Exclusive Feature Papers of Quantum Reports in 2024–2025

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Wigner Research Centre for Physics, P.O. Box 49, 114, 1525 Budapest, Hungary
Interests: foundations; measurement and decoherence; quantum-to-classical transition; open systems; quantum information
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Dear Colleagues,

We are pleased to announce the new Special Issue “Exclusive Feature Papers of Quantum Reports in 2024–2025”, a collection of significant high-quality papers (original research articles or comprehensive review papers) published in an open access format by editorial board members or leading scholars invited by the editorial board and guest editors. This Special Issue aims to discuss emerging knowledge and new developments on the frontiers in the field of quantum science research via the publication of selected works that will, hopefully, greatly contribute to society. We hope that this Special Issue will serve as the best forum for disseminating outstanding research results and sharing innovative ideas in the field.

Prof. Dr. Lajos Diósi
Guest Editor

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Keywords

  • quantum mechanics
  • quantum field theory
  • quantum Information
  • quantum neural networks
  • quantum gravity
  • quantum computing
  • quantum optics
  • quantum chemistry
  • quantum biology
  • quantum device

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Related Special Issue

Published Papers (11 papers)

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Research

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11 pages, 297 KiB  
Article
Transition from Inflation to Dark Energy in Superfluid Vacuum Theory
by Konstantin G. Zloshchastiev
Quantum Rep. 2025, 7(1), 7; https://doi.org/10.3390/quantum7010007 (registering DOI) - 8 Feb 2025
Viewed by 190
Abstract
The laminar constant-velocity superflow of a physical vacuum modelled by logarithmic quantum Bose liquid is considered. We demonstrate that this three-dimensional non-relativistic quantum flow generates a four-dimensional relativistic quinton system, which comprises the dilaton and quintom (a combination of the quintessence and tachyonic [...] Read more.
The laminar constant-velocity superflow of a physical vacuum modelled by logarithmic quantum Bose liquid is considered. We demonstrate that this three-dimensional non-relativistic quantum flow generates a four-dimensional relativistic quinton system, which comprises the dilaton and quintom (a combination of the quintessence and tachyonic phantom fields); all three fields are thus shown to be projections of the dynamical evolution of superfluid vacuum density and its fluctuations onto the measuring apparatus of a relativistic observer. The unified model describes the transition from the inflationary period in the early universe to the contemporary accelerating expansion of the universe, commonly referred to as the “dark energy” period. The quintessence and tachyonic scalar components of the derived model turn out to be non-minimally coupled, which is a hitherto unexplored generalization of cosmological phantom models. Full article
(This article belongs to the Special Issue Exclusive Feature Papers of Quantum Reports in 2024–2025)
20 pages, 642 KiB  
Article
Decoherence, Locality, and Why dBB Is Actually MWI
by Per Arve
Quantum Rep. 2025, 7(1), 6; https://doi.org/10.3390/quantum7010006 - 31 Jan 2025
Viewed by 557
Abstract
In the de Broglie Bohm pilot-wave theory and the many-worlds interpretation, unitary development of the quantum state is universally valid. They differ in that de Broglie and Bohm assumed that there are point particles with positions that evolve in time and that our [...] Read more.
In the de Broglie Bohm pilot-wave theory and the many-worlds interpretation, unitary development of the quantum state is universally valid. They differ in that de Broglie and Bohm assumed that there are point particles with positions that evolve in time and that our observations are observations of the particles. The many-worlds interpretation is based on the fact that the quantum state can explain our observations. Both interpretations rely on the decoherence mechanism to explain the disappearance of interference effects at a measurement. From this fact, it is argued that for the pilot-wave theory to work, circumstances must be such that the many-worlds interpretation is a viable alternative. However, if this is the case, the de Broglie–Bohm particles become irrelevant to any observer. They are truly hidden. The violation of locality and the corresponding violation of Lorenz invariance are good reasons to believe that dBB particles do not exist. Full article
(This article belongs to the Special Issue Exclusive Feature Papers of Quantum Reports in 2024–2025)
63 pages, 3691 KiB  
Article
Contribution to the Statistical Mechanics of Static Triplet Correlations and Structures in Fluids with Quantum Spinless Behavior
by Luis M. Sesé
Quantum Rep. 2024, 6(4), 564-626; https://doi.org/10.3390/quantum6040038 - 3 Nov 2024
Viewed by 1013
Abstract
The current developments in the theory of quantum static triplet correlations and their associated structures (real r-space and Fourier k-space) in monatomic fluids are reviewed. The main framework utilized is Feynman’s path integral formalism (PI), and the issues addressed cover quantum [...] Read more.
The current developments in the theory of quantum static triplet correlations and their associated structures (real r-space and Fourier k-space) in monatomic fluids are reviewed. The main framework utilized is Feynman’s path integral formalism (PI), and the issues addressed cover quantum diffraction effects and zero-spin bosonic exchange. The structures are associated with the external weak fields that reveal their nature, and due attention is paid to the underlying pair-level structures. Without the pair, level one cannot fully grasp the triplet extensions in the hierarchical ladder of structures, as both the pair and the triplet structures are essential ingredients in the triplet response functions. Three general classes of PI structures do arise: centroid, total continuous linear response, and instantaneous. Use of functional differentiation techniques is widely made, and, as a bonus, this leads to the identification of an exact extension of the “classical isomorphism” when the centroid structures are considered. In this connection, the direct correlation functions, as borrowed from classical statistical mechanics, play a key role (either exact or approximate) in the corresponding quantum applications. Additionally, as an auxiliary framework, the traditional closure schemes for triplets are also discussed, owing to their potential usefulness for rationalizing PI triplet results. To illustrate some basic concepts, new numerical calculations (path integral Monte Carlo PIMC and closures) are reported. They are focused on the purely diffraction regime and deal with supercritical helium-3 and the quantum hard-sphere fluid. Full article
