arXiv subjects

Juan Borge

Publications and source records attributed to Juan Borge.

10 recordsLinked to original sources

arXiv2026

Toward Quantum Utility in Correlated Topological Matter: Variational Preparation of Fractional Quantum Hall Manifolds

We investigate the use of variational quantum algorithms to prepare and characterize fractional quantum Hall states on near-term quantum processors. Focusing on the $\nu=1/3$ Laughlin phase described by the $V_1$ Haldane pseudopotential, we formulate the lowest-Landau-level problem in second quantization, and implement particle-number-preserving variational circuits combined with the variational quantum eigensolver (VQE) and variational quantum deflation (VQD). We benchmark the approach in two complementary geometries: Haldane sphere and torus shape. On the Haldane sphere, the target state is a unique zero-energy Laughlin ground state, providing a controlled test of the variational workflow and of excited-state reconstruction. On the torus, the problem retains the genuinely two-dimensional periodic character of the quantum Hall liquid and exhibits the threefold topological ground-state degeneracy expected for the $\nu=1/3$ fractional filling factor. This feature makes the torus a more demanding benchmark than the quasi-one-dimensional cylinder or thin-torus limits commonly exploited in state-preparation quantum protocols. We benchmark the hardware-optimized variational states against exact diagonalization using energy estimates, error-mitigated observables, and subspace-containment diagnostics. Our results show that hybrid quantum algorithms can approximately reconstruct the low-energy structure of small fractional quantum Hall systems, including the topological ground-state manifold on the torus. Beyond serving as a benchmark for quantum hardware, this geometry-resolved approach provides a route toward quantum simulations of fractional Chern insulators and strongly correlated topological phases in realistic two-dimensional materials.

quant-ph↗

arXiv2026

Evidence for spin swapping from modulation of transverse resistance in magnetic heterostructures with Rashba interface

We investigate the transverse response under the out-of-plane magnetic field for magnetic heterostructures with Cu/Bi2O3 or Ag/Bi2O3 Rashba interfaces. We detect opposite contributions on the transverse resistance by the Cu/Bi2O3 and the Ag/Bi2O3 interfaces, which interestingly coincide well with the opposite signs of the spin/charge interconversion from the two interfaces. We suppose the opposite influences on the transverse resistance feature spin swapping occurrence of the converted spin current. The transverse spin flow emerges due to the spin swapping in both Cu and Ag layer, but the direction of the spin flow is opposed dependent on the spin direction of the converted spin current.

cond-mat.mes-hall↗

arXiv2025

A Useful Metric for the NISQ Era: Qubit Error Probability and Its Role in Zero Noise Extrapolation

Accurate assessment and management of errors is indispensable for extracting useful results from noisy intermediate-scale quantum (NISQ) devices. In this work, we propose the qubit error probability (QEP), a device specific metric that combines relaxation, dephasing, gate, and measurement contributions into a single per qubit figure of merit computable before execution. Leveraging QEP as the control variable, we revisit zero noise extrapolation (ZNE) by adding pairs of controlled native two-qubit gates on all connected qubit pairs to generate circuits with successively larger mean QEP; the zero error limit is then approximated by a linear regression of the measured observable against those values. Benchmarking on IBM Quantum Heron processors, we apply QEP guided ZNE to first order Trotterized simulations of the two dimensional transverse field Ising model, chosen as a representative interacting many body system, involving up to 68 qubits and 15 Trotter steps. In regimes where the raw circuits exhibit a finite mean QEP, the method suppresses observable errors beyond those attainable with circuit depth scaled ZNE, while requiring only three noise scaled evaluations and no additional classical post processing. These results demonstrate that QEP serves as a transparent and efficient error metric, and that its integration into ZNE provides a practical route to reliability gains on current superconducting hardware, without the resource costs associated with full quantum error correction.

quant-ph↗

arXiv2024

Error estimation in current noisy quantum computers

One of the main important features of the noisy intermediate-scale quantum (NISQ) era is the correct evaluation and consideration of errors. In this paper, we analyze the main sources of errors in current (IBM) quantum computers and we present a useful tool (TED-qc) designed to facilitate the total error probability expected for any quantum circuit. We propose this total error probability as the best way to estimate a lower bound for the fidelity in the NISQ era, avoiding the necessity of comparing the quantum calculations with any classical one. In order to contrast the robustness of our tool we compute the total error probability that may occur in three different quantum models: 1) the Ising model, 2) the Quantum-Phase Estimation (QPE), and 3) the Grover's algorithm. For each model, the main quantities of interest are computed and benchmarked against the reference simulator's results as a function of the error probability for a representative and statistically significant sample size. The analysis is satisfactory in more than the $99\%$ of the cases. In addition, we study how error mitigation techniques are able to eliminate the noise induced during the measurement. These results have been calculated for the IBM quantum computers, but both the tool and the analysis can be easily extended to any other quantum computer.

quant-ph↗

arXiv2020

Thermoelectric relations in the conformal limit in Dirac and Weyl semimetals

In the Fermi liquid description of metals, electrical and thermoelectric transport coefficients are linked by robust relations which can be challenged by strong interactions or when the electron liquid enters a different regime. These relations have been very powerful in the characterisation of novel materials. We show that Dirac and Weyl semimetals at zero doping and zero temperature (the conformal limit) have a very singular behavior due to a quantum anomaly. Away from this point, a Mott relation can be established.

