entropy-logo

Journal Browser

Journal Browser

Quantum Information and Quantum Optics

A special issue of Entropy (ISSN 1099-4300). This special issue belongs to the section "Quantum Information".

Deadline for manuscript submissions: closed (21 May 2022) | Viewed by 46348

Special Issue Editors

Department of Mathematics and Computer Science, University of Palermo, 90133 Palermo, PA, Italy
Interests: quantum electrodynamics; open systems; time dependent spin Hamiltonians; quantum and semiclassical Rabi models
Special Issues, Collections and Topics in MDPI journals
Department of Chemical Sciences, University of Padua, Via Francesco Marzolo, 1, 35131 Padova, PD, Italy
Interests: quantum chemistry; quantum dynamics in condensed phases; nanoscale electronics; charge, energy, and information transfer; matter–radiation interaction
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Quantum information is a steadily growing field of investigation in virtue of our increasing capability to observe and describe exquisite quantum effects appearing in diverse systems ranging from atomic and atom-radiation systems to complex chemical and biophysical systems. In all these systems, quantum information is produced by quantum coherence and, more specifically, by the quantum correlations inherent in their short-time coherent evolution. Conversely, the same quantum information framework is used to describe such correlations and determine their value in terms of information production and transfer, with potential applications of technological relevance. In fact, different entropy measures have been developed over the years to characterize quantum-type correlations, including quantum conditional entropy, mutual entropy, (relative) entropy of entanglement, and the strictly related entanglement of formation.

Quantum coherence plays a crucial role in quantum optics and could be used to convey quantum information. All fundamental models in the field of quantum optics imply the coherent evolution of quantum systems on appropriately short timescales. In fact, many non-classical features in the physical behavior of confined matter-radiation are attributable to the coherence inherent in the dynamic evolution of the system. A role for quantum correlations is clearly expected where even partial quantum coherence is involved in the time evolution of composite quantum systems.

Similarly, quantum coherence is critically important in a myriad of chemical and biological processes. Tunneling of electrons and protons are emblematic cases of coherence effects in charge and energy transfer reactions. Nontrivial quantum coherence effects have been highlighted, in recent years, by the evolution of spectroscopic techniques such as two-dimensional electronic spectroscopy. The application of such techniques has shown that, despite the disorder of chemical and biological systems, quantum correlations might survive long enough to influence their behavior. This observation has motivated the rapid growth of research that aims to use quantum coherence to enhance the function of biophysical systems. Within this framework, information theory concepts such as, e.g., the relative entropy of entanglement have been used to characterize the possible presence of quantum entanglement in photosynthetic systems.

We solicit contributions to this Special Issue of Entropy focused on the underlying role of quantum coherence in the abovementioned research areas, as well as on fruitful links among such areas, based on similar coherence effects and on their characterization and relevance in terms of quantum information.

Prof. Dr. Antonino Messina
Dr. Agostino Migliore
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Entropy is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • quantum information
  • quantum optics
  • quantum coherence
  • entanglement
  • entropy
  • 2D spectroscopy

Published Papers (21 papers)

Order results
Result details
Select all
Export citation of selected articles as:

Research

11 pages, 3187 KiB  
Article
Quantum Coherence in Loopless Superconductive Networks
by Massimiliano Lucci, Valerio Campanari, Davide Cassi, Vittorio Merlo, Francesco Romeo, Gaetano Salina and Matteo Cirillo
Entropy 2022, 24(11), 1690; https://doi.org/10.3390/e24111690 - 18 Nov 2022
Cited by 2 | Viewed by 1057
Abstract
Measurements indicating that planar networks of superconductive islands connected by Josephson junctions display long-range quantum coherence are reported. The networks consist of superconducting islands connected by Josephson junctions and have a tree-like topological structure containing no loops. Enhancements of superconductive gaps over specific [...] Read more.
Measurements indicating that planar networks of superconductive islands connected by Josephson junctions display long-range quantum coherence are reported. The networks consist of superconducting islands connected by Josephson junctions and have a tree-like topological structure containing no loops. Enhancements of superconductive gaps over specific branches of the networks and sharp increases in pair currents are the main signatures of the coherent states. In order to unambiguously attribute the observed effects to branches being embedded in the networks, comparisons with geometrically equivalent—but isolated—counterparts are reported. Tuning the Josephson coupling energy by an external magnetic field generates increases in the Josephson currents, along the above-mentioned specific branches, which follow a functional dependence typical of phase transitions. Results are presented for double comb and star geometry networks, and in both cases, the observed effects provide positive quantitative evidence of the predictions of existing theoretical models. Full article
(This article belongs to the Special Issue Quantum Information and Quantum Optics)
Show Figures

