We introduce a new parameter to investigate replica symmetry breaking transitions using finite-size scaling methods. Based on exact equalities initially derived by F. Guerra this parameter is a direct check of the self-averaging character of the spin-glass order parameter. This new parameter can be used to study models with time reversal symmetry but its greatest interest lies in models where this symmetry is absent. We apply the method to long-range and short-range Ising spin-glasses with and without a magnetic field as well as short-range multispin interaction spin-glasses.We introduce a new parameter to investigate replica symmetry breaking transitions using finite-size scaling methods. Based on exact equalities initially derived by F. Guerra this parameter is a direct check of the self-averaging character of the spin-glass order parameter. This new parameter can be used to study models with time reversal symmetry but its greatest interest lies in models where this symmetry is absent. We apply the method to long-range and short-range Ising spin-glasses with and without a magnetic field as well as short-range multispin interaction spin-glasses.

arXiv:cond-mat/9802309Physical Review LettersAug 24, 199846 citations

Methods of the Many-Body Theory in Superconductivity

Alexandre M. Zagoskin

Graduate texts in physicsJan 1, 20142 citations

Consistent statistical treatment of the renormalized mean-field t−J model

Jakub Jȩdrak, Józef Spałek

A variational treatment of the Gutzwiller---renormalized $t\text{\ensuremath{-}}J$ Hamiltonian combined with the mean-field (MF) approximation is proposed, with a simultaneous inclusion of additional consistency conditions. Those conditions guarantee that the averages calculated variationally coincide with those calculated from the self-consistent equations. This is not ensured a priori because the effective Hamiltonian contains renormalization factors which depend explicitly on the mean-field averages. A comparison with previous mean-field treatments is made for both superconducting $(d\text{-RVB})$ and normal states and encompasses calculations of the superconducting gap and the renormalized hopping amplitudes, as well as the electronic structure. The ${C}_{4v}$ -symmetry breaking in the normal phase---the Pomeranchuk instability---is also analyzed.A variational treatment of the Gutzwiller---renormalized $t\text{\ensuremath{-}}J$ Hamiltonian combined with the mean-field (MF) approximation is proposed, with a simultaneous inclusion of additional consistency conditions. Those conditions guarantee that the averages calculated variationally coincide with those calculated from the self-consistent equations. This is not ensured a priori because the effective Hamiltonian contains renormalization factors which depend explicitly on the mean-field averages. A comparison with previous mean-field treatments is made for both superconducting $(d\text{-RVB})$ and normal states and encompasses calculations of the superconducting gap and the renormalized hopping amplitudes, as well as the electronic structure. The ${C}_{4v}$-symmetry breaking in the normal phase---the Pomeranchuk instability---is also analyzed.

arXiv:0908.4411Physical Review BFeb 24, 201035 citations

Functional averages in the theory of superconductivity

Hans -Ulrich Everts

The European Physical Journal AApr 1, 19676 citations

Probing the symmetry breaking of a light–matter system by an ancillary qubit

Shuai-Peng Wang, A. Ridolfo, Tiefu Li +4 more

Hybrid quantum systems in the ultrastrong, and even more in the deep-strong, coupling regimes can exhibit exotic physical phenomena and promise new applications in quantum technologies. In these nonperturbative regimes, a qubit-resonator system has an entangled quantum vacuum with a nonzero average photon number in the resonator, where the photons are virtual and cannot be directly detected. The vacuum field, however, is able to induce the symmetry breaking of a dispersively coupled probe qubit. We experimentally observe the parity symmetry breaking of an ancillary Xmon artificial atom induced by the field of a lumped-element superconducting resonator deep-strongly coupled with a flux qubit. This result opens a way to experimentally explore the novel quantum-vacuum effects emerging in the deep-strong coupling regime.Hybrid quantum systems in the ultrastrong, and even more in the deep-strong, coupling regimes can exhibit exotic physical phenomena and promise new applications in quantum technologies. In these nonperturbative regimes, a qubit-resonator system has an entangled quantum vacuum with a nonzero average photon number in the resonator, where the photons are virtual and cannot be directly detected. The vacuum field, however, is able to induce the symmetry breaking of a dispersively coupled probe qubit. We experimentally observe the parity symmetry breaking of an ancillary Xmon artificial atom induced by the field of a lumped-element superconducting resonator deep-strongly coupled with a flux qubit. This result opens a way to experimentally explore the novel quantum-vacuum effects emerging in the deep-strong coupling regime.

arXiv:2209.05747Nature CommunicationsJul 20, 202315 citations

(d\text{-RVB})

and normal states and encompasses calculations of the superconducting gap and the renormalized hopping amplitudes, as well as the electronic structure. The

{C}_{4v}

-symmetry breaking in the normal phase---the Pomeranchuk instability---is also analyzed.