Quantum lock-in amplifier phonon detectors

Project Information

Q-LAMP

Grant agreement ID: 101155102

DOI

10.3030/101155102

Project closed

EC signature date 19 March 2024

Start date 1 April 2024

End date 31 March 2026

Funded under

• Marie Skłodowska-Curie Actions (MSCA)

Total cost

No data

EU contribution

€ 199 694,40

Coordinated by

AALTO KORKEAKOULUSAATIO SR
Finland

Periodic Reporting for period 1 - Q-LAMP (Quantum lock-in amplifier phonon detectors)

Reporting period: 2024-04-01 to 2026-03-31

Summary of the context and overall objectives of the project

Phonons, the quantum excitations of atomic vibrations, are central to heat transport, superconductivity, and many quantum technologies [Phys. Rev. B, 109, 144303, (2024)]. Yet standard phonon probes such
as Raman spectroscopy mainly reveal phonon frequency and intensity, while giving limited access to phase and time-domain dynamics [ACS Nano, 14, 28–117, (2019)]. This restricts the study of coherent
phonon processes in quantum materials.

Q-Lamp addresses this gap by developing a quantum lock-in amplifier for phonon detection. The goal is a sensor that can detect both acoustic phonons, linked to strain, and thermal phonons, linked
to dissipation and heating, within one platform [Nat. Commun., 15, 4979, (2024); Nat. Photonics, 5, 222–229, (2011)]. Existing technologies usually detect only one of these channels, for example thermal phonons with transition-edge sensors or mechanical phonons with superconducting qubit-acoustic
devices [Phys. Rev. Appl., 22, 024051, (2024); Phys. Rev. B, 97, 205443, (2018)].

The project uses suspended two-dimensional NbSe2 as the active material. In this system, strain can tune superconductivity through changes in electron-phonon coupling, while thermal effects modify vortex motion and energy loss [Nat. Commun., 12, 2314, (2021); Nano Lett., 18, 2623–2629, (2018); Phys. Rev. B, 93, 134508, (2016)]. Suspension is essential because it increases both mechanical compliance and thermal isolation.

To support device design, the project combines two theoretical tools. Density functional theory with Electron-Phonon Wannier calculations links strain to electron-phonon coupling and critical temperature[Computer Physics Communications, 209, 116–133, (2016); Phys. Rev. B, 76, 165108, (2007); Computer Physics Communications, 185, 2309–2310, (2014)]. Time-dependent Ginzburg-Landau simulations linked to heat diffusion describe thermal feedback and vortex dynamics [Supercond. Sci. Technol., 31, 055007, (2018); Phys. Rev. Lett., 40, 1041–1044, (1978)]. Together, these methods guide the design of a dual-mode quantum phonon detector with relevance for sensing and dark matter searches [Phys. Rev. D, 109, 023010, (2024)].

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

Q-Lamp has established suspended NbSe2 as a promising platform for controllable superconductivity under combined strain and thermal modulation [arXiv:2511.05763 (2025), main work]. The work shows that
suspension is not only a fabrication choice but a functional route to stronger coupling between mechanical deformation, heating, and the superconducting state.

A first achievement is the demonstration of a practical route to strain-controlled superconductivity. Electrostatic deformation in suspended structures provides reversible tuning of superconducting
behaviour, in line with published evidence that thin NbSe2 is highly sensitive to strain, thickness, and electron-phonon coupling.

A second achievement is the identification of enhanced thermal response in suspended devices. Removing the supporting substrate reduces heat sinking and mechanical clamping, which strengthens local
heating effects and makes thermal-superconducting coupling easier to observe. With the thermal couping, we achieved the observation and interpretation of multi-stage hysteresis and negative differential resistance.
These effects are consistent with strong thermal feedback and non-equilibrium superconducting transport, and they indicate access to multiple dissipative states that may be useful for sensing and signal amplification [Sci. Adv., 6, eaba1377, (2020); Nat. Phys., 15, 947–953, (2019); Phys. Rev. B, 93, 134508, (2016)].

A fourth achievement is the development of a combined modelling strategy. Microscopic DFT/EPW calculations quantify how strain changes electron-phonon coupling and critical temperature, while TDGL-based thermal simulations reproduce vortex-driven transport behaviour and heating effects. This creates
a direct link between material design and device performance. The code of TDGL coupling with thermal is uploaded in https://github.com/fangrh/TDGLThermal.git

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

The current state of the art in phonon sensing is fragmented. Existing platforms usually target either thermal phonons, as in transition-edge sensors, or mechanically coupled phonons, as in superconducting
qubit-acoustic systems [Phys. Rev. Appl., 22, 024051, (2024); Phys. Rev. B, 97, 205443, (2018)]. In parallel, advanced modelling tools exist for electron-phonon coupling and superconducting transport,
but they are often applied separately rather than as one design workflow [Computer Physics Communications, 209, 116–133, (2016); Computer Physics Communications, 291, 108799, (2023)].

Q-Lamp goes beyond this state of the art by bringing these elements together in one suspended superconducting platform. Suspended NbSe2 is used not only as a sensitive material, but as a device
architecture in which strain and thermal effects can both modulate superconductivity [Nano Lett., 18, 2623–2629, (2018); arXiv:2511.05763 (2025)]. This creates a route toward dual-mode phonon detection
within one system rather than two separate detector classes.

The project also goes beyond the state of the art by linking material-level and device-level modelling in a single framework. Q-Lamp combines DFT/EPW calculations for strain-dependent electron-phonon
coupling with TDGL-based thermal transport simulations for vortex dynamics and dissipation [Computer Physics Communications, 209, 116–133, (2016); Supercond. Sci. Technol., 31, 055007, (2018)]. This
improves predictive design and reduces reliance on trial-and-error optimization.

Finally, Q-Lamp treats nonlinear superconducting behaviour as a functional advantage. Hysteresis, multistability, and negative differential resistance are not only signatures of complex transport, but potential
resources for signal amplification and sensitive readout [Sci. Adv., 6, eaba1377, (2020); Nat. Phys.,15, 947–953, (2019)]. These advances open applications in quantum sensing, studies of electron-phonon
coupling in two-dimensional materials, and phonon-based dark matter detection [Nat. Photonics, 5,222–229, (2011); Phys. Rev. D, 109, 023010, (2024)].