Figure 1

18 pages, 362 KiB  
Article
Symmetry-Induced Emergence of a Pseudo-Qutrit in the Dipolar Coupling of Two Qubits
by Yury Belousov, Vladimir I. Man’ko, Agostino Migliore, Alessandro Sergi and Antonino Messina
Entropy 2022, 24(2), 223; https://doi.org/10.3390/e24020223 - 31 Jan 2022
Cited by 2 | Viewed by 1927
Abstract
We investigate a system of two identical and distinguishable spins 1/2, with a direct magnetic dipole–dipole interaction, in an external magnetic field. Constraining the hyperfine tensor to exhibit axial symmetry generates the notable symmetry properties of the corresponding Hamiltonian model. In fact, we [...] Read more.
We investigate a system of two identical and distinguishable spins 1/2, with a direct magnetic dipole–dipole interaction, in an external magnetic field. Constraining the hyperfine tensor to exhibit axial symmetry generates the notable symmetry properties of the corresponding Hamiltonian model. In fact, we show that the reduction of the anisotropy induces the invariance of the Hamiltonian in the 3×3 subspace of the Hilbert space of the two spins in which S^2 invariably assumes its highest eigenvalue of 2. By means of appropriate mapping, it is then possible to choose initial density matrices of the two-spin system that evolve in such a way as to exactly simulate the time evolution of a pseudo-qutrit, in the sense that the the actual two-spin system nests the subdynamics of a qutrit regardless of the strength of the magnetic field. The occurrence of this dynamic similitude is investigated using two types of representation for the initial density matrix of the two spins. We show that the qutrit state emerges when the initial polarizations and probability vectors of the two spins are equal to each other. Further restrictions on the components of the probability vectors are reported and discussed. Full article
(This article belongs to the Special Issue Quantum Information and Quantum Optics)
9 pages, 3375 KiB  
Article
Quantum Entanglement of Monochromatic and Non-Monochromatic Photons on a Waveguide Beam Splitter
by Dmitry Makarov and Yuliana Tsykareva
Entropy 2022, 24(1), 49; https://doi.org/10.3390/e24010049 - 27 Dec 2021
Cited by 3 | Viewed by 2549
Abstract
It is well known that the waveguide beam splitter can be used as a source for the quantum entanglement of photons. The analysis of such quantum entanglement is a difficult problem even for monochromatic photons, since the system under study is multiparametric. This [...] Read more.
It is well known that the waveguide beam splitter can be used as a source for the quantum entanglement of photons. The analysis of such quantum entanglement is a difficult problem even for monochromatic photons, since the system under study is multiparametric. This paper will show that quantum entanglement can be represented in a simple form not only for monochromatic photons but also for non-monochromatic ones. It will be shown that quantum entanglement for non-monochromatic photons can be very different from monochromatic photons, which can be used to create large quantum entanglement. Full article
(This article belongs to the Special Issue Quantum Information and Quantum Optics)
Show Figures

