Qubits placed in a open waveguide may play a role of mirror for microwave radiation. These are not standard mirrors though as the reflectivity is frequency and power dependent. If there are more than one qubit in a waveguide these properties may give rise interesting effects (for the first experiments with two qubit in a waveguide see this paper). But else they can be good for? Following the idea of Arjan van Loo we can use qubits for drawing pictures!
We have uploaded a theoretical proposal proposal on cooling the large quartz reosnator by coupling it to a superconducting qubit. Unlike nanomechanical oscillators Bulk Acoustic Wave (BAW) oscillators offer exceptional mechanical properties such as extremely high quality factors. Yet them coupling to qubits it is not easy due to unavoidable large stray capacitance. Our paper investigates a possible solution to this problem which should allow to cool BAW oscillator to its ground state.
Three-dimensional (3D) superconducting microwave cavities have exceptional quality factors but do not allow magnetic field to penetrate inside them. It is also hard to thermalize them to the cold stage of a dillution refrigirator. A copper cavity can be thermalized and allows for magnetic control but its quality factor is limited. In our new work we tried to reach a compomise between quality factor and magnetic tunability by creating "hybrid cavity" which consists of both superconductor and normal metal. Find out what were the outcomes in our new paper.
One of the biggest experimental efforts of our lab came finally to the end. We used all the advances we developed for superconducting circuits to probe quantum conetxtuality first time for superconducting circuits. Contextuality is one of the most fundamental properties of quantum mechanics, distinguishing it from classical physics without a need for nonlocality or entanglement. It is also a critical resource for exponential speedup in universal surface-code quantum computing. Our result is the first experiment violating a noncontextuality inequality with an indivisible system where entanglement cannot be defined which also addresses all known major loopholes, such as the detection, compatibility and individual-existence loopholes. Violating noncontextuality with superconducting circuits, a leading candidate for implementing surface-code quantum computing, comprises an important conceptual milestone in demonstrating their suitability for quantum technological applications.