arXiv subjects

Thomas Luschmann

Publications and source records attributed to Thomas Luschmann.

7 recordsLinked to original sources

arXiv2026

Niobium Titanium Nitride as a High Tensile Stress Material for Nanomechanics

Over the past decades, high-coherence mechanical resonators have been continuously pushed to new limits, using techniques such as dissipation dilution and clamp-tapering to enhance their quality factor beyond intrinsic material limitations. Today, these mechanical resonators are often fabricated from silicon-nitride, silicon-carbide or aluminum. Recently, however, interest in novel material platforms has grown, especially those allowing for the integration within superconducting circuits. Among these, superconducting nitrides stand out as particularly promising due to their high transition temperatures compared to elementary superconductors. Here, we introduce them as nanomechanical resonators and report on the fabrication and characterization of highly stressed, doubly clamped niobium titanium nitride (NbTiN) nanostring resonators. Using optical interferometry, we determine the elastic properties and mechanical quality factor from room temperature to 13 K. We observe high tensile stress up to 0.81 GPa along with a Young's modulus of 181 GPa and an intrinsic mechanical quality factor up to 850. With these favorable mechanical properties, NbTiN constitutes a promising material platform for future applications in cavity electro- and nanomechanics.

quant-ph↗

arXiv2025

Resolving Abrikosov vortex entry in superconducting nano-string resonators via displacement-noise spectroscopy in cavity-optomechanics

Abrikosov vortices in type-II superconductors critically influence current flow and coherence, thereby imposing fundamental limits on superconducting quantum technologies. Quantum circuits employ superconducting elements at micro- and mesoscopic scales, where individual vortices can significantly impact device performance, necessitating investigation of vortex entry, motion, and pinning in these constrained geometries. Cavity-optomechanical platforms combining flux-tunable microwave resonators with superconducting nanomechanical elements offer a promising route to the single-photon strong-coupling regime and enable highly sensitive probing of the mechanical degree of freedom under elevated magnetic fields. Here, we exploit this platform to investigate vortex entry processes at the single-event level. We observe discrete jumps of the mechanical resonance frequency attributable to individual vortex entry, corresponding to attonewton-scale forces and allowing quantitative extraction of single-vortex pinning energies. These signatures are superimposed on a smooth power-law background characteristic of the collective Campbell-regime of vortex elasticity. Our results establish optomechanics-inspired sensing as a powerful method for exploring fundamental superconducting properties and identifying decoherence pathways in quantum circuits. Beyond advancing vortex physics, this work opens new opportunities for integrating mechanical sensing into superconducting device architectures, bridging condensed matter physics and quantum information science.

cond-mat.mes-hall↗

arXiv2023

Chiral phonons and phononic birefringence in ferromagnetic metal - bulk acoustic resonator hybrids

Magnomechanical devices, in which magnetic excitations couple to mechanical vibrations, have been discussed as efficient and broadband microwave signal transducers in the classical and quantum limit. We experimentally investigate the magnetoelastic coupling between the ferromagnetic resonance (FMR) modes in a metallic Co$_{25}$Fe$_{75}$ thin film, featuring ultra-low magnetic damping as well as sizable magnetostriction, and standing transverse elastic phonon modes in sapphire, silicon and gadolinium gallium garnet by performing broadband FMR spectroscopy at cryogenic temperatures. For all these substrate materials, we observe an interaction between the resonant acoustic and magnetic modes, which can be tailored by the propagation direction of the acoustic mode with respect to the crystallographic axes. We identify these phonon modes as transverse shear waves propagating with slightly different velocities with relative magnitudes of $\Delta v/v\simeq10^{-5}$, i.e., all substrates show phononic birefringence. Upon appropriately choosing the phononic mode, the hybrid magnomechanical system enters the Purcell enhanced coupling regime.

cond-mat.mes-hall↗

arXiv2023

Surface acoustic wave resonators on thin film piezoelectric substrates in the quantum regime