Figure 1

14 pages, 1918 KiB  
Article
Entropic Uncertainty for Two Coupled Dipole Spins Using Quantum Memory under the Dzyaloshinskii–Moriya Interaction
by Ahmad N. Khedr, Abdel-Baset A. Mohamed, Abdel-Haleem Abdel-Aty, Mahmoud Tammam, Mahmoud Abdel-Aty and Hichem Eleuch
Entropy 2021, 23(12), 1595; https://doi.org/10.3390/e23121595 - 28 Nov 2021
Cited by 10 | Viewed by 1653
Abstract
In the thermodynamic equilibrium of dipolar-coupled spin systems under the influence of a Dzyaloshinskii–Moriya (D–M) interaction along the z-axis, the current study explores the quantum-memory-assisted entropic uncertainty relation (QMA-EUR), entropy mixedness and the concurrence two-spin entanglement. Quantum entanglement is reduced at increased [...] Read more.
In the thermodynamic equilibrium of dipolar-coupled spin systems under the influence of a Dzyaloshinskii–Moriya (D–M) interaction along the z-axis, the current study explores the quantum-memory-assisted entropic uncertainty relation (QMA-EUR), entropy mixedness and the concurrence two-spin entanglement. Quantum entanglement is reduced at increased temperature values, but inflation uncertainty and mixedness are enhanced. The considered quantum effects are stabilized to their stationary values at high temperatures. The two-spin entanglement is entirely repressed if the D–M interaction is disregarded, and the entropic uncertainty and entropy mixedness reach their maximum values for equal coupling rates. Rather than the concurrence, the entropy mixedness can be a proper indicator of the nature of the entropic uncertainty. The effect of model parameters (D–M coupling and dipole–dipole spin) on the quantum dynamic effects in thermal environment temperature is explored. The results reveal that the model parameters cause significant variations in the predicted QMA-EUR. Full article
(This article belongs to the Special Issue Quantum Information and Quantum Optics)
Show Figures

Figure 1

13 pages, 2881 KiB  
Article
Dissipation-Dependent Thermal Escape from a Potential Well
by Chungho Cheng, Matteo Cirillo and Niels Grønbech-Jensen
Entropy 2021, 23(10), 1315; https://doi.org/10.3390/e23101315 - 09 Oct 2021
Cited by 1 | Viewed by 1444
Abstract
Langevin simulations are conducted to investigate the Josephson escape statistics over a large set of parameter values for damping and temperature. The results are compared to both Kramers and Büttiker–Harris–Landauer (BHL) models, and good agreement is found with the Kramers model for high [...] Read more.
Langevin simulations are conducted to investigate the Josephson escape statistics over a large set of parameter values for damping and temperature. The results are compared to both Kramers and Büttiker–Harris–Landauer (BHL) models, and good agreement is found with the Kramers model for high to moderate damping, while the BHL model provides further good agreement down to lower damping values. However, for extremely low damping, even the BHL model fails to reproduce the progression of the escape statistics. In order to explain this discrepancy, we develop a new model which shows that the bias sweep effectively cools the system below the thermodynamic value as the potential well broadens due to the increasing bias. A simple expression for the temperature is derived, and the model is validated against direct Langevin simulations for extremely low damping values. Full article
(This article belongs to the Special Issue Quantum Information and Quantum Optics)
Show Figures

Figure 1

19 pages, 721 KiB  
Article
Coherent Superpositions of Photon Creation Operations and Their Application to Multimode States of Light
by Nicola Biagi, Saverio Francesconi, Alessandro Zavatta and Marco Bellini
Entropy 2021, 23(8), 999; https://doi.org/10.3390/e23080999 - 31 Jul 2021
Cited by 6 | Viewed by 2714
Abstract
We present a concise review of recent experimental results concerning the conditional implementation of coherent superpositions of single-photon additions onto distinct field modes. Such a basic operation is seen to give rise to a wealth of interesting and useful effects, from the generation [...] Read more.
We present a concise review of recent experimental results concerning the conditional implementation of coherent superpositions of single-photon additions onto distinct field modes. Such a basic operation is seen to give rise to a wealth of interesting and useful effects, from the generation of a tunable degree of entanglement to the birth of peculiar correlations in the photon numbers and the quadratures of multimode, multiphoton, states of light. The experimental investigation of these properties will have an impact both on fundamental studies concerning, for example, the quantumness and entanglement of macroscopic states, and for possible applications in the realm of quantum-enhanced technologies. Full article
(This article belongs to the Special Issue Quantum Information and Quantum Optics)
Show Figures

