Non-classicality thresholds for multiqubit states - numerical analysis

Equivalence of classicality and separability based on P phase-space representation of symmetric multiqubit states

Classical and quantum world views differ in peculiar ways. Understanding decisive quantum features -- for which no classical explanation exist -- and their interrelations is of foundational interest. Moreover, recognizing non-classical features carries practical significance in information processing tasks as it offers insights as to why quantum protocols work better than their classical counterparts. We focus here on two celebrated notions of non-classicality viz., negativity of P phase-space representation and entanglement in symmetric multiqubit systems. We prove that they imply each other.

Locality and Classicality: role of entropic inequalities

The use of the so-called entropic inequalities is revisited in the light of new quantum correlation measures, specially nonlocality. We introduce the concept of {\it classicality} as the non-violation of these classical inequalities by quantum states of several multiqubit systems and compare it with the non-violation of Bell inequalities, that is, {\it locality}. We explore --numerically and analytically-- the relationship between several other quantum measures and discover the deep connection existing between them. The results are surprising due to the fact that these measures are very differ…

On the non-classicality features of new classes of nonlinear coherent states

In this paper, using an exponential function of intensity of radiation field, two new classes of nonlinear coherent states will be constructed. For the first class, we choose the nonlinearity function as f(n) = exp(βn), where βcharacterizes the strength of the nonlinearity of the quantum system. We show that, the corresponding β-states possess a collection of non-classicality features, only for the particular values of βand z. But, interestingly there exists finite (threshold) values of β, for which all of the non-classicality signs will disappear, in appropriate regions around the origin of t…

Speedup of adiabatic multiqubit state-transfer by ultrastrong coupling of matter and radiation

Ultrastrongly coupled quantum hardware may increase the speed of quantum state processing in distributed architectures, allowing to approach fault-tolerant threshold. We show that circuit QED architectures in the ultrastrong coupling regime, which has been recently demonstrated with superconductors, may show substantial speedup for a class of adiabatic protocols resilient to the main source of errors, namely the interplay of dynamical Casimir effect and cavity losses.

哪种经典性？有限量子逻辑中的关联、单纯形和乘积规则测试

Which Classicality? Incidence, Simplex, and Product-Rule Tests in Finite Quantum Logics

研究有限量子逻辑结构在不同测试下的经典性特征，区分关联、单纯形和算子函数测试，通过集体GHZ联合测量等示例说明，还计算选定片段的状态去极化阈值，表明其是片段和噪声模型属性。

可预测性筛，指针状态和量子轨迹的经典性

Predictability sieve, pointer states, and the classicality of quantum trajectories

本文研究了受退相干影响的开放量子系统的经典态的各种度量。尽管存在退相干，经典态仍被认为是稳定的，并被认为会在环境中留下明显的印记。在这里，这些预期的特征，环境诱导的超选择（einselection）使用四种不同的标准进行量化：可预报性筛（选择产生最小熵的状态），净化时间（寻找最容易从它们对环境留下的印记中找到的状态），效率阈值（它发现可以从对环境的最小部分的测量中推断出的状态），和纯度损失时间（寻找损失其初始纯度的设定分数花费最长时间的状态）。我们表明，当指针状态--由可预测性筛选择的开放量子系统的最可预测的状态--被很好地定义时，所有四个标准都认为它们确实是最经典的状态。我们用两个例子来说明这一点：一个欠阻尼谐振子，它的相干态是所有标准一致选择的;一个经历量子布朗运动的自由粒子，它的大多数标准选择几乎相同的高斯态（尽管在这种情况下，可预测性筛不选择定义良好的指针态）。