In a groundbreaking discovery, a team of scientists at Los Alamos National Laboratory has developed a novel approach to generate a stream of circularly polarized single photons, opening up new possibilities for quantum information and communication applications. This chiral quantum light source is a result of stacking two different atomically thin materials, demonstrating that monolayer semiconductors can emit circularly polarized light without the need for an external magnetic field. This innovative technique offers significant advantages over previous methods, including low-cost fabrication and reliability.
The research team, working at the Center for Integrated Nanotechnologies, stacked a single-molecule-thick layer of tungsten diselenide semiconductor onto a thicker layer of nickel phosphorus trisulfide magnetic semiconductor. By using atomic force microscopy, the team created a series of nanometer-scale indentations on the thin stack of materials. These indentations, with a diameter of approximately 400 nanometers, allow for over 200 indents to be fit across the width of a human hair.
The indentations serve two crucial purposes when a laser is focused on the stack of materials. Firstly, they create wells or depressions in the potential energy landscape, causing electrons from the tungsten diselenide monolayer to fall into the depressions and stimulate the emission of a stream of single photons. Secondly, the nanoindentations disrupt the magnetic properties of the underlying nickel phosphorus trisulfide crystal, resulting in the creation of local magnetic moments that circularly polarize the emitted photons.
To confirm the validity of this mechanism, the team conducted high magnetic field optical spectroscopy experiments in partnership with the National High Magnetic Field Laboratory’s Pulsed Field Facility at Los Alamos. Additionally, they collaborated with the University of Basel in Switzerland to measure the minute magnetic field of the local magnetic moments. These experiments provided concrete evidence that the team had successfully demonstrated a novel approach to control the polarization state of a single photon stream.
The team is currently conducting further research to explore ways to modulate the degree of circular polarization of the single photons using electrical or microwave stimuli. Such capabilities would enable the encoding of quantum information into the photon stream, unlocking new possibilities for quantum cryptography and communication. Additionally, the team is investigating methods to couple the photon stream into waveguides, microscopic conduits of light, to create photonic circuits that allow for the propagation of photons in a specific direction. These circuits would serve as the fundamental building blocks of an ultra-secure quantum internet.
The development of a chiral quantum light source capable of generating circularly polarized single photons represents a significant step forward in the field of quantum information and communication. This innovative approach, using stacked atomically thin materials, eliminates the need for high magnetic fields or complex nanoscale structures, while offering the benefits of low-cost fabrication and reliability. With ongoing research to modulate the polarization state and couple the photon stream into waveguides, the potential applications for this breakthrough are limitless, paving the way for a more secure and advanced quantum internet.
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