About

Peter Littlewood is the Chair of the Department of Physics at the University of Chicago and holds the title of Harry Pratt Judson Distinguished Service Professor in the Department of Physics, the James Franck Institute, and the College. He earned a BA and PhD in Physics from the University of Cambridge. His professional background includes being a member of technical staff and later head of the theoretical physics research group at Bell Laboratories in New Jersey. In 1997, he moved to Cambridge as head of the Theory of Condensed Matter group and subsequently became the head of the Cavendish Laboratory and the Department of Physics. He joined the University of Chicago in 2011 as Associate Lab Director and then Lab Director at Argonne National Laboratory, returning full-time to the university in 2017. Littlewood serves on the advisory boards of several prestigious institutes, including the Faraday Institution, the Simons Foundation, the Paul Scherer Institute, the Carnegie Institute for Science, and the Max Planck Institutes at Halle and Hamburg. His research interests encompass superconductivity and superfluids, strongly correlated electronic materials, collective dynamics of glasses, density waves in solids, neuroscience, and applications of materials for energy and sustainability. His current research focuses include connectomics—measuring and modeling the connectivity of every neuron in a brain—non-equilibrium phase transitions in strongly coupled light-matter systems, and materials, technologies, and policy for energy.

Research topics

• Evolutionary biology
• Computational biology
• Mechanical engineering
• Quantum mechanics
• Theoretical physics
• Statistical physics
• Waste management
• Physics
• Biology
• Classical mechanics
• Genetics
• Materials science
• Engineering
• Process engineering
• Chemistry

Selected publications

• Theory of two-component superfluidity of microcavity polaritons

  Journal of Physics Condensed Matter · 2026-05-12

  articleOpen accessSenior author

  Abstract We develop a microscopic mean-field theory describing the coexistence of Bose–Einstein condensates of upper and lower polaritons (UP/LP) in a semiconductor microcavity. Incorporating interbranch scattering within a modified polariton Hamiltonian, we introduce a phenomenological population–split parameter <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mi>α</mml:mi> </mml:mrow> </mml:math> that quantifies the relative LP/UP occupations. At zero detuning, the critical temperature becomes independent of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mi>α</mml:mi> </mml:mrow> </mml:math> , converging to a single value that marks the balanced, resonant regime. Away from resonance, variations in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mi>α</mml:mi> </mml:mrow> </mml:math> lead to distinctive and experimentally resolvable changes in both the sound velocity <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msub> <mml:mi>c</mml:mi> <mml:mrow> <mml:mi mathvariant="normal">s</mml:mi> </mml:mrow> </mml:msub> </mml:mrow> </mml:math> and critical temperature <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msub> <mml:mi>T</mml:mi> <mml:mrow> <mml:mi mathvariant="normal">c</mml:mi> </mml:mrow> </mml:msub> </mml:mrow> </mml:math> , relative to the single-component (LP-only) condensate limit. The system under study consists of excitons confined in a transition metal dichalcogenide monolayer, particularly WSe 2 embedded within a planar optical microcavity of GaAs where they strongly couple to cavity photons. Our analysis focuses on monolayer WSe 2 embedded in a GaAs microcavity. We present results for GaAs/AlGaAs quantum wells embedded in a GaAs microcavity in the appendix. While mean-field in scope, the framework provides analytic benchmarks and physical insight for future treatments that include dissipation and fluctuations in nonequilibrium polariton superfluids.

