Eur. Phys. J. D (2012) 66: 156
https://doi.org/10.1140/epjd/e2012-30057-9

Regular Article

Observation of entanglement witnesses for orbital angular momentum states

¹ Dept. of Physics, University of Ottawa, 150 Louis Pasteur, K1N 6N5 Ottawa, Ontario, Canada
² Institute of Optics, University of Rochester, Rochester, 14627 New York, USA

^a e-mail: jonathan.leach@gmail.com

Received: 23 January 2012
Published online: 29 June 2012

Abstract

Entanglement witnesses provide an efficient means of determining the level of entanglement of a system using the minimum number of measurements. Here we demonstrate the observation of two-dimensional entanglement witnesses in the high-dimensional basis of orbital angular momentum (OAM). In this case, the number of potentially entangled subspaces scales as d(d − 1)/2, where d is the dimension of the space. The choice of OAM as a basis is relevant as each subspace is not necessarily maximally entangled, thus providing the necessary state for certain tests of nonlocality. The expectation value of the witness gives an estimate of the state of each two-dimensional subspace belonging to the d-dimensional Hilbert space. These measurements demonstrate the degree of entanglement and therefore the suitability of the resulting subspaces for quantum information applications.