Publications

Order by: publication date number of citations

• Quantum-enhanced multiparameter estimation and compressed sensing of a field

  Youcef Baamara, Manuel Gessner, Alice Sinatra

  SciPost Phys. 14, 050 (2023) · published 27 March 2023 | Toggle abstract · pdf

  We show that a significant quantum gain corresponding to squeezed or over-squeezed spin states can be obtained in multiparameter estimation by measuring the Hadamard coefficients of a 1D or 2D signal. The physical platform we consider consists of two-level atoms in an optical lattice in a squeezed-Mott configuration, or more generally by correlated spins distributed in spatially separated modes. Our protocol requires the possibility to locally flip the spins, but relies on collective measurements. We give examples of applications to scalar or vector field mapping and compressed sensing.

  3 citations

• Quantum chaos in perturbative super-Yang-Mills Theory

  Tristan McLoughlin, Raul Pereira, Anne Spiering

  SciPost Phys. 14, 049 (2023) · published 27 March 2023 | Toggle abstract · pdf

  We provide numerical evidence that the perturbative spectrum of anomalous dimensions in maximally supersymmetric $SU(N)$ Yang-Mills theory is chaotic at finite values of $N$. We calculate the probability distribution of one-loop level spacings for subsectors of the theory and show that for large $N$ it is given by the Poisson distribution of integrable models, while at finite values it is the Wigner-Dyson distribution of the Gaussian orthogonal ensemble random matrix theory. We extend these results to two-loop order and to a one-parameter family of deformations. We further study the spectral rigidity for these models and show that it is also well described by random matrix theory. Finally we demonstrate that the finite-$N$ eigenvectors possess properties of chaotic states.

  2 citations

• Enhancement of chiral edge currents in ($d$+1)-dimensional atomic Mott-band hybrid insulators

  Matteo Ferraretto, Andrea Richaud, Lorenzo Del Re, Leonardo Fallani, Massimo Capone

  SciPost Phys. 14, 048 (2023) · published 24 March 2023 | Toggle abstract · pdf

  We consider the effect of a local interatomic repulsion on synthetic heterostructures where a discrete synthetic dimension is created by Raman processes on top of $SU(N)$-symmetric two-dimensional lattice systems. At a filling of one fermion per site, increasing the interaction strength, the system is driven towards a Mott state which is adiabatically connected to a band insulator. The chiral currents associated with the synthetic magnetic field increase all the way to the Mott transition, where they reach the maximum value, and they remain finite in the whole insulating state. The transition towards the Mott-band insulator is associated with the opening of a gap within the low-energy quasiparticle peak, while a mean-field picture is recovered deep in the insulating state.

  5 citations

• Greedy optimization of the geometry of Majorana Josephson junctions

  André Melo, Tanko Tanev, Anton R. Akhmerov

  SciPost Phys. 14, 047 (2023) · published 23 March 2023 | Toggle abstract · pdf

  Josephson junctions in a two-dimensional electron gas with spin-orbit coupling are a promising candidate to realize topological superconductivity. While it is known that the geometry of the junction strongly influences the size of the topological gap, the question of how to construct optimal geometries remains unexplored. We introduce a greedy numerical algorithm to optimize the shape of Majorana junctions. The core of the algorithm relies on perturbation theory and is embarrassingly parallel, which allows it to explore the design space efficiently. By introducing stochastic variations in the junction Hamiltonian, we avoid overfitting geometries to specific system parameters. Furthermore, we constrain the optimizer to produce smooth geometries by applying image filtering and fabrication resolution constraints. We run the algorithm in various setups and find that it reliably produces geometries with increased topological gaps over large parameter ranges. The results are robust to variations in the optimization starting point and the presence of disorder, which suggests the optimizer is capable of finding global maxima.

  2 citations

• Low-temperature electron mobility in doped semiconductors with high dielectric constant

  Khachatur G. Nazaryan, Mikhail Feigel'man

  SciPost Phys. 14, 046 (2023) · published 23 March 2023 | Toggle abstract · pdf

  We propose and study theoretically a new mechanism of electron-impurity scattering in doped seminconductors with large dielectric constant. It is based upon the idea of vector character of deformations caused in the crystalline lattice by any point defects siting asymmetrically in the unit cell. In result, local lattice compression due to the elastic deformations decay as $1/r^2$ with distance from impurity. Electron scattering (due to standard deformation potential) on such defects leads to low-temperature mobility $\mu(n)$ scaling with electron density $n$ of the form $\mu(n) \propto n^{-2/3}$ that is close to experimental observations on a number of relevant materials.

