Publications

Order by: publication date number of citations

• Universal Entanglement Dynamics following a Local Quench

  Romain Vasseur, Hubert Saleur

  SciPost Phys. 3, 001 (2017) · published 6 July 2017 | Toggle abstract · pdf

  We study the time dependence of the entanglement between two quantum wires after suddenly connecting them via tunneling through an impurity. The result at large times is given by the well known formula $S(t) \approx {1\over 3}\ln {t}$. We show that the intermediate time regime can be described by a universal cross-over formula $S=F(tT_K)$, where $T_K$ is the crossover (Kondo) temperature: the function $F$ describes the dynamical "healing" of the system at large times. We discuss how to obtain analytic information about $F$ in the case of an integrable quantum impurity problem using the massless Form-Factors formalism for twist and boundary condition changing operators. Our results are confirmed by density matrix renormalization group calculations and exact free fermion numerics.

  3 citations

• Viability of rotation sensing using phonon interferometry in Bose-Einstein condensates

  Charles W. Woffinden, Andrew J. Groszek, Guillaume Gauthier, Bradley J. Mommers, Michael. W. J. Bromley, Simon A. Haine, Halina Rubinsztein-Dunlop, Matthew J. Davis, Tyler W. Neely, Mark Baker

  SciPost Phys. 15, 128 (2023) · published 2 October 2023 | Toggle abstract · pdf

  We demonstrate the use of a ring-shaped Bose-Einstein condensate as a rotation sensor by measuring the interference between two counter-propagating phonon modes imprinted azimuthally around the ring. We observe rapid decay of the excitations, quantified by quality factors of at most Q ≈ 27. We numerically model our experiment using the c-field methodology, allowing us to estimate the parameters that maximise the performance of our sensor. We explore the damping mechanisms underlying the observed phonon decay, and identify two distinct Landau scattering processes that each dominate at different driving amplitudes and temperatures. Our simulations reveal that Q is limited by strong damping of phonons even in the zero temperature limit. We perform an experimental proof-of-principle rotation measurement using persistent currents imprinted around the ring. We demonstrate a rotation sensitivity of up to $\Delta \Omega ≈ 0.3 rad s^{-1}$ from a single image, with a theoretically achievable value of $\Delta \Omega ≈ 0.04 rad s^{-1}$ in the atomic shot-noise limit. This is a significant improvement over the shot-noise-limited $\Delta \Omega ≈ 1 rad s^{-1}$ sensitivity obtained by Marti et al. [Phys. Rev. A 91, 013602 (2015)] for a similar setup.

  3 citations

• Phases of cold holographic QCD: Baryons, pions and rho mesons

  Nicolas Kovensky, Aaron Poole, Andreas Schmitt

  SciPost Phys. 15, 162 (2023) · published 13 October 2023 | Toggle abstract · pdf

  We improve the holographic description of isospin-asymmetric baryonic matter within the Witten-Sakai-Sugimoto model by accounting for a realistic pion mass, computing the pion condensate dynamically, and including rho meson condensation by allowing the gauge field in the bulk to be anisotropic. This description takes into account the coexistence of baryonic matter with pion and rho meson condensates. Our main result is the zero-temperature phase diagram in the plane of baryon and isospin chemical potentials. We find that the effective pion mass in the baryonic medium increases with baryon density and that, as a consequence, there is no pion condensation in neutron-star matter. Our improved description also predicts that baryons are disfavored at low baryon chemical potentials even for arbitrarily large isospin chemical potential. Instead, rho meson condensation sets in on top of the pion condensate at an isospin chemical potential of about $9.4 m_\pi$. We further observe a highly non-monotonic phase boundary regarding the disappearance of pion condensation.

  3 citations

• Quantum enhanced metrology in the search for fundamental physical phenomena

  Konrad W. Lehnert

  SciPost Phys. Lect. Notes 40 (2022) · published 11 March 2022 | Toggle abstract · pdf

  These notes summarize lectures given at the 2019 Les Houches summer school on Quantum Information Machines. They describe and review an application of quantum metrology concepts to searches for ultralight dark matter. In particular, for ultralight dark matter that couples as a weak classical force to a laboratory harmonic oscillator, quantum squeezing benefits experiments in which the mass of the dark matter particle is unknown. This benefit is present even if the oscillatory dark matter signal is much more coherent than the harmonic oscillator that it couples to, as is the case for microwave frequency searches for dark matter axion particles.

