scholarly journals Wigner’s Friend Scenarios and the Internal Consistency of Standard Quantum Mechanics

Entropy ◽  
2021 ◽  
Vol 23 (9) ◽  
pp. 1186
Author(s):  
Dmitri Sokolovski ◽  
Alexandre Matzkin
Keyword(s):  
Quantum Mechanics ◽  
Internal Consistency ◽  
A Priori ◽  
Quantum Measurements ◽  
Standard Quantum ◽  
Physical Evidence ◽  
Wigner’S Friend ◽  
Feynman Rules ◽  
Made In

Wigner’s friend scenarios involve an Observer, or Observers, measuring a Friend, or Friends, who themselves make quantum measurements. In recent discussions, it has been suggested that quantum mechanics may not always be able to provide a consistent account of a situation involving two Observers and two Friends. We investigate this problem by invoking the basic rules of quantum mechanics as outlined by Feynman in the well-known “Feynman Lectures on Physics”. We show here that these “Feynman rules” constrain the a priori assumptions which can be made in generalised Wigner’s friend scenarios, because the existence of the probabilities of interest ultimately depends on the availability of physical evidence (material records) of the system’s past. With these constraints obeyed, a non-ambiguous and consistent account of all measurement outcomes is obtained for all agents, taking part in various Wigner’s Friend scenarios.

NONLOCAL MEASUREMENTS IN THE TIME-SYMMETRIC QUANTUM MECHANICS

2006 ◽  
Vol 20 (11n13) ◽  
pp. 1528-1535 ◽  
Author(s):  
LEV VAIDMAN ◽  
IZHAR NEVO
Keyword(s):  
Quantum Mechanics ◽  
Quantum Systems ◽  
Quantum Measurements ◽  
Quantum States ◽  
Standard Quantum ◽  
Time Direction ◽  
Quantum Formalism ◽  
Symmetric Quantum ◽  
Time Symmetric Quantum Mechanics

Although for some nonlocal variables the standard quantum measurements which are reliable, instantaneous, and nondemolition, are impossible, demolition reliable instantaneous measurements of all variables are possible. It is shown that this is correct also in the framework of the time-symmetric quantum formalism, i.e. nonlocal variables of composite quantum systems with quantum states evolving both forward and backward in time are measurable in a demolition way. The result follows from the possibility to reverse with certainty the time direction of backward evolving quantum states.

scholarly journals Lectures on dynamical models for quantum measurements

2014 ◽  
Vol 28 (21) ◽  
pp. 1430014
Author(s):  
Theo M. Nieuwenhuizen ◽  
Marti Perarnau-Llobet ◽  
Roger Balian
Keyword(s):  
Quantum Mechanics ◽  
Quantum Theory ◽  
Density Matrix ◽  
Quantum Measurements ◽  
Quantum Spin ◽  
Spin Component ◽  
Time Interval ◽  
Large Set ◽  
Standard Quantum ◽  
The One

In textbooks, ideal quantum measurements are described in terms of the tested system only by the collapse postulate and Born's rule. This level of description offers a rather flexible position for the interpretation of quantum mechanics. Here we analyse an ideal measurement as a process of interaction between the tested system S and an apparatus A, so as to derive the properties postulated in textbooks. We thus consider within standard quantum mechanics the measurement of a quantum spin component ŝz by an apparatus A, being a magnet coupled to a bath. We first consider the evolution of the density operator of S + A describing a large set of runs of the measurement process. The approach describes the disappearance of the off-diagonal terms ("truncation") of the density matrix as a physical effect due to A, while the registration of the outcome has classical features due to the large size of the pointer variable, the magnetization. A quantum ambiguity implies that the density matrix at the final time can be decomposed on many bases, not only the one of the measurement. This quantum oddity prevents to connect individual outcomes to measurements, a difficulty known as the "measurement problem". It is shown that it is circumvented by the apparatus as well, since the evolution in a small time interval erases all decompositions, except the one on the measurement basis. Once one can derive the outcome of individual events from quantum theory, the so-called collapse of the wavefunction or the reduction of the state appears as the result of a selection of runs among the original large set. Hence nothing more than standard quantum mechanics is needed to explain features of measurements. The employed statistical formulation is advocated for the teaching of quantum theory.

scholarly journals Does Decoherence Select the Pointer Basis of a Quantum Meter?

