arXiv subjects

C. Undershute

Publications and source records attributed to C. Undershute.

6 recordsLinked to original sources

arXiv2026

Electromagnetic and Acoustic Fano Interference in Surface Acoustic Wave Resonators

Surface acoustic wave-based resonators are sensitive probes of condensed matter systems, as well as surface-selective sensors for chemistry and biology. Surface acoustic wave devices have also been integrated into hybrid quantum systems with qubit platforms for applications in quantum information processing and sensing. The sensitivity of piezoelectric surface wave-based resonators to investigate these various systems can be enhanced by optimizing the device architecture and electrical measurement techniques. Alternatively, tailoring the spectral symmetry, arising from interference effects, offers a promising route to further improve sensitivity. In this work, we demonstrate the simultaneous introduction of both electromagnetic and acoustic Fano interference to shape the spectral response of GHz-frequency surface acoustic wave resonators. By systematically modifying the acoustic reflectivity of the resonators, we are able to isolate and analyze each interference mechanism independently. The broad range of temperature operation, from ambient to cryogenic temperatures highlights the potential for both classical and quantum sensing applications.

cond-mat.mes-hall↗

arXiv2024

Plasmon Mode Engineering with Electrons on Helium

An ensemble of electrons trapped above superfluid helium offers a paradigm system for investigating and controlling collective charge dynamics in low-dimensional electronic matter. Of particular interest is the ability to spatially control and engineer surface plasmons for integration with hybrid quantum systems and circuit quantum electrodynamic device architectures. Here we present experiments using an electron-on-helium microchannel device that hosts microwave-frequency plasmons, generated via local microwave excitation in an electrostatically defined central channel. By precisely varying the electron density, we demonstrate tunability of plasmon mode frequencies over several GHz. Additionally, we find that the power dependence of these modes can be used to investigate both homogeneous and inhomogeneous sources of spectral broadening. These results demonstrate the versatility of electrons on helium for probing collective excitations in low-dimensional Coulomb liquids and solids, and demonstrate a path for integrating engineered plasmons in electrons on helium with hybrid circuit quantum electrodynamic systems.

cond-mat.mes-hall↗

arXiv2024

Free-space coupling and characterization of transverse bulk phonon modes in lithium niobate in a quantum acoustic device

Transverse bulk phonons in a multimode integrated quantum acoustic device are excited and characterized via their free-space coupling to a three-dimensional (3D) microwave cavity. These bulk acoustic modes are defined by the geometry of the Y-cut lithium niobate substrate in which they reside and couple to the cavity electric field via a large dipole antenna, with an interaction strength on the order of the cavity line-width. Using finite element modeling (FEM) we determine that the bulk phonons excited by the cavity field have a transverse polarization with a shear velocity matching previously reported values. We demonstrate how the coupling between these transverse acoustic modes and the electric field of the 3D cavity depends on the relative orientation of the device dipole, with a coupling persisting to room temperature. Our study demonstrates the versatility of 3D microwave cavities for mediating contact-less coupling to quantum, and classical, piezoacoustic devices.

quant-ph↗

arXiv2023

Phononic bath engineering of a superconducting qubit

Phonons, the ubiquitous quanta of vibrational energy, play a vital role in the performance of quantum technologies. Conversely, unintended coupling to phonons degrades qubit performance and can lead to correlated errors in superconducting qubit systems. Regardless of whether phonons play an enabling or deleterious role, they do not typically admit control over their spectral properties, nor the possibility of engineering their dissipation to be used as a resource. Here we show that coupling a superconducting qubit to a bath of piezoelectric surface acoustic wave phonons enables a novel platform for investigating open quantum systems. By shaping the loss spectrum of the qubit via the bath of lossy surface phonons, we demonstrate preparation and dynamical stabilization of superposition states through the combined effects of drive and dissipation. These experiments highlight the versatility of engineered phononic dissipation and advance the understanding of mechanical losses in superconducting qubit systems.

quant-ph↗

arXiv2023

Quantum acoustic Fano interference of surface phonons

Quantum acoustic systems, which integrate surface or bulk phonons with superconducting qubits, offer a unique opportunity to investigate phononic $interference$ and $scattering$ processes in the quantum regime. In particular the interaction between a superconducting qubit and a phononic oscillator allows the qubit to sense the oscillator's excitation spectrum and underlying interference effects. Here we present measurements revealing Fano interference of a resonantly trapped piezoelectric surface acoustic wave (SAW) mode with a broad continuum of surface phonons in a system consisting of a SAW resonator coupled to a superconducting qubit. The experiments highlight the existence of additional weakly coupled mechanical modes and their influence on the qubit-phonon interaction and underscore the importance of phononic interference in quantum acoustic architectures that have been proposed for quantum information processing applications.

quant-ph↗

arXiv2022

Surface-dominated finite size effects in nanoconfined superfluid helium

Superfluid $^4$He (He-II) is a widely studied model system for exploring finite-size effects in strongly confined geometries. Here, we study He-II confined in mm-scale channels of 25 and 50 nm height at high pressures using a nanofluidic Helmholtz resonator. We find that the superfluid density is measurably suppressed in the confined geometry from the transition temperature down to 0.6 K. Importantly, this suppression can be accounted for by roton-like thermal excitation with an energy gap of 5 K. We show that the surface-bound excitations lead to the previously unexplained lack of finite-size scaling of suppression of the superfluid density.

cond-mat.mes-hall↗