Publications

2024

• Spin-orbit correlations in the nucleon in the large-$N_{c}$ limit
  
  • Kim June-Young
  • Won Ho-Yeon
  • Kim Hyun-Chul
  • Weiss Christian
  Physical Review D, American Physical Society, 2024, 110 (5), pp.054026. We study the twist-3 spin-orbit correlations of quarks described by the nucleon matrix elements of the parity-odd rank-2 tensor QCD operator (the parity-odd partner of the QCD energy-momentum tensor). Our treatment is based on the effective dynamics emerging from the spontaneous breaking of chiral symmetry and the mean-field picture of the nucleon in the large-$N_c$ limit. The twist-3 QCD operators are converted to effective operators, in which the QCD interactions are replaced by spin-flavor-dependent chiral interactions of the quarks with the pion field. We compute the nucleon matrix elements of the twist-3 effective operators and discuss the role of the chiral interactions in the spin-orbit correlations. We derive the first-quantized representation in the mean-field picture and develop a quantum-mechanical interpretation. The chiral interactions give rise to new spin-orbit couplings and qualitatively change the correlations compared to the quark model picture. We also derive the twist-3 matrix elements in the topological soliton picture where the quarks are integrated out (skyrmion). The methods used here can be extended to other QCD operators describing higher-twist nucleon structure and generalized parton distributions. (10.1103/PhysRevD.110.054026)
  DOI : 10.1103/PhysRevD.110.054026
• Aspects of higher spin symmetry in flat space
  
  • Pekar Simon Alexandre
  Riv.Nuovo Cim., 2024, 47 (1), pp.1-90. We review some aspects of higher spin symmetry, in (Anti-)de Sitter and flat space–times, aiming at closing the gap between the constantly curved and flat cases. On (Anti-)de Sitter space, non-Abelian higher spin algebras are at the core of the construction of interacting theories of higher spin gravity. By considering a suitable contraction of these algebras, we show that similar considerations can apply to Minkowski space–time. We identify a unique candidate to the role of higher spin symmetry in flat space that can also be built as a quotient of the universal enveloping algebra of the isometries of the vacuum, as in the (Anti-)de Sitter case. We then show how to recover the free dynamics from the gauging of the resulting algebra at the linear level. Finally, we show how to realise this gauge algebra as a subset of the global symmetries of a Carrollian conformal scalar field theory living on the null infinity of Minkowski space–time. This theory emerges as the limit of vanishing speed of light of a free massless relativistic scalar. The identification of the same higher spin algebra that rules the dynamics in the bulk of space–time within the global symmetries of this boundary theory paves the way to a flat counterpart of higher spin holography. (10.1007/s40766-024-00051-2)
  DOI : 10.1007/s40766-024-00051-2
• Borel summability of the $\frac 1N$-expansion in quartic $\text{O}(N)$-vector models
  
  • Ferdinand Léonard
  • Gurau Razvan
  • Perez-Sanchez Carlos I.
  • Vignes-Tourneret Fabien
  Annales Henri Poincaré, Springer Verlag, 2024, 25 (3), pp.2037-2064. We consider a quartic O(N)-vector model. Using the Loop Vertex Expansion, we prove the Borel summability in 1/N along the real axis of the partition function and of the connected correlations of the model. The Borel summability holds uniformly in the coupling constant, as long as the latter belongs to a cardioid like domain of the complex plane, avoiding the negative real axis. (10.1007/s00023-023-01350-w)
  DOI : 10.1007/s00023-023-01350-w
• Spin-orbit entanglement in the Color Glass Condensate
  
  • Bhattacharya Shohini
  • Boussarie Renaud
  • Hatta Yoshitaka
  Physics Letters B, Elsevier, 2024, 859, pp.139134. We compute the spin-orbit correlations of quarks and gluons at small-$x$ and show that the helicity and the orbital angular momentum of individual partons are strongly anti-aligned even in unpolarized or spinless hadrons and nuclei. Combined with the fact that gluons in the Color Glass Condensate are linearly polarized, our finding indicates that the helicity and the orbital angular momentum of single gluons are maximally entangled in a quantum mechanical sense. (10.1016/j.physletb.2024.139134)
  DOI : 10.1016/j.physletb.2024.139134
• Localization and spectral structure in two-dimensional quasicrystal potentials
  
