Publications

Order by: publication date number of citations

• Measurement-induced phase transition in teleportation and wormholes

  Alexey Milekhin, Fedor K. Popov

  SciPost Phys. 17, 020 (2024) · published 25 July 2024 | Toggle abstract · pdf

  We demonstrate that some quantum teleportation protocols exhibit measurement induced phase transitions in Sachdev-Ye-Kitaev model. Namely, Kitaev-Yoshida and Gao-Jafferis-Wall protocols have a phase transition if we apply them at a large projection rate or at a large coupling rate respectively. It is well-known that at small rates they allow teleportation to happen only within a small time-window. We show that at large rates, the system goes into a new steady state, where the teleportation can be performed at any moment. In dual Jackiw-Teitelboim gravity these phase transitions correspond to the formation of an eternal traversable wormhole. In the Kitaev-Yoshida case this novel type of wormhole is supported by continuous projections.

  4 citations

• The quantum perfect fluid in 2D

  Aurélien Dersy, Andrei Khmelnitsky, Riccardo Rattazzi

  SciPost Phys. 17, 019 (2024) · published 24 July 2024 | Toggle abstract · pdf

  We consider the field theory that defines a perfect incompressible 2D fluid. One distinctive property of this system is that the quadratic action for fluctuations around the ground state features neither mass nor gradient term. Quantum mechanically this poses a technical puzzle, as it implies the Hilbert space of fluctuations is not a Fock space and perturbation theory is useless. As we show, the proper treatment must instead use that the configuration space is the area preserving Lie group ${S\mathrm{Diff}}$. Quantum mechanics on Lie groups is basically a group theory problem, but a harder one in our case, since ${S\mathrm{Diff}}$ is infinite dimensional. Focusing on a fluid on the 2-torus $T^2$, we could however exploit the well known result ${S\mathrm{Diff}}(T^2)\sim SU(N)$ for $N\to ∞$, reducing for finite $N$ to a tractable case. $SU(N)$ offers a UV-regulation, but physical quantities can be robustly defined in the continuum limit $N\to∞$. The main result of our study is the existence of ungapped localized excitations, the vortons, satisfying a dispersion $\omega \propto k^2$ and carrying a vorticity dipole. The vortons are also characterized by very distinctive derivative interactions whose structure is fixed by symmetry. Departing from the original incompressible fluid, we constructed a class of field theories where the vortons appear, right from the start, as the quanta of either bosonic or fermionic local fields.

  1 citation

• The fate of the spin polaron in the 1D antiferromagnets

  Piotr Wrzosek, Adam Kłosiński, Yao Wang, Mona Berciu, Cliò Efthimia Agrapidis, Krzysztof Wohlfeld

  SciPost Phys. 17, 018 (2024) · published 19 July 2024 | Toggle abstract · pdf

  The stability of the spin polaron quasiparticle, well established in studies of a single hole in the 2D antiferromagnets, is investigated in the 1D antiferromagnets using a $t$-$J$ model. We perform an exact slave fermion transformation to the holon-magnon basis, and diagonalize numerically the resulting model in the presence of a single hole. We demonstrate that the spin polaron collapses - and the spin-charge separation takes over - due to the specific role played by the magnon-magnon interactions and the magnon hard-core constraint in the 1D $t$-$J$ model. Moreover, we prove that the spin polaron is stable for any strength of the magnon-magnon interaction other than the unique value found in a 1D antiferromagnet with the continuous symmetry of the spin interactions. Fine-tuning to this unique value is extremely unlikely to occur in quasi-1D antiferromagnets, therefore the spin polaron is the stable quasiparticle of realistic 1D materials. Our results lead to a new interpretation of the ARPES spectra of quasi-1D antiferromagnets in the spin polaron language.

• Loop equations for generalised eigenvalue models

  Edoardo Vescovi, Konstantin Zarembo

  SciPost Phys. 17, 017 (2024) · published 18 July 2024 | Toggle abstract · pdf

  We derive the loop equation for the 1-matrix model with generic difference-type measure for eigenvalues and develop a recursive algebraic framework for solving it to an arbitrary order in the coupling constant in and beyond the planar approximation. The planar limit is solved exactly for a one-parametric family of models and in the general case at strong coupling. The Wilson loop in the $\mathcal{N}=2^*$ super-Yang-Mills theory and the Hoppe model are used to illustrate our methods.

• Vortex loop operators and quantum M2-branes

  Nadav Drukker, Omar Shahpo

  SciPost Phys. 17, 016 (2024) · published 16 July 2024 | Toggle abstract · pdf

  We study M2-branes in $AdS_4× S^7/\mathbb{Z}_k$ dual to 1/2 and 1/3 BPS vortex loop operators in ABJM theory and compute their one-loop correction beyond the classical M2-brane action. The correction depends only on the parity of $k$ and is independent of all continuous parameters in the definition of the vortex loops. The result for odd $k$ agrees with the answers for the 1/2 BPS Wilson loop in the $k=1$ theory and for even $k$ with the one in the $k = 2$ theory. Combining with the classical part, we find that the natural expansion parameter seems to be $1/\sqrt{kN}$ rather than $1/\sqrt{N}$. This provides a further setting where semiclassical quantisation can be applied to M2-branes and produces new results inaccessible by other methods.