  PublisherOA PDFDOI

• Fermi surface origin of the low-temperature magnetoresistance anomaly

  ArXiv.org · 2025-01-22

  preprintOpen access

  A magnetoresistance (MR) anomaly at low temperatures has been observed in a variety of systems, ranging from low-dimensional chalcogenides to spin and charge density wave (SDW/CDW) metals and, most recently, topological semimetals. In some systems parabolic magnetoresistance can rise to hundreds of thousands of times its low-temperature, zero-field value. While the origin of such a dramatic effect remains unresolved, these systems are often low-carrier-density compensated metals, and the physics is expected to be quasi-classical. Here we demonstrate that this MR anomaly in temperature also exists in high conductivity good metals with large Fermi surfaces, namely Cr, Mo, and W, for both linear and quadratic field-dependent regimes with their non-saturation attributed to open orbit and electron-hole compensation, respectively. We provide evidence that quantum transport across sharp Fermi surface arcs, but not necessarily the full cyclotron orbit, governs this low-temperature MR anomaly. In Cr, extremely sharp curvatures are induced by superposed lattice and SDW band structures. One observes an overlay of the temperature dependence of three phenomena: namely, MR at a constant high field, linear MR in the low-field limit, and Shubnikov-de Haas (SdH) oscillations of the lightest orbit. In Mo, the temperature dependence of low-T MR anomaly extends beyond those of its SdH oscillations but disappears at temperatures where Kohler's scaling reemerges. In the low-temperature and high-field limit, large magnetoresistance from carriers circling quantum orbits is the three-dimensional analogy to the zero-conductance state of carrier localization in the integer quantum Hall effect, especially with regard to the adverse effect of disorder.

  PublisherOA PDFDOI

• Phase Transitions in Nonreciprocal Driven-Dissipative Condensates

  St Andrews Research Repository (St Andrews Research Repository) · 2025-02-07

  preprintOpen access

  We investigate the influence of boundaries and spatial nonreciprocity on nonequilibrium driven-dissipative phase transitions. We focus on a one-dimensional lattice of nonlinear bosons described by a Lindblad master equation, where the interplay between coherent and incoherent dynamics generates nonreciprocal interactions between sites. Using a mean-field approach, we analyze the phase diagram under both periodic and open boundary conditions. For periodic boundaries, the system always forms a condensate at nonzero momentum and frequency, resulting in a time-dependent traveling wave pattern. In contrast, open boundaries reveal a far richer phase diagram, featuring multiple static and dynamical phases, as well as exotic phase transitions, including the spontaneous breaking of particle-hole symmetry associated with a critical exceptional point and phases with distinct bulk and edge behavior. Our model does not require post-selection and is experimentally realizable in platforms such as superconducting circuits.

  PublisherDOI

• Optical probes of coherence in two dimensional Bose gases of polaritons

  ArXiv.org · 2025-03-11

  preprintOpen accessSenior author

  Due to their photonic components, exciton-polariton systems provide a convenient platform to study the coherence properties of weakly-interacting Bose gases. In particular, optical interferometry enables the measurement of the first-order coherence function which provides information about the intrinsic correlations of the system. In this paper, we derive a universal curve for the coherent fraction of a noninteracting, equilibrium, homogeneous, two-dimensional Bose gas, with density expressed in units of the observation area, and compare to recent experimental results. Although there is a sharp transition from normal to superfluid phases in the thermodynamic limit, the coherent fraction of the gas varies continuously across this transition due to the finite system size. We find that the theory agrees nearly perfectly with the experimental data in the low-density limit with no free parameters other than the effective temperature, highly constrained by the measurements. At higher density, the experiments are consistent with standard weakly-interacting Bose gas theory. By having a theory that treats both the optical diffraction and Bose coherence, we can clearly see the effect of the quantum statistics on the coherence.

  PublisherOA PDFDOI

• Scattering Induced Mode Chirality in Ring Resonators

  ArXiv.org · 2025-11-10

  preprintOpen access

  Non-Hermitian physics can be used to break time reversal symmetry and is important for interactions in a wide range of systems, from active matter and neural networks to metamaterials and non-equilibrium thermodynamics. In integrated photonic devices, non-Hermitian physics can be used for direction-dependent light propagation, reconfigurable light paths, selective energy localization and optical isolators. In this work, we report previously unexplored direction-dependent mode splitting in ring microresonators, achieved by adding multiple scatterers around the cavity. Through experiments, simulations, and theoretical modeling, we unveil the underlying physics that changes the resonance shapes in resonant systems with backscattering. By engineering the spatial configuration of the scatterers, we can produce a predictable and repeatable direction-dependent mode splitting, enabling new ways to route light through optical resonators and photonic networks. In addition, the direction dependent mode-splitting can be used for precise near-field measurements, enhancing traditional sensing in integrated photonic chips.

