NCCR QSIT, Subproject Hybrid quantum systems using microwave frequency on-chip resonators as a coupling bus

The long-term success of quantum computers relies on the ability to perform fault-tolerant quantum computations using quantum error correction. In this approach, errors are detected through the repeated measurement of multi-qubit parity operators and corrected using feedback operations conditioned on the measurement outcomes. In the work [Andersen et.al., npj Quantum Info 5, 69 (2019)], we demonstrate, for the first time with superconducting qubits, all major ingredients for performing quantum error correction implemented simultaneously with the same setup.

We have realized a novel device in which a semiconductor double quantum dot is dipole coupled to a GHz-frequency high-quality transmission line resonator. This approach allows us to characterize the properties of the double dot by measuring both its dispersive and dissipative interaction with the resonator. In addition to providing a new readout mechanism, this architecture has the potential to isolate the dots from the environment and to provide long distance coupling between spatially separated dots.

Tomography is the main method used for measuring the fidelity of an experimentally implemented quantum process. However, it is a very inefficient method since the number of measurements as well as the time needed for the data post-processing scale exponentially with the number of qubits. With the ongoing experimental progress and growth in system size, quantum process tomography will soon become infeasible in state-of-the art experiments.

Transferring the state of an information carrier between two parties is an essential primitive in both classical and quantum communication and information processing. Quantum teleportation describes the concept of transferring an unknown quantum state from a sender to a physically separated receiver without transmitting the physical carrier of information itself.

In this article, we present a simple technique that measures static and microwave field distributions on a mm-scale and with a resolution of approximately 100 micrometer in the vicinity of a superconducting, chip-based microwave guide.