Abstract
The nature of the quantum-to-classical crossover remains one of the most challenging open question of Science to date. In this respect, moving objects play a specific role. Pioneering experiments over the last few years have begun exploring quantum behaviour of micron-sized mechanical systems, either by passively cooling single GHz modes, or by adapting laser cooling techniques developed in atomic physics to cool specific low-frequency modes far below the temperature of their surroundings. Here instead we describe a very different approach, passive cooling of a whole micromechanical system down to 500 μK, reducing the average number of quanta in the fundamental vibrational mode at 15 MHz to just 0.3 (with even lower values expected for higher harmonics); the challenge being to be still able to detect the motion without disturbing the system noticeably. With such an approach higher harmonics and the surrounding environment are also cooled, leading to potentially much longer mechanical coherence times, and enabling experiments questioning mechanical wave-function collapse, potentially from the gravitational background, and quantum thermodynamics. Beyond the average behaviour, here we also report on the fluctuations of the fundamental vibrational mode of the device in-equilibrium with the cryostat. These reveal a surprisingly complex interplay with the local environment and allow characteristics of two distinct thermodynamic baths to be probed.
Highlights
The nature of the quantum-to-classical crossover remains one of the most challenging open question of Science to date
One extremely promising technology is the microwave version of optomechanics, where the mechanical element modulates the resonance frequency of an RLC circuit[15,16]. It inherits the properties of conventional optomechanics, is directly compatible with quantum electronics technologies[17,18], with the great advantage of low energy photons being more compatible with cryogenic setups[16,19,20]
The microwave circuitry is fully compatible with standard quantum electronics; which means that future developments will incorporate a quantum bit[18]. This would enable experiments directly focused on the study of quantum mechanical decoherence, as proposed, e.g., in ref
Summary
The nature of the quantum-to-classical crossover remains one of the most challenging open question of Science to date. We report on in-equilibrium ground-state cooling of a whole 15-micron diameter aluminium mechanical device resonating at ωm = 2π × 15.1 MHz in its first flexure and coupled to a ωc = 2π × 5.7 GHz microwave cavity, installed on a nuclear demagnetisation cryostat reaching ~500 μK.
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