Tim Wolz

Karlsruhe Institute of Technology

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Martin Weides

University of Glasgow

A. V. Ustinov

National Research University Higher School of Economics

Andre Schneider

Karlsruhe Institute of Technology

Alexander Stehli

Karlsruhe Institute of Technology

Isabella Boventer

Centre National de la Recherche Scientifique

Jan David Brehm

Karlsruhe Institute of Technology

Hannes Rotzinger

Karlsruhe Institute of Technology

Rair Macêdo

University of Glasgow

Mathias Kläui

Johannes Gutenberg University Mainz

Luke J. McLellan

University of Glasgow

Cooperative Institutions

Karlsruhe Institute of Technology

University of Glasgow

National University of Science and Technology

Russian Quantum Center

Johannes Gutenberg University Mainz

National Institute of Standards and Technology

Heriot-Watt University

Lawrence Livermore National Laboratory

University of Colorado Boulder

Centre National de la Recherche Scientifique

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Flux-noise spectroscopy on a superconducting transmon qubit

Tim Wolz Andre Schneider Jochen Braumüller A. V. Ustinov Martin Weides

Transmon

Flux qubit

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Waveguide bandgap engineering with an array of superconducting qubits

npj Quantum Materials (2021)

Jan David Brehm Alexander N. Poddubny Alexander Stehli Tim Wolz Hannes Rotzinger

Abstract Waveguide quantum electrodynamics offers a wide range of possibilities to effectively engineer interactions between artificial atoms via a one-dimensional open waveguide. While these interactions have been experimentally studied in the few qubit limit, the collective properties of such systems for larger arrays of qubits in a metamaterial configuration has so far not been addressed. Here, we experimentally study a metamaterial made of eight superconducting transmon qubits with local frequency control coupled to the mode continuum of a waveguide. By consecutively tuning the qubits to a common resonance frequency we observe the formation of super- and subradiant states, as well as the emergence of a polaritonic bandgap. Making use of the qubits quantum nonlinearity, we demonstrate control over the latter by inducing a transparency window in the bandgap region of the ensemble. The circuit of this work extends experiments with one and two qubits toward a full-blown quantum metamaterial, thus paving the way for large-scale applications in superconducting waveguide quantum electrodynamics.

Transmon

Waveguide

10.1038/s41535-021-00310-z

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Citations (46)

Frequency fluctuations of ferromagnetic resonances at millikelvin temperatures

Applied Physics Letters (2021)

Tim Wolz Luke J. McLellan Andre Schneider Alexander Stehli Jan David Brehm

Unwanted fluctuations over time, in short, noise, are detrimental to device performance, especially for quantum coherent circuits. Recent efforts have demonstrated routes to utilizing magnon systems for quantum technologies, which are based on interfacing single magnons to superconducting qubits. However, the coupling of several components often introduces additional noise to the system, degrading its coherence. Researching the temporal behavior can help to identify the underlying noise sources, which is a vital step in increasing coherence times and the hybrid device performance. Yet, the frequency noise of the ferromagnetic resonance (FMR) has so far been unexplored. Here, we investigate such FMR frequency fluctuations of a YIG sphere down to mK-temperatures, and find them independent of temperature and drive power. This suggests that the measured frequency noise in YIG is dominated by so far undetermined noise sources, which properties are not consistent with the conventional model of two-level systems, despite their effect on the sample linewidth. Moreover, the functional form of the FMR frequency noise power spectral density (PSD) cannot be described by a simple power law. By employing time-series analysis, we find a closed function for the PSD that fits our observations. Our results underline the necessity of coherence improvements to magnon systems for useful applications in quantum magnonics.

