Anticrossing of A Plasmonic Nanoresonator Mode and A Single Quantum Dot at Room Temperature

Strong coupling between a single quantum emitter and a resonant plasmonic mode at room temperature is vital for quantum information processing and sensing. Beating dephasing in these systems by ultrafast energy transfer requires coupling single emitters to a plasmonic nanoresonator with ultrasmall mode volume and optimal spectral overlap. Typically, strong coupling is inferred from normal mode splittings in luminescence spectra, offering rough estimates of coupling strength. However, achieving a full anticrossing and characterizing uncoupled components in advance is challenging. Here, the oxygen‐dependent blue‐shift of CdSe/ZnS quantum dots, recorded at 33 ms time resolution, is leveraged to deterministically tune their transition energy across a scanning plasmonic slit resonator to yield a complete anticrossing, after characterizing both uncoupled states beforehand. The findings provide clear evidence of strong coupling at room temperature, with a Rabi splitting at zero detuning of , consistent with theoretical modeling. This work advances the development of deterministic plexitonic devices utilizing single‐photon nonlinearities at ambient conditions.