Abstract
Exploiting the notion of measurement-induced nonlocality (Luo and Fu in Phys Rev Lett 106:120401, 2011), we introduce a new measure to quantify the nonbilocal correlation. We establish a simple relation between the nonlocal and nonbilocal measures for the arbitrary pure input states. Considering the mixed states as inputs, we derive two upper bounds of affinity-based nonbilocal measure. Finally, we have studied the nonbilocality of a different combinations of input states.
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Acknowledgements
This work was financially supported by the Council of Scientific and Industrial Research (CSIR), Government of India, under Grant No. 03(1444)/18/EMR-II.
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Appendix
Appendix
Let \(|\varPsi _{ab}\rangle =\sum _is_i|i_ai_b\rangle \) and \(|\varPsi _{cd}\rangle =\sum _jr_j|j_cj_d\rangle \) are the two pure input states with \(s_i\) and \(r_j\) are the respective Schmidt coefficients of input states.
Noting that
One can compute the marginal state
For pure state \(\sqrt{\rho }=\rho \). From the above equation, the post-measurement state \(\varPi ^{bc}(\sqrt{\rho _{ab}\otimes \rho _{cd}})\) can be rewritten as
Here, the von Neumann projective measurement is expressed as
Consequently,
Then, the affinity between the pre- and post-measurement state is computed as
The nonbilocal measure for pure state is
where the optimization is over all von Neumann measurements given in Eq. (32), leaving the marginal state \(\rho ^{bc}\) invariant. That is,
is a spectral decomposition of \(\rho ^{bc}\) since \(\{U|h_{b}k_{c}\rangle \}\) is an orthonormal base. Comparing the above equation with Eq. (31), we obtained
Hence, the theorem is proved. It is worth mentioning that the affinity-based nonbilocal measure for pure state is equal to the Hellinger distance and Hilbert–Schmidt norm-based nonbilocal measures [38, 39].
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Muthuganesan, R., Balakrishnan, S. & Chandrasekar, V.K. Characterizing nonbilocal correlation: a geometric perspective. Quantum Inf Process 21, 216 (2022). https://doi.org/10.1007/s11128-022-03561-2
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DOI: https://doi.org/10.1007/s11128-022-03561-2