Researchers at QuTech, a collaboration between TU Delft and TNO, have invented a new readout method that is an important step forward on the road towards such a large-scale quantum computer.
The approach of the team to building a quantum computer is based on so-called spin qubits in quantum dot arrays. Quantum dots are very tiny islands that can each confine one or multiple electrons and are tunnel coupled to their neighbors. The spin of the electron acts as a qubit. The spin of a single electron in a semiconductor quantum dot provides a well-controlled and long-lived qubit implementation. The electron charge in turn allows control of the position of individual electrons in a quantum dot array, and enables charge sensors to probe the charge configuration. Spin qubits in quantum dots are read out via a very sensitive detector that measures the charge in its environment.
The team has showed that the Coulomb repulsion allows an initial charge transition to induce subsequent charge transitions, inducing a cascade of electron hops, like toppling dominoes. A cascade can transmit information along a quantum dot array over a distance that extends by far the effect of the direct Coulomb repulsion. They demonstrated that a cascade of electrons can be combined with Pauli spin blockade to read out distant spins and showed results with potential for high fidelity using a remote charge sensor in a quadruple quantum dot device.
They have implemented and analysed several operating modes for cascades and analysed their scaling behaviour. They also proposed the application of cascade-based spin readout to densely-packed two-dimensional quantum dot arrays with charge sensors placed at the periphery. The high connectivity of such arrays greatly improves the capabilities of quantum dot systems for quantum computation and simulation.
The new readout scheme invented by the scientists makes sure that even a spin qubit far away from the charge sensor will still be read out with high accuracy. (Phys.org)
The findings have been published in Nature Communications.