Searcharxiv⌕ Search

arXiv subjects

Kazuki Ikeda

Publications and source records attributed to Kazuki Ikeda.

At least 37 records · Page 2Linked to original sources
arXiv2025

Optimal Observables for the Chiral Magnetic Effect from Machine Learning

The detection of the Chiral Magnetic Effect (CME) in relativistic heavy-ion collisions remains challenging due to substantial background contributions that obscure the expected signal. In this Letter, we present a novel machine learning approach for constructing optimized observables that significantly enhance CME detection capabilities. By parameterizing generic observables constructed from flow harmonics and optimizing them to maximize the signal-to-background ratio, we systematically develop CME-sensitive measures that outperform conventional methods. Using simulated data from the Anomalous Viscous Fluid Dynamics framework, our machine learning observables demonstrate up to 90\% higher sensitivity to CME signals compared to traditional $γ$ and $δ$ correlators, while maintaining minimal background contamination. The constructed observables provide physical insight into optimal CME detection strategies, and offer a promising path forward for experimental searches of CME at RHIC and the LHC.

hep-ph↗
arXiv2025

Exceeding the maximum classical energy density in fully charged quantum batteries

Quantum batteries are anticipated to achieve significant advancements in energy storage capacity. In classical batteries, the energy density at each subsystem reaches its maximum value, denoted as $E_C$, which is determined by dividing the maximum energy by the number of subsystems. We demonstrate that this limit can be surpassed in quantum batteries by protocols of Quantum Energy Teleportaion (QET), allowing for the energy density at a subsystem to exceed the value of $E_C$. Our protocol offers enhanced efficiency, reduces experimental complexity on quantum computers, and enables instantaneous energy charging through Local Operations and Classical Communication (LOCC). Leveraging quantum entanglement, this protocol significantly improves quantum energy storage systems, promising advances in quantum computing and new technological applications. This work represents a crucial step towards revolutionizing quantum energy storage and transfer.

quant-ph↗
arXiv2025

How to Write a Simulator for Quantum Circuits from Scratch: A Tutorial

This tutorial guides a competent programmer through the crafting of a quantum circuit simulator from scratch, even for readers with almost no prior experience in quantum computing. Open source simulators for quantum circuits already exist, but a deeper understanding is gained by writing ones own. With roughly 1000-2000 lines of code, one can simulate Hadamard, Pauli X, Y, Z, SWAP, and other quantum logic gates, with arbitrary combinations of control and anticontrol qubits, on circuits of up to 20+ qubits, with no special libraries, on a personal computer. We explain key algorithms for a simulator, in particular: qubit-wise multiplication for updating the state vector, and partial trace for finding a reduced density matrix. We also discuss optimizations, and how to compute qubit phase, purity, and other statistics. A complete example implementation in JavaScript is available at https://github.com/MJMcGuffin/muqcs.js , which also demonstrates how to compute von Neumann entropy, concurrence (to quantify entanglement), and magic, while remaining much smaller and easier to study than other popular software packages.

quant-ph↗
arXiv2025

Towards a Real-Time Computation of Timelike Hadronic Vacuum Polarization and Light-by-Light Scattering: Schwinger Model Tests

Hadronic vacuum polarization (HVP) and light-by-light scattering (HLBL) are crucial for evaluating the Standard Model predictions concerning the muon's anomalous magnetic moment. However, direct first-principle lattice gauge theory-based calculations of these observables in the timelike region remain challenging. Discrepancies persist between lattice quantum chromodynamics (QCD) calculations in the spacelike region and dispersive approaches relying on experimental data parametrization from the timelike region. Here, we introduce a methodology employing 1+1-dimensional quantum electrodynamics (QED), i.e. the Schwinger Model, to investigate the HVP and HLBL. To that end, we use both tensor network techniques, specifically matrix product states, and classical emulators of digital quantum computers. Demonstrating feasibility in a simplified model, our approach sets the stage for future endeavors leveraging digital quantum computers.

hep-ph↗
arXiv2024

Local symmetries and extensive ground-state degeneracy of a 1D supersymmetric fermionic chain