  • Zhu Zhaoxuan
  • Yu Shengjie
  • Johnstone Dean
  • Sanchez-Palencia Laurent
  Physical Review A, American Physical Society, 2024, 109 (1), pp.013314. Quasicrystals, a fascinating class of materials with long-range but nonperiodic order, have revolutionized our understanding of solid-state physics due to their unique properties at the crossroads of long-range-ordered and disordered systems. Since their discovery, they continue to spark broad interest for their structural and electronic properties. The quantum simulation of quasicrystals in synthetic quantum matter systems offers a unique playground to investigate these systems with unprecedented control parameters. Here, we investigate the localization properties and spectral structure of quantum particles in two-dimensional quasicrystalline optical potentials. While states are generally localized at low energy and extended at high energy, we find alternating localized and critical states at intermediate energies. Moreover, we identify a complex succession of gaps in the energy spectrum. We show that the most prominent gap arises from strongly localized ring states, with the gap width determined by the energy splitting between states with different quantized winding numbers. In addition, we find that these gaps are stable for quasicrystals with different rotational symmetries and potential depths, provided that other localized states do not enter the gap generated by the ring states. Our findings shed light on the unique properties of quantum quasicrystals and have implications for their many-body counterparts. (10.1103/PhysRevA.109.013314)
  DOI : 10.1103/PhysRevA.109.013314
• Fracton infrared triangle
  
  • Pérez Alfredo
  • Prohazka Stefan
  • Seraj Ali
  Physical Review Letters, American Physical Society, 2024, 133 (2), pp.021603. In theories with conserved dipole moment, isolated charged particles (fractons) are immobile, but dipoles can move. We couple these dipoles to the fracton gauge theory and analyze the universal infrared structure. This uncovers an observable double kick memory effect which we relate to a novel dipole soft theorem. Together with their asymptotic symmetries this constitutes the first realization of an infrared triangle beyond Lorentz symmetry. This demonstrates the robustness of these IR structures and paves the way for their investigation in condensed matter systems and beyond. (10.1103/PhysRevLett.133.021603)
  DOI : 10.1103/PhysRevLett.133.021603
• The nucleon axial radius
  
  • Chen Yi
  • Li Yang
  • Lorcé Cédric
  • Wang Qun
  Physical Review D, American Physical Society, 2024, 110 (9), pp.L091503. We present a systematic study of the relativistic axial-vector four-current distributions inside a nucleon. We show in particular that the slope of the axial form factor $G_A(Q^2)$ in the forward limit -- conventionally denoted as $R^2_A$ in the literature -- does not represent the three-dimensional mean-square axial radius in the Breit frame, but corresponds instead to a contribution to the mean-square spin radius. We derive explicit expressions for the latter in different frames and find in general additional contributions that depend on both the nucleon mass and the forward values of the axial-vector form factors $G_A(0)$ and $G_P(0)$. (10.1103/PhysRevD.110.L091503)
  DOI : 10.1103/PhysRevD.110.L091503
• Perturbative RG flows in AdS: an étude
  
  • Lauria Edoardo
  • Milam Michael
  • van Rees Balt C
  Journal of High Energy Physics, Springer, 2024, 2024 (03), pp.005. We discuss general properties of perturbative RG flows in AdS with a focus on the treatment of boundary conditions and infrared divergences. In contrast with flat-space boundary QFT, general covariance in AdS implies the absence of independent boundary flows. We illustrate how boundary correlation functions remain conformally covariant even if the bulk QFT has a scale. We apply our general discussion to the RG flow between consecutive unitary diagonal minimal models which is triggered by the $\phi_{(1,3)}$ operator. For these theories we conjecture a flow diagram whose form is significantly simpler than that in flat-space boundary QFT. In several stand-alone appendices we discuss two-dimensional BCFTs in general and the minimal model BCFTs in particular. These include both an extensive review as well as the computation of several new BCFT correlation functions. (10.1007/JHEP03(2024)005)
  DOI : 10.1007/JHEP03(2024)005
• Can we measure Double DVCS at JLab and the EIC?
  
