https://www.sciencedaily.com/releases/2019/08/190822165018.htm

"The sequence of events can become quantum mechanical," said co-author Igor Pikovski, a physicist at the Center for Quantum Science and Engineering at Stevens Institute of Technology. " We looked at quantum temporal order where there is no distinction between one event causing the other or vice versa."

The work, reported in the August 22 issue of Nature Communications, is among the first to reveal the quantum properties of time, whereby the flow of time doesn't observe a straight arrow forward, but one where cause and effect can co-exist both in the forward and backward direction. In the upcoming era of quantum computers, the work holds particular promise: quantum computers that exploit the quantum order of performing operations might beat devices that operate using only fixed sequences.