arXiv subjects

Eytan Grosfeld

Publications and source records attributed to Eytan Grosfeld.

At least 19 recordsLinked to original sources

arXiv2026

Boundary quenches in (1+1)-dimensional conformal field theory

We investigate a class of local quantum quenches in which the conformal boundary condition of a (1+1)-dimensional conformal field theory is abruptly changed. We derive a remarkably simple and universal expression for the time evolution of one-point functions on the half-line. This result provides a direct description of the propagation of the disturbance generated by the quench and, in turn, allows us to determine the dynamics of bipartite entanglement for subsystems adjacent to the boundary. We show that, once the subsystem becomes fully causally connected to the quench event, the entanglement entropy undergoes a sharp finite jump whose magnitude is universally given by the logarithm of the ratio of the boundary g-factors associated with the initial and final boundary conditions. We benchmark these analytical predictions against Matrix Product State simulations of the critical Ising spin chain, finding excellent agreement. The numerical analysis further allows us to investigate the time evolution of the spin-flip entanglement asymmetry, revealing how the symmetry-breaking perturbation emitted from the boundary propagates through the system. Our results uncover universal dynamical signatures of boundary quenches and establish a direct connection between nonequilibrium entanglement dynamics and boundary critical phenomena.

cond-mat.stat-mech↗

arXiv2026

Emergence of multiple zero modes bound to vortices in extended topological Josephson junctions

We study planar Josephson junctions formed on the surface of a three-dimensional topological insulator (Fu-Kane proposal). We examine the experimentally relevant parameter regimes in which the frequently used effective description in terms of two counter-propagating one-dimensional Majorana modes with hybridization dependent on the Josephson phase difference reaches its validity limit. This happens when the effective velocity of the emergent one-dimensional Majorana modes approaches zero. As parameters like the chemical potential or the width of the junction are tuned, instances of vanishing effective velocity mark the emergence of additional `Dirac cones' at zero energy and finite momentum. If the junction is subjected to an external magnetic field, Josephson vortices may then bind a number of zero modes in addition to the topological Majorana mode. The additional zero modes are `symmetry-protected' and can be lifted by a broken mirror symmetry (which is to be expected in realistic scenarios) as well as by an in-plane magnetization (or Zeeman field). We note that the ensuing presence of additional low-energy Andreev states can significantly contribute to measured quantities like the Josephson current or microwave absorption spectra.

cond-mat.mes-hall↗

arXiv2026

Flux-driven delocalization transition in disordered topological insulator nanowires

Topological insulator nanowires provide a tunable platform for studying the interplay between disorder, quantum interference, and symmetry-protected transport. Here we investigate quantum transport in disordered topological insulator nanowires threaded by an axial magnetic flux. By computing the conductance as a function of wire length, magnetic flux, chemical potential, and disorder strength, we extract the localization length to characterize the flux-driven delocalization transition near half-integer flux quanta. We find that the localization length diverges with a robust critical exponent $ν=2$, independent of the chemical potential and disorder strength considered here. This exponent differs from that of the integer quantum Hall transition, pointing to distinct scaling behavior. Near integer flux quanta, we further find that the conductance evolves from a weak-localization dip at low chemical potential to a weak anti-localization peak at higher chemical potential, which splits and is eventually suppressed as the system crosses over to the strongly localized regime.

cond-mat.mes-hall↗

arXiv2026

Current Flow in Topological Insulator Josephson Junctions due to Imperfections

Recent experiments on planar superconductor-topological insulator-superconductor (S-TI-S) junctions, e.g., in Corbino geometry, have reported low-temperature nonzero Josephson currents in states with integer fluxoid (flux) induced in the junction by a perpendicular magnetic field. This effect was discussed in connection with Majorana zero modes localized in Josephson vortices of such junctions. Here, we provide an explanation for this phenomenon, attributing it to imperfections. We focus on the ``atomic" limit in which the low-energy bound states of different vortices do not overlap. In this limit, we can associate the nonvanishing critical current with the irregularities, e.g., in the junction's width. The low-temperature contribution to the current is provided by the bound states with low but nonzero energy. We also propose clear experimental tests based on microwave spectroscopy, revealing distinctive selection rules for vortex transitions.

