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Register a new userAnalytically Computable Symmetric Quantum Correlations
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Analytic quantifiers of the symmetric quantum discord for two-qubit X type states and block-diagonal states and the symmetric measurement induced nonlocality for any two qubit states are established on the basis of the quantum skew information.
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Local available quantum correlations (LAQC), as defined by Mundarain et al., are analyzed for two subsets of 2-qubit X states. We start by studying X-states that are symmetric under the exchange of subsystems, that is, those with the same non-null local Bloch vector. We also analyze the subset of states that are anti-symmetric under subsystem exchange, that is, those that have non-null local Bloch vectors with an equal magnitude but opposite direction. We present various examples and compare the obtained results to concurrence as an entanglement measure and with quantum discord. We have also included markovian decoherence, with the analysis of amplitude damping decoherence for Werner states. As was previously observed for depolarization and phase damping decoherence, LAQC did not exhibit sudden death behavior for Werner states under amplitude damping decoherence.
In this article we extend results from our previous work [Bendersky, de la Torre, Senno, Figueira and Acin, Phys. Rev. Lett. 116, 230406 (2016)] by providing a protocol to distinguish in finite time and with arbitrarily high success probability any algorithmic mixture of pure states from the maximally mixed state. Moreover, we introduce a proof-of-concept experiment consisting in a situation where two different random sequences of pure states are prepared; these sequences are indistinguishable according to quantum mechanics, but they become distinguishable when randomness is replaced with pseudorandomness within the preparation process.
Quantum steering describes the ability of one observer to nonlocally affect the other observers state through local measurements, which represents a new form of quantum nonlocal correlation and has potential applications in quantum information and quantum communication. In this paper, we propose a computable steering criterion that is applicable to bipartite quantum systems of arbitrary dimensions. The criterion can be used to verify a wide range of steerable states directly from a given density matrix without constructing measurement settings. Compared with the existing steering criteria, it is readily computable and testable in experiment, which can also be used to verify entanglement as all steerable quantum states are entangled.
We construct an entanglement witness for many-qubit systems, based on symmetric two-body correlations with two measurement settings. This witness is able to detect the entanglement of some Dicke states for any number of particles, and such detection exhibits some robustness against white noise and thermal noise under the Lipkin-Meshkov-Glick Hamiltonian. In addition, it detects the entanglement of spin-squeezed states, with a detection strength that approaches the maximal value for sufficiently large numbers of particles. As spin-squeezed states can be experimentally generated, the properties of the witness with respect to these states may be amenable to experimental investigation. Finally, we show that while the witness is unable to detect GHZ states, it is instead able to detect superpositions of Dicke states with GHZ states.
We investigate genuinely entangled $N$-qubit states with no $N$-partite correlations in the case of symmetric states. Using a tensor representation for mixed symmetric states, we obtain a simple characterization of the absence of $N$-partite correlations. We show that symmetric states with no $N$-partite correlations cannot exist for an even number of qubits. We fully identify the set of genuinely entangled symmetric states with no $N$-partite correlations in the case of three qubits, and in the case of rank-2 states. We present a general procedure to construct families for an arbitrary odd number of qubits.
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