Hybrid Cavities Create Indistinguishable Photons with Far Simpler Designs

A new method generates indistinguishable photons from emitters that usually produce incoherent light. Anastasios Fasoulakis of Technical University, and colleagues at Imperial College London and University of Bristol, present a hybrid plasmonic-dielectric cavity architecture that sharply reduces the required quality factor of the outer dielectric cavity by approximately two orders of magnitude compared to existing cascaded cavity systems. The design also enhances photon collection efficiency by a factor of 12, a key improvement in the probability of detecting emitted photons and enabling more practical quantum photonic devices.

Plasmonic-dielectric hybrid architecture enhances photon collection from incoherent light sources

The core of this advance lies in cavity funneling, a system designed to collect weak light signals and concentrate them into a single, strong beam, much like a funnel collecting rainwater. Combining a plasmonic nanoresonator with an outer dielectric cavity creates a hybrid architecture that surpasses traditional designs relying solely on high-quality dielectric cavities. These plasmonic components strongly interact with light, initially capturing emissions from dephased emitters, light sources producing waves that are out of step, akin to a group failing to march in time.

Utilising both plasmonic nanoresonators and dielectric cavities, a hybrid light-trapping system improves photon collection from dephased emitters. By lowering the minimum required quality factor by two to three orders of magnitude, this design circumvents the need for the extremely high-quality dielectric cavities typical of alternative approaches. Direct coupling between the emitter and the outer cavity is enabled, potentially increasing photon collection efficiency, denoted by β, by a factor of twelve; numerical modelling confirms improved photon indistinguishability and extraction efficiency with increased coupling rates.

Hybrid plasmonic-dielectric cavities enhance single-photon extraction and indistinguishability

A newly demonstrated hybrid plasmonic-dielectric cavity architecture achieves a 12-fold increase in photon extraction efficiency, a crucial metric for practical quantum technologies. Generating indistinguishable photons from dephased emitters previously demanded extremely high quality factors in dielectric cavities, a significant obstacle at visible wavelengths. Employing a plasmonic nanoresonator coupled to an outer dielectric cavity circumvents this limitation, reducing the required outer cavity quality factor by approximately two orders of magnitude compared to cascaded dielectric systems.

The resulting design enables direct coupling between the emitter and the outer cavity, boosting the probability of photon collection and opening avenues for more streamlined quantum photonic devices. Measurements demonstrate that an indistinguishability of 91.69% is achievable when the outer cavity decay rate is 600 times greater than the emitter’s natural rate, relying on a specific coupling rate 1,300 times that same emitter rate. This high level of indistinguishability represents a funneling ratio of 16.3 decibels, meaning 43 times more photons are collected compared to a simple filtering system. The design’s geometry enables partial direct coupling between the emitter and the outer cavity, a mechanism absent in previous cascaded cavity systems, simplifying the system to behave like a single emitter-single cavity setup with modified decay rates. For a typical hexagonal boron nitride defect emitting at 625nm with a 2.5 nanosecond lifetime, a quality factor of 12,558 is sufficient for over 90% indistinguishability; even reducing the lifetime to 2 nanoseconds only requires a quality factor of 10,047.

Plasmonic enhancement predicts relaxed tolerances for visible light quantum photon sources

Cavity funneling offers a potential solution to the longstanding challenge of generating indistinguishable photons, essential for quantum technologies, from sources that typically produce incoherent light. Current designs, however, rely on exquisitely crafted dielectric cavities, demanding near-perfect materials to achieve the necessary performance, particularly at visible wavelengths. This work proposes integrating plasmonic nanostructures with dielectric cavities, focusing on estimated improvements derived from modelling.

These findings currently rely on computational modelling rather than experimental validation, but the predicted reduction in required cavity quality, by as much as two orders of magnitude, represents a strong step forward for practical device fabrication. Lowering these demands eases the burden on material science, as visible light cavities are notoriously difficult to perfect. This hybrid design potentially unlocks viable quantum photon sources using less-than-perfect materials, broadening the scope of research and development.

This new hybrid architecture successfully combines plasmonic nanoresonators with dielectric cavities, offering a pathway to efficient photon collection from emitters that typically produce incoherent light. A plasmonic nanoresonator initially captures emissions, then transfers them to the surrounding dielectric cavity, circumventing the need for extremely high-quality dielectric cavities previously required for ‘cavity funneling’, a technique used to concentrate weak light signals. Consequently, the minimum required quality factor for the outer cavity is substantially reduced, potentially simplifying device fabrication and broadening material choices for quantum technologies.

The research demonstrated a new hybrid architecture for cavity funneling that relaxes the stringent requirements for high-quality dielectric cavities. This is significant because previous designs needed near-perfect materials, which are difficult to produce, especially at visible wavelengths. By integrating plasmonic nanoresonators, the team’s modelling suggests the minimum quality factor can be reduced by approximately two orders of magnitude, potentially increasing photon collection efficiency by a factor of 12. The authors indicate this approach could enable the creation of viable quantum photon sources with more readily available materials.