Single-particle nonlocality and entanglement with the vacuum - art. no. 042106

We propose a single-particle experiment that is equivalent to the conventio nal two-particle experiment used to demonstrate a violation of Bell's inequ alities. Hence, we argue that quantum mechanical nonlocality can be demonst rated by single-particle states. The validity of such a claim has been disc ussed in the literature, but without reaching a clear consensus. We show th at the disagreement can be traced to what part of the total state of the ex periment one assigns to the (macroscopic) measurement apparatus. However, w ith a conventional and legitimate interpretation of the measurement process one is led to the conclusion that even a single particle can show nonlocal properties.