We give an explicit characterisation of the quantum states which saturate the strong subadditivity inequality for the von Neumann entropy. By combining a result of Petz characterising the equality case for the monotonicity of relative entropy with a recent theorem by Koashi and Imoto, we show that such states will have the form of a so-called short quantum Markov chain, which in turn implies that two of the systems are independent conditioned on the third, in a physically meaningful sense. This characterisation simultaneously generalises known necessary and sufficient entropic conditions for quantum error correction as well as the conditions for the achievability of the Holevo bound on accessible information.
The strong subadditivity inequality of von Neumann entropy relates the entropy of subsystems of a tripartite state $ρ_{ABC}$ to that of the composite system. Here, we define $\boldsymbol{T}^{(a)}(ρ_{ABC})$ as the extent to which $ρ_{ABC}$ fails to satisfy the strong subadditivity inequality $S(ρ_{B})+S(ρ_{C}) \le S(ρ_{AB})+S(ρ_{AC})$ with equality and investigate its properties. In particular, by introducing auxiliary subsystem $E$, we consider any purification $|ψ_{ABCE}\rangle$ of $ρ_{ABC}$ and formulate $\boldsymbol{T}^{(a)}(ρ_{ABC})$ as the extent to which the bipartite quantum correlation…
Recently, there has been a surge of interest in using Rényi entropies as quantifiers of correlations in many-body quantum systems. However, it is well known that in general these entropies do not satisfy the strong subadditivity inequality, which is a central property ensuring the positivity of correlation measures. In fact, in many cases they do not even satisfy the weaker condition of subadditivity. In the present paper we shed light on this subject by providing a detailed survey of Rényi entropies for bosonic and fermionic Gaussian states. We show that for bosons the Rényi entropies always …
The Chinese University of Hong Kong, Shenzhen（香港中文大学（深圳））；International Quantum Academy (SIQA)（深圳国际量子学院）；Nagoya University（名古屋大学）；The Chinese University of Hong Kong（香港中文大学）
We consider two-dimensional states of matter satisfying an uniform area law for entanglement. We show that the topological entanglement entropy is equal to the minimum relative entropy distance from the reduced state to the set of thermal states of local models. The argument is based on strong subadditivity of quantum entropy. For states with zero topological entanglement entropy, in particular, the formula gives locality of the states at the boundary of a region as thermal states of local Hamiltonians. It also implies that the entanglement spectrum of a two-dimensional region is equal to the …
A Unified Treatment of Convexity of Relative Entropy and Related Trace Functions, with Conditions for Equality
我们介绍了一个推广的相对熵来自Wigner-Yanase-Dyson熵，并给出了一个简单的，自足的证明，它是凸的。此外，特殊情况产生了相对熵的联合凸性，并且对于映射（A，B）--> Tr K^* A^p K B^{1-p}，0 < p < 1时是Lieb的联合凸性，1 < p < 2时是Ando的联合凸性。这种方法使我们能够获得这些情况下的平等条件，以及由此产生的一些不平等的平等条件。其中包括部分迹下的单调性，以及由Lieb和Carlen证明的关于混合（p，q）范数的Minkowski型矩阵不等式。在所有情况下，等式条件与p无关;对于三个空间的扩张，它们与相对熵的强次可加性中的等式条件相同。
We show that the density-matrix states of noncomposite qudit systems satisfy entropic and information relations like the subadditivity condition, strong subadditivity condition, and Araki--Lieb inequality, which characterize hidden quantum correlations of observables associated with these indivisible systems. We derive these relations employing a specific map of the entropic inequalities known for density matrices of multiqudit systems to the inequalities for density matrices of single-qudit systems. We present the obtained relations in the form of mathematical inequalities for arbitrary Hermi…
The uncertainty principle determines the distinction between the classical and quantum worlds. This principle states that it is not possible to measure two incompatible observables with the desired accuracy simultaneously. In quantum information theory, Shannon entropy has been used as an appropriate measure to express the uncertainty relation. According to the applications of entropic uncertainty relation, studying and trying to improve the bound of this relation is of great importance. Uncertainty bound can be altered by considering an extra quantum system as the quantum memory $B$ which is …
We investigate relations between the ranks of marginals of multipartite quantum states. These are the Schmidt ranks across all possible bipartitions and constitute a natural quantification of multipartite entanglement dimensionality. We show that there exist inequalities constraining the possible distribution of ranks. This is analogous to the case of von Neumann entropy (α-Rényi entropy for α=1), where nontrivial inequalities constraining the distribution of entropies (such as e.g. strong subadditivity) are known. It was also recently discovered that all other α-Rényi entropies for $α\in(0,1)…
We investigate the connection between recent results in quantum thermodynamics and fluctuation relations by adopting a fully quantum mechanical description of thermodynamics. By including a work system whose energy is allowed to fluctuate, we derive a set of equalities which all thermodynamical transitions have to satisfy. This extends the condition for maps to be Gibbs-preserving to the case of fluctuating work, providing a more general characterisation of maps commonly used in the information theoretic approach to thermodynamics. For final states, block diagonal in the energy basis, this set…
In 1981, Takeuti introduced set theory based on quantum logic by constructing a model analogous to Boolean-valued models for Boolean logic. He defined the quantum logical truth value for every sentence of set theory. He showed that equality axioms do not hold, while axioms of ZFC set theory hold if appropriately modified with the notion of commutators. Here, we consider the problem in Takeuti's quantum set theory that De Morgan's laws do not hold for bounded quantifiers. We construct a counter-example to De Morgan's laws for bounded quantifiers in Takeuti's quantum set theory. We redefine the …
