Engineering Mesoscopic Quantum Phenomena with Si Optomechanical Crystals

Achieving the sensitivity needed to measure quantum fluctuations necessitates reaching the Standard Quantum Limit (SQL). Several experiments have successfully achieved SQL in different physical systems [1],[2],[3],[4]. To reach these precision levels in nanomechanical systems, it is crucial for the oscillator to be in its mechanical ground state. However, thermal interactions from the environment hide the quantum characteristics of a mesoscopic resonator, as coherent states are necessary to reveal quantum phenomena. Mitigating decoherence involves cooling the oscillator and decoupling it from thermal noise. Alternative methods to cryogenic cooling, such as back-action cooling, have achieved low thermal occupation in various systems [5],[6],[7].
Optomechanical systems provide an effective framework for achieving quantum-limited precision, cooling, and shielding from the environment. Various optomechanical systems have demonstrated these capabilities [8],[9]. Among different configurations, optomechanical crystals are particularly promising for their ability to confine and control both optical and mechanical modes at the nanoscale. By operating in the resolved sideband regime, it is possible to cool down the mechanical oscillator to its ground state, thus enabling the exploration of quantum phenomena in larger systems [10].
To enable the above-mentioned capabilities, we have designed an innovative optomechanical crystal aimed at advancing the field of quantum optomechanics. Our device comprises a photonic crystal with an infrared-wavelength photonic defect mode embedded in a phononic crystal, which shields the mechanical defect mode at 2,5 GHz. The optical mode is optimized to work in the resolved sideband regime (Q_op,>>ω_op /Ω_m , being Q_op the optical quality factor and ω_op and Ω_m the optical and mechanical frequencies). The design optimization has been performed using 3D finite element method (FEM) simulations in COMSOL, further enhanced the Q_opt by machine learning techniques up to 10⁶ . The system shows an optomechanical vacuum coupling rate of g₀,/2π=600kHz, obtaining a minimum number of phonons in the mechanical mode of 0,01 by simply confining tens of photons in the cavity at liquid helium temperatures, which would allow for optimized noise performance. Our careful design considerations and theoretical analyses show the potential of our optomechanical crystal to achieve these significant milestones even at higher temperatures.
This novel design seeks to unlock new possibilities in quantum applications. By integrating advanced simulation and machine learning techniques, our work provides a robust platform for exploring the quantum regime and achieving high levels of measurement sensitivity and coherence in a macroscopic system.
[1] Schreppler, S. et al. Science 344, 1486–1489 (2014).
[2] The LIGO Scientifc Collaboration. Nat. Phys. 201, 962–965 (2011)
[3] LaHaye, M. D., et al. Science 304, 74–77 (2004).
[4] Rossi, M., et al. Nature, 563, 53–58 (2018).
[5] A. Naik, et al. Nature, 443:193–196, 9 2006
[6] A. D. O’Connell, et al. Nature, 464(7289):697–703, 4 2010
[7] J. D. Teufel, et al. Nature, 475:359–363, 7 2011.
[8] A. Schliesser, et al. Nature Physics, 5(7):509–514, 2009.
[9] Sampo A. Saarinen, et al. Optica, 10:364, 3 2023.
[10] J. D. Teufel, et al. Nature Nanotechnology, 4(12):820–823, 2009.