Figure 1

9 pages, 599 KiB  
Article
Strong Coupling Optomechanics Mediated by a Qubit in the Dispersive Regime
by Ahmad Shafiei Aporvari and David Vitali
Entropy 2021, 23(8), 966; https://doi.org/10.3390/e23080966 - 27 Jul 2021
Cited by 5 | Viewed by 2139
Abstract
Cavity optomechanics represents a flexible platform for the implementation of quantum technologies, useful in particular for the realization of quantum interfaces, quantum sensors and quantum information processing. However, the dispersive, radiation–pressure interaction between the mechanical and the electromagnetic modes is typically very weak, [...] Read more.
Cavity optomechanics represents a flexible platform for the implementation of quantum technologies, useful in particular for the realization of quantum interfaces, quantum sensors and quantum information processing. However, the dispersive, radiation–pressure interaction between the mechanical and the electromagnetic modes is typically very weak, harnessing up to now the demonstration of interesting nonlinear dynamics and quantum control at the single photon level. It has already been shown both theoretically and experimentally that if the interaction is mediated by a Josephson circuit, one can have an effective dynamics corresponding to a huge enhancement of the single-photon optomechanical coupling. Here we analyze in detail this phenomenon in the general case when the cavity mode and the mechanical mode interact via an off-resonant qubit. Using a Schrieffer–Wolff approximation treatment, we determine the regime where this tripartite hybrid system behaves as an effective cavity optomechanical system in the strong coupling regime. Full article
(This article belongs to the Special Issue Quantum Information and Quantum Optics)
Show Figures

Figure 1

14 pages, 488 KiB  
Article
Multilevel Laser Induced Continuum Structure
by Kaloyan Zlatanov and Nikolay Vitanov
Entropy 2021, 23(7), 891; https://doi.org/10.3390/e23070891 - 13 Jul 2021
Cited by 3 | Viewed by 1801
Abstract
Laser-induced-continuum-structure (LICS) allows for coherent control techniques to be applied in a Raman type system with an intermediate continuum state. The standard LICS problem involves two bound states coupled to one or more continua. In this paper, we discuss the simplest non-trivial multistate [...] Read more.
Laser-induced-continuum-structure (LICS) allows for coherent control techniques to be applied in a Raman type system with an intermediate continuum state. The standard LICS problem involves two bound states coupled to one or more continua. In this paper, we discuss the simplest non-trivial multistate generalization of LICS which couples two bound levels, each composed of two degenerate states through a common continuum state. We reduce the complexity of the system by switching to a rotated basis of the bound states, in which different sub-systems of lower dimension evolve independently. We derive the trapping condition and explore the dynamics of the sub-systems under different initial conditions. Full article
(This article belongs to the Special Issue Quantum Information and Quantum Optics)
Show Figures

Figure 1

25 pages, 1345 KiB  
Article
Entanglement Robustness via Spatial Deformation of Identical Particle Wave Functions
by Matteo Piccolini, Farzam Nosrati, Giuseppe Compagno, Patrizia Livreri, Roberto Morandotti and Rosario Lo Franco
Entropy 2021, 23(6), 708; https://doi.org/10.3390/e23060708 - 03 Jun 2021
Cited by 16 | Viewed by 3143
Abstract
We address the problem of entanglement protection against surrounding noise by a procedure suitably exploiting spatial indistinguishability of identical subsystems. To this purpose, we take two initially separated and entangled identical qubits interacting with two independent noisy environments. Three typical models of environments [...] Read more.
We address the problem of entanglement protection against surrounding noise by a procedure suitably exploiting spatial indistinguishability of identical subsystems. To this purpose, we take two initially separated and entangled identical qubits interacting with two independent noisy environments. Three typical models of environments are considered: amplitude damping channel, phase damping channel and depolarizing channel. After the interaction, we deform the wave functions of the two qubits to make them spatially overlap before performing spatially localized operations and classical communication (sLOCC) and eventually computing the entanglement of the resulting state. This way, we show that spatial indistinguishability of identical qubits can be utilized within the sLOCC operational framework to partially recover the quantum correlations spoiled by the environment. A general behavior emerges: the higher the spatial indistinguishability achieved via deformation, the larger the amount of recovered entanglement. Full article
(This article belongs to the Special Issue Quantum Information and Quantum Optics)
Show Figures

