A Toy Made Tiny: Newton’s Cradle and Quantum Mechanics

Newton’s cradle—you’ve probably seen one in your school science lab, and you may even have played with one. You pull one of the metal balls back and let is swing til it hits its neighbour, and watch as the ball on the other end swings forward. Scientists are now creating a microscopic version of this toy in the hopes of learning more about thermal equilibrium in quantum systems.

Thermalisation is the process by which bodies interact to reach thermal equilibrium. For example, leaving a mug of hot tea out will warm up the room slightly and cool down the tea until both are the same temperature. On a quantum level, this process becomes more obscure and there is a lack of understanding in the field of physics as to exactly how it works.

The quantum version of Newton’s Cradle, created by physicist Benjamin Lev of Stanford University, uses atoms instead of metal spheres which are set in motion by a laser. To achieve thermalisation the atoms must be moving randomly; this was achieved by using dysprosium atoms which are magnetic and so would push and pull at each other as well as colliding in the Newton’s Cradle. It was observed that the atoms approached thermal equilibrium very rapidly, but then slowed to a more leisurely rate. The results of such studies into quantum thermalisation could be important for designing quantum computers in the future, which would be used to perform extremely efficient calculations. Since thermalisation would hinder the information-processing capabilities of such a computer, research would be geared towards understanding and hindering this process on a quantum level.

Applicants for Physics should get a feel for some of the new research emerging in the field, and find an area or examples of study that interests them.  Students interested in quantum mechanics should be familiar with the basics and may also wish to learn about developments in how quantum processes are being applied.