Abstract

There is no single test that will determine whether a general quantum state is separable or entangled. There are, however, a number of sufficient conditions, including the partial-transpose condition and entanglement witnesses. Here we present a class of sufficient conditions based on expectation values of non-hermitian operators. Initially we examine bipartite systems. The application of these conditions to multimode states of the electromagnetic field and to spin systems is discussed. We show that our original conditions can be strengthened if we make them invariant under certain classes of local unitary transformations. We then go on to study multipartite systems and present conditions that can be used to show that a state is not totally separable. Some simple applications of these conditions are also presented.

© 2011 Optical Society of America