Abstract
We demonstrate that it is possible to effectively eliminate radiative losses during excitonic energy transport in systems with an intrinsic energy gradient. By considering chainlike systems of repeating “unit” cells that can each consist of multiple sites, we show that tuning a single system parameter (the intra-unit-cell coupling) leads to efficient and highly robust transport over relatively long distances. This remarkable transport performance is shown to originate from a partitioning of the system’s eigenstates into energetically separated bright and dark subspaces, allowing long-range transport to proceed efficiently through a “dark chain” of eigenstates. Finally, we discuss the effects of intrinsic dipole moments, which are of particular relevance to molecular architectures, and demonstrate that appropriately aligned dipoles can lead to additional protection against other (nonradiative) loss processes. Our dimensionless open quantum systems model is designed to be broadly applicable to a range of experimental platforms.
- Received 2 February 2022
- Accepted 10 May 2022
DOI:https://doi.org/10.1103/PRXQuantum.3.020354
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
In both macroscopic and microscopic systems, transporting energy inevitably leads to unwanted losses. In nanoscale systems this can have severe effects on the efficiency of energy generation technologies such as solar cells. As such, minimizing these losses is of vital importance to future technological applications. One of the primary loss mechanisms in nanoscale energy transport systems is so-called 'radiative recombination' where the energy-carrying particles (known as excitons) disappear, re-emitting their energy as electromagnetic waves, i.e. light. Here, we study computational models of excitonic energy transport and reveal that radiative recombination processes can be drastically reduced in systems which satisfy only few general criteria: most importantly, the presence of an intrinsic energy gradient combined with the ability to engineer network geometries consisting of multiple parallel 'wires'. The underlying quantum mechanical phenomenon enabling this remarkable suppression of loss results from the interaction between the transport system and the vibrational and electromagnetic environments within which it is embedded. Specifically, by careful choice of network geometry, the lowest-energy states of the system - which are the most important for energy transport - can be converted to near-perfect 'dark states' which are well-protected from radiative recombination, thereby enabling significant improvements in energy transport efficiency. Our results are a clear demonstration that coherent quantum effects can play a vital role in future technologies with the prospect of enabling dramatic improvements over existing technologies.
