Quantum technology has opened up exciting possibilities in various fields, and researchers at Los Alamos National Laboratory have now achieved a significant breakthrough in the generation of circularly polarized single photons. By stacking two different atomically thin materials, the research team has successfully created a chiral quantum light source without the need for an external magnetic field. This approach holds great promise for quantum information and communication applications, paving the way for advancements in quantum cryptography and the development of an ultra-secure quantum internet.
Traditionally, circularly polarized light emission has required high magnetic fields generated by bulky superconducting magnets, complex nanoscale photonics structures, or the injection of spin-polarized carriers into quantum emitters. However, the Los Alamos team’s proximity-effect approach offers a simpler and more cost-effective solution. Han Htoon, a scientist at Los Alamos National Laboratory, explains that “our research shows that it is possible for a monolayer semiconductor to emit circularly polarized light without the help of an external magnetic field. Our proximity-effect approach has the advantage of low-cost fabrication and reliability.”
The stacked materials not only generate a stream of single photons but also introduce polarization, effectively combining two devices into one. This achievement is a significant step forward in the development of quantum cryptography and quantum communication. By encoding the photon’s polarization state, the researchers have unlocked new possibilities for secure communication and information processing.
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. Using atomic force microscopy, Xiangzhi Li, a postdoctoral research associate, created nanometer-scale indentations on the thin stack of materials. These indentations, only 400 nanometers in diameter, play a crucial role in achieving the desired effects.
When a laser is focused on the stack of materials, the indentations create wells or depressions in the potential energy landscape. Electrons from the tungsten diselenide monolayer fall into these wells, stimulating the emission of a stream of single photons. Additionally, the nanoindentations disrupt the magnetic properties of the underlying nickel phosphorus trisulfide crystal, creating a local magnetic moment that circularly polarizes the emitted photons.
To confirm this mechanism, the research team conducted high magnetic field optical spectroscopy experiments in collaboration with the National High Magnetic Field Laboratory’s Pulsed Field Facility at Los Alamos. They also measured the minute magnetic field of the local magnetic moments in collaboration with the University of Basel in Switzerland. The results provided experimental confirmation of the team’s novel approach to control the polarization state of a single photon stream.
Currently, the team is exploring ways to modulate the degree of circular polarization of the single photons by applying electrical or microwave stimuli. This advancement would allow for the encoding of quantum information into the photon stream, pushing the boundaries of quantum information processing further. Additionally, the researchers are investigating the coupling of the photon stream into waveguides, microscopic conduits of light that enable the propagation of photons in one direction. These waveguides would be the building blocks of an ultra-secure quantum internet.
The breakthrough achieved by the Los Alamos research team opens up new possibilities for the field of quantum information and communication. The generation of circularly polarized single photons without the need for high magnetic fields or complex nanoscale structures presents a more accessible and cost-effective approach. As researchers continue to explore the modulation of photon polarization and the development of photonic circuits, the realization of an ultra-secure quantum internet is becoming increasingly feasible. The advancements in quantum light emitters showcased in this research represent a significant step towards a future where quantum technology revolutionizes communication and information processing.
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