The single-exciton strong coupling with the localized plasmon mode (LPM) at room temperature is highly desirable for exploiting quantum technology. However, its realization has been a very low probability event due to the harsh critical conditions, severely compromising its application. Here, we present a highly efficient approach for achieving such a strong coupling by reducing the critical interaction strength at the exceptional point based upon the damping inhibition and matching of the coupled system, instead of enhancing the coupling strength to overcome the system’s large damping. Experimentally, we compress the LPM’s damping linewidth from about 45 nm to about 14 nm using a leaky Fabry–Perot cavity, a good match to the excitonic linewidth of about 10 nm. This method dramatically relaxes the harsh requirement in mode volume by more than an order of magnitude and allows a maximum direction angle of the exciton dipole relative to the mode field of up to around 71.9°, significantly improving the success rate of achieving the single-exciton strong coupling with LPMs from about 1% to about 80%.

Experimental realization of strong coupling between a single exciton and plasmons remains challenging as it requires deterministic positioning of the single exciton and alignment of its dipole moment with the plasmonic fields. This study aims to combine the host–guest chemistry approach with the cucurbit[7]uril-mediated active self-assembly to precisely integrate a single methylene blue molecule in an Au nanodimer at the deterministic position (gap center of the nanodimer) with the maximum electric field (EF_max) and perfectly align its transition dipole moment with the EF_max, yielding a large spectral Rabi splitting of 116 meV for a single-molecule exciton—matching the analytical model and numerical simulations. Statistical analysis of vibrational spectroscopy and dark-field scattering spectra confirm the realization of the single exciton strong coupling at room temperature. Our work may suggest an approach for achieving the strong coupling between a deterministic single exciton and plasmons, contributing to the development of room-temperature single-qubit quantum devices.

Strong coupling between quantum emitters and photonic modes, at which the level splitting (LS) of the mixed quantum states occurs, has aroused great interest due to diverse important quantum applications. The spectral Rabi-splitting (SRS) in photon emission or absorption has been extensively used to characterize strong coupling based on the equality assumption by assigning the SRS to LS. Here, we demonstrate that the equality assumption is usually invalid via a unified quantum treatment on the coupled plasmon-exciton system. It is revealed that the strong coupling characterized by the SRS is easily observed from the subsystem with larger decay, manifesting itself in relativity and diversity, which is highly correlated to the dissipative decays of the coupling subsystems. The plasmon-exciton interactions can be classified into the weak coupling, pseudo-, dark-, intermediate- and super-strong coupling regimes. Our work not only enriches the underlying physics of strong light-matter interactions, but also may stimulate further experimental researches in this field.

Developing reliable and efficient single-photon sources is crucial for advancing quantum technologies, relying on nonlinear frequency conversion or spontaneous emission from individual quantum emitters. While different types of single-photon sources excel in specific applications, none meet all criteria for an “ideal” source: exceptional brightness, high purity, and indistinguishability. To address this challenge, coupling single-photon emitters with designer nanostructures can significantly enhance emission performance, a pivotal area in quantum nanophotonics. This review summarizes recent advancements over the past decade in generating and manipulating single photons, emphasizing the pivotal role of nanostructure coupling. Single-photon emission systems—such as nonlinear crystals, solid-state defects, quantum dots, carbon nanotubes, and two-dimensional materials—are categorized quantitatively based on their ability to achieve high purity, indistinguishability, and brightness, presented in a three-dimensional technology map. Furthermore, nanostructure engineering is showcased for manipulating properties such as emission direction, polarization, chirality, and entanglement of single photons. By elucidating these critical aspects, this review aims to advance understanding of how advancements in nanostructured environments promise to shape the future of single-photon generation and manipulation within quantum nanophotonics.

While strategies to enhance the quantum coherence of plasmonic resonances have attracted a lot of attention in the past, the advent of non-Hermitian optics carries promising possibilities in this direction, mostly of which are still unexplored. In this work, we show that the quantum coherence of plasmonic resonances can be enhanced by integrating a plasmonic antenna in a photonic cavity operated at a chiral exceptional point (CEP), where the phase of light offers an additional degree of freedom for flexibly manipulating the quantum dynamics. The few-mode quantization theory is employed to demonstrate the advantages and related quantum-optics applications of the proposed hybrid cavity in both off- and on-resonance plasmon-photon coupling. For the former case, the local density of states evolves into sub-Lorentzian lineshape, resulting in reduced dissipation of polaritonic states. On resonance, we identify two mechanisms improving the quantum yield by two orders of magnitude at room temperature: the reduction of plasmonic absorption through Fano interference and the enhancement of cavity radiation through superscattering. Our results establish CEP-engineered plasmonic resonances as a promising platform for controlling quantum states and building high-performance quantum devices.