Designing Coherence in Perovskite Quantum Dot Assemblies by Choice of Ligand

Loss of coherence in the quantum subsystem by coupling to environment limits its applications to quantum information technology. Perovskite quantum dots because of their large absorption coefficient and high single-photon emission rates have garnered considerable attention for applications in quantum systems, but they are limited by rapid loss of coherence due to electron-phonon coupling. In this paper, we study the coherence timescales in dimer assemblies of cesium lead bromide quantum dots, bridged by different ligands. Typically, non-conjugated organic ligands give longer coherence in quantum dot dimers compared to monomers. However, if ligand frontier orbitals extend onto perovskite band edges, or if mid-gap ligand states appear, then coherence is short. In dimers with conjugated ligands, coherences can be elongated by selecting ligands whose frontier orbitals do not hybridize with the perovskite band edges. A number of factors guide the improved coherence times, including enhanced delocalization, surface passivation, and suppression of certain phonon modes in dimers compared to monomer. This study explores materialengineering strategy to enhance coherence in perovskite quantum dots for application in quantum information technology.