Scientists confirmed that bilayer graphene can produce better results working as a semiconductor than silicon or gallium arsenide when the materials are used for hosting quantum bits in quantum information processing. At Forschungszentrum Jülich’s Helmholtz Nano Facility, scientists created double quantum dots in bilayer graphene that exhibited near perfect electron-hole symmetry. Their efforts are paving the way to achieve efficient quantum computers.

A team of scientists exploited the unique properties of bilayer graphene to construct double quantum dots, an ideal platform for quantum computation, and achieved near perfect electron-hole symmetry, according to Forschungszentrum Jülich and RWTH Aachen University.

Christoph Stampfer, an experimental physics professor and co-author at RWTH Aachen University, noted that bilayer graphene is a fairly new material, and it is unique as a semiconductor because it “shares several properties with monolayer graphene, such as low spin-orbit coupling and a low-energy spectrum that is perfectly electron-hole symmetric.”

The properties of bilayer graphene are making it a hot candidate for quantum technologies. One notable property, Stampfer added, is that bilayer graphene “has a band gap that can be tuned from zero to about 120 milli-electronvolts by an external electric field.”

In addition, the low-energy limit plus the small, tunable band gap of bilayer graphene are features that scientists used to their advantage to create double quantum dots using gate geometries similar to those used in silicon. Scientists showed that each quantum dot can successfully host at most one electron or one hole.

The international team is the first to prove symmetry between electron and hole states in bilayer graphene. They also demonstrated that even when electrons and holes are physically separated into different quantum dots, symmetry is almost perfectly preserved. This led to a robust blockade mechanism, which led to a read-out scheme for spin and valley qubits with high fidelity.

The results of this experiment can have major implications for quantum computing. Stampfer noted this newly created device can be used to couple qubits together over a longer distance. Just recently in the year 2022, researchers from QuTech, a research institute for quantum computing, have been credited with creating only 6 silicon-based spin qubits. There is still a long way to go.

“This goes beyond what can be done in conventional semiconductors or any other two-dimensional electron system,” said Fabian Hassler, a professor and co-author of the JARA Institute for Quantum Information at RWTH Aachen University. “The near perfect symmetry that we observe in our work and the strong selection rules that result from this symmetry are very attractive not only for qubit operation but also for implementing single particle tera-Hertz detectors. In addition, it will be interesting to couple bilayer graphene quantum dots with superconductors – two systems where electron-hole symmetry plays an important role. These hybrid devices could be exploited to create efficient sources of entangled particle pairs or engineered topological systems, thus bringing us one step further towards realizing topological quantum computing devices.”

The successful experiment was conducted by a team of researchers from Forschungszentrum Jülich (Germany), RWTH Aachen University (Germany), and the National Institute for Materials Science (Japan), and documented in a paper published by Nature. Researchers have also publicly provided the data and Python scripts used to perform the simulations in the Zenodo Repository.

To learn more about this research, read the reporting from Forschungszentrum Jülich and RWTH Aachen University.