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Comment on White, Mutus, Dressel, et al., "Preserving entanglement..." [arXiv:1504.02707]

David H. Oaknin

Published Jun 3, 2020• 0 citations
OpenAlex

Abstract

In the cited paper [White, T., Mutus, J., Dressel, J. et al., Preserving entanglement during weak measurement demonstrated with a violation of the Bell-Leggett-Garg inequality, npj Quantum Information 2, 15022 (2016), arXiv:1504.02707], experimental results were presented that clearly prove that the quantum entanglement between two qubits is preserved after weak enough measurements are performed on them. The theoretical interpretation of the reported results, however, requires further consideration.

Related papers

Comment on White, Mutus, Dressel, et al., "Preserving entanglement during weak measurement ... " [arXiv:1504.02707]

David H. Oaknin

In the cited paper [White, T., Mutus, J., Dressel, J. et al., "Preserving entanglement during weak measurement demonstrated with a violation of the Bell-Leggett-Garg inequality", npj Quantum Information 2, 15022 (2016), arXiv:1504.02707], experimental results were presented that clearly prove that the quantum entanglement between two qubits is preserved after weak enough measurements are performed on them. The theoretical interpretation of the reported results, however, requires further consideration. The remarks made in this paper may have serious implications both for quantum foundations and for quantum cryptography.

arXiv:2006.02861•Jun 3, 2020•0 citations

Comment on 'White, T., Mutus, J., Dressel, J. et al., "Preserving entanglement during weak measurement demonstrated with a violation of the Bell-Leggett-Garg inequality", npj Quantum Information 2, 15022 (2016).'

David H. Oaknin

In the paper cited in the title, experimental results were presented that clearly prove that the quantum entanglement between two qubits is preserved after weak enough measurements are performed on them. The theoretical interpretation of the reported results, however, requires further consideration.

•Apr 25, 2020•0 citations

Preserving entanglement during weak measurement demonstrated with a violation of the Bell–Leggett–Garg inequality

T. White, J. Mutus, Justin Dressel +18 more

Abstract Weak measurement has provided new insight into the nature of quantum measurement, by demonstrating the ability to extract average state information without fully projecting the system. For single-qubit measurements, this partial projection has been demonstrated with violations of the Leggett–Garg inequality. Here we investigate the effects of weak measurement on a maximally entangled Bell state through application of the Hybrid Bell–Leggett–Garg inequality (BLGI) on a linear chain of four transmon qubits. By correlating the results of weak ancilla measurements with subsequent projective readout, we achieve a violation of the BLGI with 27 s.d.s. of certainty.

arXiv:1504.02707•npj Quantum Information•Feb 16, 2016•61 citations

Comment on “Single-particle entanglement”

Aurélien Drezet

We show that contrarily to what it is claimed in Phys. Rev. A 72, 064306 (2005) entanglement is not necessary for explaining experimental results associated with the ``single particle-vacuum'' state $\ensuremath{\mid}\ensuremath{\psi}⟩\ensuremath{\sim}\ensuremath{\mid}0{⟩}_{A}\ensuremath{\mid}1{⟩}_{B}+\ensuremath{\mid}1{⟩}_{A}\ensuremath{\mid}0{⟩}_{B}$.

Physical Review A•Aug 21, 2006•30 citations

Experimental Violation of a Non-Local Leggett-Garg Inequality using Non-Local Weak Measurements

Curtis J. Broadbent, Justin Dressel, Andrew N. Jordan +1 more

We experimentally demonstrate the violation of a non-local Leggett-Garg inequality using non-local weak measurements on polarization entangled biphotons. Due to measurement degeneracy, multiple strange weak values are required to infer violation of the Leggett-Garg inequality.

Frontiers in Optics•Jan 1, 2010•0 citations

Can measuring entanglement be easy?

S. J. van Enk

I raise some doubts concerning a protocol recently applied in an experiment (Walborn et al, Nature) to measure entanglement. The protocol is much simpler than other known entanglement-verification methods, but, I argue, needs assumptions (namely that the state generated is known and pure) that are too strong to be allowed and that are not justified in most experiments. An extension of the protocol suggested in quant-ph/0605250 is much harder to implement and still relies on assumptions not justified in entanglement-verification protocols, as demonstrated by an explicit example.

arXiv:quant-ph/0606017•Jun 1, 2006•3 citations
In the cited paper [White, T., Mutus, J., Dressel, J. et al., Preserving entanglement during weak measurement demonstrated with a violation of the Bell-Leggett-Garg inequality, npj Quantum Information 2, 15022 (2016), arXiv:1504.02707], experimental results were presented that clearly prove that the quantum entanglement between two qubits is preserved after weak enough measurements are performed on them. The theoretical interpretation of the reported results, however, requires further consideration.
In the cited paper [White, T., Mutus, J., Dressel, J. et al., "Preserving entanglement during weak measurement demonstrated with a violation of the Bell-Leggett-Garg inequality", npj Quantum Information 2, 15022 (2016), arXiv:1504.02707], experimental results were presented that clearly prove that the quantum entanglement between two qubits is preserved after weak enough measurements are performed on them. The theoretical interpretation of the reported results, however, requires further consideration. The remarks made in this paper may have serious implications both for quantum foundations and for quantum cryptography.
Abstract Weak measurement has provided new insight into the nature of quantum measurement, by demonstrating the ability to extract average state information without fully projecting the system. For single-qubit measurements, this partial projection has been demonstrated with violations of the Leggett–Garg inequality. Here we investigate the effects of weak measurement on a maximally entangled Bell state through application of the Hybrid Bell–Leggett–Garg inequality (BLGI) on a linear chain of four transmon qubits. By correlating the results of weak ancilla measurements with subsequent projective readout, we achieve a violation of the BLGI with 27 s.d.s. of certainty.
I raise some doubts concerning a protocol recently applied in an experiment (Walborn et al, Nature) to measure entanglement. The protocol is much simpler than other known entanglement-verification methods, but, I argue, needs assumptions (namely that the state generated is known and pure) that are too strong to be allowed and that are not justified in most experiments. An extension of the protocol suggested in quant-ph/0605250 is much harder to implement and still relies on assumptions not justified in entanglement-verification protocols, as demonstrated by an explicit example.