Very Fast Quantum Calculations with Germanium Transistors

The researchers at QuTech, a collaboration of TU Delft and TNO, have built two germanium transistors that can be the building blocks for fast quantum computing.

Before this work it was not possible to perform quantum calculations using only transistors. Other elements were needed and this provided a limitation for upscaling. This work shows a single transistor can function as a quantum bit by using germanium.

Nature – Fast two-qubit logic with holes in germanium

Universal quantum information processing requires the execution of single-qubit and two-qubit logic. Across all qubit realizations, spin qubits in quantum dots have great promise to become the central building block for quantum computation. Excellent quantum dot control can be achieved in gallium arsenide and high-fidelity qubit rotations and two-qubit logic have been demonstrated in silicon but universal quantum logic implemented with local control has yet to be demonstrated. Here we make this step by combining all of these desirable aspects using hole quantum dots in germanium. Good control over tunnel coupling and detuning is obtained by exploiting quantum wells with very low disorder, enabling operation at the charge symmetry point for increased qubit performance. Spin–orbit coupling obviates the need for microscopic elements close to each qubit and enables rapid qubit control with driving frequencies exceeding 100 MHz. We demonstrate a fast universal quantum gate set composed of single-qubit gates with a fidelity of 99.3 percent and a gate time of 20 nanoseconds, and two-qubit logic operations executed within 75 nanoseconds. Planar germanium has thus matured within a year from a material that can host quantum dots to a platform enabling two-qubit logic, positioning itself as an excellent material for use in quantum information applications.