  PublisherOA PDFDOI

• Artificial Intelligence for Materials Discovery, Development, and Optimization

  ACS Nano · 2025-07-25 · 91 citations

  review

  This review highlights the recent transformative impact of artificial intelligence (AI), machine learning (ML), and deep learning (DL) on materials science, emphasizing their applications in materials discovery, development, and optimization. AI-driven methods have revolutionized materials discovery through structure generation, property prediction, high-throughput (HT) screening, and computational design while advancing development with improved characterization and autonomous experimentation. Optimization has also benefited from AI's ability to enhance materials design and processes. The review will introduce fundamental AI and ML concepts, including supervised learning, unsupervised learning, semi-supervised learning, and reinforcement learning (RL), alongside advanced DL models such as recurrent neural networks (RNNs), convolutional neural networks (CNNs), graph neural networks (GNNs), generative models, and Transformer-based models, which are critical for analyzing complex material data sets. It also covers core topics in materials informatics, including structure-property relationships, material descriptors, quantitative structure-property relationships (QSPR), and strategies for managing missing data and small data sets. Despite these advancements, challenges such as inconsistent data quality, limited model interpretability, and a lack of standardized data-sharing frameworks persist. Future efforts will focus on improving robustness, integrating causal reasoning and physics-informed AI, and leveraging multimodal models to enhance scalability and transparency, unlocking new opportunities for more advanced materials discovery, development, and optimization. Furthermore, the integration of quantum computing with AI will enable faster and more accurate results, and ethical frameworks will ensure responsible human-AI collaboration, addressing concerns of bias, transparency, and accountability in decision-making.

  PublisherDOI

• Field Theory of Birhythmicity

  ArXiv.org · 2025-01-24

  preprintOpen accessSenior author

  Non-equilibrium dynamics are present in many aspects of our lives, ranging from microscopic physical systems to the functioning of the brain. What characterizes stochastic models of non-equilibrium processes is the breaking of the fluctuation-dissipation relations as well as the existence of non-static stable states, or phases. A prototypical example is a dynamical phase characterized by a limit cycle - the order parameter of finite magnitude rotating or oscillating at a fixed frequency. Consequently, birhythmicity, where two stable limit cycles coexist, is a natural extension of the simpler single limit cycle phase. Both the abundance of real systems exhibiting such states as well as their relevance for building our understanding of non-equilibrium phases and phase transitions are strong motivations to build and study models of such behavior. Field theoretic tools can be used to provide insights into either phase and the transition between them. In this work we explore a simple linear model of the single limit cycle phase with phase-amplitude coupling. We demonstrate how such non-equilibrium coupling affects the fluctuation spectrum of the theory. We then extend this model to include a continuous transition to a two-cycle phase. We give various results, such as an appearance of a critical exceptional point, the destruction of the transition, enhancement of noise for the phase and the presence of KPZ dynamics. Finally, we qualitatively demonstrate these results with numerics and discuss future directions.