We study a $1$D supersymmetric (SUSY) hard-core fermion model first proposed by Fendley, Schoutens, and de Boer [Phys. Rev. Lett. 90, 120402 (2003)]. We focus on the full Hilbert space instead of a restricted subspace. Exact diagonalization shows the degeneracy of zero-energy states scales exponentially with size of the system, with a recurrence relation between different system sizes. We solve the degeneracy problem by showing the ground states can be systematically constructed by inserting immobile walls of fermions into the chain. Mapping the counting problem to a combinatorial one and obtaining the exact generating function, we prove the recurrence relation on both open and periodic chains. We also provide an explicit mapping between ground states, giving a combinatorial explanation of the recurrence relation.

cond-mat.stat-mech↗
arXiv2024

Bulk and boundary entanglement transitions in the projective gauge-Higgs model

In quantum many-body spin systems, the interplay between the entangling effect of multi-qubit Pauli measurements and the disentangling effect of single-qubit Pauli measurements may give rise to two competing effects. By introducing a randomized measurement pattern with such bases, a phase transition can be induced by altering the ratio between them. In this work, we numerically investigate a measurement-based model associated with the $(2+1)$d $\mathbb{Z}_2$ Fradkin-Shenker Hamiltonian model, encompassing the deconfining, confining, and Higgs phases. We determine the phase diagram in our measurement-only model by employing entanglement measures. For the bulk topological order, we use the topological entanglement entropy. We also use the mutual information between separated boundary regions to diagnose the boundary phase transition associated with the Higgs or the bulk SPT phase. We observe the structural similarity between our phase diagram and the one in the standard quantum Hamiltonian formulation of the Fradkin-Shenker model with the open rough boundary. First, a deconfining phase is detected by nonzero and constant topological entanglement entropy. Second, we find a (boundary) phase transition curve separating the Higgs=SPT phase from the rest. In certain limits, the topological phase transitions reside at the critical point of the formation of giant homological cycles in the bulk 3d spacetime lattice, as well as the bond percolation threshold of the boundary 2d spacetime lattice when it is effectively decoupled from the bulk. Additionally, there are analogous mixed-phase properties at a certain region of the phase diagram, emerging from how we terminate the measurement-based procedure. Our findings pave an alternative pathway to study the physics of Higgs=SPT phases on quantum devices in the near future.

quant-ph↗
arXiv2024

Efficient charge-preserving excited state preparation with variational quantum algorithms

Determining the spectrum and wave functions of excited states of a system is crucial in quantum physics and chemistry. Low-depth quantum algorithms, such as the Variational Quantum Eigensolver (VQE) and its variants, can be used to determine the ground-state energy. However, current approaches to computing excited states require numerous controlled unitaries, making the application of the original Variational Quantum Deflation (VQD) algorithm to problems in chemistry or physics suboptimal. In this study, we introduce a charge-preserving VQD (CPVQD) algorithm, designed to incorporate symmetry and the corresponding conserved charge into the VQD framework. This results in dimension reduction, significantly enhancing the efficiency of excited-state computations. We present benchmark results with GPU-accelerated simulations using systems up to 24 qubits, showcasing applications in high-energy physics, nuclear physics, and quantum chemistry. This work is performed on NERSC's Perlmutter system using NVIDIA's open-source platform for accelerated quantum supercomputing - CUDA-Q.

quant-ph↗
arXiv2024

Real-time chiral dynamics at finite temperature from quantum simulation

In this study, we explore the real-time dynamics of the chiral magnetic effect (CME) at a finite temperature in the (1+1)-dimensional QED, the massive Schwinger model. By introducing a chiral chemical potential $μ_5$ through a quench process, we drive the system out of equilibrium and analyze the induced vector currents and their evolution over time. The Hamiltonian is modified to include the time-dependent chiral chemical potential, thus allowing the investigation of the CME within a quantum computing framework. We employ the quantum imaginary time evolution (QITE) algorithm to study the thermal states, and utilize the Suzuki-Trotter decomposition for the real-time evolution. This study provides insights into the quantum simulation capabilities for modeling the CME and offers a pathway for studying chiral dynamics in low-dimensional quantum field theories.

