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Gaussian states with nonclassical properties such as squeezing and entanglement serve as crucial resources for quantum information processing. Accurately quantifying these properties within multimode Gaussian states has posed some challenges. To address this, we introduce a unified quantification: the “classical-nonclassical polarity,” represented by P. For a single mode, a positive value of P captures the reduced minimum quadrature uncertainty below the vacuum noise, while a negative value represents an enlarged uncertainty due to classical mixtures. For multimode systems, a positive P indicates bipartite quantum entanglement. We show that the sum of the total classical-nonclassical polarity is conserved under arbitrary linear optical transformations for any two-mode and three-mode Gaussian states. For any pure multimode Gaussian state, the total classical-nonclassical polarity equals the sum of the mean photon number from single-mode squeezing and two-mode squeezing. Our results provide a new perspective on the quantitative relation between single-mode nonclassicality and entanglement, which may find applications in a unified resource theory of nonclassical features.
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Steganographic entanglement sharing
In a previous work [Avritzer and Brun, Phys. Rev. A 109, 032401 (2024)] we discussed a theoretical grounding for classical steganography using quantum Fock and coherent states in an optical channel, building on previous work by Wu et al. [Opt. Express 14, 3738 (2006); Opt. Express 21, 2065 (2013)]. In that work, we discussed protocols that disguise communications to mimic the thermal state of a harmonic oscillator. In this work we extend this to transmission of quantum information and demonstrate the utility of steganographic entanglement sharing in practical contexts like nonclassical state teleportation. We show that non-Gaussian entangled resources can be transmitted covertly while mimicking a Gaussian thermal state and still retain sufficient entanglement to violate a qubit Bell inequality, even with an eavesdropper present. We also examine the performance of other quantum protocols that utilize entanglement, such as dense coding and teleportation of unentangled but nonclassical states, to determine the effectiveness of the steganographic entanglement sharing under a variety of active and passive eavesdropper conditions.
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- PAR ID:
- 10682803
- Publisher / Repository:
- American Physical Society
- Date Published:
- Journal Name:
- Physical Review A
- Volume:
- 112
- Issue:
- 2
- ISSN:
- 2469-9926
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
-
Accepted Manuscript
- Journal Article:
- https://doi.org/10.1103/kxpv-46v3
