Some NMR experiments reporting pseudo-entanglement

The general conclusion of the authors is that there is more to quantum information processing than entanglement and that, keeping in mind the limitations of room temperature liquid-state experiments, the NMR of these systems is an excellent test bed for the principles of quantum information and quantum computation. 

Experimental demonstration of fully coherent quantum feedback - This paper of 1999 by Nelson and co-workers describes a quantum circuit which implements a coherent quantum feedback by NMR [15]. The idea is to transmit a quantum state with its correlations from a quantum register to a target. A classical feedback can be used to control quantum states, but it involves a measurement step, which destroys quantum correlations. On the contrary, quantum feedback control is able to transmit full quantum states with correlations altogether. The experiment involves three spins (qubits) A, B, and C. The proposal is to use the quantum feedback control circuit to transmit the quantum correlations, initially between B and C, to A and C. Starting from the equilibrium state, a sequence of pulses applied over qubits B and C creates a density matrix proportional to the spin operators -1 + 21 if - Such a density matrix describes a thermal 

The efiBcacy of the process was evaluated by a measure of fidelity, which reached 91.5%. 

Experimental demonstration of GHZ correlations using NMR - This experiment is a report of 2000, by Nelson and co-workers [17]. It aims to demonstrate, using NMR, the existence of quantum correlations present in the GHZ state  

The authors emphasize that, due to the local intrinsic nature of NMR experiments, the results cannot rule out completely the possibility of interpretation in terms of hidden variables, but it demonstrates unambiguously the quantum correlations of the state. The argument is based on the following set of expectation values for the product of spin 

---