About

Sarang Gopalakrishnan is an Associate Professor of Electrical and Computer Engineering at Princeton University. His research broadly focuses on the dynamics of quantum systems and devices, with particular emphasis on the dynamics of quantum information. He investigates how information encoded in quantum states scrambles and becomes inaccessible over time, exploring how this process can be mitigated or harnessed for useful tasks. His work primarily lies at the interface between quantum statistical mechanics and quantum information theory, and extends into related fields such as computer science, data compression, and approximation theory. Gopalakrishnan collaborates with experimentalists in photonics, atomic physics, and condensed matter physics to advance understanding in these areas.

Research topics

• Physics
• Quantum mechanics
• Statistical physics
• Mathematics
• Atomic physics
• Theoretical physics
• Mathematical analysis

Selected publications

• Theory of Two-Qubit $T_2$ Spectroscopy of Quantum Many-Body Systems

  arXiv (Cornell University) · 2026-03-18

  preprintOpen access

  Multi-qubit quantum sensors are rapidly emerging as platforms that extend the capabilities of conventional single-qubit sensing. In this work we show how suitable pulse sequences applied to a two-qubit sensor enable separate extraction of the response and noise of a probed environment within a $T_2$ spectroscopy framework. By resorting to representative examples, we demonstrate that this approach can resolve the spatio-temporal spreading of correlations in a many-body system. In particular, the resulting correlated dephasing signal captures features such as the dispersion of low-energy excitations, which manifest as light-cone-like profiles in the propagation of correlations. We further show that non-equilibrium conditions, for instance those induced by external driving, can modify this profile by producing additional fringes outside the light-cone. As a complementary application, we demonstrate that the method clearly distinguishes between different transport regimes in the system, including ballistic spreading, diffusive broadening, and the crossover between them.

  PublisherDOI

• Algorithmic Locality via Provable Convergence in Quantum Tensor Networks

  arXiv (Cornell University) · 2026-04-23

  articleOpen accessSenior author

  Belief propagation has recently emerged as a powerful framework for evaluating tensor networks in higher dimensions, combining computational efficiency with provable analytical guarantees. In this work, we develop the first end-to-end theory of tensor network belief propagation for a class of projected entangled pair states satisfying \emph{strong injectivity}. We show that when the injectivity parameter exceeds a constant threshold, BP fixed points can be found efficiently, and a cluster-corrected BP algorithm computes physical quantities to $1/\mathrm{poly}(N)$ error in $\mathrm{poly}(N)$ time for an $N$ qubit system. We identify a striking phenomenon we term \emph{algorithmic locality}: local perturbations of the tensor network affect the BP fixed point with an influence decaying rapidly with distance. As a result, updates to the fixed point after a local perturbation can be carried out using only local recomputation. Moreover, through the cluster expansion, this locality extends to observables, implying that local expectation values can be approximated from local data with controlled accuracy. Our results provide the first rigorous guarantee for the effectiveness of tensor-network belief propagation on a wide class of many-body states, bridging a gap between widely used numerical practice and provable algorithmic performance.

  PublisherOA PDF

• Noncommuting zero-noise and zero-frequency limits in particle-hole symmetric fluids

  arXiv (Cornell University) · 2026-01-05

  preprintOpen accessSenior author

  In charged fluids obeying particle-hole symmetry, such as the Dirac fluid in graphene, charge transport is diffusive despite the presence of ballistically propagating sound waves: sound waves "hydrodynamically decouple" from the slower charge fluctuations. For quasi-one-dimensional fluids, we show that this symmetry-protected charge diffusion is not smoothly connected to the normal diffusion that arises when momentum conservation is broken by noise (or static impurities). Instead, the charge diffusion constant is a discontinuous function of noise, which (in the weak-noise limit) depends only on the ratio of momentum and energy relaxation rates. In the special limit of momentum-conserving noise (e.g., spatially uniform fluctuations of the Hamiltonian), the diffusion constant diverges in the presence of noise. We describe the resulting superdiffusion in terms of coupled Burgers equations. We present a general mechanism--hydrodynamic recoupling--by which weak noise can induce singular changes in transport coefficients. Our results highlight the limits of zero-noise extrapolation for predicting dynamical quantities like diffusion constants.

