Fig. 1: Single-spin quantum heat engine in a trapped 40Ca+ ion exhibiting a Liouvillian exceptional point (LEP).
From: Dynamical control of quantum heat engines using exceptional points
A Schematic of the experimental setup. AOM: acousto-optic modulator. PMT: photomultiplier tube. AWG: arbitrary waveform generator. B Energy levels of the 40Ca+ ion, where the straight red arrows represent transitions by laser irradiation with wavelengths labeled and the blue wavy arrow denotes spontaneous emission. Such a three-level configuration equals an effective two-level system with controllable driving and decay, as plotted in (C). D Schematic diagram for work done in the exact- and broken-phases separated in the parameter space by an LEP at Ω/γeff = 1/4, where a bifurcation occurs due to coherence-induced oscillations in the exact phase. E Four strokes of our quantum Otto engine, where strokes from Step 1 to Step 2 and from Step 3 to Step 4 are adiabatic processes; while strokes from Step 2 to Step 3 and from Step 4 to Step 1 represent isochoric processes. The green dashed line represents an ideal quantum Otto cycle, and the solid line corresponds to the cycle obtained by solving the master equation using experimentally available parameter values. F Experimental operation sequences for an Otto cycle, where the duration t2 of the second stroke (isochoric heating) is varied to quantify the quantumness involved in the cycle.
