Talks

Ordered phases of matter have close connections to computation. Two prominent examples are spin glass order, with wide-ranging applications in machine learning and optimization, and topological order, closely related to quantum error correction. Here, we introduce the concept of topological quantum spin glass (TQSG) order which marries these two notions, exhibiting both the complex energy landscapes of spin glasses, and the quantum memory and long-range entanglement characteristic of topologically ordered systems. Our work introduces a topological analog of spin glasses that preserves quantum information and displays robust many-body entanglement even at finite temperatures, opening new avenues for both statistical mechanics and quantum computer science.

Microbial communities assemble and thrive in strongly fluctuating boom-and-bust environments by adopting distinct metabolic strategies to consume resources. While much attention has been given to understanding these strategies in isolated species, their ecological implications in complex communities remain poorly understood. Here, we combine theoretical and computational frameworks to investigate the assembly and ecological properties of microbial communities with diauxic (sequential) and co-utilization strategies.
We show that diauxic microbial communities, where species sequentially utilize resources, spontaneously develop complementary resource preferences during assembly. This complementarity arises because sequential utilization disproportionately relies on the top-choice resource for growth, leading to intuitive ecological partitioning. A geometric approach to analyzing these serially diluted communities further explains emergent patterns, such as the absence of species preferring suboptimal resources for growth.
Comparing sequential and co-utilization strategies, we find that sequential utilizers dominate in species-rich, high-competition communities, leveraging their resilience to fluctuating resource ratios. Their ecological advantage lies in growth rate distributions characterized by wider upper tails, despite lower averages, enabling efficient niche packing and structural stability. Conversely, co-utilizers thrive in low-diversity communities, benefiting from consistently higher average growth rates.
Our work provides a unified explanation for the coexistence of sequential and co-utilizing strategies in natural ecosystems and predicts patterns of community assembly shaped by metabolic strategies. These findings offer testable hypotheses for understanding the dynamics of microbial communities in natural and synthetic environments.

The characterization of identical quantum particles as bosons or fermions goes back to the early days of quantum mechanics. It was realized much later that in two space dimensions, particles with any statistics (`anyons') can exist. Such particles can emerge as quasiparticles in quantum phases of matter. The prime experimental example is in the Fractional Quantum Hall Effect (FQHE). After a brief review of the FQHE, I will discuss recent developments on the observation of the phenomenon in zero magnetic field, and the associated questions and opportunities.

Microbial ecosystems frequently exhibit multiple alternative stable states under identical environmental conditions, separated by abrupt regime shifts. These shifts complicate the understanding, manipulation, and control of such systems, with significant implications for natural, industrial, and health-related contexts. In this talk, I present a unified framework combining insights from nutrient competition and phage-bacteria interactions to explore these dynamics.
First, I will discuss models that predict stable states in microbial ecosystems based on different resource utilization strategies. The first model [1] describes communities of diauxically growing microbes, where species dynamically switch between nutrient preferences depending on environmental availability. In contrast, the second model [2] focuses on specialist species, each limited by two essential nutrients, such as carbon and nitrogen, represented by multiple metabolites. Both models draw inspiration from the stable marriage problem in economics, developed by Gale and Shapley in the 1960s and awarded the Nobel Prize in Economics in 2012. Using ranked tables of species' competitive abilities for nutrients, these models identify all feasible stable states and the specific environmental conditions—characterized by nutrient fluxes—where they occur. This framework reveals a complex network of transitions between stable states and highlights perturbations that induce regime shifts versus those with transient effects.
Next, I address alternative stable states in phage-bacteria systems, building on the findings in [3]. These systems demonstrate how bacterial growth rates, phage burst sizes, and defense mechanisms like CRISPR and abortive infection drive regime shifts. For example, a fast-growing bacterium may exclude slow-growing one via nutrient depletion, but phage predation can invert this dynamic, favoring the slower-growing bacterium.
References:
[1] Goyal A, Dubinkina V, Maslov S. Multiple stable states in microbial communities explained by the stable marriage problem. ISME J. 2018;12: 2823–2834. https://doi.org/10.1038/s41396-018-0222-x
[2] Dubinkina V, Fridman Y, Pandey PP, Maslov S. Multistability and regime shifts in microbial communities explained by competition for essential nutrients. eLife. 2019;8:e49720. https://doi.org/10.7554/eLife.49720
[3] Maslov S, Sneppen K. Regime shifts in a phage-bacterium ecosystem and strategies for its control. mSystems. 2019;4:e00470-19. https://doi.org/10.1128/mSystems.00470-19

Quantum physics has reshaped our understanding of materials and created opportunities to design materials for novel device applications. For example, superconductivity, an emergent quantum phenomenon in which electrons move without dissipating energy, has been exploited for devices that enable quantum computing and communications. In addition, modern electronics rely heavily on technology that confines electrons in the interfacial layers of atoms, where the electrons move in an effective two-dimensional (2D) space, a flatland. The unique properties of these low-dimensional material systems are generally understood by considering enhanced quantum effects. In recent years, scientists have discovered that they can stack atomically thin 2D quantum materials to create engineered materials with a wide variety of electronic and optical properties. In this talk, we will discuss several research efforts to realize emergent physical phenomena in stacked atomically thin layered materials and possible applications based on these materials.

Physicists have been trying to develop a theory that puts together general relativity and quantum mechanics. We will highlight some interesting theoretical ideas and point out a couple of concrete predictions.