Abstract

The problem of quantum entanglement has attracted much attention since the early days of quantum mechanics [1], Although methods to entangle two-particles have been known for a long time, it is only recently that three-particle entanglements have been demonstrated experimentally [2]. One of the most intriguing features of quantum behavior is that non-interacting parts of a system can show non-local correlations reflecting interactions that occurred in the past. Following the proposal by Deutsch for a quantum computer [3] and the discoveries of algorithms that outperform those of classical computation [4,5], research on the foundations of quantum mechanics has now moved to the center of the new field of quantum information. As a result, the question of entanglement (as well as that of decoherence [1]) have acquired practical significance. In this work, we report an experimental demonstration of many-particle entanglement involving the spins of four or more Mn²⁺ ions (S =5/2) in an external magnetic field B. Let 10〉 and |1〉 denote, respectively, the ground (S_z= 5/2) and the first-excited (S_z = 3/2) states of a single ion and N the number of ions. The entangled states relevant to our problem are superpositions of the form.

© 1999 Optical Society of America