Controlling superconducting quantum circuits for quantum information processing
Prof. Dr. Stefan Filipp (Walther-Meißner-Institut, Bayerische Akademie der Wissenschaften)

The rapid development of quantum technologies in the recent past has brought us a step closer to operational quantum computers that hold promise to outperform conventional computers in certain types of problems. While a large number of qubits is necessary to run complex algorithms, fast and high-fidelity gate operations of different types are as important. We utilize a system based on fixed-frequency superconducting qubits that are characterized by their stability, relatively long coherence times and scalability. On this platform we explore different ways to increase the performance of future quantum processors. We demonstrate that optimal control techniques allow us to shape microwave control pulses and realize fast single-qubit pulses without sacrificing their fidelity. Furthermore, we explore measurement techniques with a high duty cycle to overcome the challenge of time-consuming optimization sequences. For the generation of entangled two-qubit states we make use of a parametrically driven tunable coupler and implement different types of gates. Since exchange-type gates preserve the number of qubit excitations these are particularly well suited for quantum chemistry algorithms in which the number of electrons in the molecule is typically fixed. With this choice of gates we can make best use of the available hardware and realize short algorithms that finish within the coherence time of the system. With gate fidelities around 95% we compute the eigenstates within an accuracy of 50 mHartree on average, a good starting point for near-term applications with scientific and commercial relevance.