  • Martinez-Fernandez Victor
  • Pire Bernard
  • Sznajder Paweł
  • Wagner Jakub
  PoS - Proceedings of Science, SISSA, 2024, pp.148. Double deeply virtual Compton scattering (DDVCS) is a very precise tool for the nucleon tomography. Its measurement requires high luminosity electron beams and precise dedicated detectors, since its amplitude is quite small in the interesting kinematical domain where collinear QCD factorization allows the extraction of quark and gluon generalized parton distributions (GPDs). We analyze the prospects for its study in the JLab energy domain as well as in higher energy electron-ion colliders. Our results are very encouraging for various observables both with an unpolarized and polarized lepton beam. Using various realistic models for GPDs, we demonstrate that DDVCS measurements are indeed very sensitive to their behaviour. Implementing our lowest order cross-section formulae in the EpIC Monte Carlo generator, we estimate the expected number of interesting events. (10.22323/1.456.0148)
  DOI : 10.22323/1.456.0148
• Prediction of the bubble wall velocity for a large jump in degrees of freedom
  
  • Sanchez-Garitaonandia Mikel
  • van de Vis Jorinde
  Physical Review D, American Physical Society, 2024, 110 (2), pp.023509. The bubble expansion velocity is an important parameter in the prediction of gravitational waves from first order phase transitions. This parameter is difficult to compute, especially in phase transitions in strongly coupled theories. In this work, we present a method to estimate the wall velocity for phase transitions with a large enthalpy jump, valid for weakly and strongly coupled theories. We find that detonations are disfavored in this limit, but wall velocities are not necessarily small. We also investigate the effect of two other features in the equation of state: non-conformal sound speeds and a limited range of temperatures for which the phases exist. We find that the former can increase the wall velocity for a given nucleation temperature, and the latter can restrict the wall velocities to small values. To test our approach, we use holographic phase transitions, which typically display these three features. We find excellent agreement with numerically obtained values of the wall velocity. We also demonstrate that the implications for gravitational waves can be significant. (10.1103/PhysRevD.110.023509)
  DOI : 10.1103/PhysRevD.110.023509
• Variational Benchmarks for Quantum Many-Body Problems
  
  • Wu Dian
  • Rossi Riccardo
  • Vicentini Filippo
  • Astrakhantsev Nikita
  • Becca Federico
  • Cao Xiaodong
  • Carrasquilla Juan
  • Ferrari Francesco
  • Georges Antoine
  • Hibat-Allah Mohamed
  • Imada Masatoshi
  • Läuchli Andreas M
  • Mazzola Guglielmo
  • Mezzacapo Antonio
  • Millis Andrew
  • Moreno Javier Robledo
  • Neupert Titus
  • Nomura Yusuke
  • Nys Jannes
  • Parcollet Olivier
  • Pohle Rico
  • Romero Imelda
  • Schmid Michael
  • Silvester J. Maxwell
  • Sorella Sandro
  • Tocchio Luca F
  • Wang Lei
  • White Steven R
  • Wietek Alexander
  • Yang Qi
  • Yang Yiqi
  • Zhang Shiwei
  • Carleo Giuseppe
  Science, American Association for the Advancement of Science (AAAS), 2024, 386 (6719), pp.296-301. The continued development of novel many-body approaches to ground-state problems in physics and chemistry calls for a consistent way to assess its overall progress. Here we introduce a metric of variational accuracy, the V-score, obtained from the variational energy and its variance. We provide the most extensive curated dataset of variational calculations of many-body quantum systems to date, identifying cases where state-of-the-art numerical approaches show limited accuracy, and novel algorithms or computational platforms, such as quantum computing, could provide improved accuracy. The V-score can be used as a metric to assess the progress of quantum variational methods towards quantum advantage for ground-state problems, especially in regimes where classical verifiability is impossible. (10.1126/science.adg9774)
  DOI : 10.1126/science.adg9774
• Holographic complexity: braneworld gravity versus the Lloyd bound
  
  • Aguilar-Gutierrez Sergio E
  • Craps Ben
  • Hernandez Juan
  • Khramtsov Mikhail
  • Knysh Maria
  • Shukla Ashish
  Journal of High Energy Physics, Springer, 2024, 03, pp.173. We explore the complexity equals volume proposal for planar black holes in anti-de Sitter (AdS) spacetime in 2+1 dimensions, with an end of the world (ETW) brane behind the horizon. We allow for the possibility of intrinsic gravitational dynamics in the form of Jackiw-Teitelboim (JT) gravity to be localized on the brane. We compute the asymptotic rate of change of volume complexity analytically and obtain the full time dependence using numerical techniques. We find that the inclusion of JT gravity on the brane leads to interesting effects on time dependence of holographic complexity. We identify the region in parameter space (the brane location and the JT coupling) for which the rate of change of complexity violates the Lloyd bound. In an equivalent description of the model in terms of an asymptotically AdS wormhole, we connect the violation of the Lloyd bound to the violation of a suitable energy condition in the bulk that we introduce. We also compare the Lloyd bound constraints to previously derived constraints on the bulk parameters in this model that are based on bounds on entanglement growth in the dual CFT state. (10.1007/JHEP03(2024)173)
  DOI : 10.1007/JHEP03(2024)173
• Beyond Drude transport in hydrodynamic metals
  