cond-mat.mes-hall↗

arXiv2025

Heavy-Tailed Hall Conductivity Fluctuations in Quantum Hall Transitions

We study the full distribution of the zero-temperature Hall conductivity in a lattice model of the IQHE using the Kubo formula across disorder realizations. Near the localization-delocalization transition, the conductivity exhibits heavy-tailed fluctuations characterized by a power-law decay with exponent $α\approx 2.3$--$2.5$, indicating a finite mean but a divergent variance. The heavy tail persists across a range of system sizes, correlation lengths of the disorder potential and fillings. Our results demonstrate a breakdown of self-averaging in transport in small, coherent samples near criticality, in agreement with findings in random matrix models of topological indices.

cond-mat.mes-hall↗

arXiv2025

Consistent Field Theory Across the Mott-Insulator to Superfluid Transition

We employ a field-theoretical approach to analyze the Bose-Hubbard model on a lattice, with a focus on the low-energy properties across the Mott insulator (MI) to superfluid (SF) transition. Prior approaches approximated the partition function using cumulant expansions around the MI ground state, which, while accurate in the MI phase, lead to inaccuracies in the SF phase where the MI state is a false ground state. By expanding around the correct mean-field vacuum, we derive the effective field theory (EFT) governing the MI to SF transition. Through this, we reveal the underlying structure of the EFT governing the nucleation of low-energy excitations, particularly the massless and lowest massive modes, offering new insights into their emergence.

cond-mat.quant-gas↗

arXiv2025

$π$/4 phase shift in the angular magnetoresistance of infinite layer nickelates

The discovery of superconductivity in nickelates has generated significant interest in condensed matter physics. Nickelate superconductors, which are hole-doped within the layered structure of RNiO$_2$, share structural similarities with high-$T_c$ cuprate superconductors. However, despite similarities in formal valence and crystal symmetry, the fundamental nature of the superconducting state and the parent compound phase in nickelates remains elusive. Strong electronic correlations in infinite-layer nickelates suggest a potentially complex phase diagram, akin to that observed in cuprates, yet a key question about the magnetic ground state remains unanswered. Through magnetoresistance measurements across varying field strengths and orientations, we observe distinct angular-dependent magnetoresistance (AMR) oscillations with four-fold symmetry. Notably, this four-fold symmetry displays a $π/4$ phase shift with doping or applied magnetic field. Our findings parallel behaviors in electron-doped cuprates, suggesting that a static or quasi-static magnetic order exists in the infinite-layer nickelates, echoing characteristics of electron-doped cuprates. Furthermore, our modeling of the system reveals that the AMR is directly related to the underlying antiferromagnetic order, reinforcing this interpretation.

cond-mat.supr-con↗

arXiv2025

Tomographic Signatures of Interacting Majorana and Andreev States in Superconductor-Semiconductor Transmon Qubits

Semiconductor-based Josephson junctions embedded within a Cooper-pair-box can host complex many-body states, such as interacting Andreev states and potentially other quasi-particles of topological origin. Here, we study the insights that could be revealed from a tomographic reconstruction of the Cooper-pair charge distribution of the junction prepared in its ground state. We posit that interacting and topological states can be identified from distinct signatures within the probability distribution of the charge states. Furthermore, the comprehensive dataset provides direct access to information theory metrics elucidating the entanglement between the charge sector of the superconductor and the microscopic degrees of freedom in the junction. We demonstrate how these metrics serve to further classify differences between the types of excitations in the junction.

