Micha Wildermuth

Karlsruhe Institute of Technology

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Hannes Rotzinger

Karlsruhe Institute of Technology

Jan Nicolas Voss

Karlsruhe Institute of Technology

Yannick Schön

Karlsruhe Institute of Technology

A. V. Ustinov

National Research University Higher School of Economics

Jared H. Cole

RMIT University

Alexey V. Ustinov

Karlsruhe Institute of Technology

Dominik Dorer

Karlsruhe Institute of Technology

Martin Weides

University of Glasgow

Sebastian T. Skacel

Institute of Automation

Andre Schneider

Karlsruhe Institute of Technology

Cooperative Institutions

Karlsruhe Institute of Technology

Russian Quantum Center

National University of Science and Technology

University of Glasgow

Johannes Gutenberg University Mainz

National Institute of Standards and Technology

Friedrich-Alexander-Universität Erlangen-Nürnberg

Institute of Materials Science of the Khabarovsk Scientific Center

Institute of Applied Mathematics

Pacific National University

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Random telegraph fluctuations in granular microwave resonators

arXiv (Cornell University) (2023)

Maximilian Kristen Jan Nicolas Voss Micha Wildermuth Hannes Rotzinger Alexey V. Ustinov

Microwave circuit electrodynamics of disordered superconductors is a very active research topic spawning a wide range of experiments and applications. For compact superconducting circuit elements, the transition to an insulating state poses a limit to the maximum attainable kinetic inductance. It is therefore vital to study the fundamental noise properties of thin films close to this transition, particularly in situations where a good coherence and temporal stability is required. In this paper, we present measurements on superconducting granular aluminum microwave resonators with high normal state resistances, where the influence of the superconductor to insulator phase transition is visible. We trace fluctuations of the fundamental resonance frequency and observe, in addition to a 1/f noise pattern, a distinct excess noise, reminiscent of a random telegraph signal. The excess noise shows a strong dependency on the resistivity of the films as well as the sample temperature, but not on the applied microwave power.

Kinetic inductance

10.48550/arxiv.2303.01079

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Josephson vortex dynamics in nanoscale Josephson junction parallel arrays

Micha Wildermuth Amadeus Dieter Yannick Schön Martin Weides Hannes Rotzinger

Superconducting tunnel junction

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Rabi oscillations in a superconducting nanowire circuit

npj Quantum Materials (2020)

Yannick Schön Jan Nicolas Voss Micha Wildermuth Andre Schneider Sebastian T. Skacel

Abstract We investigate the circuit quantum electrodynamics of anharmonic superconducting nanowire oscillators. The sample circuit consists of a capacitively shunted nanowire with a width of about 20 nm and a varying length up to 350 nm, capacitively coupled to an on-chip resonator. By applying microwave pulses we observe Rabi oscillations, measure coherence times and the anharmonicity of the circuit. Despite the very compact design, simple top-down fabrication and high degree of disorder in the oxidized (granular) aluminum material used, we observe lifetimes in the microsecond range.

Microsecond

Rabi cycle

Circuit quantum electrodynamics

10.1038/s41535-020-0220-x

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Giant Two-Level Systems in a Granular Superconductor

Physical Review Letters (2024)

M Donnell Kristen Jan Nicolas Voss Micha Wildermuth Alexander Bilmes Jürgen Lisenfeld

Disordered thin films are a common choice of material for superconducting, high impedance circuits used in quantum information or particle detector physics. A wide selection of materials with different levels of granularity are available, but, despite low microwave losses being reported for some, the high degree of disorder always implies the presence of intrinsic defects. Prominently, quantum circuits are prone to interact with two-level systems (TLS), typically originating from solid state defects in the dielectric parts of the circuit, like surface oxides or tunneling barriers. We present an experimental investigation of TLS in granular aluminum thin films under applied mechanical strain and electric fields. The analysis reveals a class of strongly coupled TLS having electric dipole moments up to 30 eÅ, an order of magnitude larger than dipole moments commonly reported for solid state defects. Notably, these large dipole moments appear more often in films with a higher resistivity. Our observations shed new light on granular superconductors and may have implications for their usage as a quantum circuit material.

10.1103/physrevlett.132.217002

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Eliminating Quantum Phase Slips in Superconducting Nanowires

ACS Nano (2021)

Jan Nicolas Voss Yannick Schön Micha Wildermuth Dominik Dorer Jared H. Cole

In systems with reduced dimensions, quantum fluctuations have a strong influence on the electronic conduction, even at very low temperatures. In superconductors, this is especially interesting, since the coherent state of the superconducting electrons strongly interacts with these fluctuations and therefore is a sensitive tool to study them. In this paper, we report on comprehensive measurements of superconducting nanowires in the quantum phase slip regime. Using an intrinsic electromigration process, we have developed a method to lower the nanowire's resistance in situ and therefore eliminate quantum phase slips in small consecutive steps. We observe critical (Coulomb) blockade voltages and superconducting critical currents, in good agreement with theoretical models. Between these two regimes, we find a continuous transition displaying a nonlinear metallic-like behavior. The reported intrinsic electromigration technique is not limited to low temperatures, as we find a similar change in resistance that spans over 3 orders of magnitude also at room temperature. Aside from superconducting quantum circuits, such a technique to reduce the resistance may also have applications in modern electronic circuits.

