Single Ion Thermodynamics

Since the onset of the industrial revolution, heat engines have played a prominent role in our modern civilization. In general, heat engines convert thermal energy into mechanical motion and form the basis for all motorized vehicles from cars to airplanes. Simultaneously, in the past decades miniaturization has led to the development of increasingly smaller devices. The thermodynamics team in Mainz deals with the question how those machines perform at the ultimate single-particle level. With our analysis of fluctuations both in energy and phase, we contribute to the emerging field of quantum thermodynamics. We are part of a newly established Forschergruppe, funded by the DFG (German Research Foundation) named “Thermische Maschinen in der Quantenwelt”.

In a first experiment we realize a heat engine using the spin of simple Ion spin as a working medium [1]. Heat reservoirs are emulated by controlling the spin polarization via optical pumping. The engine is coupled to the ion's harmonic-oscillator degree of freedom via spin-dependent optical forces originating from a phase-stable standing wave (see image). The motion stores the work produced by the heat engine and therefore acts as a flywheel. We fully characterize the heat engine by measuring the temporally varying spin polarization and the state of the flywheel by reconstructing its Husimi Q function (see image). We infer the deposited energy and the work fluctuations for varying engine runtimes at the onset of operation starting in the oscillator ground state. We also determine the ergotropy, i.e. the maximum amount of work which can be extracted via a cyclic unitary. The future aim is to perform experiments with trapped ion crystals deep in the quantumregime, and to understand the role of entanglement coherence and quantum fluctuations for the operation of machines.

In a experiment, an ion was confined in a linear Paul trap with tapered geometry (see image) and driven to a coherent state of motion by coupling to designed "hot" and "cold" reservoirs alternatingly [2,3]. We determine the thermodynamic cycles (see image) from power and efficiency of the engine consistent with analytical estimations.

[1] D. von Lindenfels et al., arXiv:1808.02390.
[2] J. Roßnagel et al., Science 352, 325 (2016).
[3] Johannes Rossnagel, Samuel Thomas Dawkins, Karl Nicolas Tolazzi, Obinna Abah, Eric Lutz, Ferdinand Schmidt-Kaler, Kilian Singer, "A single-atom heat engine", arXiv:1510.03681, (2015)

idw- Informationsdienst Wissenschaft v. 04.07.2018