantum physics in the domain of solid state physics. Second, and in contrast to quantum optics, mesoscopic probes are inevitably coupled to macroscopic bodies (leads etc.), opening the possibility to address quantitatively the issue of quantum decoherence. Finally, mesoscopic probes offer the possibility of practical applications.