Graphene-Based Logic Gate Shows Promise for Quantum Computing

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VIENNA, May 7, 2019 — Physicists from the University of Vienna and the Institute of Photonic Sciences have shown that graphene structures can be tailored to enable single photons to interact with one another. Their findings have led them to propose a new potential architecture for a two-photon logic gate for quantum computing.

Logic gates — the devices that allow one photon to change the state of a second photon — will be needed in large numbers to build a photonic quantum computer. One way to achieve this is to build gates using a nonlinear material in which two photons can interact. However, standard nonlinear materials are too inefficient to be used for this purpose.

Graphene-based two-photon quantum logic gate for quantum computing, University of Vienna.

Schematic of a graphene-based two-photon gate. Courtesy of University of Vienna/Thomas Rögelsperger.

A team led by professor Philip Walther proposes to use graphene to create a quantum logic gate. The team further proposes to enhance the interaction of photons within the gate by creating plasmons in the graphene. 

In a plasmon, light is bound to electrons on the surface of the material. These electrons can help the photons to interact more strongly. Nonlinear interactions can be enhanced by using plasmons, and the peculiar configuration of the electrons in graphene leads to both a strong nonlinear interaction and plasmons that live for a long time. Plasmons in standard materials decay before the needed quantum effects can take place

In their proposed graphene-based quantum logic gate, the scientists show that if single plasmons are created in nanoribbons made out of graphene, two plasmons in different nanoribbons can interact through their electric fields. Provided that each plasmon stays in its own ribbon, multiple gates, which are required for quantum computation, can be applied to the plasmons. “We have shown that the strong nonlinear interaction in graphene makes it impossible for two plasmons to hop into the same ribbon,” said researcher Irati Alonso Calafell.

The proposed universal two-qubit quantum logic gate, where qubits are encoded in surface plasmons in graphene nanostructures, exploits graphene’s strong third-order nonlinearity and long plasmon lifetimes to enable single-photon-level interactions.

The team in Vienna is currently performing experimental measurements on a graphene-based system to confirm the feasibility of using its gate with current technology. Since the gate is small and operates at room temperature, it should readily lend itself to being scaled up, the team said. According to the researchers, the gate has achieved fidelities and success rates well above the fault-tolerance threshold, suggesting that graphene plasmonics offers a route toward scalable photonic quantum computers.

The research was published in npj Quantum Information ( 


Published: May 2019
Nanophotonics is a branch of science and technology that explores the behavior of light on the nanometer scale, typically at dimensions smaller than the wavelength of light. It involves the study and manipulation of light using nanoscale structures and materials, often at dimensions comparable to or smaller than the wavelength of the light being manipulated. Aspects and applications of nanophotonics include: Nanoscale optical components: Nanophotonics involves the design and fabrication of...
Plasmonics is a field of science and technology that focuses on the interaction between electromagnetic radiation and free electrons in a metal or semiconductor at the nanoscale. Specifically, plasmonics deals with the collective oscillations of these free electrons, known as surface plasmons, which can confine and manipulate light on the nanometer scale. Surface plasmons are formed when incident photons couple with the conduction electrons at the interface between a metal or semiconductor...
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:...
nonlinear optics
Nonlinear optics is a branch of optics that studies the optical phenomena that occur when intense light interacts with a material and induces nonlinear responses. In contrast to linear optics, where the response of a material is directly proportional to the intensity of the incident light, nonlinear optics involves optical effects that are not linearly dependent on the input light intensity. These nonlinear effects become significant at high light intensities, such as those produced by...
Research & TechnologyeducationEuropeUniversity of ViennaOpticsMaterialsnanophotonicsplasmonicssingle photonsquantum logic gatesphotonic quantum computinggraphenenonlinear opticsnanostructuresEuro News

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