We develop a framework to simulate jet quenching in nuclear environments on a quantum computer. The formulation is based on the light-front Hamiltonian dynamics of QCD. The Hamiltonian consists of three parts relevant for jet quenching studies: kinetic, diffusion and splitting terms. In the basis made up of $n$-particle states in momentum space, the kinetic Hamiltonian is diagonal. Matrices representing the diffusion and splitting parts are sparse. The diffusion part of the Hamiltonian depends on classical background gauge fields, which need to be sampled classically before constructing quantum circuits for the time evolution. The cost of the sampling scales linearly with the time length of the evolution and the momentum grid volume. The framework automatically keeps track of quantum interference and thus it can be applied to study the Landau-Pomeranchuk-Migdal effect in cases with more than two splittings, which is beyond the scope of state-of-the-art analyses, no matter whether the medium is static or expanding, thin or thick, hot or cold. We apply this framework to study a toy model and gluon in-medium radiation on a small lattice. The Landau-Pomeranchuk-Migdal effect that suppresses the total radiation probability is observed in the quantum simulation results of both the toy model and the gluon case.

Accurate predictions of inclusive scattering cross sections in the linear response regime require efficient and controllable methods to calculate the spectral density in a strongly-correlated many-body system. In this work we reformulate the recently proposed Gaussian Integral Transform technique in terms of Fourier moments of the system Hamiltonian which can be computed efficiently on a quantum computer. One of the main advantages of this framework is that it allows for an important reduction of the computational cost by exploiting previous knowledge about the energy moments of the spectral density. For a simple model of medium mass nucleus like ⁴⁰Ca and target energy resolution of 1 MeV we find an expected speed-up of ≈ 125 times for the calculation of the giant dipole response and of ≈ 50 times for the simulation of quasi-elastic electron scattering at typical momentum transfers.

The time-evolution of multi-neutrino entanglement and correlations are studied in two-flavor collective neutrino oscillations, relevant for dense neutrino environments, building upon previous works. Specifically, simulations performed of systems with up to 12 neutrinos using Quantinuum’s H1-1 20 qubit trapped-ion quantum computer are used to compute n-tangles, and two- and three-body correlations, probing beyond mean-field descriptions. n-tangle re-scalings are found to converge for large system sizes.

An adiabatic state preparation technique, called the adiabatic spiral, is proposed for the Heisenberg model. This technique is suitable for implementation on a number of quantum simulation platforms such as Rydberg atoms, trapped ions, or superconducting qubits. Classical simulations of small systems suggest that it can be successfully implemented in the near future. A comparison to Trotterized time evolution is performed and it is shown that the adiabatic spiral is able to outperform Trotterized adiabatics.

Strongly-coupled gauge theories far from equilibrium may exhibit unique features that could illuminate the physics of early universe and of hadron and ion colliders. Studying real-time phenomena has proven challenging with classical-simulation methods, but is a natural application of quantum-simulation devices. To demonstrate this prospect, we quantum compute non-equal time correlation functions and perform entanglement tomography of non-equilibrium states of a simple lattice gauge theory, the Schwinger model, using a trapped-ion quantum computer by IonQ Inc. As an ideal target for near-term devices, a recently-predicted dynamical quantum phase transition in this model is studied by preparing, quenching, and tracking the subsequent non-equilibrium dynamics in three ways: i) overlap echos signaling dynamical transitions, ii) non-equal time correlation functions with an underlying topological nature, and iii) the entanglement structure of non-equilibrium states, including Entanglement Hamiltonians. These results constitute the first observation of a dynamical quantum phase transition in a lattice gauge theory on a quantum computer, and are a first step toward investigating topological phenomena in nuclear and high-energy physics using quantum technologies.

