Quantum Systems and Their Applications

Journal Name	Impact Factor	CiteScore	Launched Year	First Decision (median)	APC
Entropy entropy	2.1	4.9	1999	20.9 Days	CHF 2600	Submit
Physics physics	1.4	3.5	2019	34.9 Days	CHF 1400	Submit
Quantum Reports quantumrep	1.8	2.7	2019	20.3 Days	CHF 1400	Submit
Symmetry symmetry	2.2	5.2	2009	16.3 Days	CHF 2400	Submit
Universe universe	2.5	5.0	2015	20.8 Days	CHF 1600	Submit

18 pages, 324 KB

Open AccessArticle

Geometry of State-Update Processes and Wave Function Collapse

by Angelo Plastino

Quantum Rep. 2026, 8(2), 48; https://doi.org/10.3390/quantum8020048 - 15 May 2026

Viewed by 380

We develop an information-geometric framework for describing quantum state-update processes associated with measurement and statistical distinguishability. The approach is based on the quantum relative entropy and the quantum Fisher information metric, which together induce a natural Riemannian geometry on the manifold of quantum [...] Read more.

We develop an information-geometric framework for describing quantum state-update processes associated with measurement and statistical distinguishability. The approach is based on the quantum relative entropy and the quantum Fisher information metric, which together induce a natural Riemannian geometry on the manifold of quantum states. Using the second-order expansion of relative entropy, we show how the Fisher metric governs the local structure of distinguishability between nearby states and defines a corresponding thermodynamic length. This geometric structure provides an effective description of finite quantum state transitions in terms of fluctuation geometry and information-space distance. The formalism is applied to thermal two-level systems and harmonic oscillator states, illustrating how the Fisher metric encodes susceptibilities, fluctuations, and geometric transition costs. We also discuss the relation between thermodynamic length, dissipation bounds, and optimal paths in state space. Within this framework, wave function collapse is interpreted not as a microscopic dynamical mechanism, but as an effective state-update process that admits a geometric characterization in the manifold of density operators. The resulting perspective unifies concepts from quantum information theory, thermodynamics, and differential geometry within a common operational framework based on statistical distinguishability. Possible connections with quantum speed limits, entanglement geometry, and holographic relations between relative entropy and gravitational dynamics are briefly discussed. Full article

(This article belongs to the Topic Quantum Systems and Their Applications)

14 pages, 1941 KB

Open AccessArticle

Continuous-Variable Quantum Secret Sharing Through Microwave-Enabled Turbulent Channels with Measurement-Device-Independent Scheme

by Weihan Zhang, Zhangtao Liang, Yun Mao, Hang Zhang and Ying Guo

Entropy 2026, 28(5), 540; https://doi.org/10.3390/e28050540 - 10 May 2026

Viewed by 290

Abstract

Quantum secret sharing (QSS) has been previously demonstrated with conceivability in optical-fiber channels. However, extending this framework to the microwave frequency band presents challenges in achieving secure quantum communications over turbulent channels, as intricate turbulence can induce amplitude and phase jitter in quantum [...] Read more.

Quantum secret sharing (QSS) has been previously demonstrated with conceivability in optical-fiber channels. However, extending this framework to the microwave frequency band presents challenges in achieving secure quantum communications over turbulent channels, as intricate turbulence can induce amplitude and phase jitter in quantum signals, leading to decoherence or even interruptions in the communication link. In this work, we propose a microwave-enabled continuous-variable quantum secret sharing (CVQSS) scheme operating over turbulent free-space channels. The protocol explicitly addresses the extreme sensitivity of microwave quantum states to environmental turbulence, which manifests as severe amplitude and phase fluctuations. It incorporates the Shamir threshold scheme to facilitate multi-user secret sharing. We suggest a flexible approach to solving problems of adaptive phase compensation and multi-aperture reception techniques when characterizing an equivalent noise channel based on the Kolmogorov turbulence model. The proposed measurement-device-independent (MDI) architecture renders the protocol immune to all detector-side attacks, provided that the state preparation at the users’ side is trusted. Numerical simulations ascertain the performance of the microwave continuous-variable measurement-device-independent quantum secret sharing (CV-MDI-QSS) system and demonstrate the feasibility of practical deployment in complicated turbulent channels. This approach offers a turbulence-resistant solution for dynamic quantum networks through harsh free-space channels implemented in microwave-propagated environments. Full article

(This article belongs to the Topic Quantum Systems and Their Applications)