(This article belongs to the Special Issue Exclusive Feature Papers of Quantum Reports in 2024–2025)
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17 pages, 630 KiB  
Article
Quantum-Based Maximum Likelihood Detection in MIMO-NOMA Systems for 6G Networks
by Helen Urgelles, David Garcia-Roger and Jose F. Monserrat
Quantum Rep. 2024, 6(4), 533-549; https://doi.org/10.3390/quantum6040036 - 22 Oct 2024
Viewed by 1655
Abstract
As wireless networks advance toward the Sixth Generation (6G), which will support highly heterogeneous scenarios and massive data traffic, conventional computing methods may struggle to meet the immense processing demands in a resource-efficient manner. This paper explores the potential of quantum computing (QC) [...] Read more.
As wireless networks advance toward the Sixth Generation (6G), which will support highly heterogeneous scenarios and massive data traffic, conventional computing methods may struggle to meet the immense processing demands in a resource-efficient manner. This paper explores the potential of quantum computing (QC) to address these challenges, specifically by enhancing the efficiency of Maximum-Likelihood detection in Multiple-Input Multiple-Output (MIMO) Non-Orthogonal Multiple Access (NOMA) communication systems, an essential technology anticipated for 6G. The study proposes the use of the Quantum Approximate Optimization Algorithm (QAOA), a variational quantum algorithm known for providing quantum advantages in certain combinatorial optimization problems. While current quantum systems are not yet capable of managing millions of physical qubits or performing high-fidelity, long gate sequences, the results indicate that QAOA is a promising QC approach for radio signal processing tasks. This research provides valuable insights into the potential transformative impact of QC on future wireless networks. This sets the stage for discussions on practical implementation challenges, such as constrained problem sizes and sensitivity to noise, and opens pathways for future research aimed at fully harnessing the potential of QC for 6G and beyond. Full article
(This article belongs to the Special Issue Exclusive Feature Papers of Quantum Reports in 2024–2025)
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16 pages, 381 KiB  
Article
Ancilla-Mediated Higher Entanglement as T-Duality, a Categorial Conjecture
by Andrei T. Patrascu
Quantum Rep. 2024, 6(3), 493-508; https://doi.org/10.3390/quantum6030033 - 13 Sep 2024
Cited by 1 | Viewed by 1276
Abstract
In this article, I start with a general presentation of the ideas behind sigma models and higher gauge theories and introduce the possibility of a higher entanglement structure. Using a higher categorial interpretation of entanglement involving gauge theories and σ-models instead of [...] Read more.
In this article, I start with a general presentation of the ideas behind sigma models and higher gauge theories and introduce the possibility of a higher entanglement structure. Using a higher categorial interpretation of entanglement involving gauge theories and σ-models instead of qubits, one recovers T-duality as a form of ancilla aided entanglement generation. This opens the way towards new dualities in gauge theories and σ-models produced by means of analogies with quantum circuits of various types. Full article
(This article belongs to the Special Issue Exclusive Feature Papers of Quantum Reports in 2024–2025)
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17 pages, 377 KiB  
Article
Hidden Variables in Quantum Mechanics from the Perspective of Boltzmannian Statistical Mechanics
by Dustin Lazarovici
Quantum Rep. 2024, 6(3), 465-481; https://doi.org/10.3390/quantum6030031 - 6 Sep 2024
Viewed by 1174
Abstract
This paper examines no-hidden-variables theorems in quantum mechanics from the point of view of statistical mechanics. It presents a general analysis of the measurement process in the Boltzmannian framework that leads to a characterization of (in)compatible measurements and reproduces several features of quantum [...] Read more.
This paper examines no-hidden-variables theorems in quantum mechanics from the point of view of statistical mechanics. It presents a general analysis of the measurement process in the Boltzmannian framework that leads to a characterization of (in)compatible measurements and reproduces several features of quantum probabilities often described as “non-classical”. The analysis is applied to versions of the Kochen–Specker and Bell theorems to shed more light on their implications. It is shown how, once the measurement device and the active role of the measurement process are taken into account, contextuality appears as a natural feature of random variables. This corroborates Bell’s criticism that no-go results of the Kochen–Specker type are based on gratuitous assumptions. In contrast, Bell-type theorems are much more profound, but should be understood as nonlocality theorems rather than no-hidden-variables theorems. Finally, the paper addresses misunderstandings and misleading terminology that have confused the debate about hidden variables in quantum mechanics. Full article
(This article belongs to the Special Issue Exclusive Feature Papers of Quantum Reports in 2024–2025)
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35 pages, 986 KiB  
Article
Digital Quantum Simulation of Scalar Yukawa Coupling
by Thierry N. Kaldenbach, Matthias Heller, Gernot Alber and Vladimir M. Stojanović
Quantum Rep. 2024, 6(3), 366-400; https://doi.org/10.3390/quantum6030024 - 18 Jul 2024
Viewed by 1267
Abstract
Motivated by the revitalized interest in the digital simulation of medium- and high-energy physics phenomena, we investigate the dynamics following a Yukawa interaction quench on IBM Q. Adopting the zero-dimensional version of the scalar Yukawa coupling model as our point of departure, we [...] Read more.