  • Goutéraux Blaise
  • Shukla Ashish
  Physical Review B, American Physical Society, 2024, 109 (16), pp.165153. In interacting theories, hydrodynamics describes the universal behavior of states close to local thermal equilibrium at late times and long distances in a gradient expansion. In the hydrodynamic regime of metals, momentum relaxes slowly with a rate $\Gamma$, which formally appears on the right-hand side of the momentum dynamical equation and causes a Drude-like peak in the frequency dependence of the thermoelectric conductivities. Here we study the structure and determine the physical implications of momentum-relaxing gradient corrections beyond Drude, i.e. arising at subleading order in the gradient expansion. We find that they effectively renormalize the weight of the Drude pole in the thermoelectric conductivities, and contribute to the dc conductivities at the same order as previously-known gradient corrections of translation-invariant hydrodynamics. Turning on a magnetic field, extra derivative corrections appear and renormalize the cyclotron frequency and the Hall conductivity. This relaxed hydrodynamics provides a field-theoretic explanation for previous results obtained using gauge-gravity duality. In strongly-coupled metals where quasiparticles are short-lived and which may be close to a hydrodynamic regime, the extra contributions we discuss are essential to interpret experimentally measured magneto-thermoelectric conductivities. They also cause a different dependence on doping in the effective mass deduced from the specific heat and from measurements of the cyclotron frequency, which do not agree in cuprate superconductors. More generally, we expect such terms to be present in any hydrodynamic theory with approximate symmetries, which arise in many physical systems. (10.1103/PhysRevB.109.165153)
  DOI : 10.1103/PhysRevB.109.165153
• Double DVCS amplitudes including kinematic twist-3 and 4 corrections
  
  • Martinez-Fernandez Victor
  • Pire Bernard
  • Sznajder Paweł
  • Wagner Jakub
  PoS - Proceedings of Science, SISSA, 2024, pp.205. Generalized parton distributions (GPDs) are off-forward matrix elements of quark and gluon operators that work as a window to the total angular momentum of partons and their transverse imaging (nucleon tomography). To access GPDs one needs to look into exclusive processes which are usually studied in a kinematic regime known as the Björken limit. In this limit, the photon virtualities are much larger than the hadron mass M, and the kick to the hadron measured by the Mandelstam's variable t. It turns out that this is not enough for the purposes of a precise GPD extraction and, in particular, of nucleon tomography for which measurements in a sizable range of t are required. Deviation with respect to the Björken limit induces kinematic higher-twist corrections which enter the amplitudes with powers of $|t|/Q^2$ and $M^2/Q^2$, where $Q^2$ denotes the scale of the process (basically, the sum of photon virtualities in the case of DDVCS). There are also corrections by the name of "genuine" higher twists which are a separate topic and are not the subject of this research study. In this manuscript, we present novel calculations of DDVCS amplitudes off a (pseudo-)scalar target including up to kinematic twist-4 corrections. These results are important for measuring DDVCS, DVCS and TCS through the Sullivan process and off helium-4 target at the future Electron-Ion Collider (EIC) and JLab experiments. Preliminary numerical estimates for the pion target are provided. (10.22323/1.469.0205)
  DOI : 10.22323/1.469.0205
• Teleparallel Geroch geometry
  
  • Bossard Guillaume
  • Cederwall Martin
  • Palmkvist Jakob
  Journal of High Energy Physics, Springer, 2024, 08, pp.076. We construct the teleparallel dynamics for extended geometry where the structure algebra is (an extension of) an untwisted affine Kac-Moody algebra. This provides a geometrisation of the Geroch symmetry appearing on dimensional reduction of a gravitational theory to two dimensions. The formalism is adapted to the underlying tensor hierarchy algebra, and will serve as a stepping stone towards the geometrisation of other infinite-dimensional, e.g. hyperbolic, symmetries. (10.1007/JHEP08(2024)076)
  DOI : 10.1007/JHEP08(2024)076
• A bootstrap study of minimal model deformations
  