cond-mat.mes-hall↗

arXiv2025

A proposal for charge basis tomography of superconducting qubits

We introduce a general protocol for obtaining the charge basis density matrix of a superconducting quantum circuit. Inspired by cavity state tomography, our protocol combines Josephson-energy pulse sequences and projective charge-basis readout to access the off-diagonal elements of the density matrix, a scheme we thus dub charge basis tomography. We simulate the reconstruction of the ground state of a target transmon using the Aharonov-Casher effect in a probe qubit to realise projective readout and show the Hilbert-Schmidt distance can detect deviations from the correct model Hamiltonian. Unlocking this ability to validate models using the ground state sets the stage for using transmons to detect interacting and topological phases, particularly in materials where time-domain and spectroscopic probes can be limited by intrinsic noise.

quant-ph↗

arXiv2023

Electromagnetic response of the surface states of a topological insulator nanowire embedded within a resonator

Exploring the interplay between topological phases and photons opens new avenues for investigating novel quantum states. Here we show that superconducting resonators can serve as sensitive probes for properties of topological insulator nanowires (TINWs) embedded within them. By combining a static, controllable magnetic flux threading the TINW with an additional oscillating electromagnetic field applied perpendicularly, we show that orbital resonances can be generated and are reflected in periodic changes of the Q-factor of the resonator as a function of the flux. This response probes the confinement of the two-dimensional Dirac orbitals on the surface of the TINW, revealing their density of states and specific transition rules, as well as their dependence on the applied flux. Our approach represents a promising cross-disciplinary strategy for probing topological solid-state materials using state-of-the-art photonic cavities, which would avoid the need for attaching contacts, thereby enabling access to electronic properties closer to the pristine topological states.

cond-mat.mes-hall↗

arXiv2023

Strong to weak interacting-topological phase transition of bosons on a lattice

We study hard-core bosons on the honeycomb lattice subjected to anisotropic nearest-neighbor hopping along with anisotropic nearest-neighbor repulsion, using a quantum Monte Carlo technique. At half-filling, we find a transition from strong interacting-topological order to weak interacting-topological order as function of the hopping anisotropy. The strong topological phase is characterized by a finite topological entanglement entropy, while the weak topological order is identified with a non-trivial value of the bipartite entanglement entropy. Some of the order parameters and their derivatives demonstrate abrupt changes when varying the parameters controlling the lattice anistropies, thus revealing the nature of this interacting-topological phase transition.

cond-mat.str-el↗

arXiv2022

Interaction-driven phase transition in one dimensional mirror-symmetry protected topological insulator

Topological crystalline insulators are phases of matter where the crystalline symmetries solely protect the topology. In this work, we explore the effect of many-body interactions in a subclass of topological crystalline insulators, namely the mirror-symmetry protected topological crystalline insulator. Employing a prototypical mirror-symmetric quasi-one-dimensional model, we demonstrate the emergence of a mirror-symmetry protected topological phase and its robustness in the presence of short-range interactions. When longer-range interactions are introduced, we find an interaction-induced topological phase transition between the mirror-symmetry protected topological order and a trivial charge density wave. The results are obtained using density-matrix renormalization group and quantum Monte-Carlo simulations in applicable limits.

cond-mat.str-el↗

arXiv2022

Electronic confinement of surface states in a topological insulator nanowire

We analyze the confinement of electronic surface states in a model of a topological insulator nanowire. Spin-momentum locking in the surface states reduces unwanted backscattering in the presence of non-magnetic disorder and is known to counteract localization for certain values of magnetic flux threading the wire. We show that intentional backscattering can be induced for a range of conditions in the presence of a nanowire constriction. We propose a geometry for a nanowire that involves two constrictions and show that these regions form effective barriers that allow for the formation of a quantum dot. We analyze the zero-temperature non-interacting electronic transport through the device using the Landauer-Büttiker approach and show how externally applied magnetic flux parallel to the nanowire and electrostatic gates can be used to control the spectrum of the quantum dot and the electronic transport through the surface states of the model device.

