arXiv subjects

Nora Reinić

Publications and source records attributed to Nora Reinić.

5 recordsLinked to original sources

arXiv2025

Entanglement transitions in a boundary-driven open quantum many-body system

We introduce a numerical framework for integrating Markovian dynamics on tree tensor operator (TTO) ansatz states. This framework enables the simulation of both transient and steady-state regimes of systems governed by the Lindblad master equation, while preserving positivity of the density matrix and providing direct access to entanglement monotones. We demonstrate its capability to probe entanglement in open quantum many-body systems and to distinguish it from other correlations by studying a boundary-driven XXZ spin chain. Our analysis uncovers entanglement transitions driven by both the coupling to the environment and the anisotropy, revealing a striking connection between spatial entanglement scaling and spin-current.

quant-ph↗

arXiv2025

A new rung on the ladder: exploring topological frustration towards two dimensions

Topological frustration arises when boundary conditions impose geometric frustration in a quantum system, creating delocalized defects in the ground states and profoundly altering the low-energy properties. While previous studies have been concerned with one-dimensional systems, showing that the ground state structure can be described in terms of quasiparticle excitations, the two-dimensional setting remains unexplored. We address this gap by studying a three-legged antiferromagnetic quantum Ising ladder on a torus using tensor network methods, where topological frustration is induced by an odd number of spins along both spatial directions. Our results reveal the first instance in which topological frustration shifts the position of the quantum critical point. By studying the entanglement structure, we find that the ground state can be characterized as hosting three delocalized quasiparticles. This work builds the quasiparticle picture of topological frustration toward higher dimensions and more complex systems than those considered so far.

cond-mat.str-el↗

arXiv2025

The Augmented Tree Tensor Network Cookbook

An augmented tree tensor network (aTTN) is a tensor network ansatz constructed by applying a layer of unitary disentanglers to a tree tensor network. The disentanglers absorb a part of the system's entanglement. This makes aTTNs suitable for simulating higher-dimensional lattices, where the entanglement increases with the lattice size even for states that obey the area law. These lecture notes serve as a detailed guide for implementing the aTTN algorithms. We present a variational algorithm for ground state search and discuss the measurement of observables, and offer an open-source implementation within the Quantum TEA library. We benchmark the performance of the ground state search for different parameters and hyperparameters in the square lattice quantum Ising model and the triangular lattice Heisenberg model for up to $32 \times 32$ spins. The benchmarks identify the regimes where the aTTNs offer advantages in accuracy relative to computational cost compared to matrix product states and tree tensor networks.

quant-ph↗

arXiv2025

Benchmarking Quantum Red TEA on CPUs, GPUs, and TPUs

We benchmark simulations of many-body quantum systems on heterogeneous hardware platforms using CPUs, GPUs, and TPUs. We compare different linear algebra backends, e.g., NumPy versus the PyTorch, JAX, or TensorFlow libraries, as well as a mixed-precision-inspired approach and optimizations for the target hardware. Quantum Red TEA out of the Quantum TEA library specifically addresses handling tensors with different libraries or hardware, where the tensors are the building blocks of tensor network algorithms. The benchmark problem is a variational search of a ground state in an interacting model. This is a ubiquitous problem in quantum many-body physics, which we solve using tensor network methods. This approximate state-of-the-art method compresses quantum correlations which is key to overcoming the exponential growth of the Hilbert space as a function of the number of particles. We present a way to obtain speedups of a factor of 34 when tuning parameters on the CPU, and an additional factor of 2.76 on top of the best CPU setup when migrating to GPUs.

quant-ph↗

arXiv2024

Finite-temperature Rydberg arrays: quantum phases and entanglement characterization

As one of the most prominent platforms for analog quantum simulators, Rydberg atom arrays are a promising tool for exploring quantum phases and transitions. While the ground state properties of one-dimensional Rydberg systems are already thoroughly examined, we extend the analysis towards the finite-temperature scenario. For this purpose, we develop a tensor network-based numerical toolbox for constructing the quantum many-body states at thermal equilibrium, which we exploit to probe classical correlations as well as entanglement monotones. We clearly observe ordered phases continuously shrinking due to thermal fluctuations at finite system sizes. Moreover, by examining the entanglement of formation and entanglement negativity of a half-system bipartition, we numerically confirm that a conformal scaling law of entanglement extends from the zero-temperature critical points into the low-temperature regime.

quant-ph↗