Many research initiatives in physics and engineering laboratories center around the topic of what physical system and which degrees of freedom within that system may be used to encode quantum bits of information, or qubits, in the context of quantum computing.
Most people already agree that superconducting qRebekka Garreis, Chuyao Tong, Wister Huang, and their colleagues in the group of Professors Klaus Ensslin and Thomas Ihn from the Department of Physics at ETH Zurich have been investigating the possibility of encoding quantum information using another degree of freedom of bilayer graphene (BLG) quantum dots, which are known to be a potential platform for spin qubits.
Their most recent discoveries, which they co-authored with researchers from Japan’s National Institute for Materials Science and recently published in Nature Physics, demonstrate that the so-called valley degree of freedom in BLG is linked to incredibly long-lived quantum states, making them worthy of further investigation as a potential resource for solid-state quantum computing.
qubits, spin qubits, and qubits encoded in the motion of trapped ions are the best options for future real-world uses of quantum computing; however, other systems still require further understanding, which makes them interesting targets for basic research.
A single layer of carbon atoms bonded together in a hexagonal lattice structure makes up the two-dimensional substance known as graphene. Graphene is one of the strongest materials on Earth, despite its sheet-like appearance; numerous industry sectors are highly interested in its mechanical and electrical qualities.
The technology the researchers utilized, called bilayer graphene, consists of two layers of carbon atoms stacked on top of one another. Since they don’t have the distinctive energy band gap present in semiconductors and, most notably, insulators, graphene and BLG are both semimetals. Nevertheless, by applying an electric field perpendicular to the plane of the sheets, a tunable band gap can be constructed in BLG.
To employ BLG as a host material for quantum dots—which are ‘boxes’ on the nanoscale that may confine one or more electrons—a band gap must be opened. Quantum dots, which are often created in semiconductor host materials, provide exceptional control over individual electrons. They are therefore a crucial platform for spin qubits, which are systems in which the degree of freedom of the electron spin contains quantum information.
Researchers studying various qubit candidates must characterize their coherence properties because, compared to classical information, quantum information is much more susceptible to environmental corruption, making it less suitable for computational tasks. These properties indicate how well and how long quantum information can survive in a qubit system.
The spin-orbit interaction, which creates an undesired coupling between the electron spin and the host lattice vibrations, and the hyperfine interaction between the electron spin and the nearby nuclear spins can both lead to electron spin decoherence in the majority of conventional quantum dots.