Motivated by the revitalized interest in the digital simulation of medium- and high-energy physics phenomena, we investigate the dynamics following a Yukawa interaction quench on IBM Q. Adopting the zero-dimensional version of the scalar Yukawa coupling model as our point of departure, we design low-depth quantum circuits, emulating its dynamics with up to three bosons. In the one-boson case, we demonstrate circuit compression, i.e., a constant-depth circuit containing only two controlled-NOT (CNOT) gates. In the more complex three-boson case, we design a circuit in which one Trotter step entails eight CNOTs. Using an analogy with the traveling salesman problem, we also provide a CNOT cost estimate for higher boson number truncations. Based on these circuits, we quantify the system dynamics by evaluating the expected boson number at an arbitrary time after the quench and the survival probability of the initial vacuum state (the Loschmidt echo). We also utilize these circuits to drive adiabatic transitions and compute the energies of the ground- and first-excited states of the considered model. Finally, through error mitigation, i.e., zero-noise extrapolation, we demonstrate the good agreement of our results with a numerically exact classical benchmark. Full article
(This article belongs to the Special Issue Exclusive Feature Papers of Quantum Reports in 2024–2025)
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7 pages, 256 KiB  
Article
Quantum Theory of Lee–Naughton–Lebed’s Angular Effect in Strong Electric Fields
by Andrei G. Lebed
Quantum Rep. 2024, 6(3), 359-365; https://doi.org/10.3390/quantum6030023 - 17 Jul 2024
Viewed by 1119
Abstract
Some time ago, Kobayashi et al. experimentally studied the so-called Lee–Naughton–Lebed’s (LNL) angular effect in strong electric fields [Kobayashi, K.; Saito, M.; Omichi E.; Osada, T. Phys. Rev. Lett. 2006, 96, 126601]. They found that strong electric fields split the [...] Read more.
Some time ago, Kobayashi et al. experimentally studied the so-called Lee–Naughton–Lebed’s (LNL) angular effect in strong electric fields [Kobayashi, K.; Saito, M.; Omichi E.; Osada, T. Phys. Rev. Lett. 2006, 96, 126601]. They found that strong electric fields split the LNL conductivity maxima in an α-(ET)2-based organic conductor and hypothetically introduced the corresponding equation for conductivity. In this paper, for the first time, we suggest the quantum mechanical theory of the LNL angular oscillations in moderately strong electric fields. In particular, we demonstrate that the approximate theoretical formula obtained by us well describes the above mentioned experiments. Full article
(This article belongs to the Special Issue Exclusive Feature Papers of Quantum Reports in 2024–2025)
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31 pages, 2408 KiB  
Article
A Dyson Brownian Motion Model for Weak Measurements in Chaotic Quantum Systems
by Federico Gerbino, Pierre Le Doussal, Guido Giachetti and Andrea De Luca
Quantum Rep. 2024, 6(2), 200-230; https://doi.org/10.3390/quantum6020016 - 16 May 2024
Cited by 3 | Viewed by 1598
Abstract
We consider a toy model for the study of monitored dynamics in many-body quantum systems. We study the stochastic Schrödinger equation resulting from continuous monitoring with a rate Γ of a random Hermitian operator, drawn from the Gaussian unitary ensemble (GUE) at every [...] Read more.
We consider a toy model for the study of monitored dynamics in many-body quantum systems. We study the stochastic Schrödinger equation resulting from continuous monitoring with a rate Γ of a random Hermitian operator, drawn from the Gaussian unitary ensemble (GUE) at every time t. Due to invariance by unitary transformations, the dynamics of the eigenvalues {λα}α=1n of the density matrix decouples from that of the eigenvectors, and is exactly described by stochastic equations that we derive. We consider two regimes: in the presence of an extra dephasing term, which can be generated by imperfect quantum measurements, the density matrix has a stationary distribution, and we show that in the limit of large size n it matches with the inverse-Marchenko–Pastur distribution. In the case of perfect measurements, instead, purification eventually occurs and we focus on finite-time dynamics. In this case, remarkably, we find an exact solution for the joint probability distribution of λ’s at each time t and for each size n. Two relevant regimes emerge: at short times tΓ=O(1), the spectrum is in a Coulomb gas regime, with a well-defined continuous spectral distribution in the n limit. In that case, all moments of the density matrix become self-averaging and it is possible to exactly characterize the entanglement spectrum. In the limit of large times tΓ=O(n), one enters instead a regime in which the eigenvalues are exponentially separated log(λα/λβ)=O(Γt/n), but fluctuations O(Γt/n) play an essential role. We are still able to characterize the asymptotic behaviors of the entanglement entropy in this regime. Full article
(This article belongs to the Special Issue Exclusive Feature Papers of Quantum Reports in 2024–2025)
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12 pages, 4665 KiB  
Article
Spectral Analysis of Proton Eigenfunctions in Crystalline Environments
by Luca Gamberale and Giovanni Modanese
Quantum Rep. 2024, 6(2), 172-183; https://doi.org/10.3390/quantum6020014 - 6 May 2024
Cited by 1 | Viewed by 1044
Abstract
The Schrödinger equation and Bloch theorem are applied to examine a system of protons confined within a periodic potential, accounting for deviations from ideal harmonic behavior due to real-world conditions like truncated and non-quadratic potentials, in both one-dimensional and three-dimensional scenarios. Numerical computation [...] Read more.
The Schrödinger equation and Bloch theorem are applied to examine a system of protons confined within a periodic potential, accounting for deviations from ideal harmonic behavior due to real-world conditions like truncated and non-quadratic potentials, in both one-dimensional and three-dimensional scenarios. Numerical computation of the energy spectrum of bound eigenfunctions in both cases reveals intriguing structures, including bound states with degeneracy matching the site number Nw, reminiscent of a finite harmonic oscillator spectrum. In contrast to electronic energy bands, the proton system displays a greater number of possible bound states due to the significant mass of protons. Extending previous research, this study rigorously determines the constraints on the energy gap and oscillation amplitude of the previously identified coherent states. The deviations in energy level spacing identified in the computed spectrum, leading to the minor splitting of electromagnetic modes, are analyzed and found not to hinder the onset of coherence. Finally, a more precise value of the energy gap is determined for the proton coherent states, ensuring their stability against thermal decoherence up to the melting temperature of the hosting metal. Full article
(This article belongs to the Special Issue Exclusive Feature Papers of Quantum Reports in 2024–2025)
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Review

