Violating the second law by the chain of quantum Maxwell demons.

The Second Law of thermodynamics states that the entropy of the isolated system is non-diminishing in the course of time evolution. In quantum systems, the Second Law can be violated by adding to the system the quantum Maxwell's demon (QMD) which reduces entropy without energy exchange. However, extending the system by including into it the QMD itself, restores the Second Law. Remarkably, enlarging system with one more demon we return to the initial situation. Therefore by sequential adding the QMD, we can construct the energy-conserving macroscopic system which evolves in time with decreasing the entropy. Here we demonstrate this general principle on the IBM quantum computer how extending the system by one extra qubit, we still observe the entropy decreasing, thus violating the second law. We utilize five QMD implemented by the extra qubits since decoherence effects restrict the number of possible qubit additions. [ABSTRACT FROM AUTHOR]