A twin pack of cooled nanoparticles – Technology Org

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Slowing down by shaking

Novotny and his collaborators then use that information to slow down the nanoparticle and, therefore, cool it. This is achieved by shaking the optical tweezer in exactly the opposite sense with respect to the oscillation of the sphere using an electronically controlled deflector that slightly changes the direction of the laser beam and hence the position of the tweezer.

When the sphere moves to the left, the tweezer is quickly shifted to the right in order to counteract the motion of the sphere; when it moves to the right, the deflector shifts the tweezer to the left. In this way, its oscillation amplitude, and hence its effective temperature, is reduced little by little – all the way down to a few thousandths of a degree above the absolute zero of -273,15 degrees Celsius.

To cool two nanoparticles at the same time the researchers use a trick. The optical tweezers in which they trap the spheres are adjusted such that the oscillation frequencies of the particles are slightly different. In that way, the motions of the two spheres can be distinguished using the same light detector, and the cooling-down strategies can be applied separately to the two tweezers.

Scaling up to several nanoparticles

“The simultaneous cooling can be straightforwardly scaled up to several nanoparticles”, Vijayan explains: “Since we have full control over the positions of the particles, we can arbitrarily tune the interactions between them; in that way, in the future we can study quantum effects of several particles, such as entanglement.”

In an entangled state, a measurement on one particle instantaneously influences the quantum state of the other one without any direct contact between the two particles. Up to now such states have been realised mainly with photons or single atoms. Vijayan hopes that one day he will be able to also create entangled states with the much larger nanoparticles.

The fact that the nanoparticles can be electrically neutral has further advantages, for instance, for developing extremely sensitive sensors. When measuring very weak gravitational forces between objects or searching for hypothetical dark matter, one would like to eliminate other forces as much as possible – and most often, those are electrostatic forces between charged particles. The method developed by the ETH researchers promises new insights in those fields, too.

Source: ETH Zurich



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