hep-ph↗
arXiv2024

Quasiparton distributions in massive QED2: Toward quantum computation

We analyze the quasi-parton distributions of the lightest $η'$ meson in massive two-dimensional Quantum electrodynamics (QED2) by performing a digital quantum simulation on a classical computer (exact diagonalization). The Hamiltonian and boost operators are mapped onto spin qubits in a spatial lattice with open boundary conditions. The lowest excited state in the exact diagonalization is shown to interpolate continuously between an anomalous $η'$ state at strong coupling,and a non-anomalous heavy meson at weak coupling, with a cusp at the critical point. The boosted $η'$ state follows relativistic kinematics but with large deviations in the luminal limit. The spatial quasi-parton distribution function and amplitude for the $η'$ state are computed numerically for increasing rapidity both at strong and weak coupling, and compared to the exact light front results. The numerical results from the boosted form of the spatial parton distributions, compare fairly with the inverse Fourier transformation of the luminal parton distributions, derived in the lowest Fock space approximation. Our analysis points out some of the limitations facing the current lattice program for the parton distributions.

hep-ph↗
arXiv2024

Beyond Energy: Teleporting Current, Charge, and More

As an homage to Quantum Energy Teleportation, we generalize the idea to arbitrary physical observables, not limited to energy, and prove a rigorous upper bound on the activated ("teleported") quantity. The essence of this protocol is a quantum feedback control with respect to the entangled ground state of a quantum many-body system. To demonstrate the concept, we explore a (1+1)-dimensional chiral Dirac system and execute the protocol for the electric current and charge. One of the most significant results is the creation of long-range correlations across the system after applying control operations only to one local site. Consequently but surprisingly, the induced charge susceptibility fully reconstructs the phase diagram, despite the model initially having no charge. Moreover, we find an activation of novel chiral dynamics induced by feedback control operations, which can be experimentally confirmed using trapped ions and neutral atoms.

hep-th↗
arXiv2024

Temporal Entanglement Entropy as a probe of Renormalization Group Flow

The recently introduced concept of timelike entanglement entropy has sparked a lot of interest. Unlike the traditional spacelike entanglement entropy, timelike entanglement entropy involves tracing over a timelike subsystem. In this work, we propose an extension of timelike entanglement entropy to Euclidean space ("temporal entanglement entropy"), and relate it to the renormalization group (RG) flow. Specifically, we show that tracing over a period of Euclidean time corresponds to coarse-graining the system and can be connected to momentum space entanglement. We employ Holography, a framework naturally embedding RG flow, to illustrate our proposal. Within cutoff holography, we establish a direct link between the UV cutoff and the smallest resolvable time interval within the effective theory through the irrelevant $T\bar T$ deformation. Increasing the UV cutoff results in an enhanced capability to resolve finer time intervals, while reducing it has the opposite effect. Moreover, we show that tracing over a larger Euclidean time interval is formally equivalent to integrating out more UV degrees of freedom (or lowering the temperature). As an application, we point out that the temporal entanglement entropy can detect the critical Lifshitz exponent $z$ in non-relativistic theories which is not accessible from spatial entanglement at zero temperature and density.

hep-th↗
arXiv2024

Quantum simulation of entanglement and hadronization in jet production: lessons from the massive Schwinger model

The possible link between entanglement and thermalization, and the dynamics of hadronization are addressed by studying the real-time response of the massive Schwinger model coupled to external sources. This setup mimics the production and fragmentation of quark jets, as the Schwinger model and QCD share the properties of confinement and chiral symmetry breaking. By using quantum simulations on classical hardware, we study the entanglement between the produced jets, and observe the growth of the corresponding entanglement entropy in time. This growth arises from the increased number of contributing eigenstates of the reduced density matrix with sufficiently large and close eigenvalues. We also investigate the physical nature of these eigenstates, and find that at early times they correspond to fermionic Fock states. We then observe the transition from these fermionic Fock states to meson-like bound states as a function of time. In other words, we observe how hadronization develops in real time. At late times, the local observables at mid-rapidity (such as the fermion density and the electric field) approach approximately constant values, suggesting the onset of equilibrium and approach to thermalization.