  • Antunes António
  • Lauria Edoardo
  • van Rees Balt C
  Journal of High Energy Physics, Springer, 2024, 2024 (05), pp.027. For QFTs in AdS the boundary correlation functions remain conformal even if the bulk theory has a scale. This allows one to constrain RG flows with numerical conformal bootstrap methods. We apply this idea to flows between two-dimensional CFTs, focusing on deformations of the tricritical and ordinary Ising model. We provide non-perturbative constraints for the boundary correlation functions of these flows and compare them with conformal perturbation theory in the vicinity of the fixed points. We also reproduce a completely general constraint on the sign of the $T\bar T$ deformation in two dimensions. (10.1007/JHEP05(2024)027)
  DOI : 10.1007/JHEP05(2024)027
• Relaxation terms for anomalous hydrodynamic transport in Weyl semimetals from kinetic theory
  
  • Amoretti Andrea
  • Brattan Daniel K
  • Martinoia Luca
  • Matthaiakakis Ioannis
  • Rongen Jonas
  Journal of High Energy Physics, Springer, 2024, 02, pp.071. We consider as a model of Weyl semimetal thermoelectric transport a $(3+1)$-dimensional charged, relativistic and relaxed fluid with a $U(1)_{V} \times U(1)_{A}$ chiral anomaly. We take into account all possible mixed energy, momentum, electric and chiral charge relaxations, and discover which are compatible with electric charge conservation, Onsager reciprocity and a finite DC conductivity. We find that all relaxations respecting these constraints necessarily render the system open and violate the second law of thermodynamics. We then demonstrate how the relaxations we have found arise from kinetic theory and a modified relaxation time approximation. Our results lead to DC conductivities that differ from those found in the literature opening the path to experimental verification. (10.1007/JHEP02(2024)071)
  DOI : 10.1007/JHEP02(2024)071
• Closed FRW holography: A time-dependent ER=EPR realization
  
  • Franken Victor
  • Partouche Hervé
  • Rondeau François
  • Toumbas Nicolaos
  Journal of High Energy Physics, Springer, 2024, 05, pp.219. We extend a recent de Sitter holographic proposal and entanglement entropy prescription to generic closed FRW cosmologies in arbitrary dimensions, and propose that for large classes of bouncing and Big Bang/Big Crunch cosmologies, the full spacetime can be encoded holographically on two holographic screens, associated to two antipodal observers. In the expanding phase, the two screens lie at the apparent horizons. In the contracting phase, there is an infinite number of possible trajectories of the holographic screens, which can be grouped in equivalence classes. In each class the effective holographic theory can be derived from a pair of ``parent'' screens on the apparent horizons. A number of cases including moduli-dominated cosmologies escape our discussion, and it is expected that two antipodal observers and their associated screens do not suffice to reconstruct these cosmologies. The leading contributions to the entanglement entropy between the screens arise from a minimal extremal trapped or anti-trapped surface lying in the region between them. This picture entails a time-dependent realization of the ER=EPR conjecture, where an effective geometrical bridge connecting the screens via the minimal extremal surface emerges from entanglement. For the Big Crunch contracting cases, the screens disentangle and the geometrical bridge closes off when the minimal extremal trapped sphere hits the Big Crunch singularity at a finite time before the collapse of the Universe. Semiclassical, thermal corrections are incorporated in the cases of radiation-dominated cosmologies. (10.1007/JHEP05(2024)219)
  DOI : 10.1007/JHEP05(2024)219
• Spin-orbital Jahn-Teller bipolarons
  
