Reduced entropy in the three-dimensional grid of super-cooled, laser-captured atoms can help accelerate progress towards quantum computing. The team of Penn State researchers can reorganize the structure of randomly distributed atoms into neatly arranged blocks. This is performing the “Maxwell’s Daemon” function – a 150-year-old thought experiment that calls for the second thermodynamic law.
Organized blocks of atoms could form the basis for a quantum computer. It uses uncharged atoms to encode data and perform computations. The article describing the research has finally appeared on September 6, 2018, in the journal Nature.
Maxwell Daemon quantum computers
“Traditional computers use transistors to encode data as bits that can be in one of two states – zero or one,” said David Weiss, a professor of physics at Penn State and the research team leader. “We are developing quantum computers that use atoms like” quantum bits “or” qubits, “which can encode data based on quantum-mechanical phenomena that allow them to be simultaneously in multiple states. And it makes the calculation simpler and more efficient. “
Law of thermodynamics in quantum computers
The second law of thermodynamics says that entropy – sometimes thought of as a failure – of the system can not decrease over time. One consequence of this law is that it excludes the possibility of building perpetual mobile (devices with perpetual-permanent-eternal motion). Sometime around 1870, James Clerk Maxwell suggested a thought experiment in which the demon could open and close the gate between the two gas chambers, allowing the warmer atoms to go in one direction and the colder atoms going in the other direction. This sorting, which did not require any energy input, would reduce entropy in the system. The temperature difference between the two chambers that could be used as a heat pump to perform the work. So thereby is breaking the second thermodynamic law.
“Later results have shown that the daemon does not actually violate the second thermodynamic law. So then many have attempted to develop experimental systems that act like a demon,” Weiss said. “There have been some successes at a very small scale, but we have created a system in which we can manipulate a large number of atoms, organize them in a way that reduces the entropy of the system as well as the demon.”
Atom grid for quantum computers
Researchers use atom capture and cooling lasers in a three-dimensional grid with 125 positions arranged as a 5 x 5 x 5 cube. Then randomly fill about half of the positions in the grid by atoms. Also by adjusting polarization of laser traps, researchers can move atoms individually or in groups, reorganize randomly spaced atoms to fill or fully fill subsets of the 5 x 5 x 2 or 4 x 4 x 3 grid.
“It is important to realize that the atoms are cooled to as low a temperature as possible. In fact, the random configuration of the atoms in the grid is almost completely defining the entropy of the system,” Weiss said. “Generally in systems where atoms are not super-cooled, atomic vibrations make up most of the entropy of the system. In such a system, the organization of atoms has little effect on entropy change. But in our experiment, we prove that the organization of atoms reduces entropy in the system by about 2.4. “
In addition to Weiss, the research team at Penn State includes Aishwarya Kumara, Tsung-Yao Wua and Felipe Giraldo Mejiu. U.S. Pat. National Science Foundation has funded this research.