Time: it’s constantly running out and we never have enough of it. Some say it’s an illusion, some say it flies like an arrow. Well, this arrow of time is a big headache in physics. Why does time have a particular direction? And can such a direction be reversed?

A new study, published in Scientific Reports, is providing an important point of discussion on the subject. An international team of researchers has constructed a time-reversal program on a quantum computer, in an experiment that has huge implications for our understanding of quantum computing. Their approach also revealed something rather important: the time-reversal operation is so complex that it is extremely improbable, maybe impossible, for it to happen spontaneously in nature.

As far as laws of physics go, in many cases, there’s nothing to stop us going forward and backward in time. In certain quantum systems it is possible to create a time-reversal operation. Here, the team crafted a thought experiment based on a realistic scenario.

Quantum computers need to preserve quantum information for a long time to be able to crack important problems faster than a normal computer. Energy losses take the state of the qubit from one to zero, destroying stored quantum information at the same time. Consequently, scientists all over the globe have traditionally worked to remove all sources of energy loss—or dissipation—from these machines.

Dr. Mikko Mottonen from Aalto University and his research team have taken a different approach. “Years ago, we realized that quantum computers actually need dissipation to operate efficiently. The trick is to have it only when you need it,” he explains.

In their paper to be published on 11 March 2019 in Nature Physics, scientists from Aalto University and the University of Oulu demonstrate that they can increase the dissipation rate by a factor of thousand in a high-quality superconducting resonator on demand—such resonators are used in prototype quantum computers.

Classical computing will require more energy than our entire energy grid by 2040.

Researchers at the University of Florence and Istituto dei Sistemi Complessi, in Italy, have recently proved that the invasiveness of quantum measurements might not always be detrimental. In a study published in Physical Review Letters, they showed that this invasive quality can actually be exploited, using quantum measurements to fuel a cooling engine.

Michele Campisi, one of the researchers involved in the study, has been studying quantum phenomena for several years. In his recent work, he investigated whether quantum phenomena can impact the thermodynamics of nanoscopic devices, such as those employed in quantum computers.

“Most colleagues in the field were looking at coherence and entanglement while only few were looking at another at genuine quantum phenomenon, i.e., the quantum measurement process,” Campisi told Phys.org. “Those studies suggested that you need to accompany measurements with feedback control, as in Maxwell’s demon, in order to exploit their potential. I started thinking about it, and eureka—since quantum measurements are very invasive, they are accompanied by energy exchanges, hence can be used to power engines without the need to do feedback control.”