Publications

Order by: publication date number of citations

• A convenient Keldysh contour for thermodynamically consistent perturbative and semiclassical expansions

  Vasco Cavina, Sadeq S. Kadijani, Massimiliano Esposito, Thomas L. Schmidt

  SciPost Phys. 15, 209 (2023) · published 27 November 2023 | Toggle abstract · pdf

  The work fluctuation theorem (FT) is a symmetry connecting the moment generating functions (MGFs) of the work extracted in a given process and in its time-reversed counterpart. We show that, equivalently, the FT for work in isolated quantum systems can be expressed as an invariance property of a modified Keldysh contour. Modified contours can be used as starting points of perturbative and path integral approaches to quantum thermodynamics, as recently pointed out in the literature. After reviewing the derivation of the contour-based perturbation theory, we use the symmetry of the modified contour to show that the theory satisfies the FT at every order. Furthermore, we extend textbook diagrammatic techniques to the computation of work MGFs, showing that the contributions of the different Feynman diagrams can be added to obtain a general expression of the work statistics in terms of a sum of independent rescaled Poisson processes. In this context, the FT takes the form of a detailed balance condition linking every Feynman diagram with its time-reversed variant. In the second part, we study path integral approaches to the calculation of the MGF, and discuss how the arbitrariness in the choice of the contour impacts the final form of the path integral action. In particular, we show how using a symmetrized contour makes it possible to easily generalize the Keldysh rotation in the context of work statistics, a procedure paving the way to a semiclassical expansion of the work MGF. Furthermore, we use our results to discuss a generalization of the detailed balance conditions at the level of the quantum trajectories.

  2 citations

• A simple theory for quantum quenches in the ANNNI model

  Jacob H. Robertson, Riccardo Senese, Fabian H. L. Essler

  SciPost Phys. 15, 032 (2023) · published 27 July 2023 | Toggle abstract · pdf

  In a recent numerical study by Haldar et al. [Phys. Rev. X 11, 031062] it was shown that signatures of proximate quantum critical points can be observed at early and intermediate times after certain quantum quenches. Said work focused mainly on the case of the axial next-nearest neighbour Ising (ANNNI) model. Here we construct a simple time-dependent mean-field theory that allows us to obtain a quantitatively accurate description of these quenches at short times, which for reasons we explain remains a fair approximation at late times (with some caveats). Our approach provides a simple framework for understanding the reported numerical results as well as fundamental limitations on detecting quantum critical points through quench dynamics. We moreover explain the origin of the peculiar oscillatory behaviour seen in various observables as arising from the formation of a long-lived bound state.

  2 citations

• 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

• Anyons in a tight wave-guide and the Tonks-Girardeau gas

  Nicolas Rougerie, Qiyun Yang

  SciPost Phys. Core 6, 079 (2023) · published 15 November 2023 | Toggle abstract · pdf

  We consider a many-body system of 2D anyons, free quantum particles with general statistics parameter $\alpha ∈ ]0,2[$. In the magnetic gauge picture they are described as bosons attached to Aharonov-Bohm fluxes of intensity $2\pi \alpha$, generating long-range magnetic forces. A dimensional reduction to 1D is obtained by imposing a strongly anisotropic trapping potential. This freezes the motion in the direction of strong trapping, leading to 1D physics along the weak direction. The latter is governed to leading order by the Tonks-Girardeau model of impenetrable bosons, independently of $\alpha$.

  2 citations

• Flavoured $(g-2)_\mu$ with dark lepton seasoning

  Harun Acaroğlu, Prateek Agrawal, Monika Blanke

  SciPost Phys. 15, 176 (2023) · published 24 October 2023 | Toggle abstract · pdf

  As a joint explanation for the dark matter (DM) problem and the muon $(g-2)$ anomaly, we propose a simplified model of lepton-flavoured complex scalar DM with couplings to both the left- and right-handed leptons of the Standard Model (SM). Both interactions are governed by the same new flavour-violating coupling matrix $\lambda$, however we allow for a relative scaling of the coupling strength. The SM is further extended by two fermion representations, transforming as an $SU(2)_L$ doublet and singlet, respectively, and mediating these interactions. The fermions additionally couple to the SM Higgs doublet via a new Yukawa coupling. To study the model's phenomenology we first investigate constraints from collider searches, flavour experiments, precision tests of the SM, the DM relic density, and direct as well as indirect detection experiments individually. We then perform a combined analysis by demanding that all mentioned constraints are satisfied simultaneously. We use the results of this combined analysis and examine if the model is capable of accommodating the $(g-2)_\mu$ anomaly within its viable parameter space without introducing fine-tuned lepton masses. For all benchmark scenarios we consider, we find that the central value of $\Delta a_\mu^\text{exp}$ can be reached without generating too large corrections to the lepton masses. We hence conclude that this model qualifies as a viable and attractive lepton-flavoured DM model that at the same time solves the $(g-2)_\mu$ anomaly.

