The rapid advancement in quantum technologies has heightened interest in surpassing classical simulators through quantum supremacy. A significant challenge in this endeavor is the effective understanding and manipulation of open quantum systems, which are crucial for the progression of advanced quantum technologies. While several approximate methods have been proposed to simulate the dynamics...
With the size of quantum information processors increasing, quantum simulation has become one of its promising near-future applications. Now it is known that when the computational problem at hand is difficult, the difficulty often appears in terms of an increased quantum circuit depth in gate based implementations or as many-body interaction terms in Hamiltonian based computation. In...
With the recent experimental realization of quantum computing devices containing tens to hundreds of qubits and fully controllable operations, the theoretical effort in designing efficient quantum algorithms for a variety of problems has seen a tremendous growth worldwide. In this talk I will discuss the potential impact of quantum computing for application in nuclear physics and present some...
Many body quantum systems internally have exponentially huge Hilbert spaces and complex dynamics. Much research has been done to find ways to exploit this complexity for practical applications and information processing. Quantum reservoir computing has garnered attention as an approach to directly utilize the complexity of quantum dynamics as a computational resource[1,2]. It is considered for...
Exact wave functions of molecules and solid-state simulation cells containing more than a few electrons are out of reach because they are NP-hard to compute in general, but approximations can be found using polynomially scaling algorithms. A key challenge in many such approaches is the choice of an approximate parameterized wave function, which must trade accuracy for efficiency. Neural...
We consider the square lattice S=½ quantum compass model (QCM) parameterized by
Jx, Jz, under an in-plane field. At the special field value, (hx,hz)=2S(Jx,Jz), we show that the QCM Hamiltonian may be written in a form such that two simple product states can be identified as exact ground-states, below a gap. Exact excited states can also be found. The exact product states are characterized by...
Ultra-cold Fermi gases exhibit a rich array of quantum mechanical properties, including the transition from a fermionic superfluid Bardeen-Cooper-Schrieffer (BCS) state to a bosonic superfluid Bose-Einstein condensate (BEC). While these properties can be precisely probed experimentally, accurately describing them poses significant theoretical challenges due to strong pairing correlations and...
Iterated backflow and neural network wave functions indicate a systematic way to improve the accuracy of quantum Monte Carlo (QMC) calculations of ground state energies of large (but finite) quantum systems in two or three spatial dimensions at zero temperature. I will illustrate recent improvements on the calculations of the ground state phase diagram of the electron gas and of the phase...
Abstract (PDF)
A strong effort will be dedicated in the coming years to extend the reach of ab initio nuclear-structure calculations to heavy doubly open-shell nuclei. In order to do so, the most efficient strategies to incorporate dominant many-body correlations at play in such nuclei must be identified. With this motivation in mind, the present work pedagogically analyses the inclusion of many-body...
Quantum many-body systems, particularly in nuclear physics, present significant computational challenges due to their complex interactions and high-dimensional state spaces. Surrogate models offer a promising solution by providing simplified yet accurate representations of these systems, reducing computational costs and enhancing scalability.
This talk will focus on the development and...
Within the field of computational quantum many-body dynamics, several approaches exist to approximating and simulating the time evolution of quantum systems with multiple particles. In this presentation, four numerical methods will be compared: the time-dependent configuration-interaction (TDCI) method, the multi-configurational time-dependent Hartree-Fock (MCTDHF) method, the time-dependent...
In this talk, I will introduce a theoretical approach to ultrafast phase transitions able to capture both the electron and phonon dynamics after laser pumping on a time scale ranging from a few femtoseconds to several picoseconds after laser irradiation.
At short times, the method relies on the solution of the Bloch equations coupled to the Ehrenfest dynamics. It includes the electric field...
In this presentation, I will report on the development of first-principles structural optimization at finite temperatures and their applications. At zero temperature, structural optimization commonly involves minimizing the energy of the system based on density functional theory. However, it is necessary to consider minimizing the free energy at finite temperatures. In doing so, it is...
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Pseudomodes have grown in popularity in recent years as an intuitive numerical method for solving the general problem of a quantum system coupled to a Gaussian environment. I will summarize the various formulations of pseudomodes that have appeared in the literature, and demonstrate how they can be used to model non-Markovian bosonic environments and the Kondo effect in the single-impurity...
