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Overview

Theory of phase transitions and critical phenomena plays an important role in condensed matter theory and statistical physics. The theoretical study has been carried out in two different but interactive paths. One path is constructed of various rigorous results, which include Onsager's exactly solution of the Ising model, Coulomb gas theory, renormalization theory, conformal field theory, Schramm-Loewner evolution etc. The other path makes use of the increasing power of computers, leading to the development of many effective computational methods, of which Markov chain Monte Carlo (MCMC) method is a nice example. Designing novel MCMC algorithms, especially cluster-type methods, and their applications have been hot topics for decades and will continue to show their effectiveness.

Quantum simulation is a quickly developing field in recent years. Computational results contribute to the understanding of behaviors of many-body quantum systems, as well as support experimental explorations.

Novel efficient algorithms and their applications in statistical physics

We've developed Markov chain Monte Carlo algorithms that can simulate both classical and quantum models, such as percolation, Ising, Potts, O(n) loop, and quantum Ising model. Certain algorithms can simulate curved space, or effectively deal with canonical ensembles.

We've observed the dynamical critical behaviors of some famous algorithms, e.g. Sweeny algorithm, Swendsen-Wang algorithm. Interesting new phenomena have been found, such as multi-time scales and the critical Speeding-up. 

Transfer matrix and its applications

Generally speaking, transfer matrix technique gives much better results than Monte Carlo method for two dimensional classical and 1+1 dimensional quantum systems, but it can hardly deal with large systems due to limitation of computational resources. We've employed transfer matrix to observe phase transitions of Potts model in two dimensions. 

Diagrammatic Monte Carlo method

Diagrammatic Monte Carlo method is a recently developed method for simulation of quantum systems. In this method, the Feynman diagrams are weighted elaborately, which may make it a candidate for alleviating the sign problem considering some Fermi systems. Employing the diagrammatic methods, we are currently working hard towards the Fermi-Hubbard model, worm-type simulation of J-Q model, multi-component Bose systems etc.

Critical finite-size scaling in canonical ensembles

In experiments, many systems undergoing phase transitions are subject to external constraints such as the conservation of particle numbers in a mixture. Such systems are described in terms of canonical ensemble, and thus typically display a behavior different from that of unconstrained models, which are described by the grand canonical ensemble. The underline mechanism of such systems can be attributed to the so called Fisher renormalization. We've developed efficient cluster algorithms and studied the constrained systems such as the Blume-Capel model, Baxter's hard-square model, and the integer Potts model with vacancies. We have also studied the finite-size behavior of several systems near critical or tricritical point. 

Conformal invariance in two or higher dimensions

Conformal invariance relates closely to the geometrical aspects of phase transitions and critical phenomena. In two-dimensional classical systems and quantum systems in 1+1 dimensions, conformal invariance is very powerful and has lead to a large number of exact results. We've developed efficient algorithms and systematically study conformal invariance in two or higher dimensions. 

Geometric properties of critical systems

Geometric description of fluctuations at and near criticality has a long history, which dates back to the formulation of phase transitions in terms of the droplet model. Phase transitions and critical phenomena in many statistical models can be observed from geometric aspect. For instance, Potts model can be mapped onto the random-cluster model, and the susceptibility of the former is related to the cluster-size distribution of the latter. The Mott-to-superfluid transition in the Bose-Hubbard model can be characterized by the winding number of the world lines of the particles. We've conducted extensive research in the geometric properties of critical systems, many fractal dimensions has been calculated theoretically or numerically. Models we usually studies include percolation, Potts, random cluster, O(n)loop model etc. 

Surface phase transitions

We've investigated critical surface phenomena of many systems. Especially, we've observed the pseudo-one-dimensional phase transition, and found that even in two-dimensional systems with short-range interactions, rich critical surface phenomena occur due to the fact that the edge spins are correlated through the critical bulk. 

Quantum simulations

With the developments in the field of atomic and molecular physics, researchers are able to engineer lots of quantum systems. Real-time control over features such as lattice structure, density, level of impurities and disorder, and interactions are within our abilities. In cooperation with coworkers in the Quantum Physics and Quantum Information Division, HFNL, we are conducting theoretical and computational exploration on quantum information processing and simulation of many-body quantum systems with cold atom and optical lattice. 

General

Besides the topics introduced above, we've also been working on others problems in statistical physics and related fields, for instance, defining new models and studying their properties. 