  PublisherOA PDFDOI

• Generalized exceptional points in nonlinear and stochastic dynamics

  Physical Review Research · 2025-05-28 · 1 citations

  articleOpen access

  We study a class of bifurcations generically occurring in dynamical systems with nonmutual couplings ranging from models of coupled neurons to predator-prey systems and nonlinear oscillators. In these bifurcations, extended attractors such as limit cycles, limit tori, and strange attractors merge and split in a similar way as fixed points in a pitchfork bifurcation. We show that this merging and splitting coincide with the coalescence of covariant Lyapunov vectors with vanishing Lyapunov exponents, a feature that generalizes the exceptional points that can exist in families of non-Hermitian matrices or operators. We distinguish two classes of bifurcations associated with generalized exceptional points, corresponding respectively to continuous and discontinuous behaviors of the covariant Lyapunov vectors at the transition depending on the presence of a <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"> <a:msub> <a:mi mathvariant="double-struck">Z</a:mi> <a:mn>2</a:mn> </a:msub> </a:math> symmetry. We outline some physical consequences of this class of theories exhibiting generalized exceptional points, including nonreciprocal responses, the destruction of isochrons, and anomalous noise effects. In particular, we show that the effective diffusion coefficient on the attractor can stay finite or even diverge when the noise strength vanishes. We illustrate our results with concrete examples from neuroscience, ecology, and physics.

  PublisherDOI

• Field theory of birhythmicity

  Physical review. E · 2025-11-21

  articleSenior author

  Nonequilibrium dynamics are present in many aspects of our lives, ranging from microscopic physical systems to the functioning of the brain. What characterizes stochastic models of nonequilibrium processes is the breaking of the fluctuation-dissipation relations as well as the existence of nonstatic stable states, or phases. A prototypical example is a dynamical phase characterized by a limit cycle-the order parameter of finite magnitude rotating or oscillating at a fixed frequency. Consequently, birhythmicity, where two stable limit cycles coexist, is a natural extension of the simpler single limit cycle phase. Both the abundance of real systems exhibiting such states and their relevance for building our understanding of nonequilibrium phases and phase transitions are strong motivations to build and study models of such behavior. Field-theoretic tools can be used to provide insights into either phase and the transition between them. In this work, we explore a simple linear model of a single limit cycle phase with phase-amplitude coupling. We demonstrate how such nonequilibrium coupling affects the fluctuation spectrum of the theory. We then extend this model to include a continuous transition to a two-cycle phase. We give various results, such as the appearance of a critical exceptional point, the destruction of the transition, the enhancement of noise for the phase, and the presence of Kardar-Parisi-Zhang(KPZ) dynamics. Finally, we qualitatively demonstrate these results with numerics and discuss future directions.

  PublisherDOI

• Phase Transitions in Nonreciprocal Driven-Dissipative Condensates

  Physical Review Letters · 2025-08-22 · 3 citations

  articleOpen access

  We investigate the influence of boundaries and spatial nonreciprocity on nonequilibrium driven-dissipative phase transitions. We focus on a one-dimensional lattice of nonlinear bosons described by a Lindblad master equation, where the interplay between coherent and incoherent dynamics generates nonreciprocal interactions between sites. Using a mean-field approach, we analyze the phase diagram under both periodic and open boundary conditions. For periodic boundaries, the system always forms a condensate at nonzero momentum and frequency, resulting in a time-dependent traveling wave pattern. In contrast, open boundaries reveal a far richer phase diagram, featuring multiple static and dynamical phases, as well as exotic phase transitions, including the spontaneous breaking of particle-hole symmetry associated with a critical exceptional point and phases with distinct bulk and edge behavior. Our model does not require postselection and is experimentally realizable in platforms such as superconducting circuits.

  PublisherDOI

Recent grants

• EAGER: Inferring Activity From Anatomy in Neuronal Cultures

  NSF · $299k · 2022–2025

Frequent coauthors

• M. H. Szymańska

  92 shared

• Jonathan Keeling

  University of St Andrews

  87 shared

• Emilio Artacho

  51 shared

• Alejandro López‐Bezanilla

  Los Alamos National Laboratory

  43 shared

• Bogdan Mihaila

  34 shared

• Yejun Feng

  Okinawa Institute of Science and Technology Graduate University

  33 shared

• P. R. Eastham

  32 shared

• G. G. Guzmán-Verri

  Universidad de Costa Rica

  30 shared

Education

• B.A.

  University of Cambridge

• Ph.D.

  University of Cambridge

Awards & honors

• 2025 Institute of Physics Gold Medal - Richard Glazebrook Me…