Experiments have shown that a single electron spin and a single microwave photon can be coupled on a silicon chip. This coupling, done by professor Lieven Vandersypen's team at Delft University of Technology (TU Delft), could make it possible to transfer quantum information between a spin and a photon, allowing quantum bits (qubits) to be connected across a chip. The process could potentially be scaled up to connect large numbers of qubits. The quantum computer of the future will be able to carry out computations far beyond the capacity of today's computers. Courtesy of TU Delft. Quantum computation requires large numbers of qubits. How to scale up spin qubit systems remains a challenge for research teams worldwide. “To use a lot of qubits at the same time, they need to be connected to each other; there needs to be good communication,” said researcher Nodar Samkharadze. Using existing technology, the electrons that are captured as qubits in silicon can only make direct contact with their immediate neighbors, which makes difficult to scale up to large numbers. “It is important to connect distant quantum bits on a silicon chip, thereby paving the way to upscaling quantum bits on silicon chips,” researcher Guoji Zheng said. As a first step in addressing this issue, the scientists trapped the electron spin in a silicon double quantum dot. The photon was stored in an on-chip high-impedance superconducting resonator. The electric field component of the cavity photon coupled directly to the charge dipole of the electron in the double dot, and indirectly to the electron spin, through a strong local magnetic field gradient from a nearby micromagnet. Researchers from left to right: Nodar Samkharadze, Lieven Vandersypen and Guoji Zheng. Courtesy of TU Delft/Marieke de Lorijn. “We can use electrical fields to capture single electrons in silicon for use as quantum bits (qubits)." Zheng said. "[Silicon] is an attractive material as it ensures the information in the qubit can be stored for a long time.” Results of the experiment could provide a route to realizing large networks of quantum dot-based spin qubit registers. “The goal now is to transfer the information via a photon from one electron spin to another,” said team leader Vandersypen. The research was published in Science (doi: 10.1126/science.aar4054).