Talk Details

Monday, March 11

  • 8:30 AM - Waseem Bakr / Probing dynamical properties of Fermi-Hubbard systems with a quantum gas microscope / The normal state of high-temperature superconductors exhibits anomalous transport and spectral properties that are poorly understood. Cold atoms in optical lattices have been used to realize the celebrated Fermi-Hubbard model, widely believed to capture the essential physics of these materials. The recent development of fermionic quantum gas microscopes has enabled studying Hubbard systems with single-site resolution. Most studies have focused on probing equal-time spin and density correlations. In this talk, I will report on using a microscope to probe response functions associated with unequal-time correlations relevant for understanding the pseudogap and strange metal regimes of Fermi-Hubbard systems. First, I will describe the development of a technique to measure microscopic diffusion, and hence resistivity, in doped Mott insulators. We have found that this resistivity exhibits a linear dependence on temperature and violates the Mott-Ioffe-Regel limit, two signatures of strange metallic behavior. Next, I will report on the development of angle-resolved photoemission spectroscopy (ARPES) for Hubbard systems and its application to studying pseudogap physics in an attractive Hubbard system across the BEC-BCS crossover, setting the stage for future studies of the pseudogap regime in repulsive Hubbard systems.
  • 9:15 AM - Hong Liu / Maximal quantum chaos and hydrodynamics /
  • 10:30 AM - Lea Santos / Thouless and Relaxation Timescales in Many-Body Quantum Systems / Using experimental observables and realistic models, we found that there is not only one, but two very long timescales involved in the relaxation process of many-body quantum systems: the Thouless time and the relaxation time. The Thouless time refers to the point beyond which the dynamics acquire universal features and relaxation happens when the evolution reaches a stationary state. Since the initial many-body state spreads over an exponentially large many-body Hilbert space, both times increase exponentially with system size. We show that in chaotic systems, the Thouless time is smaller than the relaxation time, while for systems approaching a many-body localized phase, they merge together. Our results for the realistic chaotic models are compared with those for random matrices, which corroborates their generality.
  • 4:00 PM - Ana Maria Rey / Unifying fast scrambling, thermalization and entanglement through the measurement of FOTOCs / One of the most exciting developments in recent years has been the emergent synergy between what used to be disparate fields in physics. Central to the dialogue has been the concept of out-of-time-order correlations (OTOCs) which are allowing us to connect many of the same underlying problems using a common language borrowed from quantum information theory. Here, I will discuss that a specific family of OTOCs which we denote as FOTOCs, not only are experimentally accessible via time reversal of the many-body dynamics followed by a fidelity measurement, but also can be used as a unifying diagnostic tool to elucidate the intrinsic connection between scrambling, volume law entanglement, ergodicity, quantum chaos, and the associated butterfly effect in the underlying semiclassical dynamics of a manybody system. I will show the utility of FOTOCs by studying them in the Dicke model, an iconic model in quantum optics recently implemented in atomic and trapped-ion setups. This model describes the coupling of a large spin to an oscillator. Our observations may open a path for the experimental use of FOTOCs to quantify fast scrambling, and to identify possible candidates of black hole analogs in controllable quantum systems.
  • 4:45 PM - Steve Gubser / From 2-adic numbers to logarithmic light cones with cold atoms / (slides) / I will discuss XXZ spins chains with sparse, non-local couplings. If a spectral parameter characterizing how these couplings depend on separation is dialed between two extreme limits, it results in an interpolation between the familiar integrable nearest neighbor XXZ model and a limit that possesses 2-adic symmetry. Such spin chains should be experimentally realizable using alkali atoms in an optical lattice. In the middle of the interpolation, we expect that information propagates across the entire system in a time that increases only logarithmically in the total number of sites---qualitatively faster than the power law increase at other points along the interpolation. I will give an overview of theoretical results on these models, partly from numerical simulation, introducing the 2-adic numbers in an elementary way and emphasizing the possibility of finding quantum chaos and fast scrambling in a simple system without randomness. Results will be based on ongoing collaboration with G. Bentsen, A. Buyskikh, A. Daley, E. Davis, T. Hashizume, and M. Schleier-Smith.
  • 6:00 PM - Herman Verlinde / Comments on the holographic dual of SYK /

Tuesday, March 12

  • 8:30 AM - Aharon Kapitunik /
  • 9:15 AM - Sean Hartnoll / Quantum Scrambling and State Dependence of the Butterfly Velocity / Operator growth in spatially local quantum many-body systems defines a scrambling velocity. I will prove that this scrambling velocity bounds the state dependence (for example, the temperature dependence) of the out-of-time-ordered correlator in local lattice models. This amounts to a basic constraint on quantum chaos from locality. Thus, for example, while operators that do not grow with time can have an associated butterfly velocity, that velocity is necessarily temperature-independent. For scrambling operators, in contrast, the butterfly velocity shows a crossover from a microscopic high temperature value to a distinct value at temperatures below the energy gap.
  • 10:30 AM - Amir Yacoby /
  • 4:00 PM - Poster session

