QUROPE Quantum Information Processing and Communication in Europe

Superconducting quantum circuits with Josephson junctions have shown in the last decade very rich and successful quantum experiments. They appeared as the most promising solid state scalable quantum system for quantum information processor. These superconducting circuits behave as artificial atoms and were extensively studied to test fundamental concepts of quantum mechanics. This research is always in strong development.

By adding a large inductance in a dc-SQUID phase qubit loop, one decouples the junctions’ dynamics and creates a superconducting artificial atom with two internal degrees of freedom. In addition to the usual symmetric plasma mode (s mode) which gives rise to the phase qubit, an antisymmetric mode (a mode) appears. These two modes can be described by two anharmonic oscillators with eigenstates |ns⟩ and |na⟩ for the s and a mode, respectively. We show that a strong nonlinear coupling between the modes leads to a large energy splitting between states |0s,1a⟩ and |2s,0a⟩.

By adding a large inductance in a dc-SQUID phase qubit loop, one decouples the junctions’ dynamics and creates a superconducting artificial atom with two internal degrees of freedom. In addition to the usual symmetric plasma mode (s mode) which gives rise to the phase qubit, an antisymmetric mode (a mode) appears. These two modes can be described by two anharmonic oscillators with eigenstates |ns⟩ and |na⟩ for the s and a mode, respectively. We show that a strong nonlinear coupling between the modes leads to a large energy splitting between states |0s,1a⟩ and |2s,0a⟩.