Abstract
Radiation properties of a pointlike source of light, such as a molecule or a semiconductor quantum dot, can be tailored by modifying its photonic environment. This phenomenon lies at the core of cavity quantum electrodynamics (CQED). Quantum dots in photonic crystal microcavities have served as a model system for exploring the CQED effects and for the realization of efficient single-photon quantum emitters. Recently, it has been suggested that quantum interference of the exciton recombination paths through the cavity and free-space modes can significantly modify the radiation. In this work, we report an unambiguous experimental observation of this fundamental effect in the emission spectra of site-controlled quantum dots positioned at prescribed locations within a photonic crystal cavity. The observed asymmetry in the polarization-resolved emission spectra strongly depends on the quantum dot position, which is confirmed by both analytical and numerical calculations. We perform quantum interferometry in the near-field zone of the radiation, retrieving the overlap and the position-dependent relative phase between the interfering free-space and cavity-mode-mediated radiative decays. The observed phenomenon is of importance for realization of photonic-crystal light emitters with near unity quantum efficiency. Our results suggest that the full description of light-matter interaction in the framework of CQED requires a modification of the conventional quantum master equation by also considering the radiation mode interference.
12 More- Received 20 October 2021
- Revised 12 February 2022
- Accepted 13 April 2022
- Corrected 12 January 2023
- Corrected 22 June 2022
DOI:https://doi.org/10.1103/PhysRevX.12.021042
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)
Corrections
22 June 2022
Correction: Inline equations in the last sentence of the fifth paragraph of Sec. II and in the first sentence of the third paragraph of Sec. IV have been fixed.
12 January 2023
Second Correction: The omission of additional support information has been fixed.
synopsis
Explaining Asymmetric Emission from Quantum Dots
Published 20 May 2022
A new experiment on the emission spectrum of quantum dots in photonic-crystal microcavities supports a recently proposed theory of cavity quantum electrodynamics.
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Popular Summary
The properties of any pointlike source of light can change when the source is placed in a nanoscale optical cavity. For example, semiconductor nanostructures known as quantum dots, when placed in these cavities, can be used in the design of efficient single-photon emitters. Recently, researchers have suggested that interference between decay paths of excitons—bound pairs of electrons and positively charged holes confined in quantum dots—can significantly modify the emission of a cavity-enclosed quantum dot. Here, we report on unambiguous experimental evidence of this phenomenon.
In a cavity, a quantum dot exciton decays by emitting a single photon either directly or via a cavity-enclosed mode. Interference between these two decay channels can be controlled by changing the difference between resonance frequencies of the exciton and the cavity-confined optical mode. Destructive interference can nearly completely suppress quantum dot emission at the exciton resonance frequency.
In this work, we experimentally demonstrate that this interference strongly affects quantum dot emission spectra, it is robust against decoherence, and reveals novel, previously not measured parameters such as an overlap and a relative phase between direct and cavity-mode-mediated emission channels. The observed interference is important for the understanding of light-matter interaction in optical cavities and must be considered in both theoretical studies and measurements. In particular, the quantum master equation, a common method to describe dynamics of a quantum system, should be completed with new terms that account for the interference effects between different emission channels.
As a bonus, we use the observed interference effect for spatially resolving the rate of the direct quantum dot emission. The latter can be used for designing photonic crystal-based optical sources with high quantum efficiency and tailored emission characteristics.