Interactive demonstrations of novel Monte Carlo methods

Worm algorithm demos from UMass group

Ising modelJ-current ModelFermi-Hubbard Model

Since 2002, we have published about 184 articles in peer-reviewed journals. These include: Nature (2), Science (3), Nature Photonics (1), Nature Physics (1), National Science Review (3), Physical Review X (1), Science Bulletin (2), Physical Review Letters (31), Physical Review Research (5), Scientific Reports (1), Computer Physics Communications (1), Physical Review B (19), Physica A (3), Nuclear Physics B (6), Physical Review A (11), Frontiers of Physics (3), Physical Review E (67), Chinese Physics Letters (1), Journal of Statistical Mechanics: Theory and Experiment (3), Journal of Physics A: Mathematical and Theoretical (6), Europhysics Letters (1), Chinese Physics B (3), Acta Physica Sinica (1), Differential Geometry and Physics (1), Journal of Physics: Conference Series (1), Soft Matter (1), Communications in Theoretical Physics (1), SciPost Physics (2) .

>>Publications

2023

1. Explosive Percolation Obeys Standard Finite-Size Scaling in an Event-Based Ensemble

    by Ming Li, Junfeng Wang, and Youjin Deng 

      Phys. Rev. Lett. 130, 147101 (2023)

2. Extraordinary-log Universality of Critical Phenomena in Plane Defects    

    by Yanan Sun, Minghui Hu, Youjin Deng , and Jian-Ping Lv

      Phys. Rev. Lett. 131, 207101 (2023)

3. Geometric properties of the complete-graph Ising model in the loop representation

    by Zhiyi Li, Zongzheng Zhou, Sheng Fang, and Youjin Deng

      Phys. Rev. E 108, 024129 (2023).

2022

1. Universal Critical Behavior of Percolation in Orientationally Ordered Janus Particles and 

    Other Anisotropic Systems

    by Hao Hu, Robert M. Ziff, and Youjin Deng 

      Phys. Rev. Lett. 129, 278002 (2022)

 2. Temperature-Dependent Decay of Quasi-Two-Dimensional Vortices across the BCS-BEC

     Crossover

    by Xiang-Pei Liu, Xing-Can Yao, Xiaopeng Li, Yu-Xuan Wang, Chun-Jiong Huang, 

    Youjin Deng, Yu-Ao Chen, and Jian-Wei Pan

     Phys. Rev. Lett. 129, 163602 (2022)

 3. Geometric Upper Critical Dimensions of the Ising Model

    by Fang Sheng, Zongzheng Zhou, and Youjin Deng

     Chin. Phys. Lett. 39, 080502 (2022)

 4. Interaction-induced particle-hole symmetry breaking and fractional exclusion statistics

    by Xibo Zhang, Yang-Yang Chen, Longxiang Liu, Youjin Deng, and Xiwen Guan

     National Science Review 9: nwac027 (2022)

 

2021   

 1. Extraordinary-Log Surface Phase Transition in the Three-Dimensional XY Model

    by Minghui Hu, Youjin Deng, and Jian-Ping Lv

     Phys. Rev. Lett. 127, 120603 (2021)

     

 2. Universal Dynamical Scaling of Quasi-Two-Dimensional Vortices in a Strongly Interacting

     Fermionic Superfluid

    by Xiang-Pei Liu, Xing-Can Yao, Youjin Deng, Xiao-Qiong Wang, Yu-Xuan Wang, Chun-Jiong 

     Huang, Xiaopeng Li, Yu-Ao Chen, and Jian-Wei Pan

      Phys. Rev. Lett. 126, 185302 (2021)

 3. Realization of an ideal Weyl semimetal band in a quantum gas with 3D spin-orbit coupling

    by Zong-Yao Wang, Xiang-Can Cheng, Bao-Zong Wang, Jin-Yi Zhang, Yue-Hui Lu, Chang-Rui 

    Yi, Sen Niu, Youjin Deng, Xiong-Jun Liu, Shuai Chen, and Jian-Wei Pan

      Science 372, 271–276 (2021)

 4. Finite-size scaling of O(n) systems at the upper critical dimensionality

    by Jian-Ping Lv, Wanwan Xu, Yanan Sun, Kun Chen, and Youjin Deng

      National Science Review 8.3 (2021): nwaa212

2020

 1. Loop-Cluster Coupling and Algorithm for Classical Statistical Models

    by Lei Zhang, Manon Michel, Eren M. Elçi, and Youjin Deng

     Phys. Rev. Lett. 125, 200603 (2020)    arXiv:1909.02719

 2. Cooling and entangling ultracold atoms in optical lattices

    Bing Yang, Hui Sun, Chun-Jiong Huang, Han-Yi Wang, Youjin Deng, Han-Ning Dai, 

    Zhen-Sheng Yuan, and Jian-Wei Pan

     Science 369, 550-553 (2020)

