Extracting entanglement from identical particles

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Date: 
2013-12-16
Author(s): 

N. Killoran, M. Cramer and M. B. Plenio

Reference: 

Physical Review Letters 112, 150501 (2014)

Identical particles and entanglement are both fundamental components of quantum mechanics. However, when identical particles are condensed in a single spatial mode, the standard notions of entanglement, based on clearly identifiable subsystems, break down. This has led many to conclude that such systems have limited value for quantum information tasks, compared to distinguishable particle systems. To the contrary, we show that any entanglement formally appearing amongst the identical particles, including entanglement due purely to symmetrization, can be extracted into an entangled state of independent modes, which can then be applied to any task. In fact, the entanglement of the mode system is in one-to-one correspondence with the entanglement between the inaccessible identical particles. This settles the long-standing debate about the resource capabilities of such states, in particular spin-squeezed states of Bose-Einstein condensates. Our results thus reveal new fundamental connections between entanglement, squeezing, and indistinguishability.