Emitter Generates Identical Single Photons on Demand

Facebook X LinkedIn Email
BERKELEY, Calif., Oct. 12, 2020 — Researchers at Lawrence Berkeley National Laboratory have developed a method of generating single identical photons on demand, a crucial step in realizing quantum communication.

The photon emitter is based on a common 2D semiconductor material (tungsten disulfide, WS2), which the researchers grew on a graphene sheet. To facilitate photon emission, the material has a sulfur atom removed from its crystal structure. That imperfection serves as a point where the application of an electric current can generate the photon.

Through simulations and experimentation, the team determined exactly where to introduce an imperfection to the structure. Then, using the gold-coated tip of a scanning tunneling microscope, an electron is injected into the defect. When the electron travels from the probe tip, a well-defined portion of its energy transforms into a single photon. Finally, the probe tip acts as an antenna that helps guide the emitted photon to an optical detector that records its wavelength and position.
A map shows the intensity and locations of photons emitted from a thin film material while a voltage is applied. Courtesy of Berkeley Lab.
A map shows the intensity and locations of photons emitted from a thin-film material while a voltage is applied. Courtesy of Berkeley Lab.
In mapping the emitted photons, the researchers pinpointed the correlation between the injected electrons, local atomic structure, and the emitted photon itself. Ordinarily, the optical resolution of that type of map is limited to a few hundred nanometers. Due to extremely localized electron injection and state-of-the-art microscopy tools, the Berkeley Lab team determined the location in the material where a photon emerged with a resolution below 1 Å, about the diameter of a single atom. 

“In terms of technique, this work has been a great breakthrough because we can map light emission from a single defect with subnanometer resolution. We visualize light emission with atomic resolution,” said Katherine Cochrane, a postdoctoral researcher at the Molecular Foundry in the Lawrence Berkeley National Laboratory and lead author on the research paper.

Historically, the challenge in developing single-photon-emitting technology hasn’t been how to generate a single photon, but how to make them identical and to produce them on demand. Photon-emitting devices such as the quantum dots used in QLED TVs are fabricated through lithography and thus subject to inherent variability.

The research provides strategy for making groups of perfectly identical photons, and the researchers intend to work on employing new materials to uses as photon sources in quantum networks and simulations.

“The demonstration of electrically driven single-photon emission at a precise point constitutes a big step in the quest for integrable quantum technologies,” said Alex Weber-Bargioni, a staff scientist at Berkeley Lab’s Molecular Foundry who led the project.

The research was published in Science Advances (

Published: October 2020
Graphene is a two-dimensional allotrope of carbon consisting of a single layer of carbon atoms arranged in a hexagonal lattice pattern. It is the basic building block of other carbon-based materials such as graphite, carbon nanotubes, and fullerenes (e.g., buckyballs). Graphene has garnered significant attention due to its remarkable properties, making it one of the most studied materials in the field of nanotechnology. Key properties of graphene include: Two-dimensional structure:...
A charged elementary particle of an atom; the term is most commonly used in reference to the negatively charged particle called a negatron. Its mass at rest is me = 9.109558 x 10-31 kg, its charge is 1.6021917 x 10-19 C, and its spin quantum number is 1/2. Its positive counterpart is called a positron, and possesses the same characteristics, except for the reversal of the charge.
A quantum of electromagnetic energy of a single mode; i.e., a single wavelength, direction and polarization. As a unit of energy, each photon equals hn, h being Planck's constant and n, the frequency of the propagating electromagnetic wave. The momentum of the photon in the direction of propagation is hn/c, c being the speed of light.
scanning tunneling microscope
A high-resolution imaging instrument that can detect and measure the positions of individual atoms on the surface of a material. A very fine conductive probe is placed at a distance of 10 to 20 Å above the surface of a conductive sample, and a bias voltage is applied between probe and surface during scanning, creating overlapping electron clouds and electrons that tunnel between the potential barrier between the probe and the sample. The probe tip is maintained at a constant distance from...
The term quantum refers to the fundamental unit or discrete amount of a physical quantity involved in interactions at the atomic and subatomic scales. It originates from quantum theory, a branch of physics that emerged in the early 20th century to explain phenomena observed on very small scales, where classical physics fails to provide accurate explanations. In the context of quantum theory, several key concepts are associated with the term quantum: Quantum mechanics: This is the branch of...
Research & Technologysingle photonsingle photon emissionsemiconductorsgraphenetungsten disulfideelectronphotonscanning tunneling microscopequantumquantum communicationquantum computingquantum networkquantum dotLawrence BerkeleyLawrence Berkeley LabLawrence Berkeley National Laboratory

We use cookies to improve user experience and analyze our website traffic as stated in our Privacy Policy. By using this website, you agree to the use of cookies unless you have disabled them.