 3. Two-Scale Scenario of Rigidity Percolation of Sticky Particles

    by Yuchuan Wang, Sheng Fang, Ning Xu, and Youjin Deng

     Phys. Rev. Lett. 124, 255501 (2020)

2019

 1. Observation of nonscalar and logarithmic correlations in two- and three-dimensional 

     percolation

    by Xiaojun Tan, Romain Couvreur, Youjin Deng, Jesper Lykke Jacobsen

      Phys. Rev. E 99, 050103(R) (2019)    arXiv:1809.06650

 2. Clock Monte Carlo methods

    by Manon Michel, Xiaojun Tan, Youjin Deng

     Phys. Rev. E 99, 010105(R) (2019)    arXiv:1706.10261

2018

 1. Random-Length Random Walks and Finite-Size Scaling in High Dimensions

    Zongzheng Zhou, Jens Grimm, Sheng Fang, Youjin Deng, Timothy M. Garoni

     Phys.  Rev. Lett. 121, 185701 (2018) arXiv:1809.00515

 2. Duality and the universality class of the three-state Potts antiferromagnet on plane 

     quadrangulations

    Jian-Ping Lv, Youjin Deng, Jesper Lykke Jacobsen, Jesús Salas, Alan D.  Sokal

     Phys.  Rev. E 97, 040104(R) (2018) arXiv:1712.07047

 3. Dynamics of Topological Excitations in a Model Quantum Spin Ice

    Chun-Jiong Huang, Youjin Deng, Yuan Wan, Zi Yang Meng

     Phys.  Rev. Lett. 120, 167202 (2018) arXiv:1707.00099

2017

 1. Geometric explanation of anomalous finite-size scaling in high dimension

    Jens Grimm, Eren Metin Elçi, Zongzheng Zhou, Tim Garoni, Youjin Deng

     Phys.  Rev. Lett. 118, 115701 (2017) arXiv:1612.01722

 2. Irreversible Markov chain Monte Carlo algorigthm for self-avoiding walk

    Hao Hu, Xiaosong Chen, Youjin Deng

     Front. Phys. 12(1), 120503 (2017) arXiv:1602.01671

2016

 1. Trapping Centers at the Superfluid-Mott-insulator Criticality: Transition between             

     Charge-quantized  States

    Yuan Huang, Kun Chen, Youjin Deng, Boris Svistunov

     Phys. Rev.  B 94, 220502(R) (2016) arXiv:1608.02232

 2. Realization of two-dimensional spin-orbit coupling for Bose-Einstein condensates

    Zhan Wu, Long Zhang, Wei Sun, Xiao-Tian Xu, Bao-Zong Wang, Si-Cong Ji, Youjin  Deng,

    Shuai Chen, Xiong-Jun Liu, Jian-Wei Pan

     Science, 354, 83-88, (2016) arXiv:1511.08170

 3. Emergent O(n) symmetry in a series of 3D Potts model

    Chengxiang Ding, Henk W. J. Blöte, Youjin Deng

     Phys. Rev.  B 94, 104402 (2016) arXiv:1508.04538

 4. No-enclave percolation corresponds to holes in the cluster backbone

    Hao Hu, Robert M. Ziff, Youjin Deng

     Phys.  Rev. Lett. 117, 185701 (2016) arXiv: 1605.03685

 5. Observation of two-species vortex lattices in a mixture of mass-imbalance Bose and Fermi

     superfluids

    Xing-Can Yao, Hao-Ze Chen, Yu-Ping Wu, Xiang-Pei Liu, Xiao-Qiong Wang, Xiao Jiang, 

