Uncomfortable bedfellows: Objective quantum Bayesianism and the von Neumann–Lüders projection postulate

In this paper I critically evaluate the justification of the von Neumann–Lüders projection postulate for state changes in projective measurement contexts from the objective quantum Bayesian perspective. I point out that the justification provided so far for the von Neumann–Lüders projection postulate is insufficient. I argue that the best way to correct this problem is to make an assumption, Benign Realism, which is contradictory to the objective quantum Bayesian interpretation of quantum states.     

Non-monotonic probability theory for n-state quantum systems

In previous work, a non-standard theory of probability was formulated and used to systematize interference effects involving the simplest type of quantum systems. The main result here is a self-contained, non-trivial generalization of that theory to capture interference effects involving a much broader range of quantum systems. The discussion also focuses on interpretive matters having to do with the actual/virtual distinction, non-locality, and conditional probabilities.     

States of ignorance and ignorance of states: Examining the Quantum Principal Principle

Earman (2018) has recently argued that the Principal Principle, a principle of rationality connecting objective chance and credence, is a theorem of quantum probability theory. This paper critiques Earman's argument, while also offering a positive proposal for how to understand the status of the Principal Principle in quantum probability theory.     

A remark on Fuchs’ Bayesian interpretation of quantum mechanics

Quantum mechanics is a theory whose foundations spark controversy to this day. Although many attempts to explain the underpinnings of the theory have been made, none has been unanimously accepted as satisfactory. Fuchs has recently claimed that the foundational issues can be resolved by interpreting quantum mechanics in the light of quantum information. The view proposed is that quantum mechanics should be interpreted along the lines of the subjective Bayesian approach to probability theory. The quantum state is not the physical state of a microscopic object. It is an epistemic state of an observer; it represents subjective degrees of belief about outcomes of measurements. The interpretation gives an elegant solution to the infamous measurement problem: measurement is nothing but Bayesian belief updating in a analogy to belief updating in a classical setting. In this paper, we analyze an argument that Fuchs gives in support of this latter claim. We suggest that the argument is not convincing since it rests on an ad hoc construction. We close with some remarks on the options left for Fuchs’ quantum Bayesian project.     

Fritz London and the scale of quantum mechanisms

Fritz London's seminal idea of “quantum mechanisms of macroscopic scale”, first articulated in 1946, was the unanticipated result of two decades of research, during which London pursued quantum-mechanical explanations of various kinds of systems of particles at different scales. He started at the microphysical scale with the hydrogen molecule, generalized his approach to chemical bonds and intermolecular forces, then turned to macrophysical systems like superconductors and superfluid helium. Along this path, he formulated a set of concepts—the quantum mechanism of exchange, the rigidity of the wave function, the role of quantum statistics in multi-particle systems, the possibility of order in momentum space—that eventually coalesced into a new conception of systems of equal particles. In particular, it was London's clarification of Bose-Einstein condensation that enabled him to formulate the notion of superfluids, and led him to the recognition that quantum mechanics was not, as it was commonly assumed, relevant exclusively as a micromechanics.     

离子阱量子计算机的发展现状与趋势

量子计算机是基于微观体系的量子力学性质——叠加性和纠缠性,对信息进行逻辑运算、存储传输的新型计算装置。通过运行基于量子硬件的量子算法,量子计算机解决某些复杂数学问题的速度和效率可大幅度超越经典计算机,对未来科技发展和国家战略竞争起着至关重要的作用。离子阱是通用量子计算机的主流技术之一,同时也对量子物理学的发展发挥过关键作用。本文围绕离子阱量子计算机的发展现状与趋势展开论述。首先回顾离子阱量子计算发展历史;接着介绍离子囚禁关键技术的现状以及趋势;然后重点介绍分布式离子阱量子计算机,分析离子－光子纠缠、分布式量子计算,以及基于离子阱量子计算机的量子互联网络等技术前沿;并介绍了离子阱量子计算产业发展,包括核心专利、研究机构、企业与融资、市场与生态等;最后,对离子阱量子计算机科研和产业发展提出政策建议。     

量子传感与测量领域国际发展态势分析

作为量子信息技术的重要发展方向之一,量子传感与测量可实现跨越式的超高精度测量,并在特定环境抵御噪声干扰,在地质勘测、空间探测、惯性制导和材料分析等重要领域具有广阔的发展和应用前景。本文梳理了近年来欧美等主要科技强国在该领域的重要战略规划与项目部署;并就量子传感与测量五大子领域的发展现状与趋势进行深入分析;最后,对我国提出了三条建议,包括以国家实验室为依托,明确重点研发方向,加快核心技术协同攻关;建立合作平台与机制,推进产业生态环境建设;重视复合型人才培养和对基础研究的长期支持。     

