QUSCOPE seminar

Speaker: Signe Seidelin, Institut Néel, CNRS, Grenoble, France

Title: Hybrid quantum systems: NV-centers, quantum dots and recent fantasies about rare-earth doped crystals

Abstract:

An exciting challenge of modern physics is to investigate the behavior of a material object - for instance a mechanical oscillator - placed in a non-classical state. One approach consists in exploiting a hybrid quantum system based on a mechanical oscillator coupled to an atom-like object. Diverse coupling mechanisms between these two radically different degrees of freedom have been demonstrated by the community in recent years [1], such as magnetic, capacitive, opto-mechanical, or via surface potentials, etc. As a starting point, I will briefly present our first hybrid system, which consisted in in a single Nitrogen Vacancy (NV) defect hosted in a diamond nanocrystal positioned at the extremity of a vibrating nanowire [2]. The coupling was achieved by an external magnetic gradient placed near the nanowire. However, a more stable, and potentially stronger coupling mechanism is based on material strain. Here, the oscillator is a bulk object containing an embedded artificial atom (dopant, quantum dot, ...) which is sensitive to the mechanical strain of the surrounding material. Vibrations of the oscillator result in a time-varying strain field that modulates the energy levels of the embedded structure. Using a quantum dot embedded in a photonic nanowire, we did a proof-of-principle experiment in which we demonstrated a coupling based on material strain [3]. However, due to the relatively large spectral linewidth of quantum dots in general, other systems might prove more suitable for reaching the so-called resolved-sideband regime. This regime - a pre-requisite for some active cooling schemes for mechanical oscillators - requires a linewidth of the emitter well below the mechanical oscillation frequency. I will discuss some ideas (fantasies?) on using rare-earth doped crystals as mechanical oscillators, which might hold promise to reach even deeper into this regime. More precisely, we are currently studying Eu³⁺  (in an Y₂SiO₅ matrix) which has an optical transition with the narrowest linewidth known for a solid-state emitter [4], and a transition which is directly sensitive to mechanical strain [5].

[1] M. Aspelmeyer, P. Meystre, and K. Schwab, Quantum optomechanics, Physics Today 65, 29 (2012)
[2] O. Arcizet, V. Jacques, A. Siria, P. Poncharal, P. Vincent, and S. Seidelin, Nature Physics 7, 879 (2011)
[3] I. Yeo et al., Strain-mediated coupling in a quantum dot–mechanical oscillator hybrid system, Nature Nanotechnology 9, 106 (2014)
[4] R. Yano, M. Mitsunaga, and N. Uesugi, Ultralong optical dephasing time in Eu³⁺:Y₂SiO_5, Optics   Letters, 16, 1884 (1991)
[5] M. J. Thorpe et al., Frequency stabilization to 6 x10^-16 via spectral-hole burning, Nature Photonics, 5, 688 (2011)

Coffee/tea and cake from 14:00