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17 pages, 649 KB

Open AccessArticle

A Two-Step Quantum Approximate Optimization Algorithm for Portfolio Optimization and Risk Assessment

by Boxuan Wu and Lei Wang

Quantum Rep. 2026, 8(2), 45; https://doi.org/10.3390/quantum8020045 - 7 May 2026

Viewed by 1036

Abstract

Quantum finance represents a pivotal and cutting-edge application domain within the burgeoning field of quantum computing. In this work, we propose a two-step quantum approximate optimization algorithm (two-step QAOA) for portfolio optimization and risk assessment. The algorithm initiates by formulating the stock selection [...] Read more.

Quantum finance represents a pivotal and cutting-edge application domain within the burgeoning field of quantum computing. In this work, we propose a two-step quantum approximate optimization algorithm (two-step QAOA) for portfolio optimization and risk assessment. The algorithm initiates by formulating the stock selection problem as a quadratic unconstrained binary optimization (QUBO) problem and employs a classical-quantum hybrid method to find the ground state of the Hamiltonian. We then introduce an energy-based characteristic indicator

U \in [0, 1)

, which quantitatively evaluates portfolio performance under customizable investment preferences, effectively capturing the trade-off between expected return and risk. The number of qubits required scales with the number of stocks N in the pool, and the number of Hamiltonian terms is

O (N^{2})

. Numerical simulations show that the algorithm provides consistent and reasonable assessment results on both training and test datasets under different investment preferences (aggressive or conservative), validating the capability of the characteristic indicator to extract intrinsic information from the portfolios. Additionally, by incorporating warm-starting and digitized counterdiabatic techniques, the algorithm achieves improved scalability and faster convergence. Our work presents a flexible and practical algorithmic framework for applying quantum computing in the financial domain. Full article

(This article belongs to the Topic Quantum Systems and Their Applications)

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13 pages, 2272 KB

Open AccessArticle

Enhancement of the Shift in the Photonic Spin Hall Effect and Its Application for Cancer Cell Detection

by Alka Verma, Devanshi Katiyar, Vimal Mishra, Rajeev Gupta and Yogendra Kumar Prajapati

Quantum Rep. 2026, 8(1), 17; https://doi.org/10.3390/quantum8010017 - 17 Feb 2026

Viewed by 1060

Abstract

The photonic spin Hall effect (PSHE) originates from the spin–orbit interaction (SOI) of light. The literature indicates that the transverse spin-dependent shift,

δ_{H}^{-}

(SDS), from the PSHE is weak (in the nanometer range) and difficult to measure directly. This study utilizes [...] Read more.

The photonic spin Hall effect (PSHE) originates from the spin–orbit interaction (SOI) of light. The literature indicates that the transverse spin-dependent shift,

δ_{H}^{-}

(SDS), from the PSHE is weak (in the nanometer range) and difficult to measure directly. This study utilizes a plasmonic structure to improve the

δ_{H}^{-}

in the PSHE. The obtained results of this study demonstrate that the inclusion of silicon nitride (Si₃N₄) significantly enhances the

δ_{H}^{-}

relative to its absence; however, plasmonic material is present in both cases. The enhanced shifts exhibit a significant dependence on the resonance angle (

θ_{r}

) and the thickness of layers of the PSHE structure to attain the maximum increase in

δ_{H}^{-}

of 350.82 µm at the plasmonic resonance condition. A systematic analysis of the centroid positions of the reflected beam indicates a distinct and constant separation of opposing spin components. Further, the improved

δ_{H}^{-}

is utilized in cancer cell detection, as changes in the refractive index (RI) of cells facilitate the identification of cancer cells from healthy to cancerous. All examined cell types demonstrate that cancerous cells had a greater

δ_{H}^{-}

than normal cells, owing to their elevated effective RI. These results illustrate that the proposed plasmonic-assisted PSHE structure offers significant enhancement and a high sensitivity of 439.30 µm/RIU for label-free detection of cancer cells. Full article

(This article belongs to the Topic Quantum Systems and Their Applications)

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41 pages, 15832 KB

Open AccessReview

Applications of Gaussian Boson Sampling to Solve Some Chemistry Problems

by Samaneh Bagheri Novir

Quantum Rep. 2025, 7(4), 56; https://doi.org/10.3390/quantum7040056 - 28 Nov 2025

Viewed by 3035

Abstract

Quantum computers, due to their superposition and entanglement properties, provide significant advantages in solving certain problems compared with classical computers. Therefore, it is crucial to identify issues that can be efficiently solved by noisy intermediate-scale quantum (NISQ) systems. Xanadu has introduced the X8 [...] Read more.

