Publications

Order by: publication date number of citations

• Status of the Muon g-2 experiment at Fermilab

  A. Driutti for the Muon g-2 Collaboration

  SciPost Phys. Proc. 1, 033 (2019) · published 21 February 2019 | Toggle abstract · pdf

  The aim of the Muon g − 2 Experiment at Fermilab (E989) is to measure the muon anomalous magnetic moment (aμ) with a relative precision of 140 parts- per-billion (ppb). This precision, which is a factor of four improvement from the current experimental result, will allow for a much more stringent test of the Standard Model. This paper present the current status of the experimental measurement of aμ after the first physics run.

  2 citations

• Integrability and complexity in quantum spin chains

  Ben Craps, Marine De Clerck, Oleg Evnin, Philip Hacker

  SciPost Phys. 16, 041 (2024) · published 7 February 2024 | Toggle abstract · pdf

  There is a widespread perception that dynamical evolution of integrable systems should be simpler in a quantifiable sense than the evolution of generic systems, though demonstrating this relation between integrability and reduced complexity in practice has remained elusive. We provide a connection of this sort by constructing a specific matrix in terms of the eigenvectors of a given quantum Hamiltonian. The null eigenvalues of this matrix are in one-to-one correspondence with conserved quantities that have simple locality properties (a hallmark of integrability). The typical magnitude of the eigenvalues, on the other hand, controls an explicit bound on Nielsen's complexity of the quantum evolution operator, defined in terms of the same locality specifications. We demonstrate how this connection works in a few concrete examples of quantum spin chains that possess diverse arrays of highly structured conservation laws mandated by integrability.

  2 citations

• Topologically stable ergodicity breaking from emergent higher-form symmetries in generalized quantum loop models

  Charles Stahl, Rahul Nandkishore, Oliver Hart

  SciPost Phys. 16, 068 (2024) · published 8 March 2024 | Toggle abstract · pdf

  We present a set of generalized quantum loop models that provably exhibit topologically stable ergodicity breaking. These results hold for both periodic and open boundary conditions, and derive from a one-form symmetry (notably not being restricted to sectors of extremal one-form charge). We identify simple models in which this one-form symmetry can be emergent, giving rise to the aforementioned ergodicity breaking as an exponentially long-lived prethermal phenomenon. We unveil a web of dualities that connects these models, in certain limits, to models that have previously been discussed in the literature. We also identify nonlocal conserved quantities in such models, which correspond to patterns of system-spanning domain walls and are robust to the addition of arbitrary $k$-local perturbations.

  2 citations

• Twist-3 partonic distributions from lattice QCD

  Shohini Bhattacharya, Krzysztof Cichy, Martha Constantinou, Andreas Metz, Aurora Scapellato, Fernanda Steffens

  SciPost Phys. Proc. 8, 057 (2022) · published 12 July 2022 | Toggle abstract · pdf

  Twist-3 partonic distributions contain important information that characterizes nucleon's structure. In this work, we show our lattice exploration of the twist-3 PDFs $g_T(x)$, and $h_L(x)$. We also present our preliminary results on the twist-3 GPD $\tilde{G}_2(x)$. We use the quasi-distribution approach to connect the lattice-extracted matrix elements, renormalized in the RI/MOM scheme, to light-cone distributions, applying the matching procedure that we developed in parallel. We also calculate the twist-2 counterparts of $g_T(x)$ and $h_L(x)$, i.e. $g_1(x)$, and $h_1(x)$, and test the Wandzura-Wilczek approximation.

  2 citations

• Hamiltonian reconstruction as metric for variational studies

  Kevin Zhang, Samuel Lederer, Kenny Choo, Titus Neupert, Giuseppe Carleo, Eun-Ah Kim

  SciPost Phys. 13, 063 (2022) · published 23 September 2022 | Toggle abstract · pdf

  Variational approaches are among the most powerful techniques to approximately solve quantum many-body problems. These encompass both variational states based on tensor or neural networks, and parameterized quantum circuits in variational quantum eigensolvers. However, self-consistent evaluation of the quality of variational wavefunctions is a notoriously hard task. Using a recently developed Hamiltonian reconstruction method, we propose a multi-faceted approach to evaluating the quality of neural-network based wavefunctions. Specifically, we consider convolutional neural network (CNN) and restricted Boltzmann machine (RBM) states trained on a square lattice spin-1/2 J1-J2 Heisenberg model. We find that the reconstructed Hamiltonians are typically less frustrated, and have easy-axis anisotropy near the high frustration point. In addition, the reconstructed Hamiltonians suppress quantum fluctuations in the large J2 limit. Our results highlight the critical importance of the wavefunction's symmetry. Moreover, the multi-faceted insight from the Hamiltonian reconstruction reveals that a variational wave function can fail to capture the true ground state through suppression of quantum fluctuations.

