Abstract In recent years, quantum nanophotonics has forged a rich nexus of nanotechnology with photonic quantum information processing, offering remarkable prospects for advancing quantum technologies beyond their current technical limits in terms of physical compactness, energy efficiency, operation speed, temperature robustness and scalability. In this perspective, we highlight a number of recent studies that reveal the especially compelling potential of nanoplasmonic cavity quantum electrodynamics for driving quantum technologies down to nanoscale spatial and ultrafast temporal regimes, whilst elevating them to ambient temperatures. Our perspective encompasses innovative proposals for quantum plasmonic biosensing, driving ultrafast single-photon emission and achieving near-field multipartite entanglement in the strong coupling regime, with a notable emphasis on the use of industry-grade devices. We conclude with an outlook emphasizing how the bespoke characteristics and functionalities of plasmonic devices are shaping contemporary research directives in ultrafast and room-temperature quantum nanotechnologies.
Abstract In recent years, quantum nanophotonics has forged a rich nexus of nanotechnology with photonic quantum information processing, offering remarkable prospects for advancing quantum technologies beyond their current technical limits in terms of physical compactness, energy efficiency, operation speed, temperature robustness and scalability. In this perspective, we highlight a number of recent studies that reveal the especially compelling potential of nanoplasmonic cavity quantum electrodynamics for driving quantum technologies down to nanoscale spatial and ultrafast temporal regimes, whilst elevating them to ambient temperatures. Our perspective encompasses innovative proposals for quantum plasmonic biosensing, driving ultrafast single-photon emission and achieving near-field multipartite entanglement in the strong coupling regime, with a notable emphasis on the use of industry-grade devices. We conclude with an outlook emphasizing how the bespoke characteristics and functionalities of plasmonic devices are shaping contemporary research directives in ultrafast and room-temperature quantum nanotechnologies.
Abstract Quantum nanophotonics places nanoscale structuring in direct dialogue with photonic quantum information—compressing functionality to the few-nanometre, few-femtosecond frontier while retaining energy efficiency, speed and room-temperature operation. We highlight nanoplasmonic cavity-QED architectures in which extreme mode confinement delivers strong coupling under ambient conditions, enabling ultrafast single-photon emission and near-field multipartite entanglement using industry-grade near-field transducers that nanofocus guided light at practical efficiencies. We set these advances against the arc from early plasmonic cQED proposals and single-emitter Purcell studies to modern time-domain measurements that resolve sub-picosecond polariton/Rabi dynamics—establishing a clear route from concept to device. In parallel, we point to low-loss, high-index Mie resonators whose spectrally sharp electric and magnetic modes afford narrow-band coherent control, filtering and radiation-pattern engineering, and which naturally co-integrate in hybrid metal–dielectric stacks that combine ultrastrong local coupling with low-loss routing and storage. Finally, we discuss quantum nanoplasmonic coherent perfect absorption (qnCPA)—a waveguide-fed, non-perturbing protocol that selectively prepares and protects plasmon–emitter dressed states via dissipation-assisted, unidirectional feeding. Together with macroscopic QED and quantum quasinormal-mode quantization, which regularize open, lossy resonators and clarify when loss can be a resource, these developments chart robust, chip-scale routes to room-temperature quantum technologies.
Quantum technologies are widely expected to bring a revolution in communications and information technologies in the coming decade allowing, for example, un-paralleled levels of secure communications. For quantum communication, photonic quantum effects have played a central role, but most photonic solutions and systems based on light-matter interaction also require cryogenic environments. Strong coupling of light and matter at the single emitter level is a fundamental quantum resource offering deterministic energy exchange between single photons and a two-level system, and the possibility to achieve single-photon nonlinearities via the anharmonicity of the Jaynes-Cummings ladder. Until recently, however, the conditions for achieving strong-coupling were most commonly met at cryogenic temperatures such that de-coherence processes are suppressed. As a major step forward, we have recently demonstrated room-temperature strong coupling of single molecules [1] and single quantum dots [2] to ultra-confined light fields in plasmonic resonators at ambient conditions. The fact that strong-coupling conditions may be reached at room temperature is of immense interest because it represents a clear route to a practical implementation and use of quantum behaviour in nanophotonic systems and its application in bio-sensing [3]. The talk will discuss how nanoplasmonics can be an enabler of ultrafast room-temperature quantum nanophotonic networks via strong coupling and ultrafast quantum dynamics [4]. We will highlight the physics associated with recently demonstrated room-temperature strong coupling of single molecules in a plasmonic nano-cavity [1] and near-field generated strong coupling of single quantum dots [2] and single quantum emitter Dicke enhancement [5] paving the road towards single-photon quantum nonlinearities. The presentation will also explain near-field enhanced single-photon emission in near-zero index materials [6] and ultrafast multi-partite quantum entanglement [7]. This provides the foundation for unprecedented control over photon number, single photon dynamics, and dynamic multi-photon coherence. These properties are all imperative for the development of next-generation, nanoscale building blocks in ambient-temperature photonic quantum communication technologies.
