ESQ PostDoc Gonzalo Manzano and ESQ Faculty Member Caslav Brukner, as part of a research team, show that quantum systems can simultaneously evolve along two opposite time arrows

A team of physicists at the Universities of Vienna, Bristol, the Balearic Islands and the Institute for Quantum Optics and Quantum Information (IQOQI-Vienna) has shown how quantum systems can simultaneously evolve along two opposite time arrows (forward and backward in time). The study has been published in the latest issue of Communications Physics.

Microscopic physical laws are time-symmetric, hence, a priori there exists no preferential temporal direction. However, the second law of thermodynamics allows one to associate the “forward” temporal direction to a positive variation of the total entropy produced in a thermodynamic process, and a negative variation with its “time-reversal” counterpart. This definition of a temporal axis is normally considered to apply in both classical and quantum contexts. Yet, quantum physics admits also superpositions between forward and time-reversal processes, whereby the thermodynamic arrow of time becomes quantum-mechanically undefined. In this work, we demonstrate that a definite thermodynamic time’s arrow can be restored by a quantum measurement of entropy production, which effectively projects such superpositions onto the forward (time-reversal) time-direction when large positive (negative) values are measured. Finally, for small values (of the order of plus or minus one), the amplitudes of forward and time-reversal processes can interfere, giving rise to entropy-production distributions featuring a more or less reversible process than either of the two components individually, or any classical mixture thereof.


For more information see:


Quantum superposition of thermodynamic evolutions with opposing time’s arrows, G. Rubino, G. Manzano and C. Brukner. Communications Physics (2021). DOI: 10.1038/s42005-021-00759-1

This project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 801110.

ESQ has received funding from the Austrian Federal Ministry of Education, Science and Research (BMBWF).



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