  2 citations

• Quantifying uncertainties in crystal electric field Hamiltonian fits to neutron data

  Allen Scheie

  SciPost Phys. Core 5, 018 (2022) · published 31 March 2022 | Toggle abstract · pdf

  We systematically examine uncertainties from fitting rare earth single-ion crystal electric field (CEF) Hamiltonians to inelastic neutron scattering data. Using pyrochlore and delafossite structures as test cases, we find that uncertainty in CEF parameters can be large despite visually excellent fits. These results show Yb$^{3+}$ compounds have particularly large $g$-tensor uncertainty because of the few available peaks. In such cases, additional constraints are necessary for meaningful fits.

  2 citations

• Dynamics of hot Bose-Einstein condensates: stochastic Ehrenfest relations for number and energy damping

  Rob G. McDonald, Peter S. Barnett, Fradom Atayee, Ashton S. Bradley

  SciPost Phys. 8, 029 (2020) · published 18 February 2020 | Toggle abstract · pdf

  Describing partially-condensed Bose gases poses a long-standing theoretical challenge. We present exact stochastic Ehrenfest relations for the stochastic projected Gross-Pitaevskii equation, including both number and energy damping mechanisms, and all projector terms that arise from the energy cutoff separating system from reservoir. We test the theory by applying it to the centre of mass fluctuations of a harmonically trapped prolate system, finding close agreement between c-field simulations and analytical results. The formalism lays the foundation to analytically explore experimentally accessible hot Bose-Einstein condensates.

  2 citations

• Remarks on Berry connection in QFT, anomalies, and applications

  Mykola Dedushenko

  SciPost Phys. 15, 167 (2023) · published 17 October 2023 | Toggle abstract · pdf

  Berry connection has been recently generalized to higher-dimensional QFT, where it can be thought of as a topological term in the effective action for background couplings. Via the inflow, this term corresponds to the boundary anomaly in the space of couplings, another notion recently introduced in the literature. In this note we address the question of whether the old-fashioned Berry connection (for time-dependent couplings) still makes sense in a QFT on $\Sigma^{(d)}× \mathbb{R}$, where $\Sigma^{(d)}$ is a $d$-dimensional compact space and $\mathbb{R}$ is time. Compactness of $\Sigma^{(d)}$ relieves us of the IR divergences, so we only have to address the UV issues. We describe a number of cases when the Berry connection is well defined (which includes the $tt^*$ equations), and when it is not. We also mention a relation to the boundary anomalies and boundary states on the Euclidean $\Sigma^{(d)} × \mathbb{R}_{≥ 0}$. We then work out the examples of a free 3D Dirac fermion and a 3D $\mathcal{N}=2$ chiral multiplet. Finally, we consider 3D theories on $\mathbb{T}^2× \mathbb{R}$, where the space $\mathbb{T}^2$ is a two-torus, and apply our machinery to clarify some aspects of the relation between 3D SUSY vacua and elliptic cohomology. We also comment on the generalization to higher genus.

  2 citations

• Lyapunov exponents and entanglement entropy transition on the noncommutative hyperbolic plane

  Sriram Ganeshan, Alexios P. Polychronakos

  SciPost Phys. Core 3, 003 (2020) · published 20 August 2020 | Toggle abstract · pdf

  We study quantum dynamics on noncommutative spaces of negative curvature, focusing on the hyperbolic plane with spatial noncommutativity in the presence of a constant magnetic field. We show that the synergy of noncommutativity and the magnetic field tames the exponential divergence of operator growth caused by the negative curvature of the hyperbolic space. Their combined effect results in a first-order transition at a critical value of the magnetic field in which strong quantum effects subdue the exponential divergence for {\it all} energies, in stark contrast to the commutative case, where for high enough energies operator growth always diverge exponentially. This transition manifests in the entanglement entropy between the `left' and `right' Hilbert spaces of spatial degrees of freedom. In particular, the entanglement entropy in the lowest Landau level vanishes beyond the critical point. We further present a non-linear solvable bosonic model that realizes the underlying algebraic structure of the noncommutative hyperbolic plane with a magnetic field.

  2 citations

• Variation along liquid isomorphs of the driving force for crystallization

  Ulf R. Pedersen, Karolina Adrjanowicz, Kristine Niss, Nicholas P. Bailey

  SciPost Phys. 2, 022 (2017) · published 21 June 2017 | Toggle abstract · pdf

  We investigate the variation of the driving force for crystallization of a supercooled liquid along isomorphs, curves along which structure and dynamics are invariant. The variation is weak, and can be predicted accurately for the Lennard-Jones fluid using a recently developed formalism and data at a reference temperature. More general analysis allows interpretation of experimental data for molecular liquids such as dimethyl phthalate and indomethacin, and suggests that the isomorph scaling exponent $\gamma$ in these cases is an increasing function of density, although this cannot be seen in measurements of viscosity or relaxation time.

  2 citations