# Discrete, Tunable Color Entanglement

Author(s): S. Ramelow, L. Ratschbacher, A. Fedrizzi, N. K. Langford, A. Zeilinger

Journal: Physical Review Letters

Volume: 103

Page(s): 25360

Year: 2009

DOI Number: 10.1103/PhysRevLett.103.253601

Abstract:

Although frequency multiplexing of information has revolutionized the field of classical communications, the color degree of freedom (DOF) has been used relatively little for quantum applications. We experimentally demonstrate a new hybrid quantum gate that transfers polarization entanglement of non-degenerate photons onto the color DOF. We create, for the first time, high quality, discretely color-entangled states (with energy bandgap up to 8.4 THz) without any filtering or postselection, and unambiguously verify and quantify the amount of entanglement (tangle, 0.611$\pm$0.009) by reconstructing a restricted density matrix; we generate a range of maximally entangled states, including a set of mutually unbiased bases for an encoded qubit space. The technique can be generalized to transfer polarization entanglement onto other photonic DOFs, like orbital angular momentum.

Note: http://arxiv.org/abs/0904.4916

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