  PublisherDOI

• Long-lived local quantum coherences from hydrodynamic large deviations

  arXiv (Cornell University) · 2026-04-29

  preprintOpen accessSenior author

  We develop a framework to describe how quantum coherences between distinct charge sectors evolve under generic charge-conserving dynamics. Our framework captures the nonperturbative interactions between quantum coherences and hydrodynamic large deviations -- i.e., rare ``voids'' of low charge entropy. Conditional on surviving, the quantum coherence and its surrounding void form a collective polaron-like object. In one dimension, even at infinite temperature, we show that the lifetime of coherences is parametrically enhanced because they bind to voids. We use our framework to address two fundamental questions about generic quantum dynamics with a conserved charge. First, we argue that gapped Ruelle-Pollicott resonances are absent in the weak-noise limit, even in sectors of operator space that contain no hydrodynamic slow modes: instead, the spectral gap in all sectors vanishes nonperturbatively in the noise strength. Second, we compute the spacetime asymptotics of the dynamical single-particle Green's function, both in the weak-noise regime and in the absence of noise. In the noiseless case, we find that the void-coherence polaron undergoes subdiffusion, with an exponent we calculate. We support our general arguments with a microscopic derivation for random charge-conserving circuits, as well as numerical evidence from tensor-network simulations.

  PublisherDOI

• Detecting vortex motion through spatially correlated nonequilibrium noise

  arXiv (Cornell University) · 2026-05-18

  preprintOpen accessSenior author

  Resistive transport near a superconducting phase can arise from the motion of normal-state quasiparticles or that of vortices. The conductivity alone does not distinguish between these mechanisms. We propose an unambiguous method for telling them apart, using the recently developed experimental tool of covariance magnetometry, which uses nitrogen-vacancy centers in diamond to probe real-time spatiotemporal correlations in magnetic noise. Our key insight is that, under an applied current, the underlying charge carriers leave a directional fingerprint in the spatially correlated magnetic noise above the sample: ordinary electric carriers drift parallel to the current, whereas vortices, owing to the Magnus force, drift perpendicular to it. The noise covariance detects this anisotropy and identifies the vortex-driven nature of transport. We compute the noise correlations expected for a representative thin-film superconductor and demonstrate that the anisotropic signal is well within the reach of current experimental capabilities.

  PublisherDOI

• Long-lived local quantum coherences from hydrodynamic large deviations

  ArXiv.org · 2026-04-29

  articleOpen accessSenior author

  We develop a framework to describe how quantum coherences between distinct charge sectors evolve under generic charge-conserving dynamics. Our framework captures the nonperturbative interactions between quantum coherences and hydrodynamic large deviations -- i.e., rare ``voids'' of low charge entropy. Conditional on surviving, the quantum coherence and its surrounding void form a collective polaron-like object. In one dimension, even at infinite temperature, we show that the lifetime of coherences is parametrically enhanced because they bind to voids. We use our framework to address two fundamental questions about generic quantum dynamics with a conserved charge. First, we argue that gapped Ruelle-Pollicott resonances are absent in the weak-noise limit, even in sectors of operator space that contain no hydrodynamic slow modes: instead, the spectral gap in all sectors vanishes nonperturbatively in the noise strength. Second, we compute the spacetime asymptotics of the dynamical single-particle Green's function, both in the weak-noise regime and in the absence of noise. In the noiseless case, we find that the void-coherence polaron undergoes subdiffusion, with an exponent we calculate. We support our general arguments with a microscopic derivation for random charge-conserving circuits, as well as numerical evidence from tensor-network simulations.

  PublisherOA PDF

• Noncommuting zero-noise and zero-frequency limits in particle-hole symmetric fluids

  ArXiv.org · 2026-01-01

  articleOpen accessSenior author

  In charged fluids obeying particle-hole symmetry, such as the Dirac fluid in graphene, charge transport is diffusive despite the presence of ballistically propagating sound waves: sound waves "hydrodynamically decouple" from the slower charge fluctuations. For quasi-one-dimensional fluids, we show that this symmetry-protected charge diffusion is not smoothly connected to the normal diffusion that arises when momentum conservation is broken by noise (or static impurities). Instead, the charge diffusion constant is a discontinuous function of noise, which (in the weak-noise limit) depends only on the ratio of momentum and energy relaxation rates. In the special limit of momentum-conserving noise (e.g., spatially uniform fluctuations of the Hamiltonian), the diffusion constant diverges in the presence of noise. We describe the resulting superdiffusion in terms of coupled Burgers equations. We present a general mechanism--hydrodynamic recoupling--by which weak noise can induce singular changes in transport coefficients. Our results highlight the limits of zero-noise extrapolation for predicting dynamical quantities like diffusion constants.

