A new approach to quantum light emitters generates a stream of circularly polarized single photons, or particles of light, which could be useful for a range of quantum information and communication applications. A team from Los Alamos National Laboratory stacked two different atomically thin materials to achieve this chiral quantum light source.
“Our research shows that it is possible for a monolayer semiconductor to emit circularly polarized light without the aid of an external magnetic field,” said Han Hutun, a scientist at Los Alamos National Laboratory.
“This effect has only been previously achieved through high magnetic fields created by oversized superconducting magnets, by coupling quantum emitters to highly complex photonic nanostructures or by injecting spin-polarized carriers into quantum emitters. The proximity effect approach has a special We have the advantage of low impact manufacturing cost and reliability.”
The polarization state is a way to encode a photon, so this achievement is an important step in the direction of quantum cryptography or quantum communication.
“With a source to generate a stream of single photons and also introduce polarization, we’ve basically combined two devices into one,” Hutton said.
Indentation Key photoluminescence
As described in nature materialsThe research team at the Center for Integrated Nanotechnology stacked a single-molecule thick layer of tungsten diselenide semiconductor on a thicker layer of magnetic nickel-phosphorus trisulfide semiconductor. Postdoctoral research associate Xiangzi Li used atomic force microscopy to create a series of nanometer-scale indentations on a thin stack of material.
These indentations are about 400 nanometers in diameter, so more than 200 of these indentations the width of a human hair can easily be made.
The indentations created by the atomic microscopy instrument have proven useful for two effects when the laser is focused on the material stack. First, the indentation forms a well, or depression, in the potential energy landscape. The electrons of the diselenide tungsten monolayer are located in the depression. This stimulates the emission of a stream of single photons from the well.
The nano-serration also disrupts the typical magnetic properties of a nickel-phosphorus trisulfide crystal, creating a local magnetic moment that points outward from the material. This magnetic moment circularly polarizes the emitted photons.
To provide experimental confirmation of this mechanism, the team first conducted high-magnetic field optical spectroscopy experiments in collaboration with the National High Magnetic Field Laboratory’s National Pulse Field Facility in Los Alamos. The team then measured the precise magnetic field of local magnetic moments in collaboration with the University of Basel in Switzerland.
The experiments demonstrated that the team had successfully demonstrated a new method for controlling the polarization state of a single photon stream.
Quantum information coding
The team is currently exploring ways to modify the degree of circular polarization of single photons using electrical or microwave stimuli. This ability would provide a way to encode quantum information into a photon stream.
Coupling the photon stream into waveguides—microscopic channels of light—providing photonic circuits that allow photons to propagate in one direction. Such circuits will be the building blocks of a super-secure quantum internet.
Xiangzhi Li et al, Proximity-induced chiral quantum light generation in strain-engineered WSe2/nips3 heterostructures, nature materials (2023). doi: 10.1038/s41563-023-01645-7
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