Electrically adjustable inductance for cryogenic RF applications M. Schubert^1*, M. Neumann¹, M. Schilling¹, B. Hampel¹ ¹Institut für Elektrische Messtechnik und Grundlagen der Elektrotechnik, TU Braunschweig, Hans-Sommer-Str. 66, Braunschweig 38106, Germany *marjan.schubert@tu-bs.de

Trapped-ion qubits are one of many approaches to realize scalable quantum computers. An ion trap has to be operated with several DC and radio frequency (RF) signals to trap and control its qubits. Many ion trap setups are operated at cryogenic temperatures to reduce thermal influences, to reach very high vacuum and to achieve high fidelity for quantum operations. The properties of materials and semiconductor components change significantly at low temperatures, which makes the impedance matching and frequency tuning of resonance circuits very difficult. Electrically adjustable components for RF circuits enable the fine-tuning during an experiment without the need of time-consuming cooldown cycles.

In this work, we integrate an electrically tunable cryogenic resonance circuit with a voltage-controlled inductor to provide RF fields for trapping ions. The structure consists of two ideally coupled coils. The current and thus the magnetic flux from one coil can be adjusted with a field-effect transistor used as a voltage-controlled resistor. The relationship between the inductance of the coil setup and the magnetic field generated by the current can be derived using the law of induction. Simulations show that with a sufficient coupling factor, significant changes in inductance can be achieved. We will present cryogenic measurements of an electrically tunable resonance circuit, which can be used to fine-tune the impedance matching and the resonant frequency of circuits.