Quantum Nano Mechanics – QNM

Physicists invented quantum mechanics mainly for explaining the properties of microscopic objects as atoms. Surprisingly, the theory elaborated during the first half of the 20th century equally treats all degrees of freedom, and nothing, in principle, prevents macroscopic objects to behave quantum-mechanically. Since the 1980s, physicists have indeed succeeded to place non-microscopic objects, mainly small superconducting electrical circuits, in the quantum regime. But a very important issue just started to be investigated very recently: do macroscopic mechanical objects follow the laws of quantum mechanics? Is it possible to prepare a mechanical object in a superposition of two states that are distinguishable at the macroscopic level? The aim of this project is to produce, control and detect ‘macroscopic and massive’ mechanical oscillators in the quantum regime. This research will also give a strong impulse to a new class of quantum-limited mechanical devices, in particular for force detection.

A nano-size mechanical oscillator provides collective position degrees of freedom that involve billions of atoms, and that can be displaced over distances large on atom’s scale. Their small size yields resonance frequencies in the 100 MHz - 1 GHz range, which allows reaching the quantum regime at temperatures in the milliKelvin domain. The originality of our project is to reach the quantum regime by operating the device at these ultra-low temperatures, which avoids using delicate active cooling methods.

Such kinds of mechanical oscillators are excited and measured using electronic techniques. These Nano Electro Mechanical Systems (NEMS) with a movable beam, embedded in a tunable microwave cavity, will be first cooled in their ground state by means of state-of-the-art cryogenic techniques. Their quantum state will then be manipulated by coupling them to an electrical two-level system, namely a ‘Transmon’ quantum bit embedded in the same cavity. Indeed, the quantum control of a harmonic oscillator requires coupling it to a non-linear device if one wants to produce non-classical states of the oscillator, which is one of the main goals in the field. We will exploit for this purpose state-of-the-art microwave methods developed for quantum bit experiments.

The project gathers together the expertise of different groups, to overcome in an original way the major hitches:
-) To cool mechanical oscillators down to ultra-low temperatures, in order to prepare them in their ground state without resorting to active cooling schemes.
-) To manipulate and measure these oscillators by coupling them to quantum bits, thus exploiting fabrication methods and measurement techniques borrowed from superconducting quantum bit physics.
-) To model the system and achieve a comprehensive understanding for operating the devices and analyze the experimental results.
-) To probe if such mechanical devices are well described by standard quantum mechanics, and if alternate theories need to be envisioned and, if so, could be probed.

The state-of-the-art in the field of mechanical quantum mechanics is represented by the work of a few groups, mostly in the USA (e.g. K. Schwab CalTech, K. Lehnert JILA, A. Cleland & J. Martinis UCSB). A crucial milestone of this research field is to produce and detect quantum superpositions of position-states of the oscillator that are macroscopically distinguishable. One expects that reaching such level of control of a macroscopic quantum system will have major applications in the field of quantum-limited measuring detectors, in particular for probing the mechanical properties of very small objects, possibly down to molecules.