Wednesday, March 13

  • 8:30 AM - Paola Cappellaro /
  • 9:15 AM - Leonid Bunimovich / Physical versus mathematical billiards /
  • 10:30 AM - Poul Jessen / Simulating Complex Dynamics on a Small-Scale, Highly Accurate Analog Quantum Simulator /
  • 11:15 AM - Subir Sachdev / Transport and Chaos from SYK Models / (slides) /
  • 4:30 PM - Physics cafe with Vedika Khemani and Bryce Gadway
  • 5:40 PM - Public lecture with Brian Swingle / Entangled Butterflies: Chaos in the Quantum World

Thursday, March 14

  • 8:30 AM - Mikhail Lukin /
  • 9:15 AM - Tomaz Prosen / Exact Spectral Form Factor and Entanglement Spreading in a Minimal Model of Maximal Many-Body Quantum Chaos / I will discuss the concept of self-duality (or dual unitarity) in periodically driven (Floquet) quantum Ising spin 1/2 chains which allows for some non-trivial exact computations, despite manifest non-integrability of the model. I will outline a rigorous derivation of random matrix spectral form factors in the model and universal entanglement spreading which saturates the minimal cut bounds.
  • 10:30 AM - Felix Izrailev / Onset of many-body chaos and thermalization in finite systems of interacting Bose and Fermi particles /
  • 4:00 PM - Bryce Gadway / Studying localization physics and chaos in synthetic lattices /
  • 4:45 PM - Sriram Ganeshan / Quantum vs chaos in models inspired by non-commutative AdS_2 /
  • 6:00 PM - Xiangyu Cao / Universal operator growth hypothesis / We present a hypothesis for the universal properties of operators evolving under Hamiltonian dynamics in many-body systems. The hypothesis states that successive Lanczos coefficients in the continued fraction expansion of the Green’s functions grow linearly with rate α in generic systems. The rate α — an experimental observable — governs the exponential growth of operator complexity in a sense we make precise. This exponential growth even prevails beyond semiclassical or large-N limits. Moreover, α upper bounds a large class of operator complexity measures, including the out- of-time-order correlator. As a result, we conjecture a sharp bound on Lyapunov exponents λ ≤ 2α, which generalizes the known universal low-temperature bound λ ≤ 2πT . We illustrate our results in paradigmatic examples such as non-integrable spin chains, the Sachdev-Ye-Kitaev model, and classical models. As a further application, we use the hypothesis in conjunction with the recursion method to develop a technique for computing diffusion constants. This talk is based on joint work with Daniel Parker, Thomas Scaffidi and Ehud Altman (arxiv: 1812.08657).

Friday, March 15

  • 8:30 AM - Richard Fletcher /
  • 9:15 AM - Vedika Khemani /
  • 10:30 AM - Masanori Hanada /
  • 11:15 AM - Xiaoliang Qi / Probing operator scrambling by initial state dependence / We propose a way to experimentally probe the operator size growth. In a quench problem with a particular ensemble of initial states, the variation of physical observable at later time is a probe of the operator size distribution.
  • 4:00 PM - Horacio Pastawski / Emergent perturbation independent decay of the Loschmidt echo in a many-spin system studied through scaled dipolar dynamics / Of particular interest for quantum technologies and the basic physics of quantum chaos [1], thermalization [2] and quantum gravity is to asses how a local information scrambles through a grid of interacting qubits/spins due to unitary evolution, i.e. a "quantum butterfly effect" (QBE), and how well the scrambled information could be recovered. Here, we introduce two protocols for our solid-state nuclear magnetic resonance spectrometer [3], i.e. our analog quantum computer, that scale down the natural dipolar Hamiltonian H (and hence the characteristic rate 1/T₂ associated with its second moment) by an arbitrary factor ±δ. By applying them to the dense network of interacting ¹H spins in polycrystalline Adamantane (each of the 16 spins in a FCC lattice site interacts quasi-randomly with each of the 16 spins in the 12 neighboring grid sites) we can perform time-reversal schemes to evaluate Out of Time Ordered Correlators (OTOCs) and Loschmidt Echoes (LE). [4] These intimately related quantities are well known as powerful metrics of information scrambling and equilibration in a many-body systems. From the OTOCs we can follow a localized quantum information as it scrambles through over 2¹⁰⁰ states of the Hilbert space, under the action of the dipolar Hamiltonian. From the LE we get the time-scale T₃ that quantifies to how well the scrambled information can be recovered through time reversal in presence of a perturbation Σ. Its time-scale TΣ was obtained from the decay of the LE for a Hamiltonian with δ=0. As we change the relative time scale TΣ respect to the Hamiltonian's time scale T₂ we get a direct measure of the limit of vanishing T₂/ TΣ, where the asymptotic relation T₂/T₃=(0.15±0.02) was obtained. This is consistent with our Central Hypothesis of Irreversibility [2], that states that in an unbounded many-spin system the LE decay enters in a perturbation independent regime with a rate 1/T₃ proportional to 1/T₂ the local second moment of the Hamiltonian, i.e. in many-body system, the QBE leads to practical irreversibility stabilizing it as a statistical equilibration mechanism.
  • 4:15 PM - Shenglong Xu /