Quantum logic in a bilinear 18-qubit germanium quantum processor

Spin qubits in semiconductor quantum dots are promising building blocks for practical quantum computers. Their nanoscale dimensions enable dense on-chip integration and interconnectivity, further supported by their compatibility with advanced semiconductor manufacturing. However, scaling to large numbers of spin qubits with substantial interconnectivity requires the implementation of extensive, high-quality, high-yield two-dimensional qubit arrays. To this end, spin qubits in strained germanium quantum wells have shown fast progress, with recent results demonstrating qubit operations in a 10-quantum-dot array. This fast, two-dimensional scaling arises from a unique combination of low material disorder yielding high qubit uniformity, low effective mass for more relaxed lithographical constraints, and strong spin-orbit interaction that enables fast, high-fidelity one- and two-qubit operations.

Here, we make the next step and present our recent progress on an 18-qubit quantum processor, based on our extensible 2xN-qubit architecture. We demonstrate the tune-up and operation of the full 18-qubit array and characterize the performance of the one- and two-qubit operations. Then, we benchmark the performance of the quantum processor by executing basic quantum algorithms. We utilize the horizontal and vertical qubit interactions to run algorithms with increased qubit connectivity. Our results establish that hole spin qubits in germanium can reliably perform quantum logic and present the next step in scaling semiconductor quantum technology.