Atomic quantum engines in optical tweezers

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Prof. E. A. Hinds, Imperial College London

Dr G. Barontini, University of Birmingham

Background. Thermodynamics is fundamental to our understanding of many topics in science and technology, including the operation of most machines and engines. As research pushes towards ever smaller devices new quantum technology is increasingly about machines with only one or a few atoms, and on this scale, standard thermodynamics fails because it has been developed to describe large ensembles of particles. In addition, quantum effects become important and the competition between quantum and thermal fluctuations plays a major role. In this regime, then, even the most basic quantities such as "heat" and "work" need to be re-defined, and thermodynamics itself must be reformulated on the basis of quantum mechanical laws [1]. This brings exciting new opportunities for exploiting quantum-mechanical effects, such as coherence and entanglement, to devise quantum engines that may outperform the best classical engines [2].

The PhD project (at the University of Birmingham) is to build, characterize and develop the first atomic quantum engines and to exploit the laws of quantum mechanics to push their performance beyond the limits of classical machines. You will create an experiment using cold atoms to test thermodynamic transformations and to develop engines at the single atom quantum level. A single two-level atom will be trapped in an optical tweezer and will be immersed in a heat bath of many atoms of a different species. All the parameters will be completely controlled - the temperature and dimensionality of the bath, the interaction between the single atom and the bath, and the internal and external degrees of freedom of the single atom. With this exceptional control, it will be possible to make cyclic thermodynamic transformations that realise quantum heat engines. This project aims to produce new results, including realisations of the quantum Carnot, Otto and Diesel engines. These experiments will help to develop an understanding of thermodynamics in the quantum realm and its practical applications.

The MRes project is to design and build an optical system that can produce compact, robust and versatile optical tweezers. Compactness is desirable for future practical applications, and also because the tweezers must be integrated into an existing apparatus. To achieve this, the tip of an optical fibre will be fused to create a microscopic lens. This will focus laser light to a waist of about 1 μm at a distance of about 1 mm from the tip, where atoms will be trapped in a very small volume by the optical dipole force. Because of a well-known blockade mechanism [3], the trap will not hold more than one atom. Machining directly on the tip guarantees near-perfect alignment of the trap, an advantage over conventional optics susceptible to small misalignments. Additionally, the fibre is broad-band, so can be used to overlap light of several different wavelengths on the trapped atom, and to collect fluorescence, exploiting the high numerical aperture subtended by the tip. The candidate will work at the University of Birmingham to develop a method to produce a lensed fibre using an advanced arc fusion fibre splicer. The candidate will then test and characterize the beam produced by the lensed fibre to ensure that it meets the requirements outlined above.

[1] S. Vinjanampathy and J. Anders, Contemp. Phys., 57, 1 (2016)

[2] Raam Uzdin, Amikam Levy, and Ronnie Kosloff, Phys. Rev. X 5, 031044 (2015); Marlan O. Scully, M. Suhail Zubairy, Girish S. Agarwal, Herbert Walther, Science 299, 862 (2003); J Jaramillo, M Beau and A del Campo, New J. Phys. 18 075019 (2016)

[3] A. M. Kaufman, B. J. Lester, and C. A. Regal, Phys. Rev. X 2, 041014 (2012)

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