• Macroscopic fluctuation theory and current fluctuations in active lattice gases

  Tal Agranov, Sunghan Ro, Yariv Kafri, Vivien Lecomte

  SciPost Phys. 14, 045 (2023) · published 22 March 2023 | Toggle abstract · pdf

  We study the current large deviations for a lattice model of interacting active particles displaying a motility-induced phase separation (MIPS). To do this, we first derive the exact fluctuating hydrodynamics of the model in the large system limit. On top of the usual Gaussian noise terms the theory also presents Poissonian noise terms, that we fully account for. We find a dynamical phase transition between flat density profiles and sharply phase-separated traveling waves, and we derive the associated phase diagram together with the large deviation function for all phases, including the one displaying MIPS. We show how the results can be obtained using methods similar to those of equilibrium phase separation, in spite of the nonequilibrium nature of the problem.

  13 citations

• Low-energy effective description of dark $Sp(4)$ theories

  Suchita Kulkarni, Axel Maas, Seán Mee, Marco Nikolic, Josef Pradler, Fabian Zierler

  SciPost Phys. 14, 044 (2023) · published 22 March 2023 | Toggle abstract · pdf

  Strongly interacting massive particles are viable dark matter candidates. We consider a dark $Sp(4)$ gauge theory with $N_f=2$ fermions in the pseudo-real fundamental representation and construct the chiral low-energy effective theory. We determine the flavour multiplet structure and the chiral Lagrangian, including the Wess-Zumino-Witten term for mass-degenerate and non-degenerate flavours. We then study the possible charge assignments under a $U(1)'$ gauge symmetry, emphasizing on dark state stability, and provide the full Lagrangian description for Goldstone bosons and vector resonances, including the Wess-Zumino-Witten term. Finally, we use dedicated lattice simulations to determine the chiral low-energy effective theory's validity and low-energy constants. This work represents a self-consistent study of this non-Abelian theory. It thereby provides a framework for future phenomenological exploration in connection to the dark matter problem.

  8 citations

• Dynamically restoring conformal invariance in (integrable) $\sigma$-models

  Rigers Aliaj, Konstantinos Sfetsos, Konstantinos Siampos

  SciPost Phys. 14, 043 (2023) · published 21 March 2023 | Toggle abstract · pdf

  Integrable $\lambda$-deformed $\sigma$-models are characterized by an underlying current algebra/coset model CFT deformed, at the infinitesimal level, by current/parafermion bilinears. We promote the deformation parameters to dynamical functions of time introduced as an extra coordinate. It is conceivable that by appropriately constraining them, the beta-functions vanish and consequently the $\sigma$-model stays conformal. Remarkably, we explicitly materialize this scenario in several cases having a single and even multiple deformation parameters. These generically obey a system of non-linear second-order ordinary differential equations. They are solved by the fixed points of the RG flow of the original $\sigma$-model. Moreover, by appropriately choosing initial conditions we may even interpolate between the RG fixed points as the time varies from the far past to the far future. Finally, we present an extension of our analysis to the Yang--Baxter deformed PCMs.

• Topological quantum phase transition of nickelocene on Cu(100)

  Germán G. Blesio, Rok Žitko, Luis O. Manuel, Armando A. Aligia

  SciPost Phys. 14, 042 (2023) · published 21 March 2023 | Toggle abstract · pdf

  Local quantum phase transitions driven by Kondo correlations have been theoretically proposed in several magnetic nanosystems; however, clear experimental signatures are scant. Modeling a nickelocene molecule on a Cu(100) substrate as a two-orbital Anderson impurity with single-ion anisotropy coupled to two conduction bands, we find that recent scanning tunneling spectra reveal the existence of a topological quantum phase transition from the usual local Fermi liquid with high zero-bias conductance to a non-Landau Fermi liquid, characterized by a non-trivial quantized Luttinger integral, with a small conductance. The effects of intermediate valence, finite temperature, and structural relaxation of the molecule position allow us to explain the different observed behaviors.

  2 citations

• Designing observables for quantum interference in jets at subleading color

  Andrew J. Larkoski

  SciPost Phys. 14, 041 (2023) · published 20 March 2023 | Toggle abstract · pdf

  The large-$N_c$ or topologically planar limit of gauge theories can be considered as a classical limit because all gauge bosons are distinguishable particles and therefore cannot exhibit interference. Quantum effects due to the flow of color therefore arise starting at subleading in $1/N_c$. We introduce kinematic observables explicitly sensitive to effects at subleading color formed from the ratio of interfering to squared color-ordered amplitudes. Such observables are in general not infrared and collinear safe, so we introduce angular observables defined from appropriate multi-point energy correlators motivated by the form of color-ordered amplitudes. We demonstrate that color interference effects are manifest as sinusoidal oscillation in the simplest system, a collinear jet with three particles, and show the limitations of predicting this observable in all-purpose, leading-color parton shower Monte Carlos.

  1 citation