cond-mat.mes-hall↗

arXiv2022

Protection of quantum information in a chain of Josephson junctions

Symmetry considerations are key towards our understanding of the fundamental laws of Nature. The presence of a symmetry implies that a physical system is invariant under specific transformations and this invariance may have deep consequences. For instance, symmetry arguments state that a system will remain in its initial state if incentives to actions are equally balanced. Here, we apply this principle to a chain of qubits and show that it is possible to engineer the symmetries of its Hamiltonian in order to keep quantum information intrinsically protected from both relaxation and decoherence. We show that the coherence properties of this system are strongly enhanced relative to those of its individual components. Such a qubit chain can be realized using a simple architecture consisting of a relatively small number of superconducting Josephson junctions.

quant-ph↗

arXiv2022

Implementation of single-qubit gates via parametric modulation in the Majorana transmon

We present a voltage gate-based method for controlling the Majorana transmon, using a sinusoidal modulation of the induced offset charge $n_g$. Working in the transmon regime and in the instantaneous eigenstates basis, we find the time evolution under this protocol that realises tunable $X$-$Z$ rotations. We optimise the parameters of the system for different single-qubit gates in both the laboratory frame and the qubit rotating frame, obtaining qubit control errors $1-\mathcal{F}$ smaller than $\sim2\times 10^{-4}$. In addition to this, we conduct an analysis of the effects of the charge noise, assuming wide-band $1/f$ additive noise in $n_g$, both for the free and the driven evolutions. For the free evolution, the relaxation and dephasing rates are calculated perturbatively, obtaining long dephasing times of the order of milliseconds at the system's sweet-spots. For the driven case, the average fidelity for the $X$-gate is obtained via a numerical simulation, demonstrating remarkable resilience.

cond-mat.mes-hall↗

arXiv2021

Classical and Quantum Chaos in Chirally-Driven, Dissipative Bose-Hubbard Systems

We study the dissipative Bose-Hubbard model on a small ring of sites in the presence of a chiral drive and explore its long-time dynamical structure using the mean field equations and by simulating the quantum master equation. Remarkably, for large enough drivings, we find that the system admits, in a wide range of parameters, a chaotic attractor at the mean-field level, which manifests as a complex Wigner function on the quantum level. The latter is shown to have the largest weight around the approximate region of phase space occupied by the chaotic attractor. We demonstrate that this behavior could be revealed via measurement of various bosonic correlation functions. In particular, we employ open system methods to calculate the out-of-time-ordered correlator, whose exponential growth signifies a positive quantum Lyapunov exponent in our system. This can open a pathway to the study of chaotic dynamics in interacting systems of photons.

cond-mat.other↗

arXiv2021

Weak topological insulating phases of hard-core-bosons on the honeycomb lattice

We study the phases of hard-core-bosons on a two-dimensional periodic honeycomb lattice in the presence of an on-site potential with alternating sign along the different y-layers of the lattice. Using quantum Monte Carlo simulations supported by analytical calculations, we identify a weak topological insulator, characterized by a zero Chern number but non-zero Berry phase, which is manifested at either density 1/4 or 3/4, as determined by the potential pattern. Additionally, a charge-density-wave insulator is observed at 1/2-filling, whereas the phase diagram at intermediate densities is occupied by a superfluid phase. The weak topological insulator is further shown to be robust against any amount of nearest-neighbor repulsion, as well as weak next-nearest-neighbor repulsion. The experimental realization of our model is feasible in an optical lattice setup.

cond-mat.str-el↗

arXiv2020

Chiral Bosonic Topological Insulator on the Honeycomb Lattice with Anisotropic Interactions

We study hard-core bosons on the honeycomb lattice in the presence of anisotropic nearest-neighbor repulsive interactions. Using a quantum Monte Carlo (QMC) technique, we extract the phase diagram of the model in terms of the filling and the anisotropy. At half-filling we find a dimer insulator phase near maximum anisotropy that is characterized by a finite topological entanglement entropy $\ln(2)/2$, indicative of a fractional quantum Hall state for bosons. We identify the presence of edge states and derive a QMC-based method to extract and verify their chirality. Remarkably, this phase arises in the absence of magnetic flux and without explicit lattice frustration.

cond-mat.str-el↗