  2 citations

• Analysis of radiation damage in silicon charge-coupled devices used for dark matter searches

  Steven J. Lee

  SciPost Phys. Proc. 12, 030 (2023) · published 4 July 2023 | Toggle abstract · pdf

  Nuclear recoils in crystal detectors generate radiation damage in the form of crystal defects that can be measured in scientific-grade CCDs as local hot spots of leakage current stimulated by temperature increases in the devices. In this proceeding, we use a neutron source to generate defects in DAMIC-M CCDs, and using increases in leakage current at different temperatures, we demonstrate a procedure for identifying crystal defects in the CCDs of the DAMIC-M experiment. This is the first time that individual defects generated from nuclear recoils have been studied. This technique could be used to distinguish nuclear recoils from electron recoils in some energy ranges, which would improve the ability of CCD detectors to search for weakly interacting dark matter.

  2 citations

• Bethe-state counting and Witten index

  Hongfei Shu, Peng Zhao, Rui-Dong Zhu, Hao Zou

  SciPost Phys. 15, 103 (2023) · published 19 September 2023 | Toggle abstract · pdf

  We count the physical Bethe states of quantum integrable models with twisted boundary conditions using the Witten index of 2d supersymmetric gauge theories. For multi-component models solvable by the nested Bethe ansatz, the result is a novel restricted occupancy problem. For the SU(3) spin chain and the t-J model, we propose formulae for the solution count on singular loci in the space of twist parameters.

  2 citations

• Equilibration of quantum cat states

  Tony Jin

  SciPost Phys. 9, 004 (2020) · published 8 July 2020 | Toggle abstract · pdf

  We study the equilibration properties of isolated ergodic quantum systems initially prepared in a cat state, i.e a macroscopic quantum superposition of states. Our main result consists in showing that, even though decoherence is at work in the mean, there exists a remnant of the initial quantum coherences visible in the strength of the fluctuations of the steady state. We back-up our analysis with numerical results obtained on the XXX spin chain with a random field along the z-axis in the ergodic regime and find good qualitative and quantitative agreement with the theory. We also present and discuss a framework where equilibrium quantities can be computed from general statistical ensembles without relying on microscopic details about the initial state, akin to the eigenstate thermalization hypothesis.

  2 citations

• Recent results of laser spectroscopy experiments of pionic helium atoms at PSI

  M. Hori, H. Aghai-Khozani, A. S\'ot\'er, A. Dax, D. Barna

  SciPost Phys. Proc. 5, 026 (2021) · published 6 September 2021 | Toggle abstract · pdf

  A review of a recent experiment carried out at PSI involving laser spectroscopy of metastable pionic helium ($\pi{\rm ^4He}^+\equiv\pi^{-}+{\rm ^4He}^{2+}+e^-$) atoms is presented. An infrared transition $(n,\ell)=(17,16)$$\rightarrow$$(17,15)$ at a resonance frequency of $\nu\approx 183760$ GHz was detected.

  2 citations

• Efficient flow equations for dissipative systems

  Gary Schmiedinghoff, Götz S. Uhrig

  SciPost Phys. 13, 122 (2022) · published 13 December 2022 | Toggle abstract · pdf

  Open quantum systems provide an essential theoretical basis for the development of novel quantum technologies, since any real quantum system inevitably interacts with its environment. Lindblad master equations capture the effect of Markovian environments. Closed quantum systems can be treated using flow equations with the particle conserving generator. We generalize this generator to non-Hermitian matrices and open quantum systems governed by Lindbladians, comparing our results with recently proposed generators by Rosso et al. (arXiv:2007.12044). In comparison, we find that our advocated generator provides an efficient flow with good accuracy in spite of truncations.

  2 citations