Fewer interfaces, longer coherence: inverting the multi-shell design rule for quantum-information colloidal quantum dots

Abstract

Cascaded type-II core/shell/shell colloidal quantum dots are widely studied as a route to extended radiative lifetimes, suppressed Auger losses, and tunable near-infrared emission. To test whether the same architecture remains advantageous for coherence-limited quantum-information applications, the cascaded core/shell/shell CdSe/CdTe/ZnTe is compared with the conventional core/shell CdSe/ZnTe at fixed core and total radii. The wave functions of the electron and the hole are obtained from a self-consistent Schrödinger–Poisson solve with experimental band offsets and BenDaniel–Duke matching. They enter as inputs to a five-channel Lindblad master equation that includes radiative recombination, two-particle Shockley–Read–Hall non-radiative recombination, acoustic-phonon pure dephasing, single-particle interface-trap dephasing, and a measurement-induced dephasing channel of dimensionless strength η=γmeasT2(0). Three independent geometric sweeps—over core radius, CdTe interlayer thickness, and ZnTe outer-shell thickness-show that the core/shell/shell architecture underperforms the core/shell architecture in coherence time by a factor of two to three and in coherence-preservation fidelity by up to ΔF=0.16 at η=1. At the smallest total radius examined, the spatial electron–hole separation Δreh is matched between the two architectures to within 2 Å, yet the fidelity gap persists. The gap therefore originates not from the spatial separation that motivated the cascaded design, but from the interface count. For coherence-limited applications in trap-dominated structures with compositionally sharp interfaces, interface minimization therefore takes precedence over band-alignment optimization, inverting the design rule established for optical and photovoltaic performance.