Figure 1

19 pages, 669 KiB  
Article
Semi-Classical Discretization and Long-Time Evolution of Variable Spin Systems
by Giovani E. Morales-Hernández, Juan C. Castellanos, José L. Romero and Andrei B. Klimov
Entropy 2021, 23(6), 684; https://doi.org/10.3390/e23060684 - 28 May 2021
Cited by 2 | Viewed by 2171
Abstract
We apply the semi-classical limit of the generalized SO(3) map for representation of variable-spin systems in a four-dimensional symplectic manifold and approximate their evolution terms of effective classical dynamics on T*S2. Using the asymptotic form [...] Read more.
We apply the semi-classical limit of the generalized SO(3) map for representation of variable-spin systems in a four-dimensional symplectic manifold and approximate their evolution terms of effective classical dynamics on T*S2. Using the asymptotic form of the star-product, we manage to “quantize” one of the classical dynamic variables and introduce a discretized version of the Truncated Wigner Approximation (TWA). Two emblematic examples of quantum dynamics (rotor in an external field and two coupled spins) are analyzed, and the results of exact, continuous, and discretized versions of TWA are compared. Full article
(This article belongs to the Special Issue Quantum Information and Quantum Optics)
Show Figures

Figure 1

10 pages, 358 KiB  
Article
Dynamical Localization Simulated on Actual Quantum Hardware
by Andrea Pizzamiglio, Su Yeon Chang, Maria Bondani, Simone Montangero, Dario Gerace and Giuliano Benenti
Entropy 2021, 23(6), 654; https://doi.org/10.3390/e23060654 - 23 May 2021
Cited by 7 | Viewed by 2032
Abstract
Quantum computers are invaluable tools to explore the properties of complex quantum systems. We show that dynamical localization of the quantum sawtooth map, a highly sensitive quantum coherent phenomenon, can be simulated on actual, small-scale quantum processors. Our results demonstrate that quantum computing [...] Read more.
Quantum computers are invaluable tools to explore the properties of complex quantum systems. We show that dynamical localization of the quantum sawtooth map, a highly sensitive quantum coherent phenomenon, can be simulated on actual, small-scale quantum processors. Our results demonstrate that quantum computing of dynamical localization may become a convenient tool for evaluating advances in quantum hardware performances. Full article
(This article belongs to the Special Issue Quantum Information and Quantum Optics)
Show Figures

Figure 1

19 pages, 314 KiB  
Article
Entropy of Quantum States
by Paolo Facchi, Giovanni Gramegna and Arturo Konderak
Entropy 2021, 23(6), 645; https://doi.org/10.3390/e23060645 - 21 May 2021
Cited by 4 | Viewed by 3008
Abstract
Given the algebra of observables of a quantum system subject to selection rules, a state can be represented by different density matrices. As a result, different von Neumann entropies can be associated with the same state. Motivated by a minimality property of the [...] Read more.
Given the algebra of observables of a quantum system subject to selection rules, a state can be represented by different density matrices. As a result, different von Neumann entropies can be associated with the same state. Motivated by a minimality property of the von Neumann entropy of a density matrix with respect to its possible decompositions into pure states, we give a purely algebraic definition of entropy for states of an algebra of observables, thus solving the above ambiguity. The entropy so-defined satisfies all the desirable thermodynamic properties and reduces to the von Neumann entropy in the quantum mechanical case. Moreover, it can be shown to be equal to the von Neumann entropy of the unique representative density matrix belonging to the operator algebra of a multiplicity-free Hilbert-space representation. Full article
(This article belongs to the Special Issue Quantum Information and Quantum Optics)
Show Figures

