Single-photon sources, key components in quantum optical devices, play a vital role in fields such as quantum computing, cryptography, and metrology. The photons these devices generate are the product of quantum emitters - molecules or atoms that release a single photon when transitioning to a lower energy state. The reliable generation of single photons on a set path demands technologically advanced systems, but the team's recent proposal offers a streamlined, more effective alternative.
The proposed design involves the incorporation of a quantum emitter into a one-dimensional waveguide formed by a periodic structure. This structure is purposefully crafted to accommodate a single guided mode of light in the quantum emitter's spectral range. The photons that the quantum emitter releases are primarily coupled to this waveguide mode, culminating in a high degree of directionality. Moreover, this mechanism also results in more than two orders of magnitude reduction in the temporal uncertainty of the emission.
The performance of a single-photon source is determined by several key factors: the efficiency of single-photon extraction, the minimization of emission time uncertainty, the increase in repetition rate, and the ability to preclude two-photon events. The research team's approach enhances extraction efficiency and reduces emission time uncertainty by leveraging the Purcell effect, a phenomenon describing how a quantum emitter's emission probability can be altered due to its environmental interactions.
The researchers' proposal departs from earlier methodologies that necessitate two- or three-dimensional structures to achieve a guided mode. The new approach only requires a one-dimensional system. Its design can be actualized using a broad range of materials and is highly resilient to manufacturing imperfections. This one-dimensional system, due to its smaller footprint compared to previously suggested two-dimensional photonic crystal structures, lends itself to more seamless device-on-chip integration.
Although the quantum emitter within the waveguide emits photons along both directions of the waveguide, there are methods to ensure photon emission in only one direction. Tactics include employing circularly polarized emitters, where the photon's electric field rotates as light propagates, or modifying one end of the waveguide to incorporate a Bragg reflector.
While this study largely focuses on waveguides formed by spherical nanostructures, the findings can be feasibly extended to other types of components, such as periodic corrugations in a rectangular waveguide.
This pioneering research is the joint effort of scientists Alejandro Manjavacas, from the "Daza de Valdes" Institute of Optics of CSIC, and F. Javier Garcia de Abajo, from the Institute of Photonic Sciences (ICFO) of Barcelona.
Research Report:Highly directional single-photon source
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