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Reduction of entropy in a network of atoms of 5x5x5 half filled randomly. Each line shows a snapshot of the 5 plans of the network. The top row shows the initial random distribution of atoms in the 3D array of 125 possible sites. The second line shows the atom distributions after the first sort and the third line shows the distribution after the second sort, at which point the target 5x5x2 subnet is completely filled. This process reduces the entropy in the system by a factor of about 2.4. Credit: Weiss Laboratory, Penn State
The reduced entropy in a three-dimensional network of super-cooled and laser-trapped atoms could help accelerate progress toward the creation of quantum computers. A team of Penn State researchers can reorganize a network of atoms randomly organized into well-organized blocks, thus fulfilling the function of a "Maxwell's demon" – a thought experiment of the 1870s that questioned the second law of thermodynamics. Organized atomic blocks could form the basis of a quantum computer using uncharged atoms to encode data and perform calculations. An article describing the research appears on September 6, 2018 in the journal Nature.
"Traditional computers use transistors to encode data in bits that can be in one of two states – zero or one," said David Weiss, professor of physics at Penn State and chief of the board. Research Team. "We design quantum computers that use atoms like" quantum bits "or" qubits "and that can encode data based on quantum mechanics phenomena that allow them to be simultaneously in multiple states. adapt a lot of atoms in a small area and make the calculation easier and more efficient. "
The second law of thermodynamics states that entropy – sometimes considered a disorder – of a system can not diminish with time. One of the consequences of this law is that it excludes the possibility of a perpetual motion device. Around 1870, James Clerk Maxwell proposed a thought experiment in which a demon could open and close a door between two gas chambers, allowing the hottest atoms to move in one direction and the colder atoms to pass into the other . This sorting, which did not require any energy input, would result in a reduction of entropy in the system and a difference in temperature between the two chambers that could be used as a heat pump to perform the work, thus violating the second one. law.
"Subsequent work has shown that the demon does not violate the second law and that, subsequently, many attempts have been made to design experimental systems that behave like the demon," Weiss said. "There have been some successes at very small scales, but we have created a system in which we can manipulate a large number of atoms, organizing them in ways that reduce the entropy of the system, just like the demon."
Researchers use lasers to trap and cool atoms in a three-dimensional network with 125 positions arranged in 5 by 5 by 5 cube. They then randomly fill about half of the lattice positions with atoms. By adjusting the polarization of the laser traps, the researchers can move the atoms individually or in groups, rearranging the randomly distributed atoms to completely fill subsets of 5 by 5 by 2 or 4 by 4 by 3 of the array.
"As atoms are cooled to a temperature almost as low as possible, the entropy of the system is almost entirely defined by the random configuration of atoms in the network," Weiss said. "In systems where the atoms are not over-cooled, the vibration of the atoms constitutes the majority of the entropy of the system.In such a system, the organization of atoms does not change entropy, but in our experience we show that the organization atoms lower the entropy in the system by a factor of about 2.4. "
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More information:
Tri-classification of ultra-cold atoms in a three-dimensional optical network in a realization of Maxwell's demon, Nature (2018). www.nature.com/articles/s41586-018-0458-7
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