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One of the fundamental problems in nuclear physics is to predict the properties of nuclei based on underlying nuclear interactions. The applicability of nuclear ab initio calculation has been expanding in the past few decades, and systematic calculations can be performed up to mass number $\sim$ 100. However, the applications for heavier systems are limited primarily due to the...
I will discuss the features of BCS-BEC crossover in nuclear systems and by extension also in fermionic ultra-cold gases in the presence of population imbalance. The phase diagram of such systems will be discussed including phases with broken space symmetries and phase separation. It will be pointed out that several tri-critical points appear on the phase diagram of such a system.
Abstract (PDF)
Abstract (PDF)
Abstract (PDF)
The Gogny-type density functionals have finite-range and density-dependent terms. The parameters of the functionals are designed not only to reproduce the basic properties of finite nuclei but also to satisfy the saturation properties of nuclear matter. Consequently, calculations using a single density functionals can describe experimental data in various mass regions. However, the mean-field...
In the inner crust of neutron stars, a Coulomb lattice of nuclei exists, immersed in a sea of superfluid neutron gas. The interplay between these nuclear crystals and the background neutrons may significantly alter nuclear dynamics, a phenomenon known as the "entrainment" effect, which is crucial for understanding several astronomical phenomena.
In our study, we have developed new...
The rapid neutron capture process ($r$-process) is the most important mechanism for the synthesis of about half of the elements heavier than iron. It occurs in an environment with relatively high temperatures and high neutron densities. The abundances of the elements created by the $r$-process strongly depend on several nuclear inputs like masses, neutron capture rates, $\beta$-decay rates,...
When the entanglement structure of the quantum state of interest is non-uniform in real space, accurately representing the state with a limited number of degrees of freedom hinges on appropriately configuring the Tensor Network (TN) to align with the entanglement pattern. Although TN states including entanglement renormalization (ER) can encompass a wider variety of entangled states, a...
The energy density functional method is able to provide systematic analysis on properties of nuclei all over the nuclear chart.
We perform the calculations for nuclei from the proton to the neutron drip lines including superheavy nuclei.
Using HFBTHO program(Axially deformed solution of the Skyrme-Hartree–Fock–Bogoliubov equations using the transformed harmonic oscillator basis (II)), the...
The generation and evolution of entanglement in many-body systems is an active area of research that spans multiple fields, from quantum information science to the simulation of quantum many-body systems encountered in condensed matter, subatomic physics, and quantum chemistry. Motivated by recent experiments exploring quantum information processing systems with electrons trapped above the...
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The shell evolution towards the extreme neutron-to-proton ratio has been a pivotal focus in nuclear physics over recent decades, since it is crucial to understand the effective nucleon-nucleon interactions and the r-process. Significant efforts have been devoted to deciphering the mechanism behind the shell evolution, such as the spin-orbit interaction, the tensor force, and the pseudospin...
Quantum computations of relativistic and many-body effects in atomic and molecular systems based on variational algorithms
Bhanu Pratap Das
Centre for Quantum Engineering Research and Education
TCG Centres for Research and Education in Science...
The nuclear Schiff moment (NSM) is produced by a nuclear force that simultaneously violates charge conjugation (C) symmetry and spatial parity (P) inversion symmetry. The experimental detection of NSM is significant as CP violation is crucial for explaining the current matter-dominated universe. Measuring NSM in molecules necessitates precise experiments and theoretical calculations that...
I will discuss
(i) some recent progress to improve the expressivity of tensor networks
(ii) the rate of convergence of tensor network calculations and the error dependence of this classical heuristics
(iii) some new classical algorithms for many-body systems motivated by noisy quantum simulation.
Tensor networks provide a new approach to studying quantum many-body problems. In particle physics, tensor networks are attracting attention as a novel numerical method, particularly for lattice theories with the sign problem. In this talk, recent progress in tensor networks for particle physics, toward their future applications to the lattice QCD, will be discussed.
We developed a strong coupling perturbation scheme for general Hubbard model around half-field particle-hole symmetric reference system [1]. The approach based on a lattice determinatal Quantum Monte Carlo method in continuous and discrete time versions [2] for a large periodic clusters in a fermionic bath. The first and second order perturbation in the shift of chemical potential and...
