@article {913,
title = {All phase-space linear bosonic channels are approximately Gaussian dilatable},
journal = {New Journal of Physics},
volume = {20},
year = {2018},
month = {Jan-11-2018},
pages = {113012},
doi = {10.1088/1367-2630/aae738},
author = {Lami, Ludovico and Sabapathy, Krishna Kumar and Winter, Andreas}
}
@article {sabapathy_non-gaussian_2017,
title = {Non-{Gaussian} operations on bosonic modes of light: {Photon}-added {Gaussian} channels},
journal = {Physical Review A},
volume = {95},
number = {6},
year = {2017},
pages = {062309},
abstract = {We present a framework for studying bosonic non-Gaussian channels of continuous-variable systems. Our emphasis is on a class of channels that we call photon-added Gaussian channels, which are experimentally viable with current quantum-optical technologies. A strong motivation for considering these channels is the fact that it is compulsory to go beyond the Gaussian domain for numerous tasks in continuous-variable quantum information processing such as entanglement distillation from Gaussian states and universal quantum computation. The single-mode photon-added channels we consider are obtained by using two-mode beam splitters and squeezing operators with photon addition applied to the ancilla ports giving rise to families of non-Gaussian channels. For each such channel, we derive its operator-sum representation, indispensable in the present context. We observe that these channels are Fock preserving (coherence nongenerating). We then report two examples of activation using our scheme of photon addition, that of quantum-optical nonclassicality at outputs of channels that would otherwise output only classical states and of both the quantum and private communication capacities, hinting at far-reaching applications for quantum-optical communication. Further, we see that noisy Gaussian channels can be expressed as a convex mixture of these non-Gaussian channels. We also present other physical and information-theoretic properties of these channels.},
doi = {10.1103/PhysRevA.95.062309},
url = {https://link.aps.org/doi/10.1103/PhysRevA.95.062309},
author = {Sabapathy, Krishna Kumar and Winter, Andreas}
}
@article {ivan_scaling_2017,
title = {Scaling maps of s-ordered quasiprobabilities are either nonpositive or completely positive},
journal = {PHYSICAL REVIEW A},
volume = {96},
number = {2},
year = {2017},
month = {aug},
abstract = {Continuous-variable systems in quantum theory can be fully described through any one of the s-ordered family of quasiprobabilities Lambda(s) (a), s is an element of [-1,1]. We ask forwhat values of (s,a) is the scalingmap Lambda(s) (alpha) -{\textgreater} a(-2) Lambda(s) (a(-1)alpha) a positive map? Our analysis based on a duality we establish settles this issue: (i) the scaling map generically fails to be positive, showing that there is no useful entanglement witness of the scaling type beyond the transpose map, and (ii) in the two particular cases (s = 1,{\textbar}a{\textbar} {\textless}= 1) and (s = -1,{\textbar}a{\textbar} {\textgreater}= 1), and only in these two nontrivial cases, the map is not only positive but also completely positive as seen through the noiseless attenuator and amplifier channels. We also present a {\textquotedblleft}phase diagram{\textquotedblright} for the behavior of the scaling maps in the s-a parameter space with regard to its positivity, obtained from the viewpoint of symmetric-ordered characteristic functions. This also sheds light on similar diagrams for the practically relevant attenuation and amplification maps with respect to the noise parameter, especially in the range below the complete-positivity (or quantum-limited) threshold.},
issn = {2469-9926},
doi = {10.1103/PhysRevA.96.022114},
author = {Ivan, J. Solomon and Sabapathy, Krishna Kumar and Simon, R.}
}
@article {701,
title = {Process output nonclassicality and nonclassicality depth of quantum-optical channels},
journal = {Physical Review A},
volume = {93},
year = {2016},
month = {4/2016},
issn = {2469-9934},
doi = {10.1103/PhysRevA.93.042103},
author = {Sabapathy, Krishna Kumar}
}
@article {703,
title = {Quantum-optical channels that output only classical states},
journal = {Physical Review A},
volume = {92},
year = {2015},
month = {11/2015},
issn = {1094-1622},
doi = {10.1103/PhysRevA.92.052301},
author = {Sabapathy, Krishna Kumar}
}