Emergence of opposing arrows of time in open quantum systems

"We focus on the derivation of the arrow of time in open quantum systems and study precisely how time-reversal symmetry is broken. 

"This derivation involves the Markov approximation applied to a system interacting with an infinite heat bath. 

"We find that the Markov approximation does not imply a violation of time-reversal symmetry. 

"Our results show instead that the time-reversal symmetry is maintained in the derived equations of motion. This imposes a time-symmetric formulation of quantum Brownian motion, Lindblad and Pauli master equations, which hence describe thermalisation that may occur into two opposing time directions. 

"As a consequence, we argue that these dynamics are better described by a time-symmetric definition of Markovianity. Our results may reflect on the formulations of the arrow of time in thermodynamics, cosmology, and quantum mechanics." 


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