A macroscopic object passively cooled into its quantum ground state of motion beyond single-mode cooling

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.

Mesoscopic Quantum Thermo-mechanics: a new frontier of experimental physics

“…It requires the definition of the most relevant baths thermodynamic temperatures, together with true steady-state quantum signatures measurements. This has been strikingly realized in a recent publication, opening the experimental field discussed in the present paper [110]: the temperature of the phonon bath (i.e. cryostat), of the internal TLSs, and of the lowest flexural mode of an Al-drum have been reported, demonstrating sideband-asymmetry in the optomechanics spectrum at the lowest temperatures.…”

“…the free QPs). In an experiment, the actual temperature of each bath deserves to be defined, and demonstrating thermal equilibrium is an issue on its own [110]. Besides, the relevance of most of the contributions depicted in Fig.…”

“…[111], ground state cooling of a MHz mode is obtained by active (sideband) cooling, while in Ref. [110] this is performed (for the first time in such systems to our knowledge) by passive cooling. The key challenge in this experiment is indeed the cooling technology: with a mechanical mode resonating at 15 MHz, the lowest temperature achieved to guarantee ground-state cooling was 500 µK [110].…”

“…[110] this is performed (for the first time in such systems to our knowledge) by passive cooling. The key challenge in this experiment is indeed the cooling technology: with a mechanical mode resonating at 15 MHz, the lowest temperature achieved to guarantee ground-state cooling was 500 µK [110]. Ultra-low temperature is one of the frontiers of Science, which is solicited today in particular by modern research in quantum materials and quantum technologies [93].…”

Feedback stabilization of the resonant frequency in tunable microwave cavities with single-photon occupancy

“…The existence of two-level-system induced 1/f -noise is well-known to limit the efficiency and sensitivity of devices across a breadth of applications -ranging from the semiconductor industry, to the emerging field of quantum computing processors [1]. Understanding its microscopic origin [2][3][4] and exploring different approaches to suppress this noise is a crucial step towards the realization of high coherence superconducting quantum circuits [5][6][7][8], ultra-sensitive electrometry/magnetometry [9][10][11][12][13][14][15], and other studies more fundamental in nature [16].…”