  3 citations

• Non-invertible symmetries and higher representation theory I

  Thomas Bartsch, Mathew Bullimore, Andrea E. V. Ferrari, Jamie Pearson

  SciPost Phys. 17, 015 (2024) · published 16 July 2024 | Toggle abstract · pdf

  The purpose of this paper is to investigate the global categorical symmetries that arise when gauging finite higher groups in three or more dimensions. The motivation is to provide a common perspective on constructions of non-invertible global symmetries in higher dimensions and a precise description of the associated symmetry categories. This paper focusses on gauging finite groups and split 2-groups in three dimensions. In addition to topological Wilson lines, we show that this generates a rich spectrum of topological surface defects labelled by 2-representations and explain their connection to condensation defects for Wilson lines. We derive various properties of the topological defects and show that the associated symmetry category is the fusion 2-category of 2-representations. This allows us to determine the full symmetry categories of certain gauge theories with disconnected gauge groups. A subsequent paper will examine gauging more general higher groups in higher dimensions.

  8 citations

• Efficient adaptive Bayesian estimation of a slowly fluctuating Overhauser field gradient

  Jacob Benestad, Jan A. Krzywda, Evert van Nieuwenburg, Jeroen Danon

  SciPost Phys. 17, 014 (2024) · published 16 July 2024 | Toggle abstract · pdf

  Slow fluctuations of Overhauser fields are an important source for decoherence in spin qubits hosted in III-V semiconductor quantum dots. Focusing on the effect of the field gradient on double-dot singlet-triplet qubits, we present two adaptive Bayesian schemes to estimate the magnitude of the gradient by a series of free induction decay experiments. We concentrate on reducing the computational overhead, with a real-time implementation of the schemes in mind. We show how it is possible to achieve a significant improvement of estimation accuracy compared to more traditional estimation methods. We include an analysis of the effects of dephasing and the drift of the gradient itself.

• Decorated defect construction of gapless-SPT states

  Linhao Li, Masaki Oshikawa, Yunqin Zheng

  SciPost Phys. 17, 013 (2024) · published 15 July 2024 | Toggle abstract · pdf

  Symmetry protected topological (SPT) phases are one of the simplest, yet nontrivial, gapped systems that go beyond the Landau paradigm. In this work, we study an extension of the notion of SPT for gapless systems, namely, gapless symmetry protected topological states. We construct several simple gapless-SPT models using the decorated defect construction, which allow analytical understanding of non-trivial topological features including the symmetry charge under twisted boundary conditions, and boundary (quasi)-degeneracy under open boundary conditions. We also comment on the stability of the gapless-SPT models under symmetric perturbations, and apply small-scale exact diagonalization when direct analytic understanding is not available.

  2 citations

• Stress correlations in near-crystalline packings

  Roshan Maharana, Kabir Ramola

  SciPost Phys. 17, 012 (2024) · published 15 July 2024 | Toggle abstract · pdf

  We derive exact results for stress correlations in near-crystalline systems in two and three dimensions. We study energy minimized configurations of particles interacting through Harmonic as well as Lennard-Jones potentials, for varying degrees of microscopic disorder and quenched forces on grains. Our findings demonstrate that the macroscopic elastic properties of such near-crystalline packings remain unchanged within a certain disorder threshold, yet they can be influenced by various factors, including packing density, pressure, and the strength of inter-particle interactions. We show that the stress correlations in such systems display anisotropic behavior at large lengthscales and are significantly influenced by the pre-stress of the system. The anisotropic nature of these correlations remains unaffected as we increase the strength of the disorder. Additionally, we derive the large lengthscale behavior for the change in the local stress components that shows a $1/r^d$ radial decay for the case of particle size disorder and a $1/r^{d-1}$ behavior for quenched forces introduced into a crystalline network. Finally, we verify our theoretical results numerically using energy-minimised static particle configurations.

• Quantum state preparation of topological chiral spin liquids via Floquet engineering

  Matthieu Mambrini, Didier Poilblanc

  SciPost Phys. 17, 011 (2024) · published 11 July 2024 | Toggle abstract · pdf

  In condensed matter, Chiral Spin Liquids (CSL) are quantum spin analogs of electronic Fractional Quantum Hall states (in the continuum) or Fractional Chern Insulators (on the lattice). As the latter, CSL are remarkable states of matter, exhibiting topological order and chiral edge modes. Preparing CSL on quantum simulators like cold atom platforms is still an open challenge. Here we propose a simple setup on a finite cluster of spin-1/2 located at the sites of a square lattice. Using a Resonating Valence Bond (RVB) non-chiral spin liquid as initial state on which fast time-modulations of strong nearest-neighbor Heisenberg couplings are applied, following different protocols (out-of-equilibrium quench or semi-adiabatic ramping of the drive), we show the slow emergence of such a CSL phase. An effective Floquet dynamics, obtained from a high-frequency Magnus expansion of the drive Hamiltonian, provides a very accurate and simple framework fully capturing the out-of-equilibrium dynamics. An analysis of the resulting prepared states in term of Projected Entangled Pair states gives further insights on the topological nature of the chiral phase. Finally, we discuss possible applications to quantum computing.