scholarly journals From Quantum Probabilities to Quantum Amplitudes

Entropy ◽  
2020 ◽  
Vol 22 (12) ◽  
pp. 1389
Author(s):  
Sofia Martínez-Garaot ◽  
Marisa Pons ◽  
Dmitri Sokolovski
Keyword(s):  
Quantum System ◽  
General Problem ◽  
Weak Measurement ◽  
Level System ◽  
Transition Path ◽  
Initial State ◽  
Quantum Probabilities ◽  
Measurement Limit ◽  
Pauli Problem

The task of reconstructing the system’s state from the measurements results, known as the Pauli problem, usually requires repetition of two successive steps. Preparation in an initial state to be determined is followed by an accurate measurement of one of the several chosen operators in order to provide the necessary “Pauli data”. We consider a similar yet more general problem of recovering Feynman’s transition (path) amplitudes from the results of at least three consecutive measurements. The three-step histories of a pre- and post-selected quantum system are subjected to a type of interference not available to their two-step counterparts. We show that this interference can be exploited, and if the intermediate measurement is “fuzzy”, the path amplitudes can be successfully recovered. The simplest case of a two-level system is analysed in detail. The “weak measurement” limit and the usefulness of the path amplitudes are also discussed.

scholarly journals Leggett-Garg Inequalities for Quantum Fluctuating Work

Entropy ◽  
2018 ◽  
Vol 20 (3) ◽  
pp. 200 ◽  
Author(s):  
◽  
Keyword(s):  
Quantum System ◽  
Quantum Correlations ◽  
Weak Measurement ◽  
Projective Measurement ◽  
Level System ◽  
Quantum Regime ◽  
Measurement Scheme ◽  
Temporal Correlations ◽  
Classical Thermodynamics ◽  
Work Done

The Leggett-Garg inequalities serve to test whether or not quantum correlations in time can be explained within a classical macrorealistic framework. We apply this test to thermodynamics and derive a set of Leggett-Garg inequalities for the statistics of fluctuating work done on a quantum system unitarily driven in time. It is shown that these inequalities can be violated in a driven two-level system, thereby demonstrating that there exists no general macrorealistic description of quantum work. These violations are shown to emerge within the standard Two-Projective-Measurement scheme as well as for alternative definitions of fluctuating work that are based on weak measurement. Our results elucidate the influences of temporal correlations on work extraction in the quantum regime and highlight a key difference between quantum and classical thermodynamics.

Broadband EM radiation amplification by means of a monochromatically driven two-level system

2017 ◽  
Vol 31 (04) ◽  
pp. 1750027 ◽  
Author(s):  
Andrey V. Soldatov
Keyword(s):  
Dipole Moment ◽  
Quantum System ◽  
High Frequency ◽  
Laser Field ◽  
Diagonal Matrix ◽  
Matrix Elements ◽  
Level System ◽  
Dipole Moment Operator ◽  
Moment Operator ◽  
Radiation Amplification

It is shown that a two-level quantum system possessing dipole moment operator with permanent non-equal diagonal matrix elements and driven by external semiclassical monochromatic high-frequency electromagnetic (EM) (laser) field can amplify EM radiation waves of much lower frequency.

LIMITATION ON THE ACCESSIBLE INFORMATION FOR QUANTUM CHANNELS WITH INEFFICIENT MEASUREMENTS

2005 ◽  
Vol 03 (supp01) ◽  
pp. 87-95
Author(s):  
KURT JACOBS
Keyword(s):  
Quantum System ◽  
Von Neumann Entropy ◽  
Quantum Channels ◽  
Initial State ◽  
Von Neumann ◽  
Classical Information ◽  
Quantum Operations ◽  
Amount Of Information ◽  
Accessible Information

To transmit classical information using a quantum system, the sender prepares the system in one of a set of possible states and sends it to the receiver. The receiver then makes a measurement on the system to obtain information about the senders choice of state. The amount of information which is accessible to the receiver depends upon the encoding and the measurement. Here we derive a bound on this information which generalizes the bound derived by Schumacher, Westmoreland and Wootters [Schumacher, Westmoreland and Wootters, Phys. Rev. Lett. 76, 3452 (1996)] to include inefficient measurements, and thus all quantum operations. This also allows us to obtain a generalization of a bound derived by Hall [Hall, Phys. Rev. A 55, 100 (1997)], and to show that the average reduction in the von Neumann entropy which accompanies a measurement is concave in the initial state, for all quantum operations.

