Alexander Stehli

Karlsruhe Institute of Technology

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A. V. Ustinov

National Research University Higher School of Economics

Martin Weides

University of Glasgow

Hannes Rotzinger

Karlsruhe Institute of Technology

Jan David Brehm

Karlsruhe Institute of Technology

Tim Wolz

Karlsruhe Institute of Technology

Andre Schneider

Karlsruhe Institute of Technology

Michael Marthaler

Quantum Simulations (United States)

Isabella Boventer

Centre National de la Recherche Scientifique

Jochen Braumüller

Massachusetts Institute of Technology

Alexander N. Poddubny

Weizmann Institute of Science

Cooperative Institutions

Karlsruhe Institute of Technology

National University of Science and Technology

Russian Quantum Center

University of Glasgow

National Institute of Standards and Technology

Johannes Gutenberg University Mainz

Heriot-Watt University

Lawrence Livermore National Laboratory

University of Colorado Boulder

Weizmann Institute of Science

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Tailoring coupling in artificial superconducting quasi-spins

Verhandlungen der Deutschen Physikalischen Gesellschaft (2017)

Alexander Stehli Jochen Braumueller Andre Schneider Hannes Rotzinger Martin Weides

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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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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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Slowing down light in a qubit metamaterial

arXiv (Cornell University) (2022)

Jan David Brehm Richard Gebauer Alexander Stehli Alexander N. Poddubny Oliver Sander

The rapid progress in quantum information processing leads to a rising demand for devices to control the propagation of electromagnetic wave pulses and to ultimately realize a universal and efficient quantum memory. While in recent years significant progress has been made to realize slow light and quantum memories with atoms at optical frequencies, superconducting circuits in the microwave domain still lack such devices. Here, we demonstrate slowing down electromagnetic waves in a superconducting metamaterial composed of eight qubits coupled to a common waveguide, forming a waveguide quantum electrodynamics system. We analyze two complementary approaches, one relying on dressed states of the Autler-Townes splitting, and the other based on a tailored dispersion profile using the qubits tunability. Our time-resolved experiments show reduced group velocities of down to a factor of about 1500 smaller than in vacuum. Depending on the method used, the speed of light can be controlled with an additional microwave tone or an effective qubit detuning. Our findings demonstrate high flexibility of superconducting circuits to realize custom band structures and open the door to microwave dispersion engineering in the quantum regime.

Slow Light

Waveguide

10.48550/arxiv.2202.07034

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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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Tunable Anderson localization of dark states

Physical review. B./Physical review. B (2021)

Jan David Brehm Paul Pöpperl A. D. Mirlin Alexander Shnirman Alexander Stehli

Random scattering of photons in disordered one-dimensional solids gives rise to an exponential suppression of transmission, which is known as Anderson localization. Here, we experimentally study Anderson localization in a superconducting waveguide quantum electrodynamics system comprising eight individually tunable qubits coupled to a photonic continuum of a waveguide. Employing the qubit frequency control, we artificially introduce frequency disorder to the system and observe an exponential suppression of the transmission coefficient in the vicinity of its subradiant dark modes. The localization length decreases with the disorder strength, which we control in situ by varying individual qubit frequencies. Employing a one-dimensional noninteracting model of coupled qubits and photons, we are able to support and complement the experimental results. The difference between our investigation and previous studies of localization in qubit arrays is the coupling via a common waveguide, allowing us to explore the localization of mediating photons in an intrinsically open system. The experiment opens the door to the study of various localization phenomena on a new platform, which offers a high degree of control and readout possibilities.

Anderson Localization

Waveguide

Transmission coefficient

Exponential decay

10.1103/physrevb.104.174202

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Analog quantum simulation of the Rabi model in the ultra-strong coupling regime

Bulletin of the American Physical Society (2017)

Jochen Braum uller Michael Marthaler Andre Schneider Alexander Stehli Hannes Rotzinger

Rabi frequency

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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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Tunable Anderson Localization of Dark States

arXiv (Cornell University) (2021)

Jan David Brehm Paul Pöpperl A. D. Mirlin Alexander Shnirman Alexander Stehli

Random scattering of photons in disordered one-dimensional solids gives rise to an exponential suppression of transmission, which is known as Anderson localization. Here, we experimentally study Anderson localization in a superconducting waveguide quantum electrodynamics system comprising eight individually tunable qubits coupled to a photonic continuum of a waveguide. Employing the qubit frequency control, we artificially introduce frequency disorder to the system and observe an exponential suppression of the transmission coefficient in the vicinity of its subradiant dark modes. The localization length decreases with the disorder strength, which we control in-situ by varying individual qubit frequencies. The experiment opens the door to the study of various localization phenomena on a new platform, which offers a high degree of control and readout possibilities.

Anderson Localization

Transmission coefficient

Waveguide

Exponential decay

Weak localization

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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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Citations (1)