Extracting Past-Future Vacuum Correlations Using Circuit QED*

In this work we propose a realistic circuit QED experiment to test the extraction of past-future vacuum entanglement to a pair of superconducting qubits. A qubit P --for past-- interacts with a quantum field along an open transmission line for an interval $T_{on}$ and then, after a time-lapse $T_{off}$ of no interaction, a second qubit F --for future-- starts interacting for a time $T_{on}$ in a symmetric fashion. After this protocol, past-future quantum correlations will have transferred to the qubits, even if the qubits do not coexist at the same time. We show that this experiment can be realized with current technology and discuss its utility as a possible implementation of a quantum memory.