The nonclassicality of a quantum system in weak measurement by means of modular values

2021 ◽  
Vol 68 (5) ◽  
pp. 295-301
Author(s):  
E. Rafiepoor ◽  
M. R. Bazrafkan ◽  
S. Batebi
Keyword(s):  
Quantum System ◽  
Weak Measurement

scholarly journals The shape of higher-dimensional state space: Bloch-ball analog for a qutrit

Quantum ◽  
2021 ◽  
Vol 5 ◽  
pp. 485
Author(s):  
Christopher Eltschka ◽  
Marcus Huber ◽  
Simon Morelli ◽  
Jens Siewert
Keyword(s):  
State Space ◽  
Quantum System ◽  
Dimensional Space ◽  
Three Dimensional ◽  
The State ◽  
Level System ◽  
Three Dimensional Model ◽  
System A ◽  
Dimensional State Space ◽  
Geometric Intuition

Geometric intuition is a crucial tool to obtain deeper insight into many concepts of physics. A paradigmatic example of its power is the Bloch ball, the geometrical representation for the state space of the simplest possible quantum system, a two-level system (or qubit). However, already for a three-level system (qutrit) the state space has eight dimensions, so that its complexity exceeds the grasp of our three-dimensional space of experience. This is unfortunate, given that the geometric object describing the state space of a qutrit has a much richer structure and is in many ways more representative for a general quantum system than a qubit. In this work we demonstrate that, based on the Bloch representation of quantum states, it is possible to construct a three dimensional model for the qutrit state space that captures most of the essential geometric features of the latter. Besides being of indisputable theoretical value, this opens the door to a new type of representation, thus extending our geometric intuition beyond the simplest quantum systems.

scholarly journals Many-Body Localization and the Emergence of Quantum Darwinism

Entropy ◽  
2021 ◽  
Vol 23 (11) ◽  
pp. 1377
Author(s):  
Nicolás Mirkin ◽  
Diego A. Wisniacki
Keyword(s):  
Quantum System ◽  
Entanglement Entropy ◽  
Redundant Information ◽  
Many Body ◽  
Initial State ◽  
Mobility Edge ◽  
Critical Degree ◽  
Quantum Darwinism ◽  
Effect Of Disorder ◽  
The Many

Quantum Darwinism (QD) is the process responsible for the proliferation of redundant information in the environment of a quantum system that is being decohered. This enables independent observers to access separate environmental fragments and reach consensus about the system’s state. In this work, we study the effect of disorder in the emergence of QD and find that a highly disordered environment is greatly beneficial for it. By introducing the notion of lack of redundancy to quantify objectivity, we show that it behaves analogously to the entanglement entropy (EE) of the environmental eigenstate taken as an initial state. This allows us to estimate the many-body mobility edge by means of our Darwinistic measure, implicating the existence of a critical degree of disorder beyond which the degree of objectivity rises the larger the environment is. The latter hints the key role that disorder may play when the environment is of a thermodynamic size. At last, we show that a highly disordered evolution may reduce the spoiling of redundancy in the presence of intra-environment interactions.

Vibrational resonance in a driven two-level quantum system, linear and nonlinear response

2021 ◽  
Vol 379 (2192) ◽  
pp. 20200231 ◽  
Author(s):  
Shibashis Paul ◽  
Deb Shankar Ray
Keyword(s):  
Quantum System ◽  
High Frequency ◽  
Second Harmonic ◽  
High Frequency Field ◽  
Level System ◽  
Vibrational Resonance ◽  
Frequency Field ◽  
Resonance Enhancement ◽  
Anti Stokes ◽  
Optimal Strength

We consider a two-level quantum system interacting with two classical time-periodic electromagnetic fields. The frequency of one of the fields far exceeds that of the other. The effect of the high-frequency field can be averaged out of the dynamics to realize an effective transition frequency of the field-dressed two-level system. We examine the linear response, second harmonic response and Stokes and anti-Stokes Raman response of the dressed two-level system, to the weak frequency field. The vibrational resonance enhancement in each case is demonstrated for optimal strength of the high-frequency field. Our theoretical scheme is corroborated by full numerical simulation of the two-level, two-field dynamics governed by loss-free Bloch equations. We suggest that quantum optics can offer an interesting arena for the study of the vibrational resonance. This article is part of the theme issue ‘Vibrational and stochastic resonance in driven nonlinear systems (part 1)’.

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