Lithium niobate (LNO) is a well established material for surface acoustic wave (SAW) devices including resonators, delay lines and filters. Recently, multi-layer substrates based on LNO thin films have become commercially available. Here, we present a systematic low-temperature study of the performance of SAW devices fabricated on LNO-on-insulator and LNO-on-Silicon substrates and compare them to bulk LNO devices. Our study aims at assessing the performance of these substrates for quantum acoustics, i.e. the integration with superconducting circuits operating in the quantum regime. To this end, we design SAW resonators with a target frequency of 5 GHz and perform experiments at millikelvin temperatures and microwave power levels corresponding to single photons or phonons. The devices are investigated regarding their internal quality factors as a function of the excitation power and temperature, which allows us to characterize and quantify losses and identify the dominating loss mechanism. For the measured devices, fitting the experimental data shows that the quality factors are limited by the coupling of the resonator to a bath of two-level-systems. Our results suggest that SAW devices on thin film LNO on silicon have comparable performance to devices on bulk LNO and are viable for use in SAW-based quantum acoustic devices.

physics.app-ph↗

arXiv2021

Magnetic field robust high quality factor NbTiN superconducting microwave resonators

We systematically study the performance of compact lumped element planar microwave $\mathrm{Nb_{70}Ti_{30}N}$ (NbTiN) resonators operating at 5 GHz in external in-plane magnetic fields up to 440 mT, a broad temperature regime from 2.2 K up to 13 K, as well as mK temperatures. For comparison, the resonators have been fabricated on thermally oxidized and pristine, (001) oriented silicon substrates. When operating the resonators in the multi-photon regime at $T=2.2$ K, we find internal quality factors $Q_{\mathrm{int}}\simeq$ $2\cdot10^5$ for NbTiN resonators grown on pristine Si substrates, while resonators grown on thermally oxidized substrates show a reduced value of $Q_{\mathrm{int}}\simeq$ $1\cdot10^4$, providing evidence for additional loss channels for the latter substrate. In addition, we investigate the $Q$-factors of the resonators on pristine Si substrates at millikelvin temperatures to asses their applicability for quantum applications. We find $Q_{\mathrm{int}}\simeq$ $2\cdot10^5$ in the single photon regime and $Q_{\mathrm{int}}\simeq$ $5\cdot10^5$ in the high power regime at $T=7$ mK.

physics.app-ph↗

arXiv2021

Mechanical frequency control in inductively coupled electromechanical systems

Nano-electromechanical systems implement the opto-mechanical interaction combining electromagnetic circuits and mechanical elements. We investigate an inductively coupled nano-electromechanical system, where a superconducting quantum interference device (SQUID) realizes the coupling. We show that the resonance frequency of the mechanically compliant string embedded into the SQUID loop can be controlled in two different ways: (i) the bias magnetic flux applied perpendicular to the SQUID loop, (ii) the magnitude of the in-plane bias magnetic field contributing to the nano-electromechanical coupling. These findings are quantitatively explained by the inductive interaction contributing to the effective spring constant of the mechanical resonator. In addition, we observe a residual field dependent shift of the mechanical resonance frequency, which we attribute to the finite flux pinning of vortices trapped in the magnetic field biased nanostring.

quant-ph↗

arXiv2020

Dia- and adiabatic dynamics in a phononic network

Mechanical resonator networks are currently discussed in the context of model systems giving insight into problems of condensed matter physics including effects in topological phases. Here, we discuss networks based on three high-quality factor nanomechanical string resonators (nanostrings) made from highly tensile-stressed Si$_{3}$N$_{4}$. The strings are strongly coupled via a shared support and thus can form a fully mechanical, classical multi-level system. Moreover, the individual strings are tunable in frequency, which allows one to explore their coupling behaviour using continuous wave spectroscopy and time domain techniques. In particular, such systems allow for the experimental exploration of quantum phenomena such as Landau-Zener transition dynamics by studying their classical analogues. Here, we extend the previous work performed on two coupled strings to three coupled resonators and discuss the additional features of the inter-string dynamics, such as the classical analog of Landau-Zener transition dynamics in a three-mode system. classical analog of Landau-Zener transition dynamics in a three-mode system.

cond-mat.mes-hall↗