Figure 1

11 pages, 257 KiB  
Article
Invariant Quantum States of Quadratic Hamiltonians
by Viktor V. Dodonov
Entropy 2021, 23(5), 634; https://doi.org/10.3390/e23050634 - 19 May 2021
Cited by 13 | Viewed by 1989
Abstract
The problem of finding covariance matrices that remain constant in time for arbitrary multi-dimensional quadratic Hamiltonians (including those with time-dependent coefficients) is considered. General solutions are obtained. Full article
(This article belongs to the Special Issue Quantum Information and Quantum Optics)
10 pages, 255 KiB  
Article
Interpolating between Positive and Completely Positive Maps: A New Hierarchy of Entangled States
by Katarzyna Siudzińska, Sagnik Chakraborty and Dariusz Chruściński
Entropy 2021, 23(5), 625; https://doi.org/10.3390/e23050625 - 18 May 2021
Cited by 1 | Viewed by 1954
Abstract
A new class of positive maps is introduced. It interpolates between positive and completely positive maps. It is shown that this class gives rise to a new characterization of entangled states. Additionally, it provides a refinement of the well-known classes of entangled states [...] Read more.
A new class of positive maps is introduced. It interpolates between positive and completely positive maps. It is shown that this class gives rise to a new characterization of entangled states. Additionally, it provides a refinement of the well-known classes of entangled states characterized in terms of the Schmidt number. The analysis is illustrated with examples of qubit maps. Full article
(This article belongs to the Special Issue Quantum Information and Quantum Optics)
11 pages, 5081 KiB  
Article
Entanglement Dynamics Induced by a Squeezed Coherent Cavity Coupled Nonlinearly with a Qubit and Filled with a Kerr-Like Medium
by Abdel-Baset A. Mohamed and Hichem Eleuch
Entropy 2021, 23(5), 496; https://doi.org/10.3390/e23050496 - 21 Apr 2021
Cited by 3 | Viewed by 1591
Abstract
An analytical solution for a master equation describing the dynamics of a qubit interacting with a nonlinear Kerr-like cavity through intensity-dependent coupling is established. A superposition of squeezed coherent states is propped as the initial cavity field. The dynamics of the entangled qubit-cavity [...] Read more.
An analytical solution for a master equation describing the dynamics of a qubit interacting with a nonlinear Kerr-like cavity through intensity-dependent coupling is established. A superposition of squeezed coherent states is propped as the initial cavity field. The dynamics of the entangled qubit-cavity states are explored by negativity for different deformed function of the intensity-dependent coupling. We have examined the effects of the Kerr-like nonlinearity and the qubit-cavity detuning as well as the phase cavity damping on the generated entanglement. The intensity-dependent coupling increases the sensitivity of the generated entanglement to the phase-damping. The stability and the strength of the entanglement are controlled by the Kerr-like nonlinearity, the qubit-cavity detuning, and the initial cavity non-classicality. These physical parameters enhance the robustness of the qubit-cavity entanglement against the cavity phase-damping. The high initial cavity non-classicality enhances the robustness of the qubit-cavity entanglement against the phase-damping effect. Full article
(This article belongs to the Special Issue Quantum Information and Quantum Optics)
Show Figures