Light-matter superposition states obtained via strong coupling play a decisive role in quantum information processing, but the deleterious effects of material dissipation and environment-induced decoherence inevitably destroy coherent light-matter polaritons over time. Here, we propose the use of coherent perfect absorption under near-field driving to prepare and protect the polaritonic states of a single quantum emitter interacting with a plasmonic nanocavity at room temperature. Our scheme of quantum nanoplasmonic coherent perfect absorption leverages an inherent frequency specificity to selectively initialize the coupled system in a chosen plasmon-emitter dressed state, while the coherent, unidirectional and non-perturbing near-field energy transfer from a proximal plasmonic waveguide can in principle render the dressed state robust against dynamic dissipation under ambient conditions. Our study establishes a previously unexplored paradigm for quantum state preparation and coherence preservation in plasmonic cavity quantum electrodynamics, offering compelling prospects for elevating quantum nanophotonic technologies to ambient temperatures.
Strong light–matter interaction is at the heart of modern quantum technological applications and is the basis for a wide range of rich optical phenomena. Coupling a single quantum emitter strongly with electromagnetic fields provides an unprecedented control over its quantum states and enables high-fidelity quantum operations. However, single-emitter strong coupling is exceptionally fragile and has been realized mostly at cryogenic temperatures. Recent experiments have, however, demonstrated that single-emitter strong coupling can be realized at room temperature by using plasmonic nanocavities that confine optical fields via surface plasmons strongly on metal surfaces and facilitate sub-picosecond light–matter interaction. Here, we outline recent theoretical developments and experimental demonstrations of room-temperature strong coupling in the plasmonic platform, from emitter ensembles down to the single emitter limit, before placing a focus on selective studies that explore and provide insight into applications of plexcitonic strong coupling including sensing of single biological molecules, qubit entanglement generation, and reconfigurable single-photon sources and provide an outline of research directions in quantum sensing, quantum information processing, and ultrafast spectroscopy.
For a quantum Internet, one needs reliable sources of entangled particles that are compatible with measurement techniques enabling time-dependent, quantum error correction. Ideally, they will be operable at room temperature with a manageable decoherence versus generation time. To accomplish this, we theoretically establish a scalable, plasmonically based archetype that uses quantum dots (QD) as quantum emitters, known for relatively low decoherence rates near room temperature, that are excited using subdiffracted light from a near-field transducer (NFT). NFTs are a developing technology that allow rasterization across arrays of qubits and remarkably generate enough power to strongly drive energy transitions on the nanoscale. This eases the fabrication of QD media, while efficiently controlling picosecond-scale dynamic entanglement of a multiqubit system that approaches maximum fidelity, along with fluctuation between tripartite and bipartite entanglement. Our strategy radically increases the scalability and accessibility of quantum information devices while permitting fault-tolerant quantum computing using time-repetition algorithms.
The next generation of quantum computers will be scaled up from those which currently incorporate a few dozen qubits, to those of a few hundred with the development of noisy intermediate-scale quantum (NISQ) devices. This greatly increases the decoherence rate of any operation performed using NISQ hardware even under cryogenic conditions. Recently, much effort has been put into researching plasmonic-based devices that are able to perform ultrafast (picosecond) logic operations on a time scale that is faster than the decoherence rate of the system, while being able to operate nearer to room temperature. Plasmonic-based structures that use quantum dots as qubits are considered viable sources for room temperature quantum networks given their relatively low decoherence rate and their overall ease to fabricate compared to the often-used superconducting, i.e., SQUID-based devices. For quantum computing, one requires a reliable source of entangled particles which are compatible with repeaters and quantum error correction. Herein, we investigate the possibilities of time-dependent multipartite entanglement using a plasmonic-based archetype which couples quantum dots to a surface plasmon mode of a near-field transducer (NFT) and is fully integrated with a photonic waveguide. We demonstrate excellent fidelities of entanglement (>0.99) while varying the dipole moment and further investigate the effect of manipulating between the weak to strongly driven regimes. Altogether, we present a novel concept suitable for the implementation of dynamic quantum logic gates on an ultrafast scale closer to room temperature.