Planar multilayer circuit quantum electrodynamics

Experimental quantum information processing with superconducting circuits is rapidly advancing, driven by innovation in two classes of devices, one involving planar micro-fabricated (2D) resonators, and the other involving machined three-dimensional (3D) cavities. We demonstrate that circuit quantum electrodynamics can be implemented in a multilayer superconducting structure that combines 2D and 3D advantages. We employ standard micro-fabrication techniques to pattern each layer, and rely on a vacuum gap between the layers to store the electromagnetic energy. Planar qubits are lithographically defined as an aperture in a conducting boundary of the resonators. We demonstrate the aperture concept by implementing an integrated, two cavity-modes, one transmon-qubit system

A dissipative quantum reservoir for microwave light using a mechanical oscillator

Engineered dissipation can be used for quantum state preparation. This is achieved with a suitably engineered coupling to a dissipative cold reservoir usually formed by an electromagnetic mode. In the field of cavity electro- and optomechanics, the electromagnetic cavity naturally serves as a cold reservoir for the mechanical mode. Here, we realize the opposite scenario and engineer a mechanical oscillator cooled close to its ground state into a cold dissipative reservoir for microwave photons in a superconducting circuit. By tuning the coupling to this dissipative mechanical reservoir, we demonstrate dynamical backaction control of the microwave field, leading to stimulated emission and maser action. Moreover, the reservoir can function as a useful quantum resource, allowing the implementation of a near-quantum-limited phase-preserving microwave amplifier. Such engineered mechanical dissipation extends the toolbox of quantum manipulation techniques of the microwave field and constitutes a new ingredient for optomechanical protocols.This work was funded by the SNF, the NCCR Quantum Science and Technology (QSIT), and the European Union Seventh Framework Program through iQUOEMS (grant no. 323924). L.D.T. is supported by Marie Curie ITN cQOM (grant no. 290161). T.J.K. acknowledges financial support from an ERC AdG (QuREM). A.N. holds a University Research Fellowship from the Royal Society and acknowledges support from the Winton Programme for the Physics of Sustainability

Demonstrating a Driven Reset Protocol of a Superconducting Qubit

5 pages, 4 figuresInternational audienceQubit reset is crucial at the start of and during quantum information algorithms. We present the experimental demonstration of a practical method to force qubits into their ground state, based on driving certain qubit and cavity transitions. Our protocol, called the double drive reset of population is tested on a superconducting transmon qubit in a three-dimensional cavity. Using a new method for measuring population, we show that we can prepare the ground state with a fidelity of at least 99.5 % in less than 3 microseconds; faster times and higher fidelity are predicted upon parameter optimization

Tracking photon jumps with repeated quantum non-demolition parity measurements

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