Entangled Fields in Multiple Cavities as a Testing Ground for Quantum Mechanics

Entangled states provide the necessary tools for conceptual tests of quantum mechanics and other alternative theories. These tests include local hidden variables theories, pre- and postselective quantum mechanics, QND measurements, complementarity, and tests of quantum mechanics itself against, e.g., the so-called causal communication constraint. We show how to produce various nonlocal entangled states of multiple cavity fields that are useful for these tests, using cavity QED techniques. First, we discuss the generation of the Bell basis states in two entangled cavities, when there is at most one photon in either of the cavities, and then a straightforward generalization to similar N-cavity states. We then show how to produce a nonlocal entangled state when there is precisely one photon hiding in three cavities. These states can be produced by sending appropriately prepared atoms through the cavities. As applications we briefly review two proposals: one to test quantum mechanics against the causal communication constraint using a two-cavity entangled state and the other to test pre- and postselective quantum mechanics using a three-cavity entangled state. The outcome of the latter experiment can be discussed from the viewpoint of the consistent histories interpretation of quantum mechanics and therefore provides an opportunity to subject quantum cosmological ideas to laboratory tests. Finally, we point out the relation between these schemes and the schemes suggested for quantum computing, teleportation, and quantum copying.     

CW aluminum ion laser in a high voltage hollow cathode discharge

Laser oscillation on transitions of Al II was investigated in a large diameter hollow cathode discharge where Al vapour was produced by cathode sputtering. The special internal anode system used considerably increased the tube voltage and resulted low threshold currents.     

Quantum nondemolition circuit for testing bipartite complementarity

We present a quantum circuit that implements a nondemolition measurement of complementary single- and bipartite properties of a two-qubit system: entanglement and single-partite visibility and predictability. The system must be in a pure state with real coefficients in the computational basis, which allows a direct operational interpretation of those properties. The circuit can be realized in many systems of interest to quantum information.