  3 citations

• Navigating through the O(N) archipelago

  Benoit Sirois

  SciPost Phys. 13, 081 (2022) · published 4 October 2022 | Toggle abstract · pdf

  A novel method for finding allowed regions in the space of CFT-data, coined navigator method, was recently proposed in arXiv:2104.09518. Its efficacy was demonstrated in the simplest example possible, i.e. that of the mixed-correlator study of the 3D Ising Model. In this paper, we would like to show that the navigator method may also be applied to the study of the family of $d$-dimensional $O(N)$ models. We will aim to follow these models in the $(d,N)$ plane. We will see that the "sailing" from island to island can be understood in the context of the navigator as a parametric optimization problem, and we will exploit this fact to implement a simple and effective path-following algorithm. By sailing with the navigator through the $(d,N)$ plane, we will provide estimates of the scaling dimensions $(\Delta_{\phi},\Delta_{s},\Delta_{t})$ in the entire range $(d,N) \in [3,4] \times [1,3]$. We will show that to our level of precision, we cannot see the non-unitary nature of the $O(N)$ models due to the fractional values of $d$ or $N$ in this range. We will also study the limit $N \xrightarrow[]{} 1$, and see that we cannot find any solution to the unitary mixed-correlator crossing equations below $N=1$.

  3 citations

• Solution of Baxter equation for the $q$-Toda and Toda$_2$ chains by NLIE

  Olivier Babelon, Karol K. Kozlowski, Vincent Pasquier

  SciPost Phys. 5, 035 (2018) · published 18 October 2018 | Toggle abstract · pdf

  We construct a basis of solutions of the scalar $\boldsymbol{ \texttt{t} }- \boldsymbol{ \texttt{Q} }$ equation describing the spectrum of the $q$-Toda and Toda$_2$ chains by using auxiliary non-linear integral equations. Our construction allows us to provide quantisation conditions for the spectra of these models in the form of thermodynamic Bethe Ansatz-like equations.

  3 citations

• Vortex states in a PbTiO$_3$ ferroelectric cylinder

  Svitlana Kondovych, Maksim Pavlenko, Yurii Tikhonov, Anna Razumnaya, Igor Lukyanchuk

  SciPost Phys. 14, 056 (2023) · published 30 March 2023 | Toggle abstract · pdf

  The past decade's discovery of topological excitations in nanoscale ferroelectrics has turned the prevailing view that the polar ground state in these materials is uniform. However, the systematic understanding of the topological polar structures in ferroelectrics is still on track. Here we study stable vortex-like textures of polarization in the nanocylinders of ferroelectric PbTiO$_3$, arising due to the competition of the elastic and electrostatic interactions. Using the phase-field numerical modeling and analytical calculations, we show that the orientation of the vortex core with respect to the cylinder axis is tuned by the geometrical parameters and temperature of the system.

  3 citations

• Towards traversable wormholes from force-free plasmas

  Nabil Iqbal, Simon F. Ross

  SciPost Phys. 12, 086 (2022) · published 9 March 2022 | Toggle abstract · pdf

  The near-horizon region of magnetically charged black holes can have very strong magnetic fields. A useful low-energy effective theory for fluctuations of the fields, coupled to electrically charged particles, is force-free electrodynamics. The low energy collective excitations include a large number of Alfven wave modes, which have a massless dispersion relation along the field worldlines. We attempt to construct traversable wormhole solutions using the negative Casimir energy of the Alfven wave modes, analogously to the recent construction using charged massless fermions. The behaviour of massless scalars in the near-horizon region implies that the size of the wormholes is strongly restricted and cannot be made large, even though the force free description is valid in a larger regime.

  3 citations

• Holographic Weyl anomaly in string theory

  Lorenz Eberhardt, Sridip Pal

  SciPost Phys. 16, 027 (2024) · published 24 January 2024 | Toggle abstract · pdf

  We compute the worldsheet sphere partition function of string theory on global AdS$_3$ with pure NS-NS flux. Because of an unfixed Möbius symmetry on the worldsheet, there is a cancellation of infinities and only a part of the answer is unambiguous. We show that it precisely reproduces the holographic Weyl anomaly and the ambiguous terms correspond to the possible counterterms of the boundary CFT.

  3 citations

• GHZ-like states in the Qubit-Qudit Rabi model

  Yuan Shen, Giampiero Marchegiani, Gianluigi Catelani, Luigi Amico, Ai Qun Liu, Weijun Fan, Leong-Chuan Kwek

  SciPost Phys. 11, 099 (2021) · published 1 December 2021 | Toggle abstract · pdf

  We study a Rabi type Hamiltonian system in which a qubit and a d-level quantum system (qudit) are coupled through a common resonator. In the weak and strong coupling limits the spectrum is analysed through suitable perturbative schemes. The analysis show that the presence of the multilevels of the qudit effectively enhance the qubit-qudit interaction. The ground state of the strongly coupled system is found to be of Greenberger-Horne-Zeilinger (GHZ) type. Therefore, despite the qubit-qudit strong coupling, the nature of the specific tripartite entanglement of the GHZ state suppresses the bipartite entanglement. We analyze the system dynamics under quenching and adiabatic switching of the qubit-resonator and qudit-resonator couplings. In the quench case, we found that the non-adiabatic generation of photons in the resonator is enhanced by the number of levels in the qudit. The adiabatic control represents a possible route for preparation of GHZ states. Our analysis provides relevant information for future studies on coherent state transfer in qubit-qudit systems.

  3 citations