Entropy ◽  
2022 ◽  
Vol 24 (1) ◽  
pp. 106
Author(s):  
Abraham G. Kofman ◽  
Gershon Kurizki
Keyword(s):  
Quantum Mechanics ◽  
Quantum State ◽  
Quantum Measurement ◽  
Measurement Theory ◽  
Quantum Measurements ◽  
Quantum Measurement Theory ◽  
Measuring Device ◽  
Standard Quantum ◽  
Pointer States ◽  
Projective Measurements

The consensus regarding quantum measurements rests on two statements: (i) von Neumann’s standard quantum measurement theory leaves undetermined the basis in which observables are measured, and (ii) the environmental decoherence of the measuring device (the “meter”) unambiguously determines the measuring (“pointer”) basis. The latter statement means that the environment monitors (measures) selected observables of the meter and (indirectly) of the system. Equivalently, a measured quantum state must end up in one of the “pointer states” that persist in the presence of the environment. We find that, unless we restrict ourselves to projective measurements, decoherence does not necessarily determine the pointer basis of the meter. Namely, generalized measurements commonly allow the observer to choose from a multitude of alternative pointer bases that provide the same information on the observables, regardless of decoherence. By contrast, the measured observable does not depend on the pointer basis, whether in the presence or in the absence of decoherence. These results grant further support to our notion of Quantum Lamarckism, whereby the observer’s choices play an indispensable role in quantum mechanics.

scholarly journals Standard quantum mechanics without observers

2021 ◽  
Vol 103 (3) ◽  
Author(s):  
Ovidiu Cristinel Stoica
Keyword(s):  
Quantum Mechanics ◽  
Standard Quantum

Nanomechanical Biosensor Using Polymer Membranes

2004 ◽  
Author(s):  
Srinath Satyanarayana ◽  
Daniel T. McCormick ◽  
Arun Majumdar
Keyword(s):  
Surface Stress ◽  
A Priori ◽  
Detection Systems ◽  
Stress Sensors ◽  
Design Flexibility ◽  
High Elasticity ◽  
Sensor Geometry ◽  
Specific Reactions ◽  
Higher Sensitivity ◽  
Made In

In recent years several surface stress sensors based on microcantilevers have been developed for biosensing [1–4]. Since these sensors are made using standard microfabrication processes, they can be easily made in an array format, making them suitable for high-throughput multiplexed analysis. Specific reactions occurring on one surface (enabled by selective modification of the surface a priori) of the sensor element change the surface stress, which in turn causes the sensor to deflect. The magnitude and the rate of deflection are then used to study the reaction. The microcantilevers in these sensors are usually fabricated using material like silicon and its oxides or nitrides. The high elasticity modulus of these materials places limitations on the sensitivity and sensor geometry. Alternately polymers, which have a much lower elastic modulus when compared to silicon or its derivatives, offers greater design flexibility, i.e. allow the exploration of innovative sensor configurations that can have higher sensitivity and at the same time are suitable for integration with microfluidics and electrical detection systems.

scholarly journals The measure problem in no-collapse (many worlds) quantum mechanics

2017 ◽  
Vol 26 (03) ◽  
pp. 1730008 ◽  
Author(s):  
Stephen D. H. Hsu
Keyword(s):  
Wave Function ◽  
Quantum Mechanics ◽  
Probability Measure ◽  
Ab Initio ◽  
Subjective Probability ◽  
State Vector ◽  
A Priori ◽  
Born Rule ◽  
Many Worlds ◽  
Measure Problem

