Mini machines can evade friction by taking quantum shortcuts

Such maneuvers help make these tiny engines maximally efficient

POWER THROUGH Car engines operate using pistons (illustrated), which convert the heat from burning fuel into motion. Friction decreases the efficiency of such engines, but quantum machines can evade that limitation.

SANTA BARBARA, Calif. — To evade friction, try taking a quantum shortcut.

Two teams of physicists are building tiny machines designed to operate with the maximum possible efficiency. According to thermodynamics, there’s an ultimate limit to the efficiency of machines known as heat engines — including steam engines and car engines — which convert heat into motion or other types of energy (SN: 3/19/16, p. 18). But real-world engines never reach that maximum efficiency, and often run well below it, because they lose energy to friction.

Now, quantum experiments are circumventing the limitations imposed by friction using specially designed shortcuts. Physicists Adolfo del Campo and Roberto Serra described two separate experiments June 25 and June 28 at the Quantum Thermodynamics meeting at the Kavli Institute for Theoretical Physics at the University of California, Santa Barbara.

The shortcuts are “a kind of quantum lubricant,” says Serra, of the Federal University of ABC in Santo André, Brazil. Similar to the way that oil can decrease friction in a standard engine, these shortcuts eliminate the friction that is present on quantum scales.

Heat engines operate by cycling through a series of steps. For example, a car engine’s cylinders execute a sequence that includes intake of fuel and air, compression, combustion, expansion and release of exhaust..

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