cond-mat.mes-hall↗

arXiv2019

Nonlocal magnetolectric effects in diffusive conductors with spatially inhomogeneous spin-orbit coupling

We present a theoretical study of nonlocal magnetoelectric effects in diffusive hybrid structures with an intrinsic linear-in-momentum spin-orbit coupling (SOC) which is assumed to be spatially inhomogeneous. Our analysis is based on the SU(2)-covariant drift-diffusion equations from which we derive the BC at hybrid interfaces. Within this formulation, the spin current is covariantly conserved when the spin relaxation is only due to the intrinsic SOC. This conservation leads to the absence of spin Hall (SH) currents in homogeneous systems. We also consider extrinsic sources of relaxation (ESR), as magnetic impurities, which break the covariant spin conservation, and may lead to SH currents. We apply our model to describe nonlocal transport in a system with an interface separating two regions: one normal region without intrinsic SOC and one with a Rashba SOC. We first explore the inverse spin-galvanic effect, i.e., a spin polarization induced by an electric field. We demonstrate how the spatial behavior of such spin density depends on both, the direction of the electric field and the strength of the ESR rate. We also study the spin-to-charge conversion, and compute the charge current and the distribution of electrochemical potential in the Rashba region induced by a spin current injected into the normal region. In systems with an inhomogeneous SOC varying in one spatial direction, we find an interesting nonlocal reciprocity between the spin density induced by a charge current at a given point in space, and the spatially integrated current induced by a spin density injected at the same point.

cond-mat.mes-hall↗

arXiv2019

Interfacial mechanism in the anomalous Hall effect of Co/Bi$_2$O$_3$ bilayers

Oxide interfaces are a source of spin-orbit coupling which can lead to novel spin-to-charge conversion effects. In this work the contribution of the Bi$_2$O$_3$ interface to the anomalous Hall effect of Co is experimentally studied in Co/Bi$_2$O$_3$ bilayers. We evidence a variation of 40% in the AHE of Co when a Bi$_2$O$_3$ capping layer is added to the ferromagnet. This strong variation is attributed to an additional source of asymmetric transport in Co/Bi$_2$O$_3$ bilayers that originates from the Co/Bi$_2$O$_3$ interface and contributes to the skew scattering.

cond-mat.mes-hall↗

arXiv2019

Boundary conditions for spin and charge diffusion in the presence of interfacial spin-orbit coupling

Breaking of the inversion symmetry at the interface between different materials may dramatically enhance spin-orbit interaction in the vicinity of the interface. We incorporate the effects of this interfacial spin-orbit coupling (ISOC) into the standard drift-diffusion theory by deriving generalized boundary conditions for diffusion equations. Our theoretical scheme is based on symmetry arguments, providing a natural classification and parametrization of all spin-charge and spin-spin conversion effects that occur due to ISOC at macroscopically isotropic interfaces between nonmagnetic materials. We illustrate our approach with specific examples of spin-charge conversion in hybrid structures. In particular, for a lateral metal-insulator structure we predict an "ISOC-gating" effect which can be used to detect spin currents in metallic films with weak bulk SOC.

cond-mat.mes-hall↗

arXiv2017

Ballistic spin transport in the presence of interfaces with strong spin-orbit coupling

The inversion symmetry breaking at the interface between different materials generates a strong interfacial spin-orbit coupling (ISOC) that may influence the spin and charge transport in hybrid structures. Here we use a simple analytically solvable model to study in the ballistic approximation various spin transport phenomena induced by ISOC in a bilayer metallic system. In this model a non-equilibrium steady state carrying a spin current is created by applying a spin dependent bias across the metallic junction. Physical observables are then calculated using the scattering matrix approach. In particular we calculate the absorption of the spin current at the interface (the interface spin-loss) and study the interface spin-to-charge conversion. The latter consists of an in-plane interface charge current generated by the spin dependent bias applied to the junction, which can be viewed as a spin galvanic effect mediated by ISOC. Finally we demonstrate that ISOC leads to an interfacial spin current swapping, that is, the "primary" spin current flowing through the spin-orbit active interface is necessarily accompanied with a "secondary' swapped spin current flowing along the interface and polarized in the direction perpendicular to that of the "primary" current. Using the exact spin continuity equation we relate the swapping effect to the intefacial spin-loss, and argue that this effect is generic and independent on the ballistic approximation used for specific calculations.

cond-mat.mes-hall↗

arXiv2015

Spin polarization induced by an electric field in the presence of weak localization effects

We evaluate the spin polarization (Edelstein or inverse spin galvanic effect) and the spin Hall current induced by an applied electric field by including the weak localization corrections for a two-dimensional electron gas. We show that the weak localization effects yield logarithmic corrections to both the spin polarization conductivity relating the spin polarization and the electric field and to the spin Hall angle relating the spin and charge currents. The renormalization of both the spin polarization conductivity and the spin Hall angle combine to produce a zero correction to the total spin Hall conductivity as required by an exact identity. Suggestions for the experimental observation of the effect are given.

cond-mat.mes-hall↗