Jump to: Research

19 pages, 610 KiB  
Review
Improving the Solving of Optimization Problems: A Comprehensive Review of Quantum Approaches
by Deborah Volpe, Giacomo Orlandi and Giovanna Turvani
Quantum Rep. 2025, 7(1), 3; https://doi.org/10.3390/quantum7010003 - 7 Jan 2025
Viewed by 958
Abstract
Optimization is a crucial challenge across various domains, including finance, resource allocation, and mobility. Quantum computing has the potential to redefine the way we handle complex problems by reducing computational complexity and enhancing solution quality. Optimization, particularly of objective functions, stands to benefit [...] Read more.
Optimization is a crucial challenge across various domains, including finance, resource allocation, and mobility. Quantum computing has the potential to redefine the way we handle complex problems by reducing computational complexity and enhancing solution quality. Optimization, particularly of objective functions, stands to benefit significantly from quantum solvers, which leverage principles of quantum mechanics like superposition, entanglement, and tunneling. The Ising and Quadratic Unconstrained Binary Optimization (QUBO) models are the most suitable formulations for these solvers, involving binary variables and constraints treated as penalties within the overall objective function. To harness quantum approaches for optimization, two primary strategies are employed: exploiting quantum annealers—special-purpose optimization devices—and designing algorithms based on quantum circuits. This review provides a comprehensive overview of quantum optimization methods, examining their advantages, challenges, and limitations. It demonstrates their application to real-world scenarios and outlines the steps to convert generic optimization problems into quantum-compliant models. Lastly, it discusses available tools and frameworks that facilitate the exploration of quantum solutions for optimization tasks. Full article
(This article belongs to the Special Issue Exclusive Feature Papers of Quantum Reports in 2024–2025)
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