  • Celiberti Lorenzo
  • Fiore Mosca Dario
  • Allodi Giuseppe
  • Pourovskii Leonid V
  • Tassetti Anna
  • Forino Paola Caterina
  • Cong Rong
  • Garcia Erick
  • Tran Phuong M
  • de Renzi Roberto
  • Woodward Patrick M
  • Mitrović Vesna F
  • Sanna Samuele
  • Franchini Cesare
  Nature Communications, Nature Publishing Group, 2024, 15 (1), pp.2429. Polarons and spin-orbit (SO) coupling are distinct quantum effects that play a critical role in charge transport and spin-orbitronics. Polarons originate from strong electron-phonon interaction and are ubiquitous in polarizable materials featuring electron localization, in particular 3d transition metal oxides (TMOs). On the other hand, the relativistic coupling between the spin and orbital angular momentum is notable in lattices with heavy atoms and develops in 5d TMOs, where electrons are spatially delocalized. Here we combine ab initio calculations and magnetic measurements to show that these two seemingly mutually exclusive interactions are entangled in the electron-doped SO-coupled Mott insulator Ba 2 Na 1-x Ca x OsO 6 (0 < x < 1), unveiling the formation of spin-orbital bipolarons. Polaron charge trapping, favoured by the Jahn-Teller lattice activity, converts the Os 5d 1 spin-orbital J eff = 3/2 levels, characteristic of the parent compound Ba 2 NaOsO 6 (BNOO), into a bipolaron 5d 2 J eff = 2 manifold, leading to the coexistence of different J-effective states in a single-phase material. The gradual increase of bipolarons with increasing doping creates robust in-gap states that prevents the transition to a metal phase even at ultrahigh doping, thus preserving the Mott gap across the entire doping range from d 1 BNOO to d 2 Ba 2 CaOsO 6 (BCOO). (10.1038/s41467-024-46621-0)
  DOI : 10.1038/s41467-024-46621-0
• Certifying ground-state properties of many-body systems
  
  • Wang Jie
  • Surace Jacopo
  • Frérot Irénée
  • Legat Benoît
  • Renou Marc-Olivier
  • Magron Victor
  • Acín Antonio
  Physical Review X, American Physical Society, 2024, 14 (3), pp.031006. A ubiquitous problem in quantum physics is to understand the ground-state properties of many-body systems. Confronted with the fact that exact diagonalisation quickly becomes impossible when increasing the system size, variational approaches are typically employed as a scalable alternative: energy is minimised over a subset of all possible states and then different physical quantities are computed over the solution state. Despite remarkable success, rigorously speaking, all what variational methods offer are upper bounds on the ground-state energy. On the other hand, so-called relaxations of the ground-state problem based on semidefinite programming represent a complementary approach, providing lower bounds to the ground-state energy. However, in their current implementation, neither variational nor relaxation methods offer provable bound on other observables in the ground state beyond the energy. In this work, we show that the combination of the two classes of approaches can be used to derive certifiable bounds on the value of any observable in the ground state, such as correlation functions of arbitrary order, structure factors, or order parameters. We illustrate the power of this approach in paradigmatic examples of 1D and 2D spin-one-half Heisenberg models. To improve the scalability of the method, we exploit the symmetries and sparsity of the considered systems to reach sizes of hundreds of particles at much higher precision than previous works. Our analysis therefore shows how to obtain certifiable bounds on many-body ground-state properties beyond energy in a scalable way. (10.1103/PhysRevX.14.031006)
  DOI : 10.1103/PhysRevX.14.031006
• Empirical Sample Complexity of Neural Network Mixed State Reconstruction
  
  • Zhao Haimeng
  • Carleo Giuseppe
  • Vicentini Filippo
  Quantum, Verein zur Förderung des Open Access Publizierens in den Quantenwissenschaften, 2024, 8, pp.1358. Quantum state reconstruction using Neural Quantum States has been proposed as a viable tool to reduce quantum shot complexity in practical applications, and its advantage over competing techniques has been shown in numerical experiments focusing mainly on the noiseless case. In this work, we numerically investigate the performance of different quantum state reconstruction techniques for mixed states: the finite-temperature Ising model. We show how to systematically reduce the quantum resource requirement of the algorithms by applying variance reduction techniques. Then, we compare the two leading neural quantum state encodings of the state, namely, the Neural Density Operator and the positive operator-valued measurement representation, and illustrate their different performance as the mixedness of the target state varies. We find that certain encodings are more efficient in different regimes of mixedness and point out the need for designing more efficient encodings in terms of both classical and quantum resources. (10.22331/q-2024-05-23-1358)
  DOI : 10.22331/q-2024-05-23-1358
• Reducing two-level system dissipations in 3D superconducting Niobium resonators by atomic layer deposition and high temperature heat treatment
  
