If quantum computers , molecular memories, and other futuristic devices for handling quantum information are to work, physicists and engineers will need rules for building the underlying circuits. And because quantum coherence is so fragile and fleeting, those rules should hold at high frequencies.
A team from École Normale Supérieure in Paris has just reported experimental evidence that supports one such rule. 1 Conceived 13 years ago by Markus Büttiker, Anna Prêtre, and Harry Thomas, the theoretical rule gives the impedance of an RC circuit when the circuit is small and cold enough for the electrons to act coherently and clean enough for the electrons to travel ballistically. 2
Jean-Marc Berroir, Christian Glattli, and Bernard Plaçais led the Paris team. Their experiment confirms one of the theory’s most striking predictions: When a resistor and capacitor are coupled, the conductance is quantized in units of 2e 2/h. An...
