Quantum non-demolition measurements of massive mechanical objects

Cavity optomechanics is an intriguing way to manipulate massive mechanical objects by the use of light. The tremendous progress in the last few years has allowed control of mechanical microresonators even at the quantum level. We intend to implement a new technique in the field, by using short optical pulses to probe the instantaneous position of a microresonator. This realizes an important tool, well known from quantum sciences: quantum non-demolition measurements, i.e. the possibility to probe a quantum property beyond the standard quantum limit, while imposing the measurement back action only on the conjugate observable. Such a back action evading measurement will enable several advancements in the field of cavity optomechanics, such as the preparation of Heisenberg limited coherent states and squeezed states of a massive mechanical oscillator. Moreover it will allow for full quantum state tomography of the motional mechanical state with a resolution beyond the standard quantum limit. This could be used in future experiments to demonstrate negative regions in the Wigner function of more complex quantum states.

A vibrating violin string behaves like a wave, swinging back and forth continuously, resulting in the sound waves we hear. According to quantum mechanics however, this motion should consist of very small, but discrete packages of energy, so-called phonons. This project aimed at controlling those phonons by employing quantum optical techniques. Initially, the researchers demonstrated that short laser pulses can be used to turn a micro-fabricated silicon resonator into an interface between phonons and light particles (photons) which works in the quantum regime. In a second step, they could demonstrate that they could to produce individual phonons and to confirm their fundamental particle aspect, utilizing a well-known test form quantum optics.