Based on a ring-shaped arrangement of interacting two-level systems, we show the important role of the phonon-mediated quantum interference in excitation energy transfer, mimicking light-harvesting antenna in natural photosynthetic systems. The pigments in a ring-shaped photosynthetic system interact with the high-energy intramolecular vibrational mode, which arises from the vibrational motion of the scaffold of the system, with different coupling phases according to the position of each pigment respect to the vibrational motion. By investigating the model systems, we demonstrate that in the presence of large detuning between donor pigments and acceptor pigments, the efficiency of excitation transfer depends directly on the relative coupling phase between two adjacent pigments. Our model system, containing more pigments, shows a better robustness of the phonon-mediated excitation energy transfer. The present results are not only helpful in understanding natural photosynthesis, but also offer an optimal design principle for artificial photosynthesis.

Experimental development of translational DNA nanomotors recently underwent a paradigm shift from bridge-burning monomers to symmetric dimers capable of truly sustainable motion. The focus of direction rectification is changed from carving the external landscape of a single particle to symmetry breaking from within a dimer. The symmetric dimer construction have the potential to facilitate efficient motors as friction, which is inevitable as a single particle moving in a viscous environment, may vanish for paired systems. However, creating high-performing nanomotors remains an open question from a fundamental physics perspective. Here, we present a realistic physical model for dimeric nanomotors that can be exactly solved to yield motor functions from experimentally accessible non-motor elements by mere physical laws—in a surprisingly rich mechanistic variety covering virtually all advanced dimeric DNA nanomotors invented to date plus major biological counterparts to a certain extent. The model exposes a high-performing regime with a sign of superlubricity for efficient motor operation. Reasonably simple for accurate treatments yet mechanistically telling, the present model has potential to evolve into a generic model to guide experimental optimization of DNA nanomotors toward low-dissipation operation.

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Negative absolute temperature has wide range of applications, such as high-efficiency quantum heat engines, quantum refrigerators, and quantum simulation. In a recent paper [Phys. Rev. Lett. 120, 060403 (2018)], the authors proposed two spin ensembles coupled to the same reservoir collectively, one ensemble relaxes to negative temperature since two ensembles have unbalanced spin sizes. However, the coherent coupling mediated by the common environment is not considered. Here, we discuss negative temperature in a system where two qubit-ensembles are coupled to a same one-dimensional waveguide. In the limit of Markovian approximation, by investigating the coherent coupling and non-cross (cross) collective decay between two qubit-ensembles, we find that the duration of negative temperature state depends on the distance between two ensembles. The decrease of negative temperature duration is due to coherent coupling between two ensembles that will hybrid the unitary evolution of the system. Some optimal points produce the longest duration time of negative temperature, but it could not occur since the distance is out of the range of appropriate regions. The negative temperature sub-ensemble plays the role of a reservoir in quantum Otto heat engine, which is performed beyond the Otto limit.