Heat flows from the hot to the cold spin at thermal contact when both are initially uncorrelated. This corresponds to the standard thermodynamic arrow of time. For initially quantum correlated spins, heat is spontaneously transferred from the cold to the hot spin. The arrow of time is here reversed
The second law permits the prediction of the direction of natural processes, thus defining a
thermodynamic arrow of time. However, standard thermodynamics presupposes the absence of
initial correlations between interacting systems. We here experimentally demonstrate the reversal
of the arrow of time for two initially quantum correlated systems. We observe a spontaneous
heat flow from the cold to the hot system. This process is enabled by a trade off between correlations
and entropy that we quantify with information-theoretical quantities. arxiv 
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A new theory explains the seemingly irreversible arrow of time while yielding insights into entropy, quantum computers, black holes, and the past-future divide. post
Reversing the arrow of time was possible for the quantum particles because they were correlated — their properties were linked in a way that isn’t possible for larger objects, a relationship akin to quantum entanglement but not as strong. This correlation means that the particles share some information. In thermodynamics information has physical significance. post
Quantum entanglement is a physical phenomenon that occurs when pairs or groups of particles interact in ways such that the quantum state of each particle cannot be described independently of the others, even when the particles are separated by a large distance. wikipedia