In the children’s book Alice in Wonderland, the Cheshire cat had a smile that could detach from its body; however that not just fiction anymore due to a new finding in the world of quantum mechanics. The ongoing experimentation with neutrons has unearth a phenomenon that particles can have bifurcated properties. This notion has been applied to the strange wonderland that it quantum mechanics and the fundamental laws that govern matter in that particles can split in both mass and charge.
In the book, Alice was mystified by the fact that the aforementioned cat would be seen with a menacing but comical grin and then the body of the cat would disappear with only the grin remaining. Tobias Denkmayr, quantum physicist at the Vienna University of Technology in Austria, leads the experimentation of the subatomic particle that essentially mirrors Alice’s experience. “The most exciting thing was that we made this idea work,” he stated.
To conduct the experiment the researchers started by isolating neutrons, the subatomic particles with no electrical charge, within the nucleus of atom. Typically, only protons and electrons have electrical charges, the former positive and the latter negative. Although neutrons are without a charge, they still retain magnetism due to the fact they are constructed from quarks – the fundamental building blocks of all we see every day.
The researchers shot a group of neutrons into a neutron interferometer, effectively a beam splitter using a silicon crystal. The molecular assembly of crystal is used to split the group of neutrons into an upper and lower beam. During this process the properties of the particle were still linked by the force of magnetism; however, individual particles were traveling concurrently in both directions of the beams.
“The magnetic field we applies only had an effect on where the neutrons weren’t supposed to be, not where they were supposed to be,” Denkmayr explained at the conclusion of the experiment.
When physicists attempt to measure particles in quantum superposition the mere act of measurement “collapses” the superposition. Quantum superposition is the phenomenon that a particle can exist in at least two places simultaneously. For example, when measuring a spinning top on a table the act of measurement would make it look like the top is spinning clockwise and counterclockwise at the same time.
This phenomenon is best explained using another feline friend, Schrödinger’s Cat. The thought experiment created by Edwin Schrödinger began with putting a cat into a box with a radioactive element and a flask of poison. If the radioactive element decays then the flask is broken. Thereby, releasing the poison and effectively killing the cat. From inside the box of horrors, if the atom does not decay and the cat is not poisoned, the cat only experiences living through the ordeal. From outside of the box, however, Schrödinger would experience the cat being both dead and alive at the same time. It would only unearth the real conclusion if he opened the box and found that his beloved cat was either alive or dead.
The Cheshire cat paradox is applied to this principle due to its grin that seems to be in a different place even though it is still on the cat’s face. Normally, this measurement paradox would make it impossible to distinguish a quantum Cheshire cat due to the fragility of a superposition.
A few decades ago, scientists discovered a way to measure particles in a superpositions without breaking the quantum barrier. This “weak measurement” strategy analyzes a group of particles rather than an individual particle in order to preserve their bizarre state. Therefore, through the weak measurement findings, scientists were able to uncover Mr. Cheshire.
“You need to do lots of observation to achieve any sort of certainty that you have seen what you think you have seen,” stated Hartmut Lemmel, researcher at the Institut Laue-Langevin in Grenoble, France, and part of Denkmayr’s team. This “Quantum Cheshire Cat” application could actually be used in a practical sense. It would allow scientists to make fastidious measurements with interrupting the naturalness of a system.
By: Alex Lemieux