Working Group Kinetic Inductance Quantum Systems

Head: Dr. Ioan Pop

Our research focuses on superconducting quantum circuits.

Josephson junctions have been proven to be reliable building blocks for superconducting quantum memories, high-speed processing units, amplifiers and detectors, operating in the microwave domain. In these types of electrical circuits, which can be manufactured using standard lithography, currents and voltages can exhibit quantum mechanical properties and can be controlled using microwave pulses. This makes them appealing for the study of fundamental quantum phenomena and the implementation of quantum information processing.

We are currently interested in the design and implementation of quantum circuits protected against decoherence.

More information

Transmon qubit samples
(a) Photograph of the copper-waveguide sample holder. In the center of the waveguide, where the electric field is maximum, we place a sapphire chip with three transmon qubits, each capacitively coupled to a dedicated readout resonator. The lower panel shows an optical image of one of the transmon qubits and its readout resonator. The top right panel depicts a SEM image of a single Josephson junction. All structures are patterned using electron-beam lithography, and are deposited by shadow-angle evaporation.
(b) Circuit diagram of the measurement setup. The transmon qubits (blue) are dispersively coupled to the readout resonators (red) and mounted inside the waveguide (black). The readout signal (red arrow) is preamplified by a Josephson-junction based amplifier ("DJJAA") and routed to a commercial HEMT mounted at 4K. At room temperature, the signal is decomposed into its in-phase and out-of-phase quadratures using a heterodyne microwave interferometer. The DJJAA pump tone (gray arrow) is fed into the signal path through a commercial power combiner. The flux bias for the DJJAA is supplied by an external magnetic-field coil.


Selected Publications

(1)   P. Winkel et al., Nondegenerate Parametric Amplifiers Based on Dispersion-Engineered Josephson-Junction Arrays, Phys. Rev. Appl. 13 (2020) 24015
(2)   L. Grünhaupt et al., Granular aluminium as a superconducting material for high-impedance quantum circuits, Nat. Mater. 18 (2019) 816
(3)   N. Maleeva et al., Circuit Quantum Electrodynamics of Granular Aluminum Resonators, Nat. Commun. 9 (2018) 3889
(4)   L. Grünhaupt et al., Loss Mechanisms and Quasiparticle Dynamics in Superconducting Microwave Resonators Made of Thin-Film Granular Aluminum, Phys. Rev. Lett. 121 (2018) 117001
(5)   I. M. Pop et al., Coherent suppression of electromagnetic dissipation due to superconducting quasiparticles, Nature 508 (2014) 369
(6)   I. M. Pop et al., Measurement of the effect of quantum phase-slips in a Josephson junction chain, Nat. Phys. 6 (2010) 589


Members (in alphabetical order)
Name Tel
Bld.-Room E-Mail
lucas martin brauchGgn9∂kit edu
lucas.brauchGgn9∂kit edu
simon geisertGgn9∂kit edu
nicolas goslingGgn9∂kit edu
soeren.ihssenGgn9∂kit edu
anil muraniGgn9∂kit edu
ameya.nambisanGgn9∂kit edu
ioan pop Ggn9∂kit edu
martin spieckerGgn9∂kit edu
francesco valentiGgn9∂kit edu
nicolas.gonzalez2Ggn9∂kit edu