Quantum computers, due to their superposition and entanglement properties, provide significant advantages in solving certain problems compared with classical computers. Therefore, it is crucial to identify issues that can be efficiently solved by noisy intermediate-scale quantum (NISQ) systems. Xanadu has introduced the X8 quantum chip, based on integrated photonic technology, along with important photonic platforms such as Strawberry Fields and Gaussian Boson Sampling (GBS), to solve specific computational problems. In this review article, after reviewing Boson Sampling (BS) and Gaussian Boson Sampling (GBS), we discuss the relationship between GBS and graph theory, including how graphs can be encoded in GBS. Some applications of GBS, particularly molecular docking and molecular vibrations, are also considered. The future goal of this study is to identify problems that can be represented as small graphs and solved using GBS with a limited number of optical modes. Full article

(This article belongs to the Topic Quantum Systems and Their Applications)

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16 pages, 858 KB

Open AccessArticle

Many-Body Effects in a Molecular Quantum NAND Tree

by Justin P. Bergfield

Quantum Rep. 2025, 7(4), 45; https://doi.org/10.3390/quantum7040045 - 10 Oct 2025

Viewed by 1407

Abstract

Molecules provide the smallest possible circuits in which quantum interference and electron correlation can be engineered to perform logical operations, including the universal NAND gate. We investigate a chemically encoded quantum NAND tree based on alkynyl-extended iso-polyacetylene backbones, where inputs are set by [...] Read more.

Molecules provide the smallest possible circuits in which quantum interference and electron correlation can be engineered to perform logical operations, including the universal NAND gate. We investigate a chemically encoded quantum NAND tree based on alkynyl-extended iso-polyacetylene backbones, where inputs are set by end-group substitution and outputs are read from the presence or absence of transmission nodes. Using quantum many-body transport theory, we show that NAND behavior persists in the presence of dynamic correlations, but that the nodal positions and their chemical shifts depend sensitively on electron–electron interactions. This sensitivity highlights the potential of these systems not only to probe the strength of electronic correlations but also to harness them in shaping logical response. The thermopower is identified as a chemically robust readout of gate logic, providing discrimination margins that greatly exceed typical experimental uncertainties, in an observable governed primarily by the variation of transport rather than its absolute magnitude. Full article

(This article belongs to the Topic Quantum Systems and Their Applications)

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25 pages, 2158 KB

Open AccessArticle

Parametric Resonance via Neuronal Microtubules: Filtering Optical Signals by Tryptophan Qubits

by Akihiro Nishiyama, Shigenori Tanaka and Jack Adam Tuszynski

Quantum Rep. 2025, 7(3), 43; https://doi.org/10.3390/quantum7030043 - 17 Sep 2025

Cited by 3 | Viewed by 4140

Abstract

This paper aims to address the possibility of parametric resonance effects in microtubules via tryptophan qubits, using the Hamiltonian of the cavity quantum electrodynamics (QED) model involving photons in a waveguide and the surrounding environment. The time evolution equations for qubits and photons [...] Read more.

This paper aims to address the possibility of parametric resonance effects in microtubules via tryptophan qubits, using the Hamiltonian of the cavity quantum electrodynamics (QED) model involving photons in a waveguide and the surrounding environment. The time evolution equations for qubits and photons are derived using the input–output formulation. Input signals with a 560 nm wavelength are amplified by Rabi oscillations for tryptophan qubits in excited states. Here, the qubits organized in multiple layers are all in excited states. When an appropriate decay to the environment occurs as internal loss, which is prepared in multiple layers, we find binary patterns of the parametric amplification of input signals and the reduction of output signals. This property might help us to understand the information processing of optical signals by filtering them with the use of tryptophan residues in microtubules and diffused nonlocal processing spreading over the whole brain in the form of holograms. Full article

(This article belongs to the Topic Quantum Systems and Their Applications)

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9 pages, 406 KB

Open AccessArticle

A Proposed Test for the Gravitational Tunnel Effect

by Alfonso González Jiménez, Enderson Falcón Gómez, Isabel Carnoto Amat and Luis Enrique García Muñoz

Universe 2025, 11(9), 291; https://doi.org/10.3390/universe11090291 - 28 Aug 2025

Viewed by 1166

Abstract

This article addresses the problem of the tunnel effect with a gravitational potential. Specifically, the quasiclassical formulation is used here, and the Wentzel–Kramers–Brillouin approximation is applied to the potential. This allows the problem to be solved for different configurations with different values (masses, [...] Read more.

