14 DAY TRIAL // Experts at the Austrian Academy of Sciences' Institute of Quantum Optics and Quantum Information, at the University of Innsbruck, managed recently to thoroughly demonstrate up to 23 steps in a quantum walk. The maneuver was performed within the confines of a quantum system, and this experiment represented the first time when trapped ions were used to demonstrate the principle in exquisite detail, AlphaGalileo reports.
A quantum walk is a fairly complex concept. Consider, for instance, a hiker that walks a known road. He or she will take the shortest way to the destination, but things change when they forget the map. In this case, the walkers will try to minimize detours as much as possible. This type of behavior is called a random walk, and the idea has been heavily used in mathematics and in physics. Similar to this is the Brownian motion, which is a chaotic series of movements in water molecules, that for example causes pollen grains that fell in water drops to exhibit irregular fluttering vibrations.
What the Austrian researchers did was basically apply the same principles in their random walk of atoms. “We trap a single atom in an electromagnetic ion trap and cool it to prepare it in the ground state. We then create a quantum mechanical superposition of two inner states and send the atom on a walk,” says Institute of Quantum Optics and Quantum Information (IQOQI) expert Christian Roos, who is also one of the researchers that led the team. Each of the two states wants the atoms to go both right or left, similar to what happens when a hiker tries to decide which path to take.
But because of superposition, both states are present in the same atom at the same time, so it doesn't really need to figure out where it's going. “Depending on the internal state, we shift the ion to the right or to the left. Thereby, the motional and internal state of the ion are entangled,” Roos reveals. In an experiment conducted with a second ion, the team also managed to give the charged atom another possibility, and namely to stay. The new investigation was only made possible by grant money secured from the Austrian Science Fund (FWF) and the European Commission.