Leo Kouwenhoven is a professor of physics at Delft University of Technology in the Netherlands. He ended the 75-year hunt for the Majorana fermion-a particle that is its own antiparticle-by creating it on a chip.

Lisa Grossman: What is a Majorana fermion?
Leo Kouwenhoven: It is named for the physicist Ettore Majorana, who found that a particle could be its own antiparticle. If a particle has properties with values unequal to zero, then its antiparticle has the opposite values. What that means is that all the properties of a Majorana fermion, the charge, energy, what have you, it’s all zero. It is a particle, but it doesn’t have properties that we can measure. That makes it very mysterious. It also makes it difficult to find.

LG: Why hunt for these tricky particles?
LK: My background is quantum computing. Measurement is problematic for a quantum computer, because observation changes the quantum state. But if you don’t have an apparatus that can measure a Majorana fermion, you cannot change it. Its insensitivity makes it a robust quantum state. This could lead toward qubits that do not collapse. Usually everything dies, but these would be very robust and could live for a long time.

LG: Qubits […]