State-conditional coherent charge qubit oscillations in a Si/SiGe quadruple quantum dot

Abstract

Universal quantum computation requires high-fidelity single-qubit rotations and controlled two-qubit gates. Along with high-fidelity single-qubit gates, strong efforts have been made in developing robust two-qubit logic gates in electrically gated quantum dot systems to realise a compact and nanofabrication-compatible architecture. Here we perform measurements of state-conditional coherent oscillations of a charge qubit. Using a quadruple quantum dot formed in a Si/SiGe heterostructure, we show the first demonstration of coherent two-axis control of a double quantum dot charge qubit in undoped Si/SiGe, performing Larmor and Ramsey oscillation measurements. We extract the strength of the capacitive coupling between a pair of double quantum dots by measuring the detuning energy shift (≈75 μeV) of one double dot depending on the excess charge configuration of the other double dot. We further demonstrate that the strong capacitive coupling allows fast, state-conditional Landau–Zener–Stückelberg oscillations with a conditional π phase flip time of about 80 ps, showing a promising pathway towards multi-qubit entanglement and control in semiconductor quantum dots. Researchers in the United States and Korea demonstrate control of individual electrons in an electronic device governed by quantum mechanics. Mark Eriksson from the University of Wisconsin-Madison and co-workers developed a building block for a quantum computer that traps single electrons between nanoscale-spaced electrical contacts on silicon–germanium. Instead of using electrical signals to create the ones and zeros used in traditional information processing, quantum computers use physical objects called quantum bits, or qubits. The qubit used by Eriksson's team is known as a quantum dot charge qubit. The team created two pairs of quantum dots and used the position of an electron in one pair to influence quantum oscillations of the electron in the other pair. Coupling double quantum dots in this way could form the basis of a compact quantum-computing architecture that is compatible with the fabrication techniques used in modern electronics.