Optical tweezers based on metallic plasmonic structures can achieve stable trapping of objects with deep subwavelength dimensions. However, due to the lack of real-time tunability of metallic plasmonic structures, manipulating trapped objects is challenging and usually requires sophisticated tuning of the excitation light source, which limits the application scope of such plasmonic tweezers. Here, we propose the operation principle and analyze the performance of a two-dimensional (2D) network of plasmonic conveyor belts employing electrically tunable graphene plasmonic structures, which can simultaneously and independently trap and transport multiple nanoparticles to arbitrary target locations within the network. Transportation of nanoparticles is achieved by dynamically reconfiguring the carrier density distribution in a graphene nanoribbon based network structure using an array of back-gates, without a need for any change to the excitation light source. Our numerical analyses show that relatively large optical forces can be induced on nanoparticles with tens of nm characteristic dimensions at a moderate excitation source intensity (e.g., 1 mW/μm2), and the corresponding trapping potential energy exceeds 10 k B T at room temperature, which guarantees stable trapping during nanoparticle manipulation. Suitable designs of the junction structures in the network are developed, and effective schemes for all-directional routing of nanoparticles at these junctions are proposed and quantitatively analyzed. Such graphene-based plasmonic conveyor belt networks have high design flexibility and system scalability and, therefore, may find a wide range of applications in different areas such as lab-on-a-chip, assembling complex nanostructures and devices, studying many-body physics, and advancing quantum information technologies.

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We experimentally demonstrate ultrastrong coupling between the intersubband transition(s) in a single semiconductor quantum well and the resonant mode of photonic nanocavities at room temperature. The Rabi splitting reaches 27% of the intersubband transition frequency.

Strong and ultrastrong coupling between intersubband transitions in quantum wells and cavity photons have been realized in mid-infrared and terahertz spectral regions. However, most previous works employed a large number of quantum wells on rigid substrates to achieve coupling strengths reaching the strong or ultrastrong coupling regime. In this work, we experimentally demonstrate ultrastrong coupling between the intersubband transition in a single quantum well and the resonant mode of photonic nanocavity at room temperature. We also observe strong coupling between the nanocavity resonance and the second-order intersubband transition in a single quantum well. Furthermore, we implement for the first time such intersubband cavity polariton systems on soft and flexible substrates and demonstrate that bending of the single quantum well does not significantly affect the characteristics of the cavity polaritons. This work paves the way to broaden the range of potential applications of intersubband cavity polaritons including soft and wearable photonics.

Existing techniques for optical trapping and manipulation of microscopic objects, such as optical tweezers and plasmonic tweezers, are mostly based on visible and near‐infrared light sources. As it is in general more difficult to confine light to a specific length scale at a longer wavelength, these optical trapping and manipulation techniques have not been extended to the mid‐infrared spectral region or beyond. Here, it is shown that by taking advantage of the fact that many materials have large permittivity dispersions in the mid‐infrared region, optical trapping and manipulation using mid‐infrared excitation can achieve additional functionalities and benefits compared to the existing techniques in the visible and near‐infrared regions. In particular, it is demonstrated that by exploiting the exceedingly high field confinement and large frequency tunability of mid‐infrared graphene plasmonics, high‐performance and versatile mid‐infrared plasmonic tweezers can be realized to selectively trap or repel nanoscale objects of different materials in a dynamically reconfigurable way. This new technique can be utilized for sorting, filtering, and fractionating nanoscale objects in a mixture.