Materials and Integration for Quantum Computing in Silicon

As much as possible, qubits for quantum computers must be isolated from their environment in order to preserve phase coherence and maintain entanglement. Remarkably, the techniques used to make classical silicon CMOS devices can be used to make qubits with excellent performance. The operation of these devices, on the other hand – from the required temperatures to the number of electrons comprising a typical qubit – is very different from what is found in even the most advanced classical integrated circuits. In this talk, I will present two recent advances in materials – and the integration of those materials – for quantum computing in silicon. Recent results have begun to demonstrate the remarkable properties of silicon quantum wells containing short wavelength oscillations in the concentration of added germanium atoms. This highly engineered material, which has concentration oscillations on the 1-2 nanometer scale, changes the band structure in ways that provide better protection for quantum states, by increasing the energy gap to energy levels outside the qubit basis. It also is predicted by theory to introduce spin-orbit coupling, which can be used to enable all-electrical control of spin qubits. I will also discuss the role of integration, including 3D integration, which enables readout of quantum dot qubits in silicon by measuring the microwave transmission of a superconducting resonator on a separate substrate, flip-chip bonded to the first.