Preparation of non-local superpositions of quasi-classical light states

Abstract

‘Schrödinger cat’ states of light1, defined as quantum superpositions of quasi-classical coherent states, have recently emerged as an alternative to single-photon qubits for quantum- information processing2–6. Their richer structure provides significant advantages for quantum teleportation, universal quantum computation, high-precision measurements and fundamental tests of quantum physics7–13 . Local superpositions of free-propagating coherent states have been realized exper- imentally, but their applications were so far limited by their extreme sensitivity to losses, and by the lack of quantum gates for coherent qubit rotations. Here, we demonstrate a simple approach to generating strongly entangled non-local superpositions of coherent states, using a very lossy quantum channel. Such superpositions should be useful for implement- ing coherent qubit-rotation gates, and for teleporting these qubits over long distances. The generation scheme may be extended to creating entangled coherent superpositions with arbitrarily large amplitudes.