Electromigration

Coulomb blockade

10.1021/acsnano.0c08721

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Insulating, metallic and superconducting behavior in a single nanowire

arXiv (Cornell University) (2020)

Jan Nicolas Voss Yannick Schön Micha Wildermuth Dominik Dorer Jared H. Cole

In systems with reduced dimensions quantum fluctuations have a strong influence on the electronic conduction, even at very low temperature. In superconductors this is especially interesting, since the coherent state of the superconducting electrons is strongly interacting with these fluctuations and therefore is a sensitive tool to study them. In this paper, we report on comprehensive measurements of superconducting nanowires in the quantum phase slip regime. Using an intrinsic electromigration process, we have developed a method to lower the resistance of lithographically fabricated highly resistive nanowires in situ and in small consecutive steps. At low temperature we observe critical (Coulomb) blockade voltages and superconducting critical currents, depending on the nanowire's normal-state resistance, in good agreement with theoretical models. Between these two regimes, we find a continuous transition displaying a nonlinear metallic-like behavior. The reported intrinsic electromigration technique is not limited to low temperatures as we find a similar change in resistance that spans over three orders of magnitude also at room temperature. Aside from superconducting quantum circuits, such a technique to reduce the resistance may also have applications in modern electronic circuits.

Electromigration

Resistive touchscreen

Coulomb blockade

10.48550/arxiv.2006.06588

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Superconducting and insulating behaviour in granular aluminum oxide nano-wires

Jan Nicolas Voss Yannick Schön Dominik Dorer Micha Wildermuth Sebastian T. Skacel

Aluminum Oxide

Superconducting wire

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Rabi Oscillations in a Superconducting Nanowire Circuit

Bulletin of the American Physical Society (2020)

Yannick Schön Jan Nicolas Voss Micha Wildermuth Andre Schneider Sebastian T. Skacel

We investigate the circuit quantum electrodynamics of anharmonic superconducting nanowire oscillators. The sample circuit consists of a capacitively shunted nanowire with a width of about 20 nm and a varying length up to 350 nm, capacitively coupled to an on-chip resonator. By applying microwave pulses we observe Rabi oscillations, measure coherence times and the anharmonicity of the circuit. Despite the very compact design, simple top-down fabrication and high degree of disorder in the oxidized (granular) aluminum material used, we observe lifetimes in the microsecond range.

Microsecond

Rabi cycle

Circuit quantum electrodynamics

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Observation of giant two-level systems in a granular superconductor

arXiv (Cornell University) (2023)

Maximilian Kristen Jan Nicolas Voss Micha Wildermuth Alexander Bilmes Jürgen Lisenfeld

Disordered thin films are a common choice of material for superconducting, high impedance circuits used in quantum information or particle detector physics. A wide selection of materials with different levels of granularity are available, but, despite low microwave losses being reported for some, the high degree of disorder always implies the presence of intrinsic defects. Prominently, quantum circuits are prone to interact with two-level systems (TLS), typically originating from solid state defects in the dielectric parts of the circuit, like surface oxides or tunneling barriers. We present an experimental investigation of TLS in granular aluminum thin films under applied mechanical strain and electric fields. The analysis reveals a class of strongly coupled TLS having electric dipole moments up to 30 eA, an order of magnitude larger than dipole moments commonly reported for solid state defects. Notably, these large dipole moments appear more often in films with a higher resistivity. Our observations shed new light on granular superconductors and may have implications for their usage as a quantum circuit material.

Granularity

10.48550/arxiv.2307.09078

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Fluxons in high-impedance long Josephson junctions

Applied Physics Letters (2022)

Micha Wildermuth Lukas Powalla Jan Nicolas Voss Yannick Schön Andre Schneider

The dynamics of fluxons in long Josephson junctions is a well-known example of soliton physics and allows for studying highly nonlinear relativistic electrodynamics on a microscopic scale. Such fluxons are supercurrent vortices that can be accelerated by bias current up to the Swihart velocity, which is the characteristic velocity of electromagnetic waves in the junction. We experimentally demonstrate slowing down relativistic fluxons in Josephson junctions whose bulk superconducting electrodes are replaced by thin films of a high kinetic inductance superconductor. Here, the amount of magnetic flux carried by each supercurrent vortex is significantly smaller than the magnetic flux quantum Φ0. Our data show that the Swihart velocity is reduced by about one order of magnitude compared to conventional long Josephson junctions. At the same time, the characteristic impedance is increased by an order of magnitude, which makes these junctions suitable for a variety of applications in superconducting electronics.

Supercurrent

Kinetic inductance

Fluxon

Superconducting tunnel junction

Magnetic flux quantum

10.1063/5.0082197

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Citations (6)