Quantum measurement and control of non-classical mechanical states

Project Information

emcc

Grant agreement ID: 101110196

DOI

10.3030/101110196

Project closed

EC signature date 20 March 2023

Start date 1 May 2023

End date 31 May 2025

Funded under

• Marie Skłodowska-Curie Actions (MSCA)

Total cost

No data

EU contribution

€ 230 774,40

Coordinated by

KOBENHAVNS UNIVERSITET
Denmark

Periodic Reporting for period 1 - emcc (Quantum measurement and control of non-classical mechanical states)

Reporting period: 2023-05-01 to 2025-05-31

Summary of the context and overall objectives of the project

Mechanical resonators offer a promising platform for emerging quantum technologies—ranging from ultra-sensitive sensors and quantum transducers to fundamental tests of quantum mechanics—but preparing non-classical states of motion in macroscopic devices remains a key challenge due to thermal noise and limited measurement strength. The emcc project set out to overcome these barriers by developing and integrating quantum measurement and control techniques to engineer two hallmark non-classical states on millimetre-scale silicon-nitride membranes: first, a heralded single-phonon Fock state at cryogenic temperature; second, a quantum-squeezed state at room temperature. To verify these states, the project also aimed to implement full Wigner-function tomography, thereby demonstrating negative quasi-probabilities and unambiguously revealing non-classicality in a mesoscopic mechanical system.

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

• 4 K optomechanical system fabrication and characterization (WP1 & 2): We assembled the membrane-in-the-middle cavity and achieved operation at 4 K. The fundamental mechanical mode’s quality factor (Q) was measured with 300 million, confirming ultracoherent performance suitable for quantum experiments.
• Photon-counting attempts for single-phonon generation (WP1): Using pulsed sideband photon counting on red and blue motional sidebands, we sought to herald single-phonon state generation. The photon statistics does not satisfy the single phonon threshold.
• Continuous-measurement protocol (WP1 & 2): To avoid the complexity of the pulsed scheme, we developed a new protocol that could be easier to achieve our goal. In partnership with Prof Klemens Hammerer, we developed a continuous measurement scheme that combines photocurrent monitoring with real-time photon counting. Detailed theoretical modeling of this hybrid approach has been completed, demonstrating its capability to produce heralded single-phonon states and enable full Wigner-function tomography (see Fig. 1.). Experimental implementation is underway.
• Squeezing project (WP3): We finalized a comprehensive theoretical analysis of measurement-based feedback squeezing at room temperature. A preprint detailing the physics and experimental feasibility has been posted on arXiv:2402.17460; manuscript submission to a peer-reviewed journal is in preparation.

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)

• Ultracoherent 4 K platform: The optomechanical parameters characterization such as Q-factor measurement at cryogenic temperature validates a mesoscopic mechanical device for quantum applications, extending beyond previous work by confirming coherence at a few kelvin.
• Novel continuous-measurement protocol: Our theoretical proposal uniquely fuses continuous photocurrent detection with discrete photon-counting events to herald non-Gaussian mechanical states without disruptive pulsed drives. This hybrid method offers a scalable route to single-phonon preparation and tomography in macroscopic systems—surpassing existing pulsed-only schemes.
• Room-temperature squeezing feasibility: The arXiv preprint presents the first detailed feasibility study showing that continuous measurement and feedback can yield mechanical variance below the zero-point level at ambient conditions, opening prospects for cryogen-free quantum sensors.