The LANL Laboratory in the United States has achieved a light source that generates a circularly polarized single photon stream using a quantum light emitter

Los Alamos National Laboratory (LANL) has developed a method for a quantum light emitter that stacks two different atomically thin materials together to achieve a light source that produces a stream of circularly polarized single photons. These light sources can in turn be used for a variety of quantum information and communication applications.

According to Los Alamos researcher Han Htoon, the work shows that single-layer semiconductors can emit circularly polarized light without the need for an external magnetic field.

"This effect has previously only been possible with high magnetic fields generated by bulky superconducting magnets, by coupling quantum emitters to very complex nanoscale photonic structures, or by injecting spin-polarized charge carriers into the quantum emitters." Our proximity effect approach has the advantage of low manufacturing costs and high reliability."

Polarization states are a means of encoding photons, so this result is an important step in the direction of quantum cryptography, or quantum communication. "With a light source that produces a single photon stream and introduces polarization, we basically have two devices in one."

The team stacked a single-molecule thick layer of tungsten diselenide semiconductors on top of a thicker layer of magnetic nickel-phosphorus trisulfide semiconductors. Using an atomic force microscope, the team created a series of nanoscale indentations on a thin layer of material.

When the laser is focused on the pile of material, the 400 nanometer-diameter indentation created by the atom microscope tool has two effects. First, the indentation forms a "well" or "depression" in the potential energy landscape. The electrons of the tungsten diselenide monolayer fall in the depression. This stimulates the emission of a single photon from the trap.

The nanoindentation also destroys the typical magnetic properties of the underlying nickel-phosphorus trisulfide crystals, creating a local magnetic moment pointing outward from the material. This magnetic moment causes the emitted photon to be circularly polarized. To experimentally confirm this mechanism, the team first conducted high-magnetic field spectroscopy experiments in collaboration with the Pulse Field Facility at the Los Alamos National High Magnetic Field Laboratory. The team then worked with the University of Basel in Switzerland to measure the tiny magnetic field of the local magnetic moment.

The team is now exploring ways to modulate the degree of circular polarization of single photons through electronic or microwave stimulation. This ability would provide a way to encode quantum information into a stream of photons. Further coupling of the photon stream to the waveguide will provide the photonic circuit so that the photons propagate in one direction. Such circuits will become a fundamental component of an ultra-secure quantum Internet.

Source: OFweek