S. E. de Graaf

Magnetic field resilient superconducting fractal resonators for coupling to free spins

We demonstrate a planar superconducting microwave resonator intended for use in applications requiring strong magnetic fields and high quality factors. In perpendicular magnetic fields of 20 mT, the niobium resonators maintain a quality factor above 25 000 over a wide range of applied powers, down to single photon population. In parallel field, the same quality factor is observed above 160 mT, the field required for coupling to free spins at a typical operating frequency of 5 GHz. We attribute the increased performance to the current branching in the fractal design. We demonstrate that our device can be used for spectroscopy by measuring the dissipation from a pico-mole of molecular spins.

Tuneable on-demand single-photon source in the microwave range

An on-demand single-photon source is a key element in a series of prospective quantum technologies and applications. Here we demonstrate the operation of a tuneable on-demand microwave photon source based on a fully controllable superconducting artificial atom strongly coupled to an open-ended transmission line. The atom emits a photon upon excitation by a short microwave π-pulse applied through a control line. The intrinsically limited device efficiency is estimated to be in the range 65–80% in a wide frequency range from 7.75 to 10.5 GHz continuously tuned by an external magnetic field. The actual demonstrated efficiency is also affected by the excited state preparation, which is about 90% in our experiments. The single-photon generation from the single-photon source is additionally confirmed by anti-bunching in the second-order correlation function. The source may have important applications in quantum communication, quantum information processing and sensing.

Galvanically split superconducting microwave resonators for introducing internal voltage bias

We present the design and performance of high-Q superconducting niobium nitride microwave resonators intended for use in hybrid quantum systems, coupling spin degrees of freedom to the cavity mode, both magnetically and electrically. We demonstrate a solution that allows to introduce static electric fields in the resonator without compromising the microwave performance. Quality factors above 105 remain unchanged in strong applied static electric fields above 10 MV/m and magnetic fields up to ∼400 mT. By design, the configuration of the dc field matches that of the microwave field, especially advantageous for experiments on electrostatically controlled spin systems.

Coupling of a locally implanted rare-earth ion ensemble to a superconducting micro-resonator

We demonstrate the coupling of rare-earth ions locally implanted in a substrate (Gd

Direct Identification of Dilute Surface Spins on Al2 O3: Origin of Flux Noise in Quantum Circuits

^{3+}

Superconducting microwave parametric amplifier based on a quasi-fractal slow propagation line

in Al

Multiplexing Superconducting Qubit Circuit for Single Microwave Photon Generation

_{2}

Angle-Dependent Microresonator ESR Characterization of Locally Doped Gd3+:Al2O3

O

Kinetic inductance as a microwave circuit design variable by multilayer fabrication

_{3}

Suppression of low-frequency charge noise in superconducting resonators by surface spin desorption

) to a superconducting NbN lumped-element micro-resonator. The hybrid device is fabricated by a controlled ion implantation of rare-earth ions in well-defined micron-sized areas, aligned to lithographically defined micro-resonators. The technique does not degrade the internal quality factor of the resonators which remain above