We explain the measure problem (cf. origin of the Born probability rule) in no-collapse quantum mechanics. Everett defined maverick branches of the state vector as those on which the usual Born probability rule fails to hold — these branches exhibit highly improbable behaviors, including possibly the breakdown of decoherence or even the absence of an emergent semi-classical reality. Derivations of the Born rule which originate in decision theory or subjective probability (i.e. the reasoning of individual observers) do not resolve this problem, because they are circular: they assume, a priori, that the observer occupies a non-maverick branch. An ab initio probability measure is sometimes assumed to explain why we do not occupy a maverick branch. This measure is constrained by, e.g. Gleason’s theorem or envariance to be the usual Hilbert measure. However, this ab initio measure ultimately governs the allocation of a self or a consciousness to a particular branch of the wave function, and hence invokes primitives which lie beyond the Everett wave function and beyond what we usually think of as physics. The significance of this leap has been largely overlooked, but requires serious scrutiny.

scholarly journals Decoherence and its role in the modern measurement problem

2012 ◽  
Vol 370 (1975) ◽  
pp. 4576-4593 ◽  
Author(s):  
David Wallace
Keyword(s):  
Wave Function ◽  
Quantum Mechanics ◽  
Quantum Measurement ◽  
Measurement Problem ◽  
Scientific Practice ◽  
Measurement Theory ◽  
Quantum Measurements ◽  
Quantum Measurement Problem ◽  
Modern Physics ◽  
Conceptual Problems

Decoherence is widely felt to have something to do with the quantum measurement problem, but getting clear on just what is made difficult by the fact that the ‘measurement problem’, as traditionally presented in foundational and philosophical discussions, has become somewhat disconnected from the conceptual problems posed by real physics. This, in turn, is because quantum mechanics as discussed in textbooks and in foundational discussions has become somewhat removed from scientific practice, especially where the analysis of measurement is concerned. This paper has two goals: firstly (§§1–2), to present an account of how quantum measurements are actually dealt with in modern physics (hint: it does not involve a collapse of the wave function) and to state the measurement problem from the perspective of that account; and secondly (§§3–4), to clarify what role decoherence plays in modern measurement theory and what effect it has on the various strategies that have been proposed to solve the measurement problem.

scholarly journals Analisa Data Penjualan SaRa Collection menggunakan metode Apriori

2021 ◽  
Vol 7 (1) ◽  
pp. 68-73
Author(s):  
Ririn Restu Aria ◽  
Susi Susilowati
Keyword(s):  
Consumer Demand ◽  
A Priori ◽  
Transaction Data ◽  
Made In ◽  
Sales Strategies

Sales are one of the most important things in the SaRa collection. To increase the number of existing sales, SaRa collection must be able to see the opportunities and needs needed by its customers. For this reason, when the Covid 19 pandemic is happening now, the SaRa collection has made a connector that can be used to beautify the use of masks to prevent transmission of the Covid 19 virus. In the process of making the connector, it is still done homemade according to the model that consumers are interested in because it takes time to process and select the model. as well as the appropriate color. Currently, sales are still being recorded manually, so the owner is still having trouble providing a stock of the connector model and color that will be made in order to meet consumer demand. In order to find out what models must be provided, accurate calculations are needed, for that the author uses the a priori algorithm as a method which is expected to be taken into consideration in marketing and sales strategies as well as connecting stock data to be made. A priori calculations with itemset and associations based on sales transaction data in Sara's collection

scholarly journals Broadening quantum cosmology with a fractional whirl

2021 ◽  
pp. 2140005
Author(s):  
S. M. M. Rasouli ◽  
S. Jalalzadeh ◽  
P. V. Moniz
Keyword(s):  
Quantum Mechanics ◽  
Fractional Calculus ◽  
Quantum Cosmology ◽  
Cosmological Solution ◽  
Isotropic Universe ◽  
Fractional Quantum ◽  
Stiff Matter ◽  
Standard Quantum

We start by presenting a brief summary of fractional quantum mechanics, as means to convey a motivation towards fractional quantum cosmology. Subsequently, such application is made concrete with the assistance of a case study. Specifically, we investigate and then discuss a model of stiff matter in a spatially flat homogeneous and isotropic universe. A new quantum cosmological solution, where fractional calculus implications are explicit, is presented and then contrasted with the corresponding standard quantum cosmology setting.

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