A New Characteristic of a Quantum System between Two Measurements — A “Weak Value”

1989 ◽  
pp. 17-22 ◽  
Author(s):  
Y. Aharonov ◽  
L. Vaidman
Keyword(s):  
Quantum System ◽  
Weak Value

scholarly journals Weak value controversy

2017 ◽  
Vol 375 (2106) ◽  
pp. 20160395 ◽  
Author(s):  
L. Vaidman
Keyword(s):  
Quantum System ◽  
Precision Measurements ◽  
Weak Values ◽  
Statistical Nature ◽  
Weak Value ◽  
Quantum Revolution

Recent controversy regarding the meaning and usefulness of weak values is reviewed. It is argued that in spite of recent statistical arguments by Ferrie and Combes, experiments with anomalous weak values provide useful amplification techniques for precision measurements of small effects in many realistic situations. The statistical nature of weak values is questioned. Although measuring weak values requires an ensemble, it is argued that the weak value, similarly to an eigenvalue, is a property of a single pre- and post-selected quantum system. This article is part of the themed issue ‘Second quantum revolution: foundational questions’.

scholarly journals Anomalous Weak Values Without Post-Selection

Quantum ◽  
2019 ◽  
Vol 3 ◽  
pp. 194 ◽  
Author(s):  
Alastair A. Abbott ◽  
Ralph Silva ◽  
Julian Wechs ◽  
Nicolas Brunner ◽  
Cyril Branciard
Keyword(s):  
Quantum System ◽  
Weak Measurement ◽  
Weak Values ◽  
Weak Measurements ◽  
Weak Value ◽  
Average Value ◽  
Causal Structures

A weak measurement performed on a pre- and post-selected quantum system can result in an average value that lies outside of the observable's spectrum. This effect, usually referred to as an ``anomalous weak value'', is generally believed to be possible only when a non-trivial post-selection is performed, i.e., when only a particular subset of the data is considered. Here we show, however, that this is not the case in general: in scenarios in which several weak measurements are sequentially performed, an anomalous weak value can be obtained without post-selection, i.e., without discarding any data. We discuss several questions that this raises about the subtle relation between weak values and pointer positions for sequential weak measurements. Finally, we consider some implications of our results for the problem of distinguishing different causal structures.

Quantum Boxes, Stringed Instruments

2017 ◽  
Author(s):  
Frank S. Levin
Keyword(s):  
Energy Level ◽  
Schrödinger Equation ◽  
Quantum System ◽  
Schrodinger Equation ◽  
Probability Distributions ◽  
Wave Functions ◽  
Energy Level Diagram ◽  
One Dimensional ◽  
Stringed Instruments ◽  
Symmetry Properties

Chapter 7 illustrates the results obtained by applying the Schrödinger equation to a simple pedagogical quantum system, the particle in a one-dimensional box. The wave functions are seen to be sine waves; their wavelengths are evaluated and used to calculate the quantized energies via the de Broglie relation. An energy-level diagram of some of the energies is constructed; on it are illustrations of the corresponding wave functions and probability distributions. The wave functions are seen to be either symmetric or antisymmetric about the midpoint of the line representing the box, thereby providing a lead-in to the later exploration of certain symmetry properties of multi-electron atoms. It is next pointed out that the Schrödinger equation for this system is identical to Newton’s equation describing the vibrations of a stretched musical string. The different meaning of the two solutions is discussed, as is the concept and structure of linear superpositions of them.

scholarly journals Quantum system compression: A Hamiltonian guided walk through Hilbert space

2021 ◽  
Vol 103 (1) ◽  
Author(s):  
Robert L. Kosut ◽  
Tak-San Ho ◽  
Herschel Rabitz
Keyword(s):  
Hilbert Space ◽  
Quantum System

scholarly journals High-precise measurement of optical rotatory dispersion based on weak value amplification

2021 ◽  
pp. 1-1
Author(s):  
Jingyi Shao ◽  
Lan Luo ◽  
Yu He ◽  
Jiacheng You ◽  
Yurong Liu ◽  
...  
Keyword(s):  
Precise Measurement ◽  
Optical Rotatory Dispersion ◽  
Rotatory Dispersion ◽  
Optical Rotatory ◽  
Weak Value ◽  
Weak Value Amplification

scholarly journals How to Erase Quantum Monogamy?

2021 ◽  
Vol 3 (1) ◽  
pp. 53-67
Author(s):  
Ghenadie Mardari
Keyword(s):  
Quantum System ◽  
Quantum Entanglement ◽  
The Other ◽  
Arrow Of Time ◽  
Quantum Level ◽  
Delayed Choice ◽  
Other Hand ◽  
The One ◽  
Quantum Erasure ◽  
Non Locality

The phenomenon of quantum erasure exposed a remarkable ambiguity in the interpretation of quantum entanglement. On the one hand, the data is compatible with the possibility of arrow-of-time violations. On the other hand, it is also possible that temporal non-locality is an artifact of post-selection. Twenty years later, this problem can be solved with a quantum monogamy experiment, in which four entangled quanta are measured in a delayed-choice arrangement. If Bell violations can be recovered from a “monogamous” quantum system, then the arrow of time is obeyed at the quantum level.

scholarly journals Tangible reduction in learning sample complexity with large classical samples and small quantum system

2021 ◽  
Vol 20 (8) ◽  
Author(s):  
Wooyeong Song ◽  
Marcin Wieśniak ◽  
Nana Liu ◽  
Marcin Pawłowski ◽  
Jinhyoung Lee ◽  
...  
Keyword(s):  
Quantum System ◽  
Learning Sample ◽  
Sample Complexity ◽  
Small Quantum
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