  • Kalboussi Yasmine
  • Delatte Baptiste
  • Bira Sarra
  • Dembele Kassiogé
  • Li Xiaoyan
  • Miserque Frederic
  • Brun Nathalie
  • Walls Michael
  • Maurice Jean-Luc
  • Dragoe Diana
  • Leroy Jocelyne
  • Longuevergne David
  • Gentils Aurélie
  • Jublot-Leclerc Stéphanie
  • Julien Gregoire
  • Eozenou Fabien
  • Baudrier Matthieu
  • Maurice Luc
  • Proslier Thomas
  Applied Physics Letters, American Institute of Physics, 2024, 124 (13), pp.134001. Superconducting qubits have arisen as a leading technology platform for quantum computing which is on the verge of revolutionizing the world's calculation capacities. Nonetheless, the fabrication of computationally reliable qubit circuits requires increasing the quantum coherence lifetimes, which are predominantly limited by the dissipations of two-level system (TLS) defects present in the thin superconducting film and the adjacent dielectric regions. In this paper, we demonstrate the reduction of two-level system losses in three-dimensional superconducting radio frequency (SRF) niobium resonators by atomic layer deposition (ALD) of a 10 nm aluminum oxide Al2O3 thin films followed by a high vacuum (HV) heat treatment at 650 {\deg}C for few hours. By probing the effect of several heat treatments on Al2O3-coated niobium samples by X-ray photoelectron spectroscopy (XPS) plus scanning and conventional high resolution transmission electron microscopy (STEM/HRTEM) coupled with electron energy loss spectroscopy (EELS) and (EDX) , we witness a dissolution of niobium native oxides and the modification of the Al2O3-Nb interface, which correlates with the enhancement of the quality factor at low fields of two 1.3 GHz niobium cavities coated with 10 nm of Al2O3. (10.1063/5.0202214)
  DOI : 10.1063/5.0202214
• Infinite $\mathrm{T\bar T}$-like symmetries of compactified LST
  
  • Georgescu Silvia
  • Guica Monica
  SciPost Physics, SciPost Foundation, 2024, 16 (1), pp.006. We show that the three-dimensional asymptotically linear dilaton background that arises in the near-horizon decoupling region of NS5-branes compactified on $T^4$ admits boundary conditions that lead to an infinite set of symmetries. The associated conserved charges, which implement field-dependent coordinate transformations, are found to be identical to the corresponding generators in a symmetric product orbifold of $T\bar T$ - deformed CFTs. Their algebra is a non-linear modification of the $\mathrm{Virasoro \times Virasoro}$ algebra, which precisely coincides with the algebra of the ``unrescaled'' symmetry generators in $T\bar T$-deformed CFTs. This further strengthens a previously proposed link between the single-trace $T\bar T$ deformation and compactified little string theory. (10.21468/SciPostPhys.16.1.006)
  DOI : 10.21468/SciPostPhys.16.1.006
• An inflationary cosmology from anti-de Sitter wormholes
  
  • Betzios Panos
  • Papadoulaki Olga
  Physical Review Letters, American Physical Society, 2024, 133 (2), pp.021501. We propose a new type of wavefunction for the universe computed from the Euclidean path integral, with asymptotically $AdS$ boundary conditions. In the semiclassical limit, it describes a Euclidean (half)-wormhole geometry, exhibiting a local maximum of the scale factor at the surface of reflection symmetry, giving rise to an expanding universe upon analytic continuation to Lorentzian signature. We find that these Euclidean wormholes set natural initial conditions for inflation and that the semi-classical Wheeler-DeWitt wavefunction can favor a long lasting inflationary epoch, resolving a well known issue of the no-boundary proposal. Due to the asymptotic $AdS$ conditions in the Euclidean past they raise the possibility of describing the physics of inflating cosmologies and their perturbations within the context of holography. (10.1103/PhysRevLett.133.021501)
  DOI : 10.1103/PhysRevLett.133.021501
• Majorana fermions and quantum information with fractional topology and disorder
  
  • Bernhardt Ephraim
  • Cheung Brian Chung Hang
  • Le Hur Karyn
  Physical Review Research, American Physical Society, 2024, 6 (2), pp.023221. The quest to identify and observe Majorana fermions in physics and condensed-matter systems remains an important challenge. Here, we introduce a qubit (spin-1/2) from the occurrence of two delocalized zero-energy Majorana fermions in a model of two spins-1/2 on the Bloch sphere within the fractional one-half topological state. We address specific protocols in time with circularly polarized light and the protection of this spin-1/2 state related to quantum information protocols. We also show how disorder can play a positive and important role allowing singlet-triplet transitions and resulting in an additional elongated region for the fractional phase, demonstrating the potential of this platform related to applications in topologically protected quantum information. (10.1103/PhysRevResearch.6.023221)
  DOI : 10.1103/PhysRevResearch.6.023221