Laser cooling a membrane-in-the-middle system close to the quantum ground state from room temperature

Abstract

Many protocols in quantum science and technology require initializing a system in a pure quantum state. In the context of the motional state of massive resonators, this enables studying fundamental physics at the elusive quantum-classical transition, and measuring force and acceleration with enhanced sensitivity. Laser cooling has been a method of choice to prepare mechanical resonators in the quantum ground state, one of the simplest pure states. However, in order to overcome the heating and decoherence by the thermal bath, this usually has to be combined with cryogenic cooling. Here, we laser-cool an ultracoherent, soft-clamped mechanical resonator close to the quantum ground state directly from room temperature. To this end, we implement the versatile membrane-in-the-middle setup with one fiber mirror and one phononic crystal mirror, which reaches a quantum cooperativity close to unity already at room temperature. We furthermore introduce a powerful combination of coherent and measurement-based quantum control techniques, which allows us to mitigate thermal intermodulation noise. The lowest occupancy we reach is 30 phonons, limited by measurement imprecision. Doing away with the necessity for cryogenic cooling should further facilitate the spread of optomechanical quantum technologies.

New in v2: a) improved fitting routine led to new sideband-cooled linewidths and calibration of mechanical spectra, both of which result in amended: 1. Fig. 2; 2. feedback-cooled occupancies (lowest occupancy is 30, instead of 20); 3. imprecision level limited by excess classical noise; 4. Fig. 4. b) SI now includes new sections 1.B and 8, and expanded section 4.A. c) minor corrections throughout

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• Membrane-in-the-middle optomechanics with a soft-clamped membrane at milliKelvin temperatures
• Self-calibrating gas pressure sensor with a 10-decade measurement range
• Coherent Control of an Optical Quantum Dot Using Phonons and Photons
• Enhancing Membrane-Based Scanning Force Microscopy Through an Optical Cavity
• Long-range optomechanical interactions in SiN membrane arrays
• Dissipative and dispersive cavity optomechanics with a frequency-dependent mirror
• Motional sideband asymmetry of a solid-state mechanical resonator at room temperature
• Membrane phononic crystals for high-Qm mechanical defect modes in piezoelectric aluminum nitride
• High-yield fabrication of micromirror templates via feedback-controlled laser ablation