如何在不使用弱测量的情况下，测量自旋为1/2的粒子的自旋分量的结果可以变成100

How the Weak Variance of Momentum Can Turn Out to be Negative

Weak values are average quantities,therefore investigating their associated variance is crucial in understanding their place in quantum mechanics. We develop the concept of a position-postselected weak variance of momentum as cohesively as possible, building primarily on material from Moyal (Mathematical Proceedings of the Cambridge Philosophical Society, Cambridge University Press, Cambridge, 1949) and Sonego (Found Phys 21(10):1135, 1991) . The weak variance is defined in terms of the Wigner function, using a standard construction from probability theory. We show this corresponds to a measur…

How the Result of Counting One Photon Can Turn Out to Be a Value of 8

In 1988, Aharonov, Albert, and Vaidman introduced a new paradigm of quantum measurement in a paper which had the unwieldy but provocative title "How the result of a measurement of a component of the spin of a spin-1=2 particle can turn out to be 100." This paradigm, so-called "weak measurement," has since been the subject of widespread theoretical and experimental attention, both for the perspective it offers on quantum reality and for possible applications to precision measurement. Yet almost all of the weak-measurement experiments carried out so far could be alternatively understood in terms…

A comment on the paper "How can a Result of a Single Coin Toss Turn Out to be 100 Heads" by C. Ferrie and J. Combes

The authors of a recent paper [Phys. Rev. Lett. 113, 120404 (2014)] suggest that "weak values are not inherently quantum but rather a purely statistical feature of pre- and postselection with disturbance". We argue that this claim is erroneous, since such values require averaging with distributions which change sign. This type of averaging arises naturally in quantum mechanics, but may not occur in classical statistics.

光子质量的测量结果如何能得出100

How the result of a measurement of a photon's mass can turn out to be 100

本研究将玻姆力学的Wiseman弱测量框架拓展至相对论区域，提出基于弱值的相对论单粒子玻姆局域质量定义，验证其与德布罗意有效质量的一致性，并在干涉装置中演示光子轨迹与该质量的关联。

纠缠产生的弱测量与控制

Weak measurement and control of entanglement generation

在本文中，我们展示了如何弱联合测量和本地反馈可以用来控制两个量子比特之间的纠缠产生。为了做到这一点，我们利用一个消相干自由子空间（DFS）。弱测量和反馈可以用来驱动系统迅速进入这个子空间。一旦进入子空间，反馈可以快速产生纠缠，或者动态地关闭纠缠产生。在弱测量的背景下，我们还考虑了净化和产生纠缠之间的一些差异。

Estimation of temporal separation of slow light pulses in atomic vapors by weak measurement

We show how two circular polarization components of a linearly polarized pulse, propagating through a coherently driven dilute atomic vapor, can be well resolved in time domain by weak measurement. Slower group velocity of one of the components due to electromagnetically induced transparency leads to a differential group delay between the two components. For low number density, this delay may not be large enough to temporally resolve the two components. We show how this can be enhanced in terms of mean time of arrival of the output pulse through a post-selected polarizer. We demonstrate the id…

非高斯波包对引力弱等效原理的强量子破坏

Strong quantum violation of the gravitational weak equivalence principle by a non-Gaussian wave-packet

引力的弱等效原理在量子水平上以两种方式被检验。首先，计算了由逆重力向上投影的非高斯波包描述的粒子在经典转向点和初始投影点附近的位置检测概率。这些概率在这两点上都表现出质量依赖性，从而反映了弱等效原理的量子违背。其次，利用量子几率流计算了自由下落粒子的平均到达时间，结果表明，量子几率流也是与质量有关的。这种质量依赖性被证明是通过增加的非高斯参数的波包，从而意味着一个更强的违反弱等效原理，通过一个更大的偏离高斯的初始波包。在大质量的极限下，位置检测概率和平均到达时间的质量依赖性消失。因此，弱等效原理和量子力学之间的兼容性恢复到后者的宏观极限。玻姆轨迹的选择展示说明这些功能在自由降落的情况下。

Weak measurement criteria for the past of a quantum particle

Vaidman, Phys.Rev. A 87, 052104 (2013), has proposed a weak value criterion for the past of a quantum particle, and applied it to photons in a particular setup of nested Mach-Zehnder interferometers. From his analysis, he draws some astonishing conclusions regarding which arms of the setup the photons populate. I argue that the weak values Vaidman employs as weak tracers in his analysis cannot be used in this case and that, consequently, the conclusions he draws cannot be upheld. The reason is that weak values are defined as a limit which in this case turns out to be discontinuous. I propose i…

Adiabatic theorem for bipartite quantum systems in weak coupling limit

We study the adiabatic approximation of the dynamics of a bipartite quantum system with respect to one of the components, when the coupling between its two components is perturbative. We show that the density matrix of the considered component is described by adiabatic transport formulae exhibiting operator-valued geometric and dynamical phases. The present results can be used to study the quantum control of the dynamics of qubits and of open quantum systems where the two components are the system and its environment. We treat two examples, the control of an atomic qubit interacting with anoth…