Beyond the Entanglement of Qubit Pairs in Multipartite Systems

S. Shelly Sharma, Naresh Kumar Sharma

Given a multipartite quantum system that consists of two-level particles (qubits), one may or may not have access to all the subsystems. What can we know about the entanglement of the multiqubit system and residual correlations beyond two-tangle if we have access only to two-qubits at a time? Algebraic analysis of two-qubit states yields monogamy constraints on distribution of entanglement between sub-systems of an N-qubit state and criterion to determine if the state has multipartite entanglement. Monogamy constraints, reported in this letter, are relations between well known entanglement measures such as one-tangle, two-tangles and three-tangles of an N-qubit pure state.

Ved Prakash Gupta, Prabha Mandayam, Viakalathur Shankar Sunder

Mazhar Ali

We investigate entanglement dynamics of bipartite as well multipartite systems beyond Markov approximation. We study two pairs of cavity–reservoir systems, modeled as four qubits and track the change of entanglement among cavity–cavity qubits, reservoir–reservoir qubits, and also for genuine entanglement of all four qubits. For cavity–cavity qubits, we find that non-Markovianity prolongs the life of entanglement besides collapse/revival phenomenon. For reservoir–reservoir qubits, entanglement sudden birth is delayed accordingly along with oscillations. For all four qubits, with a specific initial state, we find that genuine entanglement develops gradually, reaches to a maximum constant value and then freezes at this value for some time before decaying. This sudden change in dynamics of genuine entanglement occurs for a time window where neither cavities nor reservoirs are entangled. In contrast to Markov process, sudden change phenomenon may be recurrent in non-Markovian regime.

Reza Hamzehofi

Akimasa Miyake, Hans J. Briegel

We propose a scheme of multipartite entanglement distillation driven by a complementary pair of stabilizer measurements to distill directly a wider range of states beyond the stabilizer code states (such as the Greenberger-Horne-Zeilinger states). We make our idea explicit by constructing a recurrence protocol for the 3-qubit state [formula: see text]. Noisy states resulting from typical decoherence can be directly purified in a few steps, if their initial fidelity is larger than a threshold. For general input mixed states, we observe distillations to hierarchical fixed points, i.e., not only to the state but also to the 2-qubit Bell pair, depending on their initial entanglement.

Vahid Azimi-Mousolou

We introduce a unified, computable measure of multipartite entanglement based on the spectral properties of an entanglement graph and its associated entanglement matrix. This framework quantifies quantum correlations among arbitrary subsystems and partitions of a composite system. We prove that the resulting spectral entanglement measure satisfies the fundamental requirements of entanglement measures. Furthermore, we derive a generic multipartite monogamy relation that extends residual entanglement beyond qubit systems and introduces spectral residual entanglement for arbitrary multipartite states.