Publications

Order by: publication date number of citations

• Separability and entanglement of resonating valence-bond states

  Gilles Parez, Clément Berthiere, William Witczak-Krempa

  SciPost Phys. 15, 066 (2023) · published 21 August 2023 | Toggle abstract · pdf

  We investigate separability and entanglement of Rokhsar-Kivelson (RK) states and resonating valence-bond (RVB) states. These states play a prominent role in condensed matter physics, as they can describe quantum spin liquids and quantum critical states of matter, depending on their underlying lattices. For dimer RK states on arbitrary tileable graphs, we prove the exact separability of the reduced density matrix of $k$ disconnected subsystems, implying the absence of bipartite and multipartite entanglement between the subsystems. For more general RK states with local constraints, we argue separability in the thermodynamic limit, and show that any local RK state has zero logarithmic negativity, even if the density matrix is not exactly separable. In the case of adjacent subsystems, we find an exact expression for the logarithmic negativity in terms of partition functions of the underlying statistical model. For RVB states, we show separability for disconnected subsystems up to exponentially small terms in the distance $d$ between the subsystems, and that the logarithmic negativity is exponentially suppressed with $d$. We argue that separability does hold in the scaling limit, even for arbitrarily small ratio $d/L$, where $L$ is the characteristic size of the subsystems. Our results hold for arbitrary lattices, and encompass a large class of RK and RVB states, which include certain gapped quantum spin liquids and gapless quantum critical systems.

  5 citations

• Giant spatial anisotropy of magnon Landau damping in altermagnets

  António T. Costa, João C. G. Henriques, Joaquín Fernández-Rossier

  SciPost Phys. 18, 125 (2025) · published 11 April 2025 | Toggle abstract · pdf

  Altermagnets are a new class of magnetic materials with zero net magnetization (like antiferromagnets) but spin-split electronic bands (like ferromagnets) over a fraction of reciprocal space. As in antiferromagnets, magnons in altermagnets come in two flavours, that either add one or remove one unit of spin to the $S=0$ ground state. However, in altermagnets these two magnon modes are non-degenerate along some directions in reciprocal space. Here we show that the lifetime of altermagnetic magnons, due to Landau damping caused by coupling to Stoner modes, has a very strong dependence on both flavour and direction. Strikingly, coupling to Stoner modes leads to a complete suppression of magnon propagation along selected spatial directions. This giant anisotropy will impact electronic, spin, and energy transport properties and may be exploited in spintronic applications.

  5 citations

• Anomalous Luttinger equivalence between temperature and curved spacetime: From black holes to thermal quenches

  Baptiste Bermond, Maxim Nikolaevich Chernodub, Adolfo G. Grushin, David Carpentier

  SciPost Phys. 16, 084 (2024) · published 25 March 2024 | Toggle abstract · pdf

  Building on the idea of Tolman and Ehrenfest that heat has weight, Luttinger established a deep connection between gravitational fields and thermal transport. However, this relation does not include anomalous quantum fluctuations that become paramount in strongly curved spacetime. In this work, we revisit the celebrated Tolman-Ehrenfest and Luttinger relations and show how to incorporate the quantum energy scales associated with these fluctuations, captured by gravitational anomalies of quantum field theories. We point out that such anomalous fluctuations naturally occur in the quantum atmosphere of a black hole. Our results reveal that analogous fluctuations are also observable in thermal conductors in flat-space time provided local temperature varies strongly. As a consequence, we establish that the gravitational anomalies manifest themselves naturally in non-linear thermal response of a quantum wire. In addition, we propose a systematic way to identify thermal analogues of black hole's anomalous quantum fluctuations associated to gravitational anomalies. We identify their signatures in propagating energy waves following a thermal quench, as well as in the energy density of heating Floquet states induced by repeated thermal quenches.

  5 citations

• Charting the conformal manifold of holographic CFT$_2$'s

  Camille Eloy, Gabriel Larios

  SciPost Phys. 17, 123 (2024) · published 31 October 2024 | Toggle abstract · pdf

  We construct new continuous families of AdS$_3× S^3× T^4$ and AdS$_3× S^3× S^3× S^1$ solutions in heterotic and type II supergravities. These families are found in three-dimensional consistent truncations and controlled by 17 parameters, which include TsT $\beta$ deformations and encompass several supersymmetric sub-families. The different uplifts are constructed in a unified fashion by means of Exceptional Field Theory (ExFT). This allows the computation of the Kaluza-Klein spectra around the deformations, to test the stability of the solutions, and to interpret them holographically and as worldsheet models. To achieve this, we describe how the half-maximal $S(8,8)$ ExFT can be embedded into E$_{8(8)}$ ExFT.

