information is physical, even in quantum systems...,

sciencenews |  Information may seem ethereal, given how easily we forget phone numbers and birthdays. But scientists say it is physical, and if a new study is correct, that goes for quantum systems, too.

Although pages of text or strings of bits seem easily erased with the press of a button, the act of destroying information has tangible physical impact, according to a principle proposed in 1961 by physicist Rolf Landauer. Deleting information is associated with an increase in entropy, or disorder, resulting in the release of a certain amount of heat for each erased bit. Even the most efficient computer would still output heat when irreversibly scrubbing out data.

This principle has been verified experimentally for systems that follow the familiar laws of classical physics. But the picture has remained fuzzy for quantum mechanical systems, in which particles can be in multiple states at once and their fates may be linked through the spooky process of quantum entanglement.

Now a team of scientists reports April 13 in Proceedings of the Royal Society A that Landauer’s principle holds even in that wild quantum landscape. “Essentially what they’ve done is test [this principle] at a very detailed and quantitative way,” says physicist John Bechhoefer of Simon Fraser University in Burnaby, Canada, who was not involved with the research. “And they’re showing that this works in a quantum system, which is a really important step.” Testing Landauer’s principle in the quantum realm could be important for understanding the fundamental limits of quantum computers, Bechhoefer says.