hep-ph↗
arXiv2024

Robustness of quantum correlation in quantum energy teleportation

We present the evolution of quantum correlation in the quantum energy teleportation (QET) protocol using quantum discord, instead of the traditionally used entanglement entropy. In the QET protocol, where local observations and conditional operations are repeated, quantum correlations become nontrivial because of the statistical creation of mixed states. In this paper, we use quantum discord as a measure of quantum correlation in mixed states and investigate its relationship to teleported energy and phase transitions. During the process of Alice and Bob performing QET, one would expect that the entanglement between Alice and Bob is completely broken by Alice's measurement of the quantum state, and thus the quantum correlation disappears. However, contrary to this expectation, it is shown using quantum discord that the quantum correlation does not disappear during the entire process of QET. To demonstrate the robustness of the quantum correlation in QET at various phase structures, we perform the numerical analysis using several benchmark models including the Nambu-Jona-Lasino (NJL) model with both the chiral chemical potential and the chemical potential, which are useful to study the phase structures mimicking the chiral imbalance between left- and right- quarks coupled to the chirality density operator. In all cases we studied, the quantum discord behaved as an order parameter of the phase transition.

hep-th↗
arXiv2024

Entanglement in massive Schwinger model at finite temperature and density

We evaluate the entanglement entropy and entropic function of massive two dimensional QED (Schwinger model) at finite temperature, density, and $θ$-angle. In the strong coupling regime, the entropic function is dominated by the boson mass for large spatial intervals, and reduces to the CFT result for small spatial intervals. We also discuss the entanglement spectrum at finite temperature and a finite $θ$-angle.

hep-th↗
arXiv2023

Quantum-classical simulation of quantum field theory by quantum circuit learning

We employ quantum circuit learning to simulate quantum field theories (QFTs). Typically, when simulating QFTs with quantum computers, we encounter significant challenges due to the technical limitations of quantum devices when implementing the Hamiltonian using Pauli spin matrices. To address this challenge, we leverage quantum circuit learning, employing a compact configuration of qubits and low-depth quantum circuits to predict real-time dynamics in quantum field theories. The key advantage of this approach is that a single-qubit measurement can accurately forecast various physical parameters, including fully-connected operators. To demonstrate the effectiveness of our method, we use it to predict quench dynamics, chiral dynamics and jet production in a 1+1-dimensional model of quantum electrodynamics. We find that our predictions closely align with the results of rigorous classical calculations, exhibiting a high degree of accuracy. This hybrid quantum-classical approach illustrates the feasibility of efficiently simulating large-scale QFTs on cutting-edge quantum devices.

hep-th↗
arXiv2023

Exploring Kondo effect by quantum energy teleportation

We consider a quantum energy teleportation (QET) method to replicate the phase diagram of a one-dimensional $XXZ$ spin chain featuring a Kondo effect coupling. In this setup, the energy supplier and receiver are spatially separated from the point impurity and do not interact directly with it. Nonetheless, they may successfully generate phase diagrams that closely mirror those produced via exact diagonalization. This can be achieved using only local operations on their respective subsystems, supplemented by classical communication. This feat is made possible due to a critical connection between the energy obtained through the QET approach and the system's quantum entanglement entropy. To substantiate these findings, we initially demonstrate that the quantum entanglement entropy serves as the relevant order parameter for the system. Intriguingly, changes in the gap spacing of the entanglement spectra align with the locations of peaks in both entanglement entropy and energy, as determined by QET. We hypothesize that this theoretical framework could, for example, be validated experimentally using a one-dimensional chain of Rydberg atoms.

quant-ph↗
arXiv2023

Demonstration of Quantum Energy Teleportation on Superconducting Quantum Hardware

Teleporting physical quantities to remote locations is a remaining key challenge for quantum information science and technology. Quantum teleportation has enabled the transfer of quantum information, but teleportation of quantum physical quantities has not yet been realized. Here we report the realization and observation of quantum energy teleportation on real superconducting quantum hardware. We achieve this by using several IBM's superconducting quantum computers. The results are consistent with the exact solution of the theory and are improved by the mitigation of measurement error. Quantum energy teleportation requires only local operations and classical communication. Therefore our results provide a realistic benchmark that is fully achievable with current quantum computing and communication technologies.

quant-ph↗