Current Seminars

Ab initio nuclear structure theory aims to predict the structure of atomic nuclei from "first principles," employing systematically improvable approximations in the determination of inter-nucleon potentials and in the solution of the many-body Schrödinger equation. Over the past decade, the in-medium similarity renormalization group (IMSRG) has been established as a powerful and flexible method to approaching the many-body problem. The IMSRG solves for a unitary transformation that approximately diagonalizes the Hamiltonian (or produces an effective interaction within a valence space for shell model applications). This approximation can be systematically relaxed by including higher-body operators in the many-body solution. Recently, we have worked on extending the IMSRG to the next order, the IMSRG(3) with normal-ordered three-body operators. The IMSRG(3) truncation is formally more involved and also computationally substantially more expensive than the IMSRG(2), the well-established truncation used in applications so far. We have shown, however, that the most expensive terms in the IMSRG(3) can be truncated with little effect on the improved accuracy of the many-body solution, allowing the IMSRG(3) to be approximated at a reasonable computational cost comparable to other high fidelity nuclear structure methods like coupled cluster with approximate triples (CCSDT-1).

A key advantage of the IMSRG is its ability to interface with the shell model via the derivation of an effective valence space Hamiltonian (and consistent effective operators). This allows the IMSRG to describe open-shell nuclei easily, and this has been used to perform comprehensive studies of all isotopes up to iron. In calcium isotopes, the IMSRG(2) describes ground-state energies quite well, but struggles to quantitatively reproduce the spectra of calcium-48, a doubly-magic nucleus. Additionally, the trends in the charge radii of neutron-rich calcium are so far unexplained by ab initio methods. I will discuss the improved description of the structure of neutron-rich calcium isotopes made possible by the IMSRG(3) and what this means for existing discrepancies to experimental trends.


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Quantum simulation holds promise of enabling a complete description of high-energy scattering processes rooted in gauge theories of the Standard Model. A first step in such simulations is preparation of interacting hadronic wave packets. To create the wave packets, one typically resorts to adiabatic evolution to bridge between wave packets in the free theory and those in the interacting theory, rendering the simulation resource intensive. In this work, we construct a wave-packet creation operator directly in the interacting theory to circumvent adiabatic evolution, taking advantage of resource-efficient schemes for ground-state preparation, such as variational quantum eigensolvers. By means of an ansatz for bound mesonic excitations in confining gauge theories, which is subsequently optimized using classical or quantum methods, we show that interacting mesonic wave packets can be created efficiently and accurately using digital quantum algorithms that we develop. Specifically, we obtain high-fidelity mesonic wave packets in the Z2 and U(1) lattice gauge theories coupled to fermionic matter in 1+1 dimensions. Our method is applicable to both perturbative and non-perturbative regimes of couplings. The wave-packet creation circuit for the case of the Z2 lattice gauge theory is built and implemented on the Quantinuum H1-1 trapped-ion quantum computer using 13 qubits and up to 308 entangling gates. The fidelities agree well with classical benchmark calculations after employing a simple symmetry-based noise-mitigation technique. This work serves as a step toward quantum computing scattering processes in quantum chromodynamics.


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During a core-collapse supernova explosion, most of the energy released is carried away by the emitting neutrinos. To understand the dynamics of this explosion, we have to treat the neutrino transport in completion. However, the extreme conditions inside the supernova core allow neutrinos not only to frequently interact with matter but also with each other, which makes it a highly non-linear many-body problem with 10^58 neutrinos. Even with state-of-the-art computational methods such as tensor networks, this problem cannot be solved on classical computers. In fact, these simulations become even more complicated when a more realistic scenario with three active flavors is considered. Quantum simulations are a more natural way to simulate such quantum many-body systems. Simulations for collective neutrino oscillations on quantum computers have already been attempted but only few-neutrino systems could be simulated in such full-fledged quantum computations because of quantum hardware limitations. However, in the current noisy intermediate-scale quantum era, it is more efficient to employ a hybrid quantum-mechanical algorithm to solve this problem. In this talk, I will discuss my attempts to employ the hybrid quantum-classical algorithm to simulate collective neutrino oscillation dynamics and present some recent results on the measure of quantum entanglement. We have also made the first attempts to incorporate all three flavors in the neutrino many-body problem and found several interesting features about the generation of quantum entanglement in such a system. I will also talk about this more realistic three-flavor scenario and the potential utilization of qutrit-based quantum computers to simulate this case.

