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Chaos controlled and disorder driven phase transitions induced by breaking permutation symmetry
Uma DivakaranICTS:30360Late-time signals from binary black hole mergers
Marina de AmicisThe Gaudin model in the Deligne category Rep $GL_t$
Leonid RybnikovLecture - QFT II, PHYS 603
Francois David CEA Saclay
Superconductor-Insulator Transition in Weakly Monitored Josephson Junction Arrays
Sumilan BanerjeeICTS:30356
Topological Superconductivity hosting Majorana States in Magnet/Superconductor Heterostructures
Arijit SahaICTS:30361Our theoretical investigation explores a feasible route to engineer the two-dimensional (2D) Kitaev model of first-order topological superconductivity (TSC) introducing a magnetic spin texture. The main outcome of 2D Kitaev’s model is that a px + py type superconductor can exhibit a gapless topological superconducting phase in bulk hosting non-dispersive Majorana flat edge mode (MFEM) at the boundary. Our proposed general minimal model Hamiltonian is suitable to describe magnet/superconductor heterostructures. It reveals robust MFEM within the emergent gap of Shiba bands, spatially localised at the edges of a 2D magnetic domain of spin- spiral. We finally verify this concept from real material perspectives by considering Mn (Cr) monolayer grown on an s-wave superconducting substrate, Nb(110) under strain (Nb(001)). In both the 2D cases, the antiferromagnetic spin-spiral solutions exhibit robust MFEM at certain domain edges. This approach, particularly when the MFEM appears in the TSC phase for such heterostructure materials, offers significant prospect to extend the realm of TSC in 2D. Very recently, we expand this theoretical framework for engineering a 2D second-order topological superconductor (SOTSC) by utilizing a heterostructure: incorporating noncollinear magnetic textures between an s-wave superconductor and a 2D quantum spin Hall insulator. It stabilizes the SOTSC phase within the Shiba band, resulting in Majorana corner modes (MCMs) at the four corners of a 2D domain. The calculated non-zero quadrupole moment characterizes the bulk higher-order topology. Analytically calculated effective pairings in the bulk illuminate the microscopic behaviour of the SOTSC. Such first and second order Majorana modes are believed to be the building blocks for the fault-tolerant topological quantum computation.
Reference: Phys. Rev. B (Letter) 109, L041409 (2024) .
Phys. Rev. B (Letter) 109, L121301 (2024).Chaos controlled and disorder driven phase transitions induced by breaking permutation symmetry
Uma DivakaranICTS:30360The effects of disorder and chaos on quantum many-body systems can be superficially similar, yet their interplay has not been sufficiently explored. We study this using an all to all interacting spin chain with disordered interacting term in presence of periodic kicks. The disorder free version of this model shows regular and chaotic dynamics within permutation symmetric subspace as the interaction strength is increased. When the disorder is increased, we find a transition from a dynamics within permutation symmetric subspace to full Hilbert space where the expectation values of various operators are given by random matrix theory in full Hilbert space. Interestingly, finite size scaling predicts a continuous phase transition at a critical disorder strength.
Towards realistic tensor network holography using loop gravity
Simon LangenscheidtPIRSA:24110084In order to understand many Quantum information aspects of the Ads/CFT correspondence, tensor network toy models of holography have been a useful and concrete tool. However, these models traditionally lack many features of their continuum counterparts, limiting their applicability in arguments about gravity. In this talk, I present a natural extension of the tensor network holography paradigm which rectifies some of these issues. Its direct inspiration originates in Loop Quantum Gravity, which allows not only lifting existing limitations of tensor networks, but also firmly grounds the models in the context of nonperturbative canonical quantum gravity.
Late-time signals from binary black hole mergers
Marina de AmicisLate-time tails emitted by binary black holes mergers contain invaluable information on the spacetime’s asymptotic structure. Perturbative numerical simulations of extreme mass-ratio mergers have revealed that these tails are enhanced by several orders of magnitude with the progenitors’ binary eccentricity. This amplification has the potential to bring tails within the realm of observation and shows that this effect carries significant astrophysical implications, other than fundamental physics content.I will present an analytical perturbative model that accurately predicts the numerically observed tail and explains its enhancement with the progenitors' binary eccentricity. The model is an integral over the system's entire history, showing how the post-ringdown tail is inherited from the non-circular inspiral in a non-local fashion. I will prove the tail to be a superposition of many power-laws, with each term's excitation coefficient depending on the specific inspiral history. A single power law is recovered only in the limit of asymptotically late times, consistent with Price's results and the classical soft-graviton theorem. Finally, I will introduce a robust framework for extracting tails in fully non-linear simulations of equal masses mergers. I will present results for late-time tails emitted by these systems and discuss their phenomenology.The Gaudin model in the Deligne category Rep $GL_t$
Leonid RybnikovDeligne's category $D_t$ is a formal way to define the category of finite-dimensional representations of the group $GL_n$ with $n=t$ being a formal parameter (which can be specialized to any complex number). I will show how to interpolate the construction of the higher Hamiltonians of the Gaudin quantum spin chain associated with the Lie algebra $\mathfrak{gl}_n$ to any complex $n$, using $D_t$. Next, according to Feigin and Frenkel, Bethe ansatz equations in the Gaudin model are equivalent to no-monodromy conditions on a certain space of differential operators of order $n$ on the projective line. We also obtain interpolations of these no-monodromy conditions to any complex $n$ and prove that they generate the relations in the algebra of higher Gaudin Hamiltonians for generic complex $n$. I will also explain how it is related to the Bethe ansatz for the Gaudin model associated with the Lie superalgebra $\mathfrak{gl}_{m|n}$.This is joint work with Boris Feigin and Filipp Uvarov,https://arxiv.org/abs/2304.04501.Lecture - QFT II, PHYS 603
Francois David CEA Saclay
Superconductor-Insulator Transition in Weakly Monitored Josephson Junction Arrays
Sumilan BanerjeeICTS:30356In recent years, ‘measurement-induced phase transitions’ (MIPT), have led to a new paradigm for dynamical phase transitions in quantum many-body systems. I will discuss a model of continuously monitored or weakly measured arrays of Josephson junctions (JJAs) with feedback. Using a variational self-consistent harmonic approximation, as well as analysis in the semiclassical limit, strong feedback and measurement limit, and weak coupling perturbative renormalization group, I will show that the model undergoes re-entrant superconductor-insulator MIPTs in its long-time non-equilibrium steady state as a function of measurement and feedback strength. I will contrast the phase diagram of monitored JJA with the well-studied case of dissipative JJA.
Measurement-induced entanglement between quantum spin chains
Masaki OshikawaICTS:30355We discuss the entanglement between two critical spin chains induced by the Bell-state measurements, when each chain was independently in the ground state before the measurement. This corresponds to a many-body version of “entanglement swapping”. We employ a boundary conformal field theory (CFT) approach and describe the measurements as conformal boundary conditions in the replicated field theory. We show that the swapped entanglement exhibits a logarithmic scaling, whose coefficient takes a universal value determined by the scaling dimension of the boundary condition changing operator. We apply our framework to the critical spin-1/2 XXZ chain and determine the universal coefficient by the boundary CFT analysis, which is verified by a numerical calculation.
This talk is based on M. Hoshino, M. O., and Y. Ashida, arXiv:2406.12377