Figure 1

20 pages, 879 KiB  
Article
Entanglement and Non-Locality in Quantum Protocols with Identical Particles
by Fabio Benatti, Roberto Floreanini and Ugo Marzolino
Entropy 2021, 23(4), 479; https://doi.org/10.3390/e23040479 - 18 Apr 2021
Cited by 5 | Viewed by 2723
Abstract
We study the role of entanglement and non-locality in quantum protocols that make use of systems of identical particles. Unlike in the case of distinguishable particles, the notions of entanglement and non-locality for systems whose constituents cannot be distinguished and singly addressed are [...] Read more.
We study the role of entanglement and non-locality in quantum protocols that make use of systems of identical particles. Unlike in the case of distinguishable particles, the notions of entanglement and non-locality for systems whose constituents cannot be distinguished and singly addressed are still debated. We clarify why the only approach that avoids incongruities and paradoxes is the one based on the second quantization formalism, whereby it is the entanglement of the modes that can be populated by the particles that really matters and not the particles themselves. Indeed, by means of a metrological and of a teleportation protocol, we show that inconsistencies arise in formulations that force entanglement and non-locality to be properties of the identical particles rather than of the modes they can occupy. The reason resides in the fact that orthogonal modes can always be addressed while identical particles cannot. Full article
(This article belongs to the Special Issue Quantum Information and Quantum Optics)
13 pages, 546 KiB  
Article
Two-Qubit Local Fisher Information Correlation beyond Entanglement in a Nonlinear Generalized Cavity with an Intrinsic Decoherence
by A.-B. A. Mohamed, E. M. Khalil, M. F. Yassen and H. Eleuch
Entropy 2021, 23(3), 311; https://doi.org/10.3390/e23030311 - 06 Mar 2021
Cited by 3 | Viewed by 1709
Abstract
In this paper, we study a Hamiltonian system constituted by two coupled two-level atoms (qubits) interacting with a nonlinear generalized cavity field. The nonclassical two-qubit correlation dynamics are investigated using Bures distance entanglement and local quantum Fisher information under the influences of intrinsic [...] Read more.
In this paper, we study a Hamiltonian system constituted by two coupled two-level atoms (qubits) interacting with a nonlinear generalized cavity field. The nonclassical two-qubit correlation dynamics are investigated using Bures distance entanglement and local quantum Fisher information under the influences of intrinsic decoherence and qubit–qubit interaction. The effects of the superposition of two identical generalized coherent states and the initial coherent field intensity on the generated two-qubit correlations are investigated. Entanglement of sudden death and sudden birth of the Bures distance entanglement as well as the sudden changes in local Fisher information are observed. We show that the robustness, against decoherence, of the generated two-qubit correlations can be controlled by qubit–qubit coupling and the initial coherent cavity states. Full article
(This article belongs to the Special Issue Quantum Information and Quantum Optics)
Show Figures

Figure 1

11 pages, 383 KiB  
Article
Quantum Hacking on an Integrated Continuous-Variable Quantum Key Distribution System via Power Analysis
by Yi Zheng, Haobin Shi, Wei Pan, Quantao Wang and Jiahui Mao
Entropy 2021, 23(2), 176; https://doi.org/10.3390/e23020176 - 30 Jan 2021
Cited by 2 | Viewed by 1902
Abstract
In quantum key distribution (QKD), there are some security loopholes opened by the gaps between the theoretical model and the practical system, and they may be exploited by eavesdroppers (Eve) to obtain secret key information without being detected. This is an effective quantum [...] Read more.
In quantum key distribution (QKD), there are some security loopholes opened by the gaps between the theoretical model and the practical system, and they may be exploited by eavesdroppers (Eve) to obtain secret key information without being detected. This is an effective quantum hacking strategy that seriously threatens the security of practical QKD systems. In this paper, we propose a new quantum hacking attack on an integrated silicon photonic continuous-variable quantum key distribution (CVQKD) system, which is known as a power analysis attack. This attack can be implemented by analyzing the power originating from the integrated electrical control circuit in state preparation with the help of machine learning, where the state preparation is assumed to be perfect in initial security proofs. Specifically, we describe a possible power model and show a complete attack based on a support vector regression (SVR) algorithm. The simulation results show that the secret key information decreases with the increase of the accuracy of the attack, especially in a situation with less excess noise. In particular, Eve does not have to intrude into the transmitter chip (Alice), and may perform a similar attack in practical chip-based discrete-variable quantum key distribution (DVQKD) systems. To resist this attack, the electrical control circuit should be improved to randomize the corresponding power. In addition, the power can be reduced by utilizing the dynamic voltage and frequency scaling (DVFS) technology. Full article
(This article belongs to the Special Issue Quantum Information and Quantum Optics)
Show Figures

