### Abstract

We investigate the universal inequalities relating the α-Rényi entropies of the marginals of a multipartite quantum state. This is in analogy to the same question for the Shannon and von Neumann entropies (α =1), which are known to satisfy several non-trivial inequalities such as strong subadditivity. Somewhat surprisingly, we find for 0 < α < 1 that the only inequality is non-negativity: in other words, any collection of non-negative numbers assigned to the non-empty subsets of n parties can be arbitrarily well approximated by the α-entropies of the 2n α 1 marginals of a quantum state. For α >1, we show analogously that there are no non-trivial homogeneous (in particular, no linear) inequalities. On the other hand, it is known that there are further, nonlinear and indeed non-homogeneous, inequalities delimiting the α-entropies of a general quantum state. Finally, we also treat the case of Rényi entropies restricted to classical states (i.e. probability distributions), which, in addition to non-negativity, are also subject to monotonicity. For α ≠ 0, 1, we show that this is the only other homogeneous relation. © 2013 The Author(s).

Original language | English |
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Article number | 20120737 |

Journal | Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences |

Volume | 469 |

DOIs | |

Publication status | Published - 8 Oct 2013 |

### Keywords

- Entropy inequalities
- Homogeneous inequalities
- Multi-partite quantum states
- Rényi entropies
- Subadditivity

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## Cite this

Linden, N., Mosonyi, M., & Winter, A. (2013). The structure of Rényi entropic inequalities.

*Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences*,*469*, [20120737]. https://doi.org/10.1098/rspa.2012.0737