Xi-Wen Guan graduated from Jilin University, China, in 1998, followed by three years of postdoctoral research in Germany and Brazil. From 2002 to 2008, he was  a Research Fellow at the Australian National University (ANU), and as a Level C Fellow there from 2009 to 2013. After leaving ANU, he joined the Innovation Academy for Precision Measurement Science and Technology (APM), Chinese Academy of Sciences, as a Full Professor of Physics. Since 2016, he has held an Honorary Professorship at the ANU. In 2014, he was appointed the C N Yang Visiting Fellow at the Chinese University of Hong Kong.  He has chaired 4 national key research grants  in China and received multiple awards, including 4 Research Breakthrough Prizes, the Outstanding Talent Award at APM, and the 2024 First Prize of Hubei Provincial Natural Science. In 2024, he was elected a Fellow of the American Physical Society (APS).

2011–2020: Advisory Panel, Journal of Physics A; 2020–2022: Board Editor, Journal of Physics A; 2023–present: Executive Board Editor, Journal of Physics A.Currently, he serves as a Committee Member of the International Union of Pure and Applied Physics (IUPAP) Mathematical Physics Commission (C18).

Guan's  research involves the study of  exactly solvable models, quantum degenerate gases, low dimensional spin materials, strongly correlated electronic systems and quantum impurity problems.  He has   made a number of  original  contributions in these fields, which have led to direct applications in recent breakthrough experiments on one-dimensional many-body systems. He has published over 150 SCI papers in exactly solvable models, ultracold atoms, and condensed matter physics, including in journals such as Science, Review  Modern  Physics,  Advances in  Physics, Report on Progress in Physics, NPJ  Quantum Information, National Science Review, Nature Communications, Physical  Review  Letters, Phys. Rev. A/B,  etc.   His work has contributed to recent experimental observations of novel phenomena, including super Tonks gases, Wilson ratios, criticality, Luttinger liquids, and spin-charge separation.

Since returning to China in 2022, he has led his research group for over a decade to profoundly uncover the microscopic nature of quantum many-body phenomena. He has guided experiments to achieve the world’s first definitive experimental verification of spin-charge separation, Tomonaga-Luttinger liquids, incoherent liquid theory, and quantum critical phenomena, addressing several long-standing challenges in the field that have drawn widespread attention for more than 40 years. His work has essentially  expanded the application scope of exactly solvable models and further advanced their critical applications in quantum technology.

1. Exactly solvable models in cold atoms, strongly correlated electron systems,  spin chains, vertex models,  spin ladder compounds. 
2. Haldane exclusion statistics, Tomonaga-Luttinger liquids, quantum criticality and quantum correlation functions. 
3. Quantum metrology, quantum information.
4. Quantum algebra, quantum groups, open boundary quantum inverse scattering method, quantum transfer matrix.  

Xi-Wen Guan’s Research Highlight

Quantum Integrable models
Quantum integrable systems have a research history of over 80 years and have found extremely important applications in both physics and mathematics. Among their key developments, the discovery of the Yang-Baxter equation plays a crucial role in solving significant quantum many-body problems, studying two-dimensional statistical models, and advancing research on quantum groups and conformal field theory in mathematics. Particularly in recent years, the realization of one-dimensional ultracold Bose and Fermi gases, along with breakthrough experiments on quantum critical phenomena, has provided a new means to better understand quantum statistics and correlation effects in quantum many-body systems. In recent years, experimental results in one-dimensional quantum many-body physics have verified the predictions of Yang-Baxter exactly solvable models.

Research and Academic Achievements

In January 2013, Guan established the Quantum Integrable Systems Research Group at the Wuhan Institute of Physics and Mathematics, Chinese Academy of Sciences. The group’s research focuses on the exact solutions of low-dimensional quantum many-body systems and the applications of integrable systems in ultracold atomic gases, spin liquids, strongly correlated electron systems, Kondo physics, and statistical physics—covering studies on fractional statistics, Luttinger liquid theory, quantum critical phenomena, and related thermodynamic properties.

In recent years, Guan has been engaged in cutting-edge research on quantum integrable systems, achieving significant results in exactly solvable models related to ultracold atomic gases, spin liquids, and strongly correlated electrons. He has applied mathematical physics models to address realistic  problems in ultracold atomic physics and condensed matter physics, with several of his theoretical predictions validated by important experiments in recent years. These include predictions on super Tonks-Girardeau gases, novel Yang-Gaudin quantum pairing states, spin-charge separation, Luther-Emery liquid, 1D  generalized hydrodynamics, measurements of dynamic response functions, quantum magnetism in 1D spin materials, integrable quantum field theory, non-equilibrium thermodynamics, and cavity QED systems. Additionally, another key research direction involves quantum criticality, and dynamic problems in one-dimensional systems.

