Abstract
Strongly driving a two-level quantum system with light leads to a ladder of Floquet states separated by the photon energy. Nanoscale quantum devices allow the interplay of confined electrons, phonons, and photons to be studied under strong driving conditions. Here, we show that a single electron in a periodically driven double quantum dot functions as a “Floquet gain medium,” where population imbalances in the double quantum dot Floquet quasienergy levels lead to an intricate pattern of gain and loss features in the cavity response. We further measure a large intracavity photon number in the absence of a cavity drive field, due to equilibration in the Floquet picture. Our device operates in the absence of a dc current—one and the same electron is repeatedly driven to the excited state to generate population inversion. These results pave the way to future studies of nonclassical light and thermalization of driven quantum systems.
- Received 27 July 2016
DOI:https://doi.org/10.1103/PhysRevX.6.041027
Published by the American Physical Society under the terms of the Creative Commons Attribution 3.0 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
Confined electrons, phonons, and photons are the key components of nanoscale quantum devices. Here, we demonstrate that a single electron, when repeatedly pushed uphill in energy, relaxes to the ground state by emitting a microwave-frequency photon. Since the device controls one and the same periodically driven electron, photons are emitted in the absence of a dc current (i.e., the net current flow through the device is negligible). The experiment could be called a Sisyphus single-photon source, in analogy to Sisyphus, the character in Greek mythology who eternally pushes a boulder—an electron—up a hill only for it to roll back down.
We opt to work at cryogenic temperatures (20 mK) to prevent thermal photons from occupying the cavity. We employ a microwave cavity containing a double quantum dot that is controlled by five gate electrodes. We use an amplification process to measure the radiation emitted from the cavity and the cavity power gain while the electron trapped in the double quantum dot is strongly driven. Unlike other experiments in which significant currents were required to produce photoemission, our cavity has a negligible net current flow.
We expect that our findings will pave the way for future work using quantum dots as light sources. Theory predicts that similar devices can be used to produce many types of radiation ranging from coherent to antibunched light.