Periodic Reporting for period 1 - T-Recs (Tunable and Reconfigurable Nanoacoustics)
Berichtszeitraum: 2023-03-01 bis 2025-08-31
Acoustic phonons—quanta of vibrational energy in solids—are often seen as a source of unwanted noise in electronics, optoelectronics, and quantum technologies. In contrast, this project explores a transformative approach in solid-state physics by positioning acoustic phonons as active resources rather than disturbances. The central goal is to design and demonstrate tunable nanodevices where acoustic phonons enable wavelength conversion, information transport, and the simulation of physical systems that are otherwise inaccessible with photonic or electronic approaches.
Conventional nanophononics focuses on engineering fixed-function nanostructures to shape the local acoustic density of states or enhance interactions. This project takes a novel direction: integrating responsive materials—which alter their elastic properties under external stimuli—into GHz–THz nanophononic platforms. While tunability is well established in photonics and electronics, its implementation in phononics remains largely unexplored.
The project is structured around three major challenges:
i) To develop hybrid tunable resonators and transducers using responsive materials;
ii) To demonstrate acoustic-phonon wavelength conversion and time-dependent phononic potentials;
iii) To realize reconfigurable artificial nanophononic graphene and dynamic acoustic-phonon devices.
This approach aims to unlock a new regime in solid-state physics, expanding the phononics toolkit with dynamic functionalities and laying the groundwork for ultrahigh-frequency phononic information processing.
Conventional nanophononics focuses on engineering fixed-function nanostructures to shape the local acoustic density of states or enhance interactions. This project takes a novel direction: integrating responsive materials—which alter their elastic properties under external stimuli—into GHz–THz nanophononic platforms. While tunability is well established in photonics and electronics, its implementation in phononics remains largely unexplored.
The project is structured around three major challenges:
i) To develop hybrid tunable resonators and transducers using responsive materials;
ii) To demonstrate acoustic-phonon wavelength conversion and time-dependent phononic potentials;
iii) To realize reconfigurable artificial nanophononic graphene and dynamic acoustic-phonon devices.
This approach aims to unlock a new regime in solid-state physics, expanding the phononics toolkit with dynamic functionalities and laying the groundwork for ultrahigh-frequency phononic information processing.
A significant portion of the reporting period was dedicated to developing experimental infrastructure tailored for coherent acoustic phonon studies at ultrahigh frequencies. Key setups developed include:
Two coherent generation/detection systems for acoustic phonons;
A Sagnac interferometer for detecting coherent surface displacements;
Experimental setups operational across a wide thermal range (4 K to 600 °C).
One major achievement is the successful implementation of a non-local acoustic transport measurement system, enabling the generation and detection of coherent, quasi-continuous phonons at 20 GHz. This system is based on a ridge waveguide with a Fabry-Perot vertical structure, simultaneously confining near-infrared photons and high-frequency phonons.
By using a focused picosecond-pulsed laser at ~80 MHz repetition rate, we achieved quasi-continuous propagation of coherent phonons with a decay rate of ~1.14 dB/m, far beyond the optical excitation volume. Spatio-temporal interference experiments further confirmed mutual coherence between phonons emitted from distinct sources. This confirms the scalability and coherence of the system, and its potential for programmable phonon networks via spatial light modulation.
In the realm of tunable nanophononic devices, we investigated VO2 thin films, known for their strong temperature-driven optical transitions. While optical signatures of the transition were clear, acoustic transitions were inconclusive, likely hindered by surface roughness impacting the propagation of nanowaves.
We also developed acoustic resonators using mesoporous materials sensitive to ambient conditions. Experimental results show clear shifts in resonance peaks with changing humidity. However, after repeated cycling, tunable behavior degraded, prompting ongoing investigations into the causes (e.g. structural hysteresis or moisture-induced aging).
Two coherent generation/detection systems for acoustic phonons;
A Sagnac interferometer for detecting coherent surface displacements;
Experimental setups operational across a wide thermal range (4 K to 600 °C).
One major achievement is the successful implementation of a non-local acoustic transport measurement system, enabling the generation and detection of coherent, quasi-continuous phonons at 20 GHz. This system is based on a ridge waveguide with a Fabry-Perot vertical structure, simultaneously confining near-infrared photons and high-frequency phonons.
By using a focused picosecond-pulsed laser at ~80 MHz repetition rate, we achieved quasi-continuous propagation of coherent phonons with a decay rate of ~1.14 dB/m, far beyond the optical excitation volume. Spatio-temporal interference experiments further confirmed mutual coherence between phonons emitted from distinct sources. This confirms the scalability and coherence of the system, and its potential for programmable phonon networks via spatial light modulation.
In the realm of tunable nanophononic devices, we investigated VO2 thin films, known for their strong temperature-driven optical transitions. While optical signatures of the transition were clear, acoustic transitions were inconclusive, likely hindered by surface roughness impacting the propagation of nanowaves.
We also developed acoustic resonators using mesoporous materials sensitive to ambient conditions. Experimental results show clear shifts in resonance peaks with changing humidity. However, after repeated cycling, tunable behavior degraded, prompting ongoing investigations into the causes (e.g. structural hysteresis or moisture-induced aging).
The project has advanced nanophononics beyond the current state of the art in several ways:
Demonstrated the first coherent, quasi-continuous acoustic phonon source in a fully integrated device architecture;
Enabled mutual coherence control between phonon sources, paving the way for complex phononic logic operations and information processing at GHz–THz frequencies;
Showed that spatially modulated light can generate arbitrary propagating acoustic waveforms, opening possibilities for reconfigurable phonon-based systems.
By developing novel experimental methodologies and platforms, this work overcomes one of the major limitations in nanophononics: the lack of standard transducers and control systems for phonon generation and detection. The developed platforms offer a route toward coherent acoustic control at the nanoscale, with potential applications in signal processing, sensing, and simulation of quantum and topological systems.
To ensure further uptake, key next steps include:
Improving material interfaces and reducing surface roughness (e.g. in VO2 films) to enable clearer acoustic tunability;
Long-term stability studies of mesoporous resonators to identify and mitigate degradation mechanisms;
IPR strategies and potential industrial partnerships for translation of programmable acoustic sources into device architectures;
Engagement with standardization bodies to define benchmarks for phononic device performance.
These developments position acoustic phonons as programmable, coherent carriers of information and energy, suggesting an emerging class of dynamically tunable nanophononic devices with broad impact across solid-state and quantum technologies.
Demonstrated the first coherent, quasi-continuous acoustic phonon source in a fully integrated device architecture;
Enabled mutual coherence control between phonon sources, paving the way for complex phononic logic operations and information processing at GHz–THz frequencies;
Showed that spatially modulated light can generate arbitrary propagating acoustic waveforms, opening possibilities for reconfigurable phonon-based systems.
By developing novel experimental methodologies and platforms, this work overcomes one of the major limitations in nanophononics: the lack of standard transducers and control systems for phonon generation and detection. The developed platforms offer a route toward coherent acoustic control at the nanoscale, with potential applications in signal processing, sensing, and simulation of quantum and topological systems.
To ensure further uptake, key next steps include:
Improving material interfaces and reducing surface roughness (e.g. in VO2 films) to enable clearer acoustic tunability;
Long-term stability studies of mesoporous resonators to identify and mitigate degradation mechanisms;
IPR strategies and potential industrial partnerships for translation of programmable acoustic sources into device architectures;
Engagement with standardization bodies to define benchmarks for phononic device performance.
These developments position acoustic phonons as programmable, coherent carriers of information and energy, suggesting an emerging class of dynamically tunable nanophononic devices with broad impact across solid-state and quantum technologies.