Observation of measurement-induced entanglement and quantum trajectories of remote superconducting qubits

Phys Rev Lett. 2014 May 2;112(17):170501. doi: 10.1103/PhysRevLett.112.170501. Epub 2014 Apr 28.

Abstract

The creation of a quantum network requires the distribution of coherent information across macroscopic distances. We demonstrate the entanglement of two superconducting qubits, separated by more than a meter of coaxial cable, by designing a joint measurement that probabilistically projects onto an entangled state. By using a continuous measurement scheme, we are further able to observe single quantum trajectories of the joint two-qubit state, confirming the validity of the quantum Bayesian formalism for a cascaded system. Our results allow us to resolve the dynamics of continuous projection onto the entangled manifold, in quantitative agreement with theory.