Figure 1

12 pages, 391 KiB  
Article
Wave-Particle Duality Relation with a Quantum Which-Path Detector
by Dongyang Wang, Junjie Wu, Jiangfang Ding, Yingwen Liu, Anqi Huang and Xuejun Yang
Entropy 2021, 23(1), 122; https://doi.org/10.3390/e23010122 - 18 Jan 2021
Cited by 3 | Viewed by 2436
Abstract
According to the relevant theories on duality relation, the summation of the extractable information of a quanton’s wave and particle properties, which are characterized by interference visibility V and path distinguishability D, respectively, is limited. However, this relation is violated upon quantum [...] Read more.
According to the relevant theories on duality relation, the summation of the extractable information of a quanton’s wave and particle properties, which are characterized by interference visibility V and path distinguishability D, respectively, is limited. However, this relation is violated upon quantum superposition between the wave-state and particle-state of the quanton, which is caused by the quantum beamsplitter (QBS). Along another line, recent studies have considered quantum coherence C in the l1-norm measure as a candidate for the wave property. In this study, we propose an interferometer with a quantum which-path detector (QWPD) and examine the generalized duality relation based on C. We find that this relationship still holds under such a circumstance, but the interference between these two properties causes the full-particle property to be observed when the QWPD system is partially present. Using a pair of polarization-entangled photons, we experimentally verify our analysis in the two-path case. This study extends the duality relation between coherence and path information to the quantum case and reveals the effect of quantum superposition on the duality relation. Full article
(This article belongs to the Special Issue Quantum Information and Quantum Optics)
Show Figures

Figure 1

10 pages, 375 KiB  
Article
The Influence of Signal Polarization on Quantum Bit Error Rate for Subcarrier Wave Quantum Key Distribution Protocol
by Andrei Gaidash, Anton Kozubov, Svetlana Medvedeva and George Miroshnichenko
Entropy 2020, 22(12), 1393; https://doi.org/10.3390/e22121393 - 09 Dec 2020
Cited by 2 | Viewed by 1875
Abstract
In this paper, we consider the influence of a divergence of polarization of a quantum signal transmitted through an optical fiber channel on the quantum bit error rate of the subcarrier wave quantum key distribution protocol. Firstly, we investigate the dependence of the [...] Read more.
In this paper, we consider the influence of a divergence of polarization of a quantum signal transmitted through an optical fiber channel on the quantum bit error rate of the subcarrier wave quantum key distribution protocol. Firstly, we investigate the dependence of the optical power of the signal on the modulation indices’ difference after the second phase modulation of the signal. Then we consider the Liouville equation with regard to relaxation in order to develop expressions of the dynamics of the Stokes parameters. As a result, we propose a model that describes quantum bit error rate for the subcarrier wave quantum key distribution depending on the characteristics of the optical fiber. Finally, we propose several methods for minimizing quantum bit error rate. Full article
(This article belongs to the Special Issue Quantum Information and Quantum Optics)
Show Figures

Figure 1

11 pages, 1796 KiB  
Article
Analysis of Controlled Rabi Flopping in a Double Rephasing Photon Echo Scheme for Quantum Memories
by Rahmat Ullah and Byoung S. Ham
Entropy 2020, 22(9), 1007; https://doi.org/10.3390/e22091007 - 09 Sep 2020
Viewed by 1983
Abstract
A double rephasing scheme of a photon echo is analyzed for inversion-free photon echo-based quantum memories using controlled Rabi flopping, where the Rabi flopping is used for phase control of collective atom coherence. Unlike the rephasing-caused π-phase shift in a single rephasing scheme, [...] Read more.
A double rephasing scheme of a photon echo is analyzed for inversion-free photon echo-based quantum memories using controlled Rabi flopping, where the Rabi flopping is used for phase control of collective atom coherence. Unlike the rephasing-caused π-phase shift in a single rephasing scheme, the control Rabi flopping between the excited state and an auxiliary third state induces coherence inversion. Thus, the absorptive photon echo in a double rephasing scheme can be manipulated to be emissive. Here, we present a quantum coherence control of atom phases in a double rephasing photon echo scheme for emissive photon echoes for quantum memory applications. Full article
(This article belongs to the Special Issue Quantum Information and Quantum Optics)
Show Figures

Figure 1

Back to TopTop