In recognition of these important achievements, Guan, together with his collaborators Professor Murray T. Batchelor and Professor Chaohong Lee, was invited to publish a review article on one-dimensional integrable Fermi gas systems in the world-renowned journal Reviews of Modern Physics [Rev. Mod. Phys. 85, 1633 (2013)]. The article elaborates in detail on the novel quantum many-body phenomena described by exactly solvable models, providing crucial guidances and references for theoretical and experimental research in this field. To date, it has become one of the most influential review papers on quantum exact solution theory in the field.

Paper  link:https://journals.aps.org/rmp/abstract/10.1103/RevModPhys.85.1633

In addition, in 2022, Guan and Dr. Peng He were invited to publish a progress report titled "New Trends in Quantum Integrability: Recent Experiments with Ultracold Atoms" in Report on Progress in Physics.  In this report, they elaborated in depth on the latest advancements in 1D experiments, including quantum holonomy, spin-charge separation, Luttinger liquids, critical phenomena, Haldane fractional quantum statistics, collective excitations, Fermi gases with SU(N) higher mathematical symmetry, and quantum impurities. The article also outlooked the potential applications of 1D ultracold atomic systems in future quantum technologies, such as their use in probing gravity, testing quantum many-body entanglement, and realizing quantum heat engines and refrigeration etc. 

Paper link: https://iopscience.iop.org/article/10.1088/1361-6633/ac95a9/pdf

Recent representative work in Integrable Models

Guan and his co-workers  have achieved a series of important research results in these fields, which have been directly applied to the latest experimental breakthroughs in low-dimensional many-body physics. These include revealing the novel  physics of many-body systems such as Heisenberg spin chains, spin ladder compounds, the 1D Hubbard model, the BCS model, Gaudin magnets, the Lieb-Liniger model, super Tonks-Girardeau gases, spin-1/2 interacting Fermi gases, and ultracold quantum spin Bose gases.

1.     Ultracold atoms: Over the past two decades, the development of experimental preparation and manipulation techniques for degenerate ultracold atomic systems has provided a unprecedented platform for investigating quantum many-body phenomena and precision measurement methods. Guan with his research team has achieved a series of progress in Tomonaga-Luttinger liquids, spin-charge separation, and quantum critical phenomena in one-dimensional (1D) quantum many-body systems, revealing the microscopic mechanisms of 1D quantum many-body phenomena. These results serve as an important benchmark for understanding higher-dimensional quantum many-body phenomena and have attracted widespread attention from international peers, for example, platforms such as Physics (the online journal of the American Physical Society), Physicsworld(the website of the European Physical Society), and the Journal Club for Condensed Matter Physics have all published articles introducing their achievements.

In the field of quantum gas research, anisotropically confined gases, formed by strong radial confinement and weak axial confinement, provide an ideal and pure system for studying integrable theories. Recently, experiments on super Tonks-Girardeau gases realized by Haller et al. in the strong attraction region of cesium atoms, published in Science 325, 1224 (2009) and Science 371, 296 (2021), respectively, have verified the predictions they predicted  based on the integrable bosonic gas model.

Paper link: https://iopscience.iop.org/article/10.1088/1742-5468/2005/10/L10001/pdf?

https://www.science.org/doi/epdf/10.1126/science.1175850

https://www.science.org/doi/epdf/10.1126/science.abb4928

In this regard, Xi-Wen Guan used exactly solvable models to predict the exotic Bardeen-Cooper-Schrieffer (BCS) and Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) Cooper pair states in the 1D Yang-Gaudin model at an early stage (Guan, et. al., Phys. Rev. B 76, 085120 (2007)). In 2010, Professor Hulet's group experimentally confirmed the FFLO pairing state in 1D attractive Fermi gases that they had predicted using the Bethe ansatz method. The low-energy excitations of 1D interacting fermions usually split into two independent Tomonaga-Luttinger liquids, which describe the collective motion of quasiparticles carrying either spin or charge, separately. This phenomenon is called spin-charge separation and is a unique universal law in 1D quantum many-body physics. Although the Tomonaga-Luttinger liquid theory was proposed more than 40 years ago, spin-charge separation has long lacked conclusive experimental verification. The reason lies in the complex interparticle interactions and rich internal degrees of freedom, which pose great challenges to the theoretical description of the system's physical properties. The Tomonaga-Luttinger liquid theory cannot meet the needs of experimental measurements, making the accurate theoretical characterization of spin-charge separation a recognized worldwide problem.