    Youjin Deng, Yu-Ao Chen, Jian-Wei Pan

     Phys.  Rev. Lett. 117, 145301 (2016) arXiv:1606.01717

 6. Spin-Ice State of the Quantum Heisenberg Antiferromagnet on the Pyrochlore Lattice

    Yuan Huang, Kun Chen, Youjin Deng, Nikolay Prokof’ev, Boris Svistunov

     Phys.  Rev. Lett. 116, 177203 (2016) arXiv:1511.08285

2015

 1. Emergent BCS regime of the two-dimensional fermionic Hubbard model: ground-state 

     phase  diagram

    Youjin Deng, Evgeny Kozik, Nikolay V. Prokof'ev, Boris V. Svistunov

     EPL 110, 57001 (2015) arXiv:1408.2088

 2. Coulomb liquid phases of bosonic cluster Mott insulators on a pyrochlore lattice

    Jian-Ping Lv, Gang Chen, Youjin Deng, Zi Yang Meng

     Phys.  Rev. Lett. 115, 037202 (2015) arXiv:1502.04788

 3. Softening of Roton and Phonon Modes in a Bose-Einstein Condensate with Spin-Orbit 

     Coupling

    Si-Cong Ji, Long Zhang, Xiao-Tian Xu, Zhan Wu, Youjin Deng, Shuai Chen, Jian-Wei  Pan

     Phys.  Rev. Lett. 114, 105301 (2015) arXiv:1408.1755

 4. Universal Critical Wrapping Probabilities in the Canonical Ensemble

    Hao Hu, Youjin Deng

     Nucl.  Phys. B 898, 157 (2015) arXiv:1507.00453

2014

 1. Experimental determination of the finite-temperature phase diagram of a spin–orbit

     coupled Bose gas

    Si-Cong Ji, Jin-Yi Zhang, Long Zhang, Zhi-Dong Du, Wei Zheng, You-Jin Deng, Hui  Zhai,

    Shuai Chen, Jian-Wei Pan

     Nature Physics 10, 314–320 (2014) arXiv:1305.7054

 2. Universal Conductivity in a Two-dimensional Superfluid-to-Insulator 

      Quantum Critical System

    Kun Chen, Longxiang Liu, Youjin Deng, Lode Pollet, Nikolay Prokof’ev

     Phys. Rev. Lett. 112,  030402 (2014) arXiv:1309.5635

2013

 1. Sequential Path Entanglement for Quantum Metrology

    Xian-Min Jin, Cheng-Zhi Peng, Youjin Deng, Marco Barbieri, Joshua Nunn, Ian A.  Walmsley

     Sci.  Rep. 3, 1779 (2013)

 2. Deconfined criticality flow in the Heisenberg model with ring-exchange interactions

    Kun Chen, Yuan Huang, Youjin Deng, A. B. Kuklov, N. V. Prokof’ev, B. V.  Svistunov

     Phys. Rev. Lett. 110,  185701 (2013) arXiv:1301.3136

 3. Universal properties of the Higgs resonance in (2+1)-dimensional U(1) critical systems

    Kun Chen, Longxiang Liu, Youjin Deng, Lode Pollet, Nikolay Prokof’ev

     Phys. Rev. Lett. 110,  170403 (2013) arXiv:1301.3139

2012

 1. Experimental demonstration of topological error correction

    Xing-Can Yao, Tian-Xiong Wang, Hao-Ze Chen, Wei-Bo Gao, Austin G. Fowler, 

    Robert  Raussendorf,  Zeng-Bing Chen, Nai-Le Liu, Chao-Yang Lu,

    You-Jin Deng, Yu-Ao Chen, Jian-Wei  Pan

     Nature 482, 489-494 (2012) arXiv:1202.5459

 2. The O(n) loop model on a three dimensional lattice

    Qingquan Liua, Youjin Deng, Timothy M. Garonib, Henk W.J. Blötec

     Nucl.  Phys. B, 859 (2012), pp. 107-128 arXiv:1112.5647

 

 3. Holographic Storage of Biphoton Entanglement

    Han-Ning Dai, Han Zhang, Sheng-Jun Yang, Tian-Ming Zhao, Jun Rui, You-Jin Deng,  Li Li,

     Nai-Le Liu, Shuai Chen, Xiao-Hui Bao, Xian-Min Jin, Bo Zhao, Jian-Wei Pan

     Phys. Rev. Lett. 108,  210501 (2012) arXiv:1204.1532

 4. Collective Dipole Oscillation of a Spin-Orbit Coupled Bose-Einstein Condensate

    Jin-Yi Zhang, Si-Cong Ji, Zhu Chen, Long Zhang, Zhi-Dong Du, Bo Yan, Ge-Sheng Pan, 