Anomalies are a powerful way to gain insight into possible lattice regularizations of a quantum field theory. In this work, we consider lattice regularizations of a class of the toy-models of QCD: the 1+1-dimensional asymptotically-free Grassmanian nonlinear sigma models with a theta term. We argue that the continuum anomaly for a given symmetry can be matched by a manifestly symmetric lattice regularization only if (i) the symmetry action is offsite, or (ii) if the continuum anomaly is reproduced exactly on the lattice. Using the Grassmanian nonlinear sigma models as a case study, we provide examples of lattice regularizations in which both possibilities are realized. For possibility (i), we generalize recent work for the  O(3)  NLSM with an arbitrary theta term, where it was regulated using model of qubits with a small extra dimension, solving a sign problem present in conventional formulations of theta vacua. We argue that Grassmannian NLSM can be obtained similarly from SU(N) antiferromagnets with a well-defined continuum limit, reproducing both the IR physics of theta vacua and the UV physics of asymptotic freedom. These results enable the application of new classical algorithms to lattice Monte Carlo studies of these quantum field theories, and provide a viable realization suited for their quantum simulation. On the other hand, we show that, perhaps surprisingly, the conventional lattice regularization of theta vacua due to Berg and Luscher reproduces the anomaly exactly on the lattice, providing a realization of the second possibility.

A framework for quantum simulations of real-time weak decays of hadrons and nuclei in a 2-flavor lattice theory in one spatial dimension is presented. A single generation of the Standard Model is mapped to spin operators via the Jordan-Wigner transformation, and both quantum chromodynamics and flavor-changing weak interactions are included in the dynamics, the latter through four-Fermi effective operators. This mapping requires 16 qubits per spatial lattice site. Quantum circuits which implement time evolution in this lattice theory are developed and run on Quantinuum’s H1 1 20-qubit trapped ion system to simulate the beta-decay of a single baryon on one lattice site. Simulations of the real-time evolution of a single baryon, including initial state preparation, are performed for both one and two Trotter time steps. We comment on the potential intrinsic error-correction properties of this type of lattice theory.

Quantum Darwinism builds on decoherence theory to explain the emergence of classical behavior within a quantum universe. We demonstrate that the differential geometric underpinnings of quantum mechanics provide a uniquely informative window into the structure of correlations needed to validate quantum Darwinism. This leads us to two crucial insights about the emergence of classical phenomenology, centered around the nullity of quantum discord. First, we show that the so-called branching structure of the joint state of system and environment is the only one compatible with zero discord. Second, we prove that for small, but nonzero discord, the structure of the globally pure state is arbitrarily close to the branching form. These provide strong evidence that this class of branching states is the only one compatible with the emergence of classical phenomenology, as described in quantum Darwinism.

The time-evolution of an Ising model with large driving fields over discrete time intervals is shown to be reproduced by an effective XXZ-Heisenberg model at leading order in the inverse field strength. For specific orientations of the drive field, the dynamics of the XXX-Heisenberg model is reproduced. These approximate equivalences, valid above a critical driving field strength set by dynamical phase transitions in the Ising model, are expected to enable quantum devices that natively evolve qubits according to the Ising model to simulate more complex systems.

The resource requirements for quantum simulations of 1+1 dimensional quantum chromodynamics are estimated. When formulated in axial gauge and with two flavors of quarks, this system requires 12 qubits per spatial site once Gauss’s law has been enforced to uniquely constrain the gauge fields. Classical computations and D-Wave’s quantum annealer Advantage are used to determine the hadronic spectrum, enabling a decomposition of the masses and a study of quark entanglement. We identify color “edge” states, resulting from open boundary conditions, that are confined within a screening length to the end of the lattice. Quantum circuits for the time evolution of SU(Nc) gauge theory with Nf flavors of quarks are developed and used to determine the resources required for large-scale quantum simulations. IBM’s 7-qubit quantum computers ibmq_jakarta and ibm_perth were used to compute the trivial vacuum-to-vacuum and trivial vacuum-to-qr qr bar probabilities in Nf=1 QCD with one spatial site from one Trotter step of the time-evolution operator.