arXiv subjects

Alina Joch

Publications and source records attributed to Alina Joch.

3 recordsLinked to original sources

arXiv2026

Emergent-Coupling-Based Ansatz Evaluated on a Superconducting Quantum Processor

The performance of the variational quantum eigensolver depends critically on the choice of ansatz. In this work, we experimentally evaluate the emergent-coupling-based ansatz (ECBA), a physically motivated variational ansatz for disordered systems. The ECBA is based on a renormalization (semi-)group approach to determine the dominant effective couplings, resulting in shallow circuits that capture the essential long-range entanglement structure while balancing local correlations. We implement the ECBA on superconducting quantum processors and benchmark it on disordered Heisenberg chain models. Using classically pre-optimized parameters and error mitigation techniques, we study systems of up to 30 qubits and observe an experimental relative energy accuracy of 96.47% for the largest system. Furthermore, we find that the ECBA can be efficiently embedded on hardware with two-dimensional square-lattice connectivity. We compare to commonly used hardware efficient ans\"atze and observe that the ECBA achieves significantly higher accuracy at a similar gate count.

quant-ph↗

arXiv2025

Entanglement-informed Construction of Variational Quantum Circuits

The Variational Quantum Eigensolver (VQE) is a promising tool for simulating ground states of quantum many-body systems on noisy quantum computers. Its effectiveness relies heavily on the ansatz, which must be both hardware-efficient for implementation on noisy hardware and problem-specific to avoid local minima and convergence problems. In this article, we explore entanglement-informed ansatz schemes that naturally emerge from specific models, aiming to balance accuracy with minimal use of two-qubit entangling gates, allowing for efficient use of techniques such as quantum circuit cutting. We focus on three models of quasi-1D Hamiltonians: (i) systems with impurities acting as entanglement barriers, (ii) systems with competing long-range and short-range interactions transitioning from a long-range singlet to a quantum critical state, and (iii) random quantum critical systems. For the first model, we observe a plateau in the ansatz accuracy, controlled by the number of entangling gates between subsystems. This behavior is explained by iterative capture of eigenvalues in the entanglement spectrum. In the second model, combining long-range and short-range entanglement schemes yields the best overall accuracy, leading to global convergence in the entanglement spectrum. For the third model, we use an renormalization group approach to build the short- and long-range entanglement structure of the ansatz. Our comprehensive analysis provides a new perspective on the design of ans\"atze based on the expected entanglement structure of the approximated state.

quant-ph↗

arXiv2023

Influence of quadrupolar interaction on NMR spectroscopy

Optically driven electronic spins coupled in quantum dots to nuclear spins show a pre-pulse signal (revival amplitude) after having been trained by long periodic sequences of pulses. The size of this revival amplitude depends on the external magnetic field in a specific way due to the varying commensurability of the nuclear Larmor precession period with the time $T_\text{rep}$ between two consecutive pulses. In theoretical simulations, sharp dips occur at fields when an integer number of precessions fits in $T_\text{rep}$; this feature could be used to identify nuclear isotopes spectroscopically. But these sharp and characteristic dips have not (yet) been detected in experiment. We study whether the nuclear quadrupolar interaction is the reason for this discrepancy because it perturbs the nuclear precessions. But our simulations show that the absolute width of the dips and their relative depth are not changed by quadrupolar interactions. Only the absolute depth decreases. We conclude that quadrupolar interaction alone cannot be the reason for the absence of the characteristic dips in experiment.

cond-mat.mes-hall↗