10.1063/5.0063668

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Introducing Coherent Time Control to Cavity Magnon Polartion Modes

Bulletin of the American Physical Society (2020)

Tim Wolz Alexander Stehli Andre Schneider Isabella Boventer Rair Macêdo

Magnon

Coherent control

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Transmon qubit in a magnetic field: Evolution of coherence and transition frequency

Physical Review Research (2019)

Andre Schneider Tim Wolz Marco Pfirrmann Martin Spiecker Hannes Rotzinger

We report on spectroscopic and time-domain measurements on a fixed-frequency concentric transmon qubit in an applied in-plane magnetic field to explore its limits of magnetic field compatibility. We demonstrate quantum coherence of the qubit up to field values of $B={40}\,\mathrm{mT}$, even without an optimized chip design or material combination of the qubit. The dephasing rate $\Gamma_\varphi$ is shown to be not affected by the magnetic field in a broad range of the qubit transition frequency. For the evolution of the qubit transition frequency, we find the unintended second junction created in the shadow angle evaporation process to be non-negligible and deduce an analytic formula for the field-dependent qubit energies. We discuss the relevant field-dependent loss channels, which can not be distinguished by our measurements, inviting further theoretical and experimental investigation. Using well-known and well-studied standard components of the superconducting quantum architecture, we are able to reach a field regime relevant for quantum sensing and hybrid applications of magnetic spins and spin systems.

Transmon

Dephasing

Quantum Metrology

Flux qubit

10.1103/physrevresearch.1.023003

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Citations (21)

Frequency fluctuations of ferromagnetic resonances at milliKelvin temperatures

arXiv (Cornell University) (2021)

Tim Wolz Luke J. McLellan Alexander Stehli Andre Schneider Jan David Brehm

Magnon

Laser linewidth

Quantum noise

Johnson–Nyquist noise

Quantum fluctuation

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Probing the Tavis -Cummings level splitting with intermediate-scale superconducting circuits

Bulletin of the American Physical Society (2019)

Martin Weides Ping Yang Jan David Brehm Juha Leppaekangas Lingzhen Guo

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Coherent superconducting qubits from a subtractive junction fabrication process

Applied Physics Letters (2020)

Alexander Stehli Jan David Brehm Tim Wolz P. G. Baity Sergey Danilin

Josephson tunnel junctions are the centerpiece of almost any superconducting electronic circuit, including qubits. Typically, the junctions for qubits are fabricated using shadow evaporation techniques to reduce dielectric loss contributions from the superconducting film interfaces. In recent years, however, sub-micron scale overlap junctions have started to attract attention. Compared to shadow mask techniques, neither an angle dependent deposition nor free-standing bridges or overlaps are needed, which are significant limitations for wafer-scale processing. This comes at the cost of breaking the vacuum during fabrication, but simplifies integration in multi-layered circuits, implementation of vastly different junction sizes, and enables fabrication on a larger scale in an industrially-standardized process. In this work, we demonstrate the feasibility of a subtractive process for fabrication of overlap junctions. In an array of test contacts, we find low aging of the average normal state resistance of only 1.6\% over 6 months. We evaluate the coherence properties of the junctions by employing them in superconducting transmon qubits. In time domain experiments, we find that both, the qubit life- and coherence time of our best device, are on average greater than $20\,\si{\micro\second}$. Finally, we discuss potential improvements to our technique. This work paves the way towards a more standardized process flow with advanced materials and growth processes, and constitutes an important step for large scale fabrication of superconducting quantum circuits.

Superconducting tunnel junction

Transmon

10.1063/5.0023533

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Citations (27)

Noise spectroscopy by dynamical decoupling of a transmon qubit

Verhandlungen der Deutschen Physikalischen Gesellschaft (2017)

Tim Wolz Andre Schneider Jochen Braumueller Martin Weides A. V. Ustinov

Transmon

Decoupling (probability)

Dynamical decoupling

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Magnons at low excitations: Observation of incoherent coupling to a bath of two-level systems

Physical Review Research (2019)

Marco Pfirrmann Isabella Boventer Andre Schneider Tim Wolz Mathias Kläui

Incoherent coupling to a bath of two-level systems is the dominating loss mechanism in magnons at quantum excitations. The authors study a hybrid system of magnons and microwave cavity photons, where they demonstrate the power saturation of the two-level systems at low temperatures and map the linewidth in the frequency detuned case to the magnon excitation ratio in the hybrid system. This allows for the fundamental linewidth to be extracted without saturation effects by excess cavity photons.

Laser linewidth

Magnon

Saturation (graph theory)

10.1103/physrevresearch.1.032023

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Citations (15)