  5 citations

• Sub-GeV dark matter models and direct detection

  Tongyan Lin

  SciPost Phys. Lect. Notes 43 (2022) · published 18 March 2022 | Toggle abstract · pdf

  Lecture notes for Les Houches Summer School 2021: Dark Matter. These lectures give a brief introduction to sub-GeV dark matter models, and then reviews theory and approaches to direct detection of sub-GeV dark matter.

  5 citations

• Certifying quantum separability with adaptive polytopes

  Ties-A. Ohst, Xiao-Dong Yu, Otfried Gühne, H. Chau Nguyen

  SciPost Phys. 16, 063 (2024) · published 1 March 2024 | Toggle abstract · pdf

  The concept of entanglement and separability of quantum states is relevant for several fields in physics. Still, there is a lack of effective operational methods to characterise these features. We propose a method to certify quantum separability of two- and multiparticle quantum systems based on an adaptive polytope approximation. This leads to an algorithm which, for practical purposes, conclusively recognises two-particle separability for small and medium-size dimensions. For multiparticle systems, the approach allows to characterise full separability for up to five qubits or three qutrits; in addition, different classes of entanglement can be distinguished. Finally, our methods allow to identify systematically quantum states with interesting entanglement properties, such as maximally robust states which are separable for all bipartitions, but not fully separable.

  5 citations

• Excitons under strain: light absorption and emission in strained hexagonal boron nitride

  Pierre Lechifflart, Fulvio Paleari, Claudio Attaccalite

  SciPost Phys. 12, 145 (2022) · published 4 May 2022 | Toggle abstract · pdf

  Hexagonal boron nitride is an indirect band gap material with a strong luminescence in the ultraviolet. This luminescence originates from bound excitons recombination assisted by different phonon modes. The coupling between excitons and phonons is so strong that the resulting light emission is as efficient as the one of direct band gap materials. In this manuscript we investigate how uniaxial strain modifies the electronic and optical properties of this material, and in particular how it affects the exciton-phonon coupling. Using a formulation of this coupling based on finite-difference displacements, recently developed by some of us, we investigate how phonon-assisted transitions change under strain. Our results open the way to the study of phonon-assisted luminescence in strained materials from first principles. Our findings are important both for experiments that directly probe \hbn under strain or for those in which it is used as substrate for other 2D material with a lattice mismatch.

  5 citations

• Concentration of quantum equilibration and an estimate of the recurrence time

  Jonathon Riddell, Nathan J. Pagliaroli, Álvaro M. Alhambra

  SciPost Phys. 15, 165 (2023) · published 16 October 2023 | Toggle abstract · pdf

  We show that the dynamics of generic quantum systems concentrate around their equilibrium value when measuring at arbitrary times. This means that the probability of finding such values away from that equilibrium is exponentially suppressed, with a decay rate given by the effective dimension. Our result allows us to place a lower bound on the recurrence time of quantum systems, since recurrences corresponds to the rare events of finding a state away from equilibrium. In many-body systems, this bound is doubly exponential in system size. We also show corresponding results for free fermions, which display a weaker concentration and earlier recurrences.

  5 citations

• Efficient higher-order matrix product operators for time evolution

  Maarten Van Damme, Jutho Haegeman, Ian McCulloch, Laurens Vanderstraeten

  SciPost Phys. 17, 135 (2024) · published 15 November 2024 | Toggle abstract · pdf

  We introduce a systematic construction of higher-order matrix product operator (MPO) approximations of the time evolution operator for generic (short and long range) one-dimensional Hamiltonians. We demonstrate the utility of our construction, by showing an order of magnitude speedup in simulation cost compared to conventional first-order MPO time evolution schemes.

  5 citations

• Moral lines of credit: Forging race projects, citizenship, and nation on online U.S. spousal reunification forums

  Gina Marie Longo

  Mig. Pol. 1, 005 (2022) · published 24 October 2022 | Toggle abstract · pdf

  This study investigates how U.S. citizens petitioning for “green cards” on behalf of foreign national spouses uphold the U.S. racial project as they navigate the spousal reunification process. It also explores the role of online communities as crucial “brokers” and mediators between citizen, noncitizen, and the state. This work troubles the dichotomy between immigration officers/couples while giving primacy to the citizen-spouse’s voices. Using content analysis of an online forum where petitioners exchange advice with similar others, I show the citizen’s complicity with the racialized hierarchical order of the American nation. Ultimately, family migration policies and regulations are exercises in state-building, and nation-building, and citizens partake in it while trying to secure their own family, disciplining themselves to align with the state’s ideal of what a proper future nation should look like.

  5 citations