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 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics><mml:mrow><mml:mn>100</mml:mn> <mml:mspace></mml:mspace> <mml:mi>m</mml:mi> <mml:mi>e</mml:mi> <mml:mi>V</mml:mi></mml:mrow> <mml:annotation>$100 \,\mathrm{m}\mathrm{e\mathrm{V}}$</mml:annotation></mml:semantics> </mml:math> , consistent with theoretical modeling. This work advances the development of deterministic plexitonic devices utilizing single-photon nonlinearities at ambient conditions.