Most of the time entangled states are thought of in terms of a nonfactorizable wavefunction of two objects - photons, say - with the spins, or another attribute correlated so that what you do to one affects the state of the other no matter where it may be. Now Paul Kwiat and colleagues at the University of Illinois at Urbana-Champaign, US, and the University of Brisbane, Australia, have demonstrated for the first time that more than one characteristic - indeed, every degree of freedom - can be entangled, leading to what is known as "hyperentanglement".
For example, with photons, not only polarizations but also orbital angular momentum and energy can be entangled, as the team has demonstrated experimentally. Possible applications to quantum computing and other quantum technologies are interesting because the discovery means that more than one "qubit" of information can be associated with a single physical particle.
Further reading
Julio Barreiro et al. 2005 Phys. Rev. Lett. 95 260501.