In a groundbreaking study, researchers from Los Alamos National Laboratory have developed a new method to generate a stream of circularly polarized single photons. This achievement has important implications for various applications in quantum information and communication. By stacking two different atomically thin materials, the team created a chiral quantum light source that can emit circularly polarized light without the need for an external magnetic field.
Traditionally, circularly polarized light generation required high magnetic fields, complex nanoscale photonics structures, or spin-polarized carriers. However, the proximity-effect approach utilized by the researchers offers several advantages. It allows for low-cost fabrication and increased reliability. By combining two devices into one, the team has created a source that not only generates a stream of single photons but also introduces polarization.
The research team stacked a single-molecule-thick layer of tungsten diselenide semiconductor onto a thicker layer of nickel phosphorus trisulfide magnetic semiconductor. Using atomic force microscopy, the team created nanometer-scale indentations on the thin stack of materials. These indentations, with diameters of approximately 400 nanometers, act as wells or depressions in the potential energy landscape. When a laser is focused on the stack, electrons fall into these indentations and stimulate the emission of a stream of single photons.
Additionally, the nanoindentations disrupt the magnetic properties of the underlying nickel phosphorus trisulfide crystal. This disruption creates a local magnetic moment that circularly polarizes the emitted photons. Experimental confirmation of this mechanism was achieved through high magnetic field optical spectroscopy experiments and the measurement of the minute magnetic field of the local magnetic moments.
The ability to generate a stream of circularly polarized single photons opens up possibilities in quantum cryptography and quantum communication. The polarization state of photons can be used to encode quantum information, making this achievement a significant step forward in these fields. The team is currently working on ways to modulate the degree of circular polarization using electrical or microwave stimuli. This modulability would enhance the encoding of quantum information into the photon stream.
Furthermore, the researchers aim to couple the photon stream into waveguides, microscopic conduits of light, to create photonic circuits that allow for the propagation of photons in one direction. These circuits could form the basis of an ultra-secure quantum internet, enabling the development of advanced quantum communication systems.
The breakthrough in generating circularly polarized single photons through the proximity-effect approach represents a significant advancement in the field of quantum light emitters. The research conducted by the team at Los Alamos National Laboratory demonstrates the feasibility of low-cost fabrication and reliable methods for controlling the polarization state of photons. This achievement paves the way for the advancement of quantum information and communication technologies, bringing us closer to the realization of an ultra-secure quantum internet.