In 2020, Guan's team, through the theory of quantum integrable systems, calculated the low-energy fractional excitation spectrum of 1D cold Fermi atomic gases with precision for the first time, and discovered the exotic properties of collective spin and charge excitations at different temperatures. They also revealed the microscopic nature of spin-charge separation and spin-incoherent liquids (Phys. Rev. Lett. 125, 190401 (2020)). This article also took the lead in proposing an experimental scheme for the conclusive observation of this phenomenon in Fermi ultracold atomic systems using Bragg spectroscopy, providing theoretical guidance for solving the problem that this iconic physical phenomenon of the Tomonaga-Luttinger liquid theory has lacked convincing experimental verification for more than 40 years.

Paper  link: https://doi.org/10.1103/PhysRevLett.125.190401

In subsequent work, Guan collaborated with the teams of Professor Randall G. Hulet and Professor Han Pu from Rice University (USA). They observed the exotic phenomenon of spin-charge separation for the first time with certainty by confining a 1D ultracold Fermi gas, and discovered the nonlinear Tomonaga-Luttinger liquid effect caused by spin backward scattering in this system. The achievement was published in Science and selected as a "Research Highlight" by the journal. Professor Thierry Giamarchi from the University of Geneva, a world-renowned physicist, commented on this work in a special feature of the international Journal Club for Condensed Matter Physics: "This is of course a remarkable result. …This opens the door to using it in situations where the theory is much less well established."

The theoretical prediction of the spin-charge separation phenomenon has obtained conclusive experimental verification.

Paper link: https://www.science.org/doi/epdf/10.1126/science.abn1719

In 2017, in collaboration with Academician Jianwei Pan from the University of Science and Technology of China and his colleague, Professor Zhensheng Yuan, through quantum control and measurement of ultracold atoms in optical lattices, combined with the theory of quantum integrable systems, the collaborative research teams obtained, for the first time internationally, the quantum critical properties of the transition between a classical gas and a quantum liquid in a 1D finite-temperature many-body system. Moreover, by measuring its phase correlations, they observed the power-law correlation characteristics of Luttinger liquids, achieving significant progress in the field of low-dimensional quantum many-body system research. This research result was published in Physical Review Letters and selected as an "Editors’ Suggestion". Physics invited Professor Giamarchi from the University of Geneva to comment on this research result in its "Viewpoint" column under the title "Theory of 1D Quantum Materials Verified in Cold Atom and Superconductor Experiments". Additionally, Physicsworld, the website of the European Physical Society, reported this achievement under the title "Atomic Systems and Josephson Junctions Simulate 1D Quantum Liquids".

Paper link: https://journals.aps.org/prl/pdf/10.1103/PhysRevLett.119.165701

Recently based on the newly developed multi-label algorithm, this study realizes high-precision calculation of all "relative excitations" of quantum integrable systems in both the ground state and finite-temperature states. For the first time, it accurately calculates the complete dynamic correlation function of the Lieb-Liniger model, obtains its full spectral function in the energy-momentum space, and reveals the singular power-law behavior at the threshold of the single-particle spectrum through the results of a large-scale system with 4000 particles. This achievement confirms, for the first time, the validity and applicable scope of the nonlinear Luttinger liquid theory, lays a foundation for dynamic studies such as non-equilibrium steady states, and further provides a quantitative basis for experimental detection of novel correlation effects.

Paper link: https://academic.oup.com/nsr/article/12/9/nwaf294/8209836

2.     Spin Systems: In the study of quantum spin chains, long-range order in 1D antiferromagnets is disrupted, leading to rich quantum magnetic effects at low temperatures. We found that integrable spin-1 chains with strong single-ion anisotropy can well describe compounds such as NENC, NDPK, and NBYC. The thermodynamic and magnetic properties of these systems can be accurately calculated using sophisticated thermodynamic Bethe ansatz and quantum transfer matrix methods.

In the research on quantum spin ladder systems, which provide a simplified model for understanding the mechanism of high-temperature superconductivity in cuprates. We established the correspondence between integrable su(N) systems and spin ladders. These models successfully describe the physical properties of realistic ladder compounds such as B5i2aT and CHpC. In particular, the Luttinger liquid parameters obtained through integrable theory are in high agreement with the experimental results of compounds like (5IAP)?CuBr?·H?O (see the research paper published in Advances in Physics 87):