    Bo  Zhao,   You-Jin Deng, Hui Zhai, Shuai Chen, Jian-Wei Pan

     Phys. Rev. Lett. 109,  115301 (2012) arXiv:1201.6018

2011

 1. Worm Monte Carlo study of the honeycomb-lattice loop model

    Qingquan Liu, Youjin Deng, Timothy M. Garoni

     Nucl.  Phys. B 846 [FS], pp. 283-315 (2011) arXiv:1011.1980

 2. Finite-temperature phase transition in a class of 4-state Potts antiferromagnets

    Youjin Deng, Yuan Huang, Jesper Lykke Jacobsen, Jesús Salas, Alan D.  Sokal

     Phys. Rev. Lett. 107,  150601 (2011) arXiv:1108.1743

 3. Preparation and storage of frequency-uncorrelated entangled photons from 

      cavity- enhanced  spontaneous parametric downconversion

    Han Zhang, Xian-Min Jin, Jian Yang, Han-Ning Dai, Sheng-Jun Yang, Tian-Ming Zhao,

    Jun Rui, Yu He,  Xiao Jiang, Fan Yang, Ge-Sheng Pan, Zhen-Sheng Yuan, Youjin Deng, 

    Zeng-Bing  Chen, Xiao-Hui Bao, Shuai Chen, Bo Zhao, Jian-Wei Pan

     Nature Photonics 5, 628-632 (2011)

2010

 1. Some geometric critical exponents for percolation and the random-cluster model

     Youjin Deng, Wei Zhang, Timothy M. Garoni, Alan D. Sokal, Andrea  Sportiello

     Phys. Rev. E 81, 020102(R)  (2010) arXiv:0904.3448

2008

 1. Percolation transitions in two dimensions

    Xiaomei Feng, Youjin Deng, Henk W. J. Blöte

     Phys. Rev. E 78, 031136  (2008) arXiv:0901.1370

2007

 1. Dynamic critical behavior of the worm algorithm for the Ising model

    Youjin Deng, Timothy M. Garoni, Jonathan Machta, Giovanni Ossola, Marco Polin,  

      Alan D. Sokal

     Phys. Rev. Lett. 99,  110601 (2007) arXiv:cond-mat/0703783

 2. Dynamic critical behavior of the Chayes-Machta-Swendsen-Wang algorithm

    Youjin Deng, Timothy M. Garoni, Jonathan Machta, Giovanni Ossola, Marco Polin,  

    Alan D. Sokal

     Phys. Rev. Lett. 99, 055701  (2007) arXiv:0705.2751

 3. Critical speeding-up in a local dynamics for the random-cluster model

    Youjin Deng, Timothy M. Garoni, Alan D. Sokal

     Phys. Rev. Lett. 98,  230602 (2007) arXiv:cond-mat/0701113

 4. Cluster simulations of loop models in two dimensions

    Youjin Deng, Timothy M. Garoni, Wenan Guo, Henk W. J. Blöte, Alan D.  Sokal

     Phys. Rev. Lett. 98,  120601 (2007) arXiv:cond-mat/0608447

 5. Ferromagnetic phase transition for the spanning-forest model (q → 0 limit of the

     Potts model)  in three or more dimensions

    Youjin Deng, Timothy M. Garoni, Alan D. Sokal

     Phys. Rev. Lett. 98, 030602  (2007) arXiv:cond-mat/0610193

2005

 1. Monte Carlo study of the site-percolation model in two and three dimensions

    Youjin Deng, Henk W. J. Blöte

     Phys. Rev. E 72, 016126  (2005)

 2. Constrained tricritical phenomena in two dimension

    Youjin Deng, Jouke R. Heringa, Henk W. J. Blöte

     Phys. Rev. E 71, 036115  (2005) 

2004

 1. Spontaneous edge order and geometric aspects of two-dimensional Potts models

    Youjin Deng, Henk W. J. Blöte

     Phys. Rev. E 70, R035107  (2004) 

 2. Geometric properties of two-dimensional critical and tricritical Potts models

    Youjin Deng, Henk W. J. Blöte, Benard Nienhuis

     Phys. Rev. E 69, 026123  (2004) 

 3. Backbone exponents of the two-dimensional q-state Potts model: a Monte Carlo study

     Youjin Deng, Henk W. J. Blöte, Bernard Nienhuis

     Phys. Rev. E 69, 026114  (2004) 

2003

 1. Simultaneous analysis of several models in the three-dimensional Ising universality class

    Youjin Deng, Henk W. J. Blöte

     Phys. Rev. E 68, 036125  (2003) 

2002

 1. Cluster Monte Carlo simulation of the transverse Ising model

    Henk W. J. Blöte, Youjin Deng

     Phys. Rev. E 66, 066110  (2002) 

 2. Conformal invariance of the Ising model in three dimensions

    Youjin Deng, Henk W. J. Blöte

     Phys. Rev.  Lett. 88, 190602 (2002)