Performance of quantum annealing for functions with continuous variables has not been well studied. We evaluate quantum annealing on a continuous-variable function with a rugged energy landscape, using domain-wall encoding to map continuous to discrete variables. We assess several algorithms and hardware, including D-Wave 2000Q, TEBD, simulated annealing, and simulated quantum annealing....
Dual-unitary circuits are a class of quantum systems for which exact calculations of various quantities are possible, even when the system is chaotic. The array of known exact results paints a picture of dual-unitary circuits as rapidly thermalising systems. However, we present a method to construct dual-unitary circuits for which some simple initial states fail to thermalise, despite the...
We have predicted in an electron-hole bilayer semiconductor system using a variational approach, a transition from an exciton superfluid to an incompressible “Chester supersolid”, which has occupancy of one on each lattice site [1].
By solving the full Gross-Pitaevskii equation for this 2D system, we carry out a complete investigation of the time-dependent dynamic exciton supersolid. Here,...
A fundamental instability in the nonequilibrium conduction band under an
electric field bias occurs via the spontaneous emission of coherent
phonons. Analytic theory, supported by numerical calculations,
establishes that the quantum avalanche, an abrupt nonequilibrium
occupation of excited bands, results from the competition between the
collapse of the band minimum via the phonon emission and...
I will describe connections between ground states of quantum Hall Hamiltonians with multiple-Landau-level orbitals, whose excitations display either Abelian or non-Abelian braiding statistics, and (non-holomorphic) symmetric polynomials. In the case of two-body interactions, these represent parton states. The emergent Entangled Pauli Principle (EPP), which defines the “DNA” of the quantum...
Doping charge carriers into Mott insulators provides a pathway to produce intriguing emergent phenomena [1]. In equilibrium systems, doping can be chemically controlled. On the other hand, photo-doping, where particles are excited across the Mott gap, provides an alternative way. Compared to chemical-doping, photo-doping creates a wider variety of charge carriers, which may lead to the...
The internal stretch mode of polar molecules adsorbed on metallic surfaces has emerged as an exceptional test-bed in which to probe many-body theories in current state-of-the-art time-revolved spectroscopy experiments. Here we study non-adiabatic effects on the internal stretch mode of CO adsorbed on the Pd(111) surface by means of first principles calculations [1, 2]. The...
I will review recent works on the study of both repulsive and attractive Bose mixtures at finite temperature using exact path-integral quantum Monte-Carlo numerical methods. Repulsive mixtures in the quantum degenerate regime undergo a first-order ferromagnetic transition as a function of the interspecies coupling constant. The magnetic behavior close to the point of phase separation is found...
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The n-body reduced density matrix (n-RDM) characterizes higher order correlations in an interacting many-body system. This quantity can be used to compute any n-body observable without direct access to the full wavefunction, and is experimentally measurable. The problem of computing higher order density matrices becomes increasingly challenging as the number of local operators grows....
Abstract (PDF)
Describing transport properties of a many-body fermionic system is one of the most important topics in many fields of physics and chemistry.
To simulate the electronic properties of nanodevices, the non-equilibrium Green function method (NEGF) has been widely employed.
However, this method suffers from substantial numerical costs for a calculation of the Green function.
To overcome this...
The so-called reduced basis method from the field of model order reduction is being actively adapted in studying nuclear many-body bound states. It provides fast and accurate interpolations (or emulations) of the expensive many-body calculations in the input parameter space. These emulators are efficient interfaces through which users can effortlessly access these calculations.
In this talk,...
We study the quantum walk on the off-diagonal Aubry-André-Harper (AAH) lattice with periodic modulation using a digital quantum computer. We investigate various initial states at the single-particle level, considering different hopping modulation strengths and phase factors. Initiating the quantum walk with a particle at the lattice edge reveals the robustness of the edge state, attributed to...
In this study, we consider the treatments of short-range and long-range interactions in solid oxygen at the epsilon-zeta phase transition using the Hubbard U and van der Waals dispersion, respectively. We show that the London dispersion may correctly capture the nonlocal interactions in solid oxygen instead of the Hartree-Fock exchange [1]. The nonlocal effect is expected to be dominant at...