This article addresses the problem of the tunnel effect with a gravitational potential. Specifically, the quasiclassical formulation is used here, and the Wentzel–Kramers–Brillouin approximation is applied to the potential. This allows the problem to be solved for different configurations with different values (masses, distances, etc.). The chosen values are intended to provide a clear comparison when varying the different parameters. Furthermore, feasible values are considered for practically replicating the experiment without resorting to astrophysical methods. Due to the low intensity of the gravitational force, these experiments will be difficult to replicate, but it is possible to improve some parameters at the expense of others. Full article

(This article belongs to the Topic Quantum Systems and Their Applications)

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18 pages, 912 KB

Open AccessArticle

A Guiding Principle for Quantum State Discrimination in the Real-Spectrum Phase of P-Pseudo-Hermitian Systems

by Qinliang Dong, Xueer Gao, Zhihang Liu, Hui Li, Jingwei Wen and Chao Zheng

Entropy 2025, 27(8), 836; https://doi.org/10.3390/e27080836 - 6 Aug 2025

Cited by 6 | Viewed by 1288

Abstract

Quantum state discrimination (QSD) is a fundamental task in quantum information processing, improving the computation efficiency and communication security. Non-Hermitian (NH) PT-symmetric systems were found to be able to discriminate two quantum states better than the Hermitian strategy. In this work, we propose [...] Read more.

Quantum state discrimination (QSD) is a fundamental task in quantum information processing, improving the computation efficiency and communication security. Non-Hermitian (NH) PT-symmetric systems were found to be able to discriminate two quantum states better than the Hermitian strategy. In this work, we propose a QSD approach based on P-pseudo-Hermitian systems with real spectra. We theoretically prove the feasibility of realizing QSD in the real-spectrum phase of a P-pseudo-Hermitian system, i.e., two arbitrary non-orthogonal quantum states can be discriminated by a suitable P-pseudo-Hermitian Hamiltonian. In detail, we decide the minimal angular separation between two non-orthogonal quantum states for a fixed P-pseudo-Hermitian Hamiltonian, and we find the orthogonal evolution time is able to approach zero under suitable conditions, while both the trace distance and the quantum relative entropy are employed to judge their orthogonality. We give a criterion to choose the parameters of a P-pseudo-Hermitian Hamiltonian that evolves the two initial orthogonal states faster than a fixed arbitrary PT-symmetric one with an identical energy difference. Our work expands the NH family for QSD, and can be used to explore real quantum systems in the future. Full article

(This article belongs to the Topic Quantum Systems and Their Applications)

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15 pages, 712 KB

Open AccessArticle

Extracting Correlations in Arbitrary Diagonal Quantum States via Weak Couplings and Auxiliary Systems

by Hui Li, Chao Zheng, Yansong Li and Xian Lu

Symmetry 2025, 17(8), 1233; https://doi.org/10.3390/sym17081233 - 4 Aug 2025

Cited by 1 | Viewed by 922

Abstract

In this work, we introduce a novel method to extract correlations in diagonal quantum states in multi-particle quantum systems, addressing a significant limitation of traditional approaches that require prior knowledge of the density matrices of quantum states. Instead of relying on classical information [...] Read more.

In this work, we introduce a novel method to extract correlations in diagonal quantum states in multi-particle quantum systems, addressing a significant limitation of traditional approaches that require prior knowledge of the density matrices of quantum states. Instead of relying on classical information processing, our method is based on weak couplings and ancillary systems, eliminating the need for classical communication, optimization, and complex calculations. The concept of mutually unbiased bases is intrinsically linked to symmetry, as it entails the uniform distribution of quantum states across distinct bases. Within the framework of our theoretical model, mutually unbiased bases are employed to facilitate weak measurements and to function as the post-selected states. To quantify the correlations in the initial state, we employ the trace distance between the initial state and the product of its marginal states, and illustrate the feasibility and effectiveness of our approach. We generalize the approach to accommodate high-dimensional multi-particle systems for potential applications in quantum information processing and quantum networks. Full article

(This article belongs to the Topic Quantum Systems and Their Applications)

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