Experimental investigations of spatial-parity qubits.

摘要

I present the novel embodiment of a photonic qubit that makes use of one continuous spatial degree of freedom of a single photon and relies on the parity of the photon's transverse spatial distribution. Using optical spontaneous parametric downconversion to produce photon pairs, I demonstrate the controlled generation of entangled-photon states in this new space. Specifically, two Bell states, and a continuum of their superpositions, are generated by simple manipulation of a classical parameter, the optical-pump spatial parity, and not by manipulation of the entangled photons themselves. I report the first experimental violation of Bell's inequality in the spatial domain using the Einstein-Podolsky Rosen state. The Bell-operator measurements are made possible by devising simple optical arrangements that perform rotations in the one-dimensional spatial-parity space of each photon of an entangled pair and projective measurements via an interferometric device, isomorphic in action to a polarizing beam splitter, which projects the spatial-parity states onto an even-odd basis. A Bell-operator value is recorded that indicates a violation of the inequality by more than 24 standard deviations. For purposes of comparison, the spatial-parity properties of classical light are investigated by performing similar experiments. This new physical realization of photonic quhits could be used as a foundation for future experiments in quantum information processing.