Researchers have, for the first time, levitated individual nanodiamonds in vacuum. The research team is led by Nick Vamivakas at the University of Rochester who thinks their work will make extremely sensitive instruments for sensing tiny forces and torques possible, as well as a way to physically create larger-scale quantum systems known as macroscopic Schr\u00f6dinger Cat states.<\/p>\n
While other researchers have trapped other types of nanoparticles in vacuum, those were not optically active. The nanodiamonds, on the other hand, can contain nitrogen-vacancy (NV) centers that emit light and also have a spin quantum number of one. In the paper, published in Nature Photonics<\/em>, the researchers from Rochester\u2019s Institute of Optics explain this is the first step towards creating a \u201chybrid quantum system.\u201d Their system combines the mechanical motion of the nanodiamond with the internal spin of the vacancy and its optical properties to make it particularly promising for a number of applications.<\/p>\n In a previous paper, the researchers had shown that nanodiamonds could be levitated in air using a trapping laser. The new paper now shows this can be done in vacuum, which they say is \u201ca critical advance over previous nanodiamond optical tweezer experiments performed in liquids or at atmospheric pressure.\u201d<\/p>\n Nanodiamonds trapped at atmospheric pressure are continuously agitated by collisions with the air molecules around them. Trapping the diamonds in vacuum removes the effect of all these air molecules. \u201cThis allows us to exert mechanical control over them,\u201d said Levi Neukirch, lead author of the paper and a PhD student in Vamivakas\u2019 group at Rochester. \u201cThey turn into little harmonic oscillators.\u201d<\/p>\n \u201cWe can measure the position of the diamond in 3D and we create a feedback signal based on the position and velocity of the nanodiamond,\u201d said Neukirch. \u201cThis lets us actively damp its motion.\u201d<\/p>\n Neukirch said that this is done by changing the trapping potential that the diamond sees. The trapping potential can be illustrated by imagining the diamond sitting at the bottom of a valley. If the diamond moves away from the bottom of the valley, it effectively moves uphill and eventually rolls back to the bottom. The feedback mechanism the researchers have created changes the shape of the optical potential well, so that the hill is steep when the diamond climbs it, but gradual when it rolls back down. Eventually the diamond would just oscillate a tiny amount at the bottom of the valley. This, Neukirch stated, is their long-term goal: to damp the diamond\u2019s motion until it is in the ground state of the system, which would make the system behave as a quantum mechanical oscillator.<\/p>\n In their previous experiments the diamond shone brightly because it contained hundreds of vacancies, all which emit light after being excited with a laser. In their recent work they chose diamonds that had few vacancies and were even able to select diamonds with a single vacancy. With a single spin in the NV center, and the system functioning as a quantum mechanical oscillator, the researchers would be able to affect the spin state of the tiny defect inside the nanodiamond by exerting mechanical control on the entire nanodiamond.<\/p>\n