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Current Trends in Quantum Phase Transitions II

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

Deadline for manuscript submissions: closed (31 March 2024) | Viewed by 6386

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Special Issue Editor

Dr. Miguel A. Bastarrachea-Magnani

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Guest Editor

Department of Physics, Universidad Autónoma Metropolitana-Iztapalapa, Ciudad de México 09340, Mexico
Interests: light–matter interaction; exciton–polariton; quantum phase transitions; quantum chaos
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Special Issue Information

Dear Colleagues,

During the last three decades, the study of quantum phase transitions (QPTs) has been under continuous development, growing into a mature and well-established field. Identified as sudden changes in the ground-state properties of quantum systems as their parameters change, QPTs occur in a wide range of different setups, from atomic physics, quantum optics, and condensed matter to quantum information and cosmology. Consequently, their research has contributed to establishing connections across several fields of physics and unraveling new features in both few- and many-body quantum problems.

Thanks to the progress in new experimental, theoretical, and numerical tools, the concept of QPT has recently been extended to other domains, including excited states and nonequilibrium setups, where the understanding of critical phenomena such as excited-state quantum phase transitions (ESQPT) and dynamical phase transitions (DQPT) still poses challenges. Unquestionably, the field is fruitful, and several questions remain open about the relationship between quantum critical phenomena and several topics such as chaos, entanglement, localization, transport, thermal and informational effects, finite-size effects, out-of-equilibrium processes, and their role in the quantum-classical correspondence, among several others.

In this second volume of the Special Issue, we continue to review recent trends in the study of quantum phase transitions, covering but not restricted to the following areas:

*) Quantum phase transitions in novel systems;

*) Mean field and many-body techniques applied to the study of quantum phase transitions;

*) Excited-state quantum phase transitions (ESQPTs);

*) Nonequilibrium effects and dynamical quantum phase transitions (DPTs);

*) Transport and dynamic properties in the quantum critical region;

*) Chaos, localization, and quantum criticality;

*) Universality and quantum criticality.

Dr. Miguel A. Bastarrachea-Magnani
Guest Editor

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Published Papers (4 papers)

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23 pages, 2586 KiB

Open AccessArticle

Phase and Amplitude Modes in the Anisotropic Dicke Model with Matter Interactions

by Ricardo Herrera Romero and Miguel Angel Bastarrachea-Magnani

Entropy 2024, 26(7), 574; https://doi.org/10.3390/e26070574 - 3 Jul 2024

Viewed by 1300 | Correction

Abstract

Phase and amplitude modes, also called polariton modes, are emergent phenomena that manifest across diverse physical systems, from condensed matter and particle physics to quantum optics. We study their behavior in an anisotropic Dicke model that includes collective matter interactions. We study the low-lying spectrum in the thermodynamic limit via the Holstein–Primakoff transformation and contrast the results with the semi-classical energy surface obtained via coherent states. We also explore the geometric phase for both boson and spin contours in the parameter space as a function of the phases in the system. We unveil novel phenomena due to the unique critical features provided by the interplay between the anisotropy and matter interactions. We expect our results to serve the observation of phase and amplitude modes in current quantum information platforms. Full article

(This article belongs to the Special Issue Current Trends in Quantum Phase Transitions II)

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13 pages, 820 KiB

Open AccessFeature PaperArticle

Quantum Phase Transitions in a Generalized Dicke Model

by Wen Liu and Liwei Duan

Entropy 2023, 25(11), 1492; https://doi.org/10.3390/e25111492 - 29 Oct 2023

Cited by 2 | Viewed by 1854

Abstract

We investigate a generalized Dicke model by introducing two interacting spin ensembles coupled with a single-mode bosonic field. Apart from the normal to superradiant phase transition induced by the strong spin–boson coupling, interactions between the two spin ensembles enrich the phase diagram by introducing ferromagnetic, antiferromagnetic and paramagnetic phases. The mean-field approach reveals a phase diagram comprising three phases: paramagnetic–normal phase, ferromagnetic–superradiant phase, and antiferromagnetic–normal phase. Ferromagnetic spin–spin interaction can significantly reduce the required spin–boson coupling strength to observe the superradiant phase, where the macroscopic excitation of the bosonic field occurs. Conversely, antiferromagnetic spin–spin interaction can strongly suppress the superradiant phase. To examine higher-order quantum effects beyond the mean-field contribution, we utilize the Holstein–Primakoff transformation, which converts the generalized Dicke model into three coupled harmonic oscillators in the thermodynamic limit. Near the critical point, we observe the close of the energy gap between the ground and the first excited states, the divergence of entanglement entropy and quantum fluctuation in certain quadrature. These observations further confirm the quantum phase transition and offer additional insights into critical behaviors. Full article

(This article belongs to the Special Issue Current Trends in Quantum Phase Transitions II)

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20 pages, 1987 KiB

Open AccessArticle

Dynamical Quantum Phase Transitions of the Schwinger Model: Real-Time Dynamics on IBM Quantum

by Domenico Pomarico, Leonardo Cosmai, Paolo Facchi, Cosmo Lupo, Saverio Pascazio and Francesco V. Pepe

Entropy 2023, 25(4), 608; https://doi.org/10.3390/e25040608 - 3 Apr 2023

Cited by 14 | Viewed by 2204

Abstract

Simulating the real-time dynamics of gauge theories represents a paradigmatic use case to test the hardware capabilities of a quantum computer, since it can involve non-trivial input states’ preparation, discretized time evolution, long-distance entanglement, and measurement in a noisy environment. We implemented an algorithm to simulate the real-time dynamics of a few-qubit system that approximates the Schwinger model in the framework of lattice gauge theories, with specific attention to the occurrence of a dynamical quantum phase transition. Limitations in the simulation capabilities on IBM Quantum were imposed by noise affecting the application of single-qubit and two-qubit gates, which combine in the decomposition of Trotter evolution. The experimental results collected in quantum algorithm runs on IBM Quantum were compared with noise models to characterize the performance in the absence of error mitigation. Full article

(This article belongs to the Special Issue Current Trends in Quantum Phase Transitions II)

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