@article {baldwin_distinct_2021,
title = {Distinct critical behaviors from the same state in quantum spin and population dynamics perspectives},
journal = {Phys. Rev. E},
volume = {103},
number = {1},
year = {2021},
note = {Place: ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA Publisher: AMER PHYSICAL SOC Type: Article},
month = {jan},
abstract = {There is a deep connection between the ground states of transverse-field spin systems and the late-time distributions of evolving viral populations-within simple models, both are obtained from the principal eigen-vector of the same matrix. However, that vector is the wave-function amplitude in the quantum spin model, whereas it is the probability itself in the population model. We show that this seemingly minor difference has significant consequences: Phase transitions that are discontinuous in the spin system become continuous when viewed through the population perspective, and transitions that are continuous become governed by new critical exponents. We introduce a more general class of models that encompasses both cases and that can be solved exactly in a mean-field limit. Numerical results are also presented for a number of one-dimensional chains with power-law interactions. We see that well-worn spin models of quantum statistical mechanics can contain unexpected new physics and insights when treated as population-dynamical models and beyond, motivating further studies.},
issn = {2470-0045},
doi = {10.1103/PhysRevE.103.012106},
author = {Baldwin, C. L. and Shivam, S. and Sondhi, S. L. and Kardar, M.}
}
@article { ISI:000555323500001,
title = {Quenched vs Annealed: Glassiness from SK to SYK},
journal = {Phys. Rev. X},
volume = {10},
number = {3},
year = {2020},
month = {AUG 4},
pages = {031026},
publisher = {AMER PHYSICAL SOC},
type = {Article},
abstract = {We show that any Sachdev-Ye-Kitaev- (SYK) like model with finite-body interactions among local degrees of freedom, e.g., bosons or spins, has a fundamental difference from the standard fermionic model: The former model fails to be described by an annealed free energy at low temperature. In this respect, such models more closely resemble spin glasses. We demonstrate this by two means: first, a general theorem proving that the annealed free energy is divergent at low temperature in any model with a tensor product Hilbert space, and second, a replica treatment of two prominent examples which exhibit phase transitions from an {\textquoteleft}{\textquoteleft}annealed{{\textquoteright}{\textquoteright}} phase to a {\textquoteleft}{\textquoteleft}nonannealed{{\textquoteright}{\textquoteright}} phase as a function of the temperature. We further show that this effect appears only at O(N)th order in a 1/N expansion, even though lower-order terms misleadingly seem to converge. Our results prove that the nonbosonic nature of the particles in the SYK model is an essential ingredient for its physics, highlight connections between local models and spin glasses, and raise important questions as to the role of fermions and/or glassiness in holography.},
issn = {2160-3308},
doi = {10.1103/PhysRevX.10.031026},
author = {Baldwin, C. L. and Swingle, B.}
}