Abstract
We report on the optical preparation of coherent superpositions of exciton and biexciton states manifested in temporal nonlinear oscillations in interacting exciton gases. The effect is illustrated for atomically thin semiconductors, where the reflected light reveals these interactions in a unique way. The occurring nonlinear coherent oscillations are counteracted by incoherent excitation-induced dephasing, a phenomenon which originates from a new type of quantum interference between excitons and the two-exciton scattering continuum. To improve the experimental accessibility, we discuss different methods to control the oscillation modulation depth by modifying the mutual interplay of the exciton-biexciton superposition and excitation-induced dephasing. We find that the coherent optical response can be manipulated by the polarization degree of the exciting light field, the laser detuning, external magnetic fields, and quantum coherent feedback. The extraordinary temporal behavior and its control distinguishes the nonlinear coherent oscillations from atomic Rabi oscillations and enables their engineering based on our proposed control schemes.
- Received 28 May 2020
- Revised 29 August 2020
- Accepted 12 October 2020
DOI:https://doi.org/10.1103/PhysRevX.10.041039
Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.
Published by the American Physical Society
Physics Subject Headings (PhySH)
Popular Summary
The coherent control of the superposition of quantum states is essential for quantum technological applications. To that end, we conduct microscopic simulations that show how to optically prepare and coherently control superpositions in a quantum gas constituted of interacting excitons (bound states of electrons and positively charged electron holes).
Excitons in atomically thin semiconductors, as energetically discrete states that are stable even at room temperature, potentially facilitate a basis for quantum state control in novel quantum technologies. In our study, we report on the control of state interference between excitons and biexcitons, a quasiparticle formed from two excitons. Our simulations show that this interference results in unique quantum superpositions that are observable in reflected light.
We illustrate this effect for atomically thin semiconductors and find that the coherent oscillations observed in the reflected light result from exciton density oscillations. These oscillations are counteracted by coherence dephasing that originates from quantum interference of excitons with a continuum of two-exciton scattering states. We demonstrate that the interplay of quantum interference and exciton-biexciton oscillations can be controlled by the polarization of the light field, pulse detuning, an external magnetic field, and quantum coherent feedback.
Our results pave the way for the coherent control of many-body excitations in exciton gases or other bosonic gases with strong Coulomb interactions in condensed-matter physics. Concurrently, the extraordinary temporal exciton density oscillations and our scheme for controlling them serve as a starting point for experimental verification and engineering.
