Relativistic entanglement of two massive particles

Nicolai Friis, Reinhold A Bertlmann, Marcus Huber, Beatrix Hiesmayr

Research output: Contribution to journalArticle (Academic Journal)peer-review

91 Citations (Scopus)


We describe the spin and momentum degrees of freedom of a system of two massive spin-1/2 particles as a four-qubit system. Then we explicitly show how the entanglement changes between different partitions of the qubits, when considered by different inertial observers. Although the two particle entanglement corresponding to a partition into Alice’s and Bob’s subsystems is, as often stated in the literature, invariant under Lorentz boosts, the entanglement with respect to other partitions of the Hilbert space on the other hand, is not. It certainly does depend on the chosen inertial frame and on the initial state considered. The change of entanglement arises, because a Lorentz boost on the momenta of the particles causes a Wigner rotation of the spin, which in certain cases entangles the spin with the momentum states. We systematically investigate the situation for different classes of initial spin states and different partitions of the four-qubit space. Furthermore, we study the behavior of Bell inequalities for different observers and demonstrate how the maximally possible degree of violation, using the Pauli-Lubanski spin observable, can be recovered by any inertial observer.
Original languageEnglish
Pages (from-to)042114
Number of pages9
JournalPhysical Review A: Atomic, Molecular and Optical Physics
Issue number4
Publication statusPublished - 30 Apr 2010


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