  PublisherOA PDF

• Theory of Two-Qubit $T_2$ Spectroscopy of Quantum Many-Body Systems

  ArXiv.org · 2026-03-18

  articleOpen access

  Multi-qubit quantum sensors are rapidly emerging as platforms that extend the capabilities of conventional single-qubit sensing. In this work we show how suitable pulse sequences applied to a two-qubit sensor enable separate extraction of the response and noise of a probed environment within a $T_2$ spectroscopy framework. By resorting to representative examples, we demonstrate that this approach can resolve the spatio-temporal spreading of correlations in a many-body system. In particular, the resulting correlated dephasing signal captures features such as the dispersion of low-energy excitations, which manifest as light-cone-like profiles in the propagation of correlations. We further show that non-equilibrium conditions, for instance those induced by external driving, can modify this profile by producing additional fringes outside the light-cone. As a complementary application, we demonstrate that the method clearly distinguishes between different transport regimes in the system, including ballistic spreading, diffusive broadening, and the crossover between them.

  PublisherOA PDF

• Data for [Strong-to-Weak Symmetry Breaking in Open Quantum Systems: From Discrete Particles to Continuum Hydrodynamics]

  Zenodo (CERN European Organization for Nuclear Research) · 2026-02-17

  datasetOpen access
  PublisherDOI

• Algorithmic Locality via Provable Convergence in Quantum Tensor Networks

  arXiv (Cornell University) · 2026-04-23

  preprintOpen accessSenior author

  Belief propagation has recently emerged as a powerful framework for evaluating tensor networks in higher dimensions, combining computational efficiency with provable analytical guarantees. In this work, we develop the first end-to-end theory of tensor network belief propagation for a class of projected entangled pair states satisfying \emph{strong injectivity}. We show that when the injectivity parameter exceeds a constant threshold, BP fixed points can be found efficiently, and a cluster-corrected BP algorithm computes physical quantities to $1/\mathrm{poly}(N)$ error in $\mathrm{poly}(N)$ time for an $N$ qubit system. We identify a striking phenomenon we term \emph{algorithmic locality}: local perturbations of the tensor network affect the BP fixed point with an influence decaying rapidly with distance. As a result, updates to the fixed point after a local perturbation can be carried out using only local recomputation. Moreover, through the cluster expansion, this locality extends to observables, implying that local expectation values can be approximated from local data with controlled accuracy. Our results provide the first rigorous guarantee for the effectiveness of tensor-network belief propagation on a wide class of many-body states, bridging a gap between widely used numerical practice and provable algorithmic performance.

  PublisherDOI

Recent grants

• CAREER: Quantum many-body physics beyond the Boltzmann paradigm: prethermalization, many-body localization, and their applications

  NSF · $484k · 2017–2022

• CAREER: Quantum many-body physics beyond the Boltzmann paradigm: prethermalization, many-body localization, and their applications

  NSF · $109k · 2022–2023

• Collaborative Research: Quantum Criticality, Localization and Dynamics in Quasiperiodic Systems

  NSF · $136k · 2023–2024

• Collaborative Research: Quantum Criticality, Localization and Dynamics in Quasiperiodic Systems

  NSF · $145k · 2021–2023

Frequent coauthors

• Romain Vasseur

  University of Massachusetts Amherst

  111 shared

• Michael Knap

  49 shared

• David A. Huse

  43 shared

• Benjamin Lev

  Stanford University

  35 shared

• J. H. Pixley

  Flatiron Health (United States)

  33 shared

• Vadim Oganesyan

  College of Staten Island

  32 shared

• Brayden Ware

  30 shared

• Michael J. Gullans

  28 shared

Labs

• Electrical and Computer EngineeringPI

Awards & honors

• NSF CAREER Award (2017)