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Lattice Quantum Chromodynamics (LQCD) stands out as one of the most successful methods for non-perturbative predictions in high-energy physics. Despite its achievements, traditional computational techniques face limitations due to the notorious sign problem when dealing with dynamic observables in physical time or at non-vanishing chemical potential. Our recent work focuses on the complex Langevin (CL) method, which aims to overcome these challenges by generalizing the Stochastic Quantization approach. Successfully applied to real-time SU(N) gauge theories on a 1+3 dimensional lattice, CL enables us to calculate unequal-time correlation functions directly from first principles. These developments may pave the way for future applications, including the computation of spectral functions and transport coefficients crucial for understanding the quark-gluon plasma (QGP).

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We employ a model based on nucleonic and mesonic degrees of freedom to describe cold and dense matter, in the region of the chiral phase transition, at zero net isospin. The model can describe both chirally broken and symmetric nucleons, and is in some sense complementary to the Nambu-Jona-Lasinio model which describes chirally broken/symmetric quarks. This model has been previously used to calculate the surface tension on a nuclear/quark matter interface, to build mixed (pasta-like) phases, and to describe hyperonic/strange matter in neutron stars. In this work we discuss the competition between isotropic and anisotropic phases at intermediate densities and zero temperature. Anisotropic phases have been extensively studied in quark models of dense matter, but equivalent progress is lacking in models using nucleonic degrees of freedom. When such models are employed, the nucleonic Dirac sea contribution to the pressure is neglected, while we show that including it produces a significant effect. Assuming isotropy, the model exhibits a chiral phase transition which is of second order in the chiral limit and becomes a crossover in the case of a realistic pion mass. This observation crucially depends on the presence of the nucleonic sea; if one neglects it, the transition becomes a first order. Allowing for an anisotropic phase in the form of a chiral density wave, we observe the smooth crossover being disrupted. We identify the regions in the parameter space of the model where a chiral density wave is energetically preferred. A high-density re-appearance of the chiral density wave with unphysical behavior, which is present in previous studies, is avoided by choosing a suitable renormalization scheme. A nonzero pion mass tends to disfavor the anisotropic phase compared to the chiral limit and we find that, within our model, the chiral density wave is only realized for baryon densities of at least about 6 times nuclear saturation density. Future works will focus on extending the study for neutron star conditions.

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In this ongoing five-year research, rotating Anti-de Sitter spacetimes are applied to model quark-gluon-like plasmas typical in heavy ion collisions. Employing AdS/CFT correspondence, we present a stationary, rotating, strongly coupled conformal plasma, modeled as a dual to a 5D Myers-Perry Anti-de Sitter Black Hole. We derive and calculate the plasma's long and short-wavelength spectra, distinguished as hydrodynamic and non-hydrodynamic modes, based on linear perturbations in the 5D gravitational theory. These perturbations, corresponding to 4D plasma fluctuations, yield distinct quasinormal modes, identified as eigenvalues of a non-Hermitian operator. Our investigation explores the application of hydrodynamics to these plasmas, particularly under rotational conditions including near-extremality. We computed the radius of convergence for hydrodynamic regimes, derived explicit hydrodynamic dispersion relations with boosted fluid transport coefficients, parameterized with momentum and vorticity. The study verifies the physical behavior of modeled plasmas, ensuring stability and causality across all temperatures and non-subluminal vorticities, aligning with prior findings on relativistic fluids. Additionally, we explore novel behaviors in the non-hydrodynamic spectrum under rotation, such as critical points, mode decay enhancement or suppression, and multiple level crossings between non-hydrodynamic modes. Similar to charged holographic fluids, we also observe features such as the emergence of branch cuts near extremality.

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