‘Shut up and contemplate!’: Lucien Hardy׳s reasonable axioms for quantum theory

Since the beginning of quantum mechanics, attempts were made to derive it from simple natural axioms or assumptions. These reconstructions suffered from various defects, including the questionable naturalness or the overabundance of the axioms, the mathematical difficulty of the derivation, and the inclusion of a wider range of theories than just quantum mechanics. Recently, in 2001, Lucien Hardy propounded “five reasonable axioms” that seem to elude such criticism. The present paper purports to give a simplified version of this new foundation, to discuss Hardy׳s original version and subsequent variants by others authors, and to investigate the nature of the relevant axioms in light of their possible connection with correspondence arguments.     

欧美量子科技政策及其背后相关科学家分析

量子科技是具有极强产业远景和关系国家战略发展的前沿领域,越来越多的国家和地区把量子科技的发展列入国家重点战略。了解量子科技发展强国的相关政策和科学家信息,可以管窥到其在政策制定上的一些特质,也可以为预测下一步的政策制定提供参考。本文梳理了欧盟和美国的量子政策发展轨迹,重点分析了其中最新的重大战略部署以及影响政策制定的相关科学家,通过与我国情况进行对比,为我国未来量子科技政策的制定提出了加快国家战略顶层设计、通过国家项目推动量子产业发展、建设量子科技人才梯队等几点建议。     

Conservatism and consensus-seeking among economic forecasters

This paper uses the track records of a panel of US economic forecasters participating in a consensus forecasting service to test for conservatism and consensus-seeking behaviour. The tests are based on a particular method-of-moments estimator, designed to allow for the heteroscedasticity and serial correlation which is inevitably present in errors from repeated forecasts for fixed target dates. Most forecasters prove to be conservative. When revising forecasts they give too much weight to their own past forecasts. Surprisingly, forecasters are not consensus-seeking but ‘variety-seeking’. When revising forecasts, they give too little weight to the known forecasts of other forecasters.     

Reflections on Kant’s concept (and intuition) of space

In this paper, I investigate an important aspect of Kant’s theory of pure sensible intuition. I argue that, according to Kant, a pure concept of space warrants and constrains intuitions of finite regions of space. That is, an a priori conceptual representation of space provides a governing principle for all spatial construction, which is necessary for mathematical demonstration as Kant understood it.     

Newtonianism and religion in the Netherlands

In the early eighteenth century Newtonianism became popular in the Netherlands both in academic (Boerhaave, ’sGravesande, Van Musschenbroek) and non-academic circles. The ‘Book of Nature’ was interpreted with the help of Newton’s natural philosophy and his ideas about a providential deity, thereby greatly enhancing the attractiveness of physico-theology in the eighteenth-century United Provinces. Like other Europeans the Dutch welcomed physico-theology as a strategic means in their battle against irreligion and atheism. Bernard Nieuwentijt, Johan Lulofs, Petrus Camper, and Johannes Florentius Martinet were prominent experts in the field. Combining Newtonian notions with Leibnizian optimism and romanticist trends, physico-theology remained popular in the Netherlands well into the nineteenth century.     

Reduction and emergence in the fractional quantum Hall state

We present the fractional quantum Hall (FQH) effect as a candidate emergent phenomenon. Unlike some other putative cases of condensed matter emergence (such as thermal phase transitions), the FQH effect is not based on symmetry breaking. Instead FQH states are part of a distinct class of ordered matter that is defined topologically. Topologically ordered states result from complex long-ranged correlations between their constituent parts, such that the system displays strongly irreducible, qualitatively novel properties.     

QED and the man who didn׳t make it: Sidney Dancoff and the infrared divergence

Sidney Dancoff׳s paper “On Radiative Corrections for Electron Scattering” is generally viewed in the secondary literature as a failed attempt to develop renormalized quantum electrodynamics (QED) a decade early, an attempt that failed because of a mistake that Dancoff made. I will discuss Dancoff׳s mistake and try to reconstruct why it occurred, by relating it to the usual practices of the quantum field theory of his time. I will also argue against the view that Dancoff was on the verge of developing renormalized QED and will highlight the conceptual divides that separate Dancoff׳s work from the QED of the late 1940s. I will finally discuss how the established view of Dancoff׳s paper came to be and how the reading of this specific anecdote relates to more general assessments of the conceptual advances of the late 1940s (covariant techniques, renormalization), in particular to their assessment as being conservative rather than revolutionary.