A longstanding open problem in quantum information theory is to find the classical capacity of an optical communication link, modeled as a Gaussian bosonic channel. It has been conjectured that this capacity is achieved by a random coding of coherent states using an isotropic Gaussian distribution in phase space. We show that proving a Gaussian minimum entropy conjecture for a quantum-limited amplifier is actually sufficient to confirm this capacity conjecture, and we provide a strong argument towards this proof by exploiting a connection between quantum entanglement and majorization theory.
Majorization provides a rather powerful partial-order classification of probability distributions depending only on the spread of the statistics, and not on the actual numerical values of the variable being described. We propose to apply majorization as a meta-measure of quantum polarization fluctuations, this is to say of the degree of polarization. We compare the polarization fluctuations of the most relevant classes of quantum and classical-like states. In particular we test Lieb's conjecture regarding classical-like states as the most polarized and a complementary conjecture that the most …
Radial Coarse Graining Restores Vacuum Majorization in Wigner Phase Space
School of Physical Sciences, University of Chinese Academy of Sciences（中国科学院大学物理科学学院）；ICTP-AP, University of Chinese Academy of Sciences（中国科学院大学 ICTP-AP）
Approximate majorization and high-order capacity of quantum depolarizing channels
The Chinese University of Hong Kong, Shenzhen（香港中文大学（深圳））；The Hong Kong University of Science and Technology (Guangzhou)（香港科技大学（广州））；National University of Singapore（新加坡国立大学）
Quantum communication theory explores the implications of quantum mechanics to the tasks of information transmission. Many physical channels can be formally described as quantum Gaussian operations acting on bosonic quantum states. Depending on the input state and on the quality of the channel, the output suffers certain amount of noise. For a long time it has been conjectured, but never proved, that output states of Gaussian channels corresponding to coherent input signals are the less noisy ones (in the sense of a majorization criterion). In this work we prove this conjecture. Specifically w…
The Majorization Principle is a fundamental statement governing the dynamics of information processing in optimal and efficient quantum algorithms. While quantum computation can be modeled to be reversible, due to the unitary evolution undergone by the system, these quantum algorithms are conjectured to obey a quantum arrow of time dictated by the Majorization Principle: the probability distribution associated to the outcomes gets ordered step-by-step until achieving the result of the computation. Here we report on the experimental observation of the effects of the Majorization Principle for t…
Recently, the longstanding Gaussian optimizer conjecture was proven for bosonic Gaussian gauge-covariant or contravariant channels in the work of Giovannetti, Holevo and Garcia-Patron [3]. In the paper of Mari, Giovannetti and Holevo [11] this result was strengthened for one-mode channels by establishing that the output for the vacuum or coherent input majorizes the output for any other input. In the present paper we give the multimode extension of the result of [11], including sufficient conditions under which the coherent states are the only optimizers. We also discuss direct implications of…
In the first part of this thesis, we present a general technique for establishing local and uniform continuity bounds for Schur concave functions. Our technique uses a particular relationship between majorization and the trace distance between quantum states. Namely, the majorization pre-order attains a minimum over $ε$-balls in this distance. By tracing the path of the majorization-minimizer as a function of the distance $ε$, we obtain the path of "majorization flow". This yields a new proof of the Audenaert-Fannes continuity bound for the von Neumann entropy in a universal framework which ex…
Combinatorial properties of holographic entropy inequalities
Brandeis University（布兰迪斯大学）；Institut des Hautes Etudes Scientifiques（高等科学研究所）；University of California, Davis（加州大学戴维斯分校）；Technion - Israel Institute of Technology（以色列理工学院）
The maximal p-norm multiplicativity conjecture is false
对于所有的1 < p < 2，我们证明了具有非乘法最大p-模的量子信道的存在性。等价地，对于所有1 < p < 2，量子信道的阶p的最小输出Renyi熵不是可加的。发现的违规行为很大。当p接近1时，产品通道的p阶最小输出Renyi熵不需要显著大于其各个因子的最小输出熵。由于p=1对应于冯诺伊曼熵，这些反例表明，如果量子信息理论的可加性猜想是正确的，它不能被证明为最大p-范数乘法的结果。
Given an arbitrary quantum state ($σ$), we obtain an explicit construction of a state $ρ^*_\varepsilon(σ)$ (resp. $ρ_{*,\varepsilon}(σ)$) which has the maximum (resp. minimum) entropy among all states which lie in a specified neighbourhood ($\varepsilon$-ball) of $σ$. Computing the entropy of these states leads to a local strengthening of the continuity bound of the von Neumann entropy, i.e., the Audenaert-Fannes inequality. Our bound is local in the sense that it depends on the spectrum of $σ$. The states $ρ^*_\varepsilon(σ)$ and $ρ_{*,\varepsilon}(σ)$ depend only on the geometry of the $\var…
