Laser refrigeration on the nanoscale: From nanocryostats to quantum optomechanics

点击翻译按钮获取中文摘要

Laser refrigeration occurs when incident light absorbed by a solid material is subsequently emitted at higher energy. This blue-shifted emission of photons with respect to the excitation wavelength leads to internal cooling by converting the internal energy of the vibrations (phonons) in the solid to photons which leave the solid via fluorescence. This process lowers the entropy and temperature of the solid. One material, yttrium lithium fluoride (YLF) doped with rare earth ytterbium ions, has been shown to be the best bulk material for this process, and very recently we demonstrated the first dramatic cooling this nanoscale material to 130 K. This proof-of-principle experiment, published in Nature Photonics (doi:10.1038/s41566-017-0005-3), was accomplished by using optical levitation to both isolate the particle from the environment and to cool it. This programme aims to capitilize on our development in two strongly interlinked strands of research. The first will develop laser refrigeration on the nanoscale, with the aim of fabricating a microscale cryogenic refrigerator using the techniques of nanophotonics to enhance the cooling and to determine the lowest minimum temperature that can be achieved using this material. We aim to lower the temperature of the solid well below 80 K with the aim to reach 10 K. By modifying the emission process using 1-D and 3-D photonic structures, we will enhance cooling while more efficiently utilising the incident light. Such a device, that can be nanofabricated, and uses laser light without direct physical contact, will rapidly find applications in cooling electronics, detectors and new quantum technologies to cryogenic temperatures . A second strand will explore application of this technology to foundational quantum mechanics within the field of levitated optomechanics. Here, the ability to cool and manipulate the centre-of-mass motion of levitated nanoparticles is now established as a promising tool for exploring macroscopic quantum mechanics. This will allow the observation of non-classical states of motion and the creation of long-lived macroscopic quantum states, as well as a providing a testing ground for the role of gravity within quantum mechanics. However, while we and other researchers have managed to remove almost all sources of decoherence, it is the control of particle internal temperature that has yet to be mastered but for which laser refrigeration offers great promise. In this part of the programme we therefore aim to refrigerate levitated particles for use in NV nanocrystal experiments to increase both spin and motional decoherence time, and use laser refrigeration to produce narrow line widths in solids doped with other rare ions to explore both Doppler and sideband cooling of levitated nanocrystals. Although firmly based in the UK, this programme will bring together both experimental and theoretical researchers in UK with international collaborators who will help to make this programme a success. This includes researchers with expertise in laser refrigeration, rare earth doped materials fabrication and characterisation, laser nano and micro optical fabrication, quantum optics and quantum optomechanics.