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arXiv:1904.08381 · Modern Physics Letters A

Remarks on the preservation of no-signaling principle in parity-time-symmetric quantum mechanics

Bijan Kumar Bagchi, Suvendu Barik

Published Jan 31, 2020• 2 citations
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Abstract

Working within the framework of parity-time-symmetric quantum mechanics, we look into the possibility of entanglement generation and demonstrate that the feature of non-violation of no-signaling principle may hold for the simplest nontrivial case of bipartite systems. Basically, our arguments are based on the computation of the reduced density matrix of one party to justify that the entropy of the other does not change.

DOI
10.1142/s021773232050090x

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Working within the framework of parity-time-symmetric quantum mechanics, we look into the possibility of entanglement generation and demonstrate that the feature of non-violation of no-signaling principle may hold for the simplest nontrivial case of bipartite systems. Basically, our arguments are based on the computation of the reduced density matrix of one party to justify that the entropy of the other does not change.
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Abstract P T -symmetric quantum mechanics, the extension of conventional quantum mechanics to the non-Hermitian Hamiltonian invariant under the combined parity ( P ) and time reversal ( T ) symmetry, has been successfully applied to a variety of fields—such as solid state physics, mathematical physics, optics, quantum field theory. Recently, the extension of P T -symmetrical theory to entangled quantum systems has been challenged, in that P T formulation within the conventional Hilbert space violates the no-signaling principle. Here, we revisit the derivation of non-signaling principle in the framework of C P T inner product prescription. Our results preserve the no-signaling principle for a two-qubit system, reaffirm the invariance of the entanglement, and reproduce the Clauser–Horne–Shimony–Holt (CHSH) inequality. We conclude that P T -symmetric quantum mechanics satisfies the requirements for a fundamental theory and provides a consistent description of quantum systems.
We show that the no-signaling principle can be violated with classical inseparable beams in the presence of a parity-time (PT) symmetric subsystem. Thus, the problems associated to PT-symmetric quantum theories recently discovered by Lee et al. [Phys. Rev. Lett. 112, 130404 (2014)] are not exclusive to quantum mechanics, but already exist in the classical case. The possibility to implement local optical PT-symmetric subsystems via light-matter interactions enables the experimental exploration of local PT symmetry and subtle quantum concepts via classical analogues.
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Entanglement is one of the key feature of quantum world and any entanglement measure must satisfy some basic laws. Most important of them is the invariance of entanglement under local unitary operations. We show that this is no longer true with local PT{\cal {PT}}PT symmetric unitary operations. If two parties share a maximally entangled state, then under local PT{\cal {PT}}PT symmetric unitary evolution the entropy of entanglement for pure bipartite states does not remain invariant. Furthermore, we show that if one of the party has access to PT{\cal {PT}}PT-symmetric quantum world, then a maximally entangled state in usual quantum theory appears as a non-maximally entangled states for the other party. This we call as the "entanglement mismatch" effect which can lead to the violation of the no-signaling condition.