Paper link: https://www.tandfonline.com/doi/abs/10.1080/00018730701265383

1D quantum spin systems in solids have long been a focus of experimental and theoretical attention. With the advancement of experimental techniques, the thermodynamic and magnetic properties of materials like CuPZn can now be well observed. However, the understanding of magnons, spinon excitations, and quantum critical properties remains incomplete. Guan with his collaborators  has conducted in-depth studies on the issues related to 1D antiferromagnetic Heisenberg chains, obtaining analytical scaling functions for various physical quantities in the quantum critical region. They pointed out that the double-peak structure of specific heat can well determine the transition temperature of the quantum critical region, and proved that the Wilson ratio is proportional to the Luttinger parameter. Furthermore, through precise comparison with experimental results, we confirmed that the theoretical interpretation is completely correct, correcting misunderstandings in the determination of transition temperatures in the quantum critical region. This holds significant guiding significance for future theoretical and experimental research (see Phys. Rev. B 96, 220401 R (2017)). After the article was published, our results were immediately verified by experimental papers [Sci. Adv. 3, eaao3773 (2017)]. In particular, recent experiments published in PNAS perfectly validated the predictions regarding Luttinger liquids and critical phenomena:

Paper link: https://academic.oup.com/pnasnexus/article/3/9/pgae363/7739746

3.     1D Hubbard model?For a long time, the Fermi-Hubbard model has been an important theoretical model for describing electron interactions in lattices. It plays a crucial role in characterizing universal strongly correlated electron phenomena and explaining numerous exotic properties of quantum materials. However, research methods for this model are rather limited: numerical calculations are constrained by the fermion sign problem, and many-body perturbation theory as well as mean-field theory cannot be practically applied. Consequently, the Fermi-Hubbard model is widely recognized as a world-renowned challenge. In relevant research, the exactly solvable 1D Fermi-Hubbard model has long been expected to provide a benchmark  for describing many-body physical phenomena in strongly correlated electron systems. Recently, experimental physicists have realized ultracold atomic systems in optical lattices and successfully constructed the exactly solvable 1D Hubbard model. They observed the dynamic transport and superdiffusive behavior of spin and charge, which offers a new perspective for explaining the microscopic nature of superconductivity and superfluidity. Nevertheless, how to understand the influence of interactions between fermions on the quantum states of spin and charge, and how to rigorously establish interaction-driven quantum phase transitions, Mott insulators, and universal thermodynamic laws remain elusive. Although mathematical physics methods have made considerable progress over decades, the universal laws of the 1D Hubbard model have not yet been obtained, which hinders in-depth understanding of many-body quantum phenomena.

Guan’s research team and its collaborators have achieved a series of important advances in the theoretical study of the 1D repulsive Hubbard model, including investigations into the exotic quantum properties, thermodynamics, and dynamic correlations of the attractive Hubbard model. Recently, they derived a set of exact analytical solutions for the 1D repulsive Hubbard model, covering fractionalized spin and charge excitations, spin-coherent and spin-incoherent Luttinger liquids, interaction-driven quantum phase transitions, and quantum refrigeration. The research results were published on October 3, 2024, in Reports on Progress 

Paper link: https://iopscience.iop.org/article/10.1088/1361-6633/ad7b70/pdf

4.     Quantum Precision Measurement and Quantum metrology?The latest frontier research in quantum many-body problems includes the study of quantum metrology at the many-body level, which also represents a key challenge in current quantum precision measurement. The research group led by Guan took deep investigation  in proposing an interaction-driven quantum liquid heat engine and its corresponding experimental scheme. Their work, published in a Nature partner journal, has become a high-impact paper in this research field.

See link: https://www.nature.com/articles/s41534-019-0204-5.pdf

They have also achieved important new progress in the research on multiparticle quantum walks in one-dimensional (1D) lattice systems and their potential applications in high-precision gravity measurement. They revealed the microscopic mechanism of 1D three-particle quantum walks and proposed, for the first time, an experimental scheme to improve the accuracy of gravity measurement via quantum walks. The relevant research results were published on August 28, 2021, in the journal Physical Review Letters under the title "Multiparticle Quantum Walks and Fisher Information in One-Dimensional Lattices".

Paper link: https://link.aps.org/doi/10.1103/PhysRevLett.127.100406

Recently, Guan’s research group and its collaborators demonstrated that in generalized phase estimation tasks, for non-entangled initial states, even if local many-body interaction Hamiltonians are used to encode parameters, it is impossible to make the measurement precision exceed the shot noise limit. Furthermore, this study revealed extensive connections between many-body physics, quantum control theory, quantum chaos, operator growth, and the application of quantum chaos in quantum metrology. The research results were published in 2024 in Physical Review Letters [132, 100803 (2024)]. In addition, they investigated the partial measurement estimation theory: targeting scenarios where only a part of the system is accessible in practical measure, they conducted an in-depth analysis of Gaussian state precision measurement tasks under such conditions. This study established an exact relationship between quantum Fisher information and bipartite entanglement, thereby clarifying the crucial role of bipartite  entanglement in dynamic encoding. It also built a definitive connection between quantum entanglement and measurement precision in the theory of partial-measurement-based precision measurement. The article was published in [Phys. Rev. B 109, L041301 (2024)].