Nav: Home

How often do quantum systems violate the second law of thermodynamics?

October 25, 2016

The likelihood of seeing quantum systems violating the second law of thermodynamics has been calculated by UCL scientists.

In two papers, published in this week's issue of Physical Review X and funded by the Engineering and Physical Sciences Research Council, the team determined a more precise version of a basic law of physics - which says that disorder tends to increase with time unless acted on by an outside force - and applied it to the smallest quantum systems.

"The vast majority of the time, the second law of thermodynamics is obeyed. It says that a cup of hot coffee in a cold room will cool down rather than heat up, and a collection of coins all initially heads up will likely produce a mixture of heads and tails when given a shake. In fact, it is thanks to the second law of thermodynamics that we instantly recognise when we are watching a movie backwards," explained PhD student Alvaro M. Alhambra (UCL Physics & Astronomy).

The team say that situations which break the second law of thermodynamics are not ruled out in principle, but are rare.

"We wanted to find out by how much disorder increases, and if disorder sometimes decrease with some probability. These questions become important for small quantum systems where violations of the second law can happen with a significant probability," added co-author Professor Jonathan Oppenheim (UCL Physics & Astronomy).

The team, which also included Dr Christopher Perry (previously at UCL and now a researcher at the University of Copenhagen), revealed how the second law of thermodynamics functions when applied to the smallest scales of the microscopic world and the calculated the maximum probability of observing a violation.

Dr Lluis Masanes (UCL Physics & Astronomy), said: "The probability of the law being violated is virtually zero for large objects like cups of tea, but for small quantum objects, it can play a significant role. We wanted to determine the probability of violations occurring, and wanted to prove a more precise version of the second law of thermodynamics."

The second law is usually expressed as an inequality e.g., the amount of energy flowing from the cup to the air has to be larger than zero. However, it can also be expressed as an equality instead, saying precisely how much energy flows from the air to the cup and with what probabilities. This equality version of the second law can be proven for the most general process allowed by the laws of quantum mechanics.

In addition, this new formulation of the second law contains a very large amount of information, dramatically constraining the probability and size of fluctuations of work and heat and, tells us that the particular fluctuations that break the second law only occur with exponentially low probability.

These findings are critical to nanoscale devices, and the rapidly developing field of quantum technologies.
-end-


University College London

Related Physics Articles:

Physics vs. asthma
A research team from the MIPT Center for Molecular Mechanisms of Aging and Age-Related Diseases has collaborated with colleagues from the U.S., Canada, France, and Germany to determine the spatial structure of the CysLT1 receptor.
2D topological physics from shaking a 1D wire
Published in Physical Review X, this new study propose a realistic scheme to observe a 'cold-atomic quantum Hall effect.'
Helping physics teachers who don't know physics
A shortage of high school physics teachers has led to teachers with little-to-no training taking over physics classrooms, reports show.
Physics at the edge
In 2005, condensed matter physicists Charles Kane and Eugene Mele considered the fate of graphene at low temperatures.
Using physics to print living tissue
3D printers can be used to make a variety of useful objects by building up a shape, layer by layer.
More Physics News and Physics Current Events

Best Science Podcasts 2019

We have hand picked the best science podcasts for 2019. Sit back and enjoy new science podcasts updated daily from your favorite science news services and scientists.
Now Playing: TED Radio Hour

Erasing The Stigma
Many of us either cope with mental illness or know someone who does. But we still have a hard time talking about it. This hour, TED speakers explore ways to push past — and even erase — the stigma. Guests include musician and comedian Jordan Raskopoulos, neuroscientist and psychiatrist Thomas Insel, psychiatrist Dixon Chibanda, anxiety and depression researcher Olivia Remes, and entrepreneur Sangu Delle.
Now Playing: Science for the People

#537 Science Journalism, Hold the Hype
Everyone's seen a piece of science getting over-exaggerated in the media. Most people would be quick to blame journalists and big media for getting in wrong. In many cases, you'd be right. But there's other sources of hype in science journalism. and one of them can be found in the humble, and little-known press release. We're talking with Chris Chambers about doing science about science journalism, and where the hype creeps in. Related links: The association between exaggeration in health related science news and academic press releases: retrospective observational study Claims of causality in health news: a randomised trial This...