# Bulletin of the American Physical Society

# 2020 Fall Meeting of the APS Division of Nuclear Physics

## Volume 65, Number 12

## Thursday–Sunday, October 29–November 1 2020; Time Zone: Central Time, USA

## Session MH: MH Mini-Symposium: Quantum Information Science and Technology for Nuclear Physics III |
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Chair: Alessandro Roggero, University of Washington-Seattle |

Saturday, October 31, 2020 2:00PM - 2:12PM |
MH.00001: Loop, String, and Hadron Dynamics in SU(2) Hamiltonian Lattice Gauge Theories Jesse Stryker, Indrakshi Raychowdhury We present a reformulation of an SU(2) Hamiltonian lattice gauge theory---a loop-string-hadron (LSH) formulation---that characterizes dynamics directly in terms of its loop, string, and hadronic degrees of freedom, while alleviating several disadvantages of quantumly simulating the Kogut-Susskind formulation. This LSH formulation, derived from Schwinger bosons, transcends the local loop formulation of ($d$+1)-dimensional lattice gauge theories by incorporating staggered quarks, furnishing an algebra of gauge-singlet operators, and succinctly encoding the dynamics among states having Gauss’s law built in to them. LSH operators are factored into explicit products of ``normalized'' ladder operators and diagonal matrices, priming them for applications in classical or quantum algorithms. Self-contained translations of the Hamiltonian are given up to $d$=3. [Preview Abstract] |

Saturday, October 31, 2020 2:12PM - 2:24PM |
MH.00002: Solving Gauss’s Law on Digital Quantum Computers with Loop-String-Hadron Digitization Indrakshi Raychowdhury, Jesse Stryker We show that using the loop-string-hadron (LSH) formulation of SU(2) lattice gauge theory (arXiv:1912.06133) as a basis for digital quantum computation easily solves an important problem of fundamental interest: implementing gauge invariance (or Gauss’s law) exactly. We first discuss the structure of the LSH Hilbert space in d spatial dimensions, its truncation, and its digitization with qubits. Error detection and mitigation in gauge theory simulations would benefit from physicality ``oracles,” so we decompose circuits that flag gauge invariant wavefunctions. We then analyze the logical qubit costs and entangling gate counts involved with the protocols. The LSH basis could save or cost more qubits than a Kogut-Susskind-type representation basis, depending on how that is digitized as well as the spatial dimension. The numerous other clear benefits encourage future studies into applying this framework. [Preview Abstract] |

Saturday, October 31, 2020 2:24PM - 2:36PM |
MH.00003: New digitization strategies for relativistic quantum field theories Niklas Mueller, Joao Barata, Andrey Tarasov, Raju Venugopalan Quantum computers may become powerful tools to simulate various problems in quantum field theory, yet at present are restricted to lower dimensions and small volumes. Common digitization strategies are based on local Hilbert-space decomposition, which may not be optimal for systems with large volumes but few (or not so few) particles. Examples are (non-relativistic) quantum chemistry or low energy nuclear physics, but also relativistic systems in high energy scattering experiments. Using a relativistic scalar $\phi^4$ theory as a simple example, we propose a novel ‘single-particle’ digitization strategy for relativistic quantum field theories and discuss quantum simulating S-matrix scattering experiments. For such problems our strategy uses significantly less resources than other approaches. We discuss renormalization and Lorentz covariance, and application in low energy nuclear physics. [Preview Abstract] |

Saturday, October 31, 2020 2:36PM - 2:48PM |
MH.00004: Gluon Field Digitization for Quantum Computers Henry Lamm IV The efficient digitization required for the quantum simulations of QCD can be obtained by approximating continuous SU(3) gluon fields by discrete subgroups. In this talk, we discuss on-going efforts to develop this program of digitization: deriving improved discrete group lattice actions, classical simulations for quantifying systematic errors, and implementable circuits for digital quantum computers. [Preview Abstract] |

Saturday, October 31, 2020 2:48PM - 3:00PM |
MH.00005: Qubit Regularization of Asymptotic Freedom Shailesh Chandrasekharan, Hersh Singh, Alex Buser, Tanmoy Bhattacharya, Rajan Gupta Qubit regularization is a method of truncating the local lattice Hilbert space while being able to reproduce the relevant continuum quantum field theory. It is an important step in designing QFTs that can be solved on a quantum computer. We provide evidence that for the two dimensional O(3) sigma model we may be able to achieve asymptotic freedom with only two qubits per lattice site. In particular we reproduce the universal step scaling function of the traditional model using a carefully chosen two-qubit model, which we call a "qubit-comb." We show that our model reproduces the traditional model up to very large correlation lengths. Our method can be considered as an alternative to the well known D-theory approach. [Preview Abstract] |

Saturday, October 31, 2020 3:00PM - 3:12PM |
MH.00006: Qubit O(N) nonlinear sigma models and large charge effective field theories Hersh Singh Recent work using an effective field theory (EFT) approach for conformal field theories (CFTs) in sectors of large global charges has shown that the leading behaviour of anomalous dimensions of large-charge operators can be expressed in terms of a few low-energy constants (LECs) of the EFT. By performing Monte Carlo computations using worm algorithms in a worldline formulation, we compute the anomalous dimensions of large-charge operators and extract the LECs of the $O(N)$ large-charge EFT up to $N=8$. To alleviate the signal-to-noise ratio problem present in traditional lattice $O(N)$ formulations, we use a ``qubit" formulation of the $O(N)$ model, which was recently shown to have a quantum critical point in the $O(N)$ Wilson-Fisher universality class in $(2+1)$ dimensions. Lattice calculations with the qubit model enable us to extract the leading LECs of the EFT. We compare against recent analytic results for the LECs from a combined large-charge and large-$N$ expansion, and find a nice agreement. [Preview Abstract] |

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