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arXiv:2608.20760

Quantum Wake Dynamics from Distinct Spectroscopic Perturbations

Umesh Kumar, Gonzalo Álvarez, David Alan Tennant, Satoshi Okamoto

Published Aug 21, 2026• 0 citations
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Abstract

Quantum wake dynamics in quantum magnets have recently been inferred from the dynamical spin structure factor, which probes only a restricted class of local perturbations. Here, we show that resonant inelastic x-ray scattering (RIXS) selection rules act as an operator filter on fractionalized excitations, producing distinct quantum wakes in the spin-$\frac{1}{2}$ Heisenberg antiferromagnetic chain. Using explicit real-time evolution of single-spin and spin-conserving bond correlators, we find that the conventional spin response propagates up to the maximum spinon velocity, $v_s=\fracπ{2} J$, whereas the bond channels concentrate their spectral weight into a slower dominant wake with $v\simeq 0.92 J$, while weaker components remain bounded by the full spinon light cone. The corresponding momentum- and frequency-resolved responses map onto experimentally accessible RIXS channels, demonstrating that different spectroscopic perturbations resolve complementary pathways of many-body propagation beyond the neutron-scattering spin structure factor. Their inelastic spectral weights further provide access to quantum Fisher information, while equal-time bond sum rules connect the same spectroscopic channels to the ground-state energy. Because the same correlators can be prepared and measured on quantum hardware, they also define direct, experimentally anchored benchmarks for quantum simulations, particularly in frustrated and higher-dimensional magnets where controlled classical real-time calculations become challenging.

DOI
10.48550/arxiv.2608.20760

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Quantum wake dynamics in quantum magnets have recently been inferred from the dynamical spin structure factor, which probes only a restricted class of local perturbations. Here, we show that resonant inelastic x-ray scattering (RIXS) selection rules act as an operator filter on fractionalized excitations, producing distinct quantum wakes in the spin-12\frac{1}{2}21​ Heisenberg antiferromagnetic chain. Using explicit real-time evolution of single-spin and spin-conserving bond correlators, we find that the conventional spin response propagates up to the maximum spinon velocity, vs=π2Jv_s=\fracπ{2} Jvs​=2π​J, whereas the bond channels concentrate their spectral weight into a slower dominant wake with v≃0.92Jv\simeq 0.92 Jv≃0.92J, while weaker components remain bounded by the full spinon light cone. The corresponding momentum- and frequency-resolved responses map onto experimentally accessible RIXS channels, demonstrating that different spectroscopic perturbations resolve complementary pathways of many-body propagation beyond the neutron-scattering spin structure factor. Their inelastic spectral weights further provide access to quantum Fisher information, while equal-time bond sum rules connect the same spectroscopic channels to the ground-state energy. Because the same correlators can be prepared and measured on quantum hardware, they also define direct, experimentally anchored benchmarks for quantum simulations, particularly in frustrated and higher-dimensional magnets where controlled classical real-time calculations become challenging.
Disentangling multi-spin dynamic correlations in the Heisenberg spin-12\frac{1}{2}21​ chain
Higher-order correlations are essential for understanding exotic phases and uncovering universal aspects of quantum dynamics. While inelastic neutron scattering provides well-established access to two-particle correlations, measuring correlations in solids involving more than two particles remains a major challenge. Focusing on magnetic excitations in the Heisenberg spin-12\frac{1}{2}21​ chain, we demonstrate that resonant inelastic X-ray scattering (RIXS) can selectively probe multi-spin dynamical correlations by exciting distinct intermediate states through energy detuning. Through theoretical modeling, we isolate the two- and multi- spin responses, and establish that: (i) The resonant energies of the two- and multi- spin dynamical correlations are separated by ≈34J\approx \frac{3}{4}J≈43​J; implying that the multi-spin part of the cross-section comes from intermediate states that contain spin flips; (ii) The spectral weight of the two-spin channel exhibits a Lorentzian resonant energy profile consistent with a single dominant electronic configuration, whereas the multi-spin channel response shows a Gaussian-like profile, implying contributions from multiple intermediate spin configurations. These characteristics are reproduced by exact diagonalization of the t−Jt-Jt−J Hamiltonian, which further reveals that the widths of Lorentzian and Gaussian resonant energy profiles depend primarily on core-hole lifetime (Γ/2Γ/2Γ/2) and 2JΓ\frac{2J}ΓΓ2J​, respectively. Controlled access to multi-spin dynamics, using RIXS energy detuning as a knob, can open new pathways to explore many-body dynamics in quantum materials.
We investigate the excitation spectra of a spin-1/2 antiferromagnetic Heisenberg trimer spin chain by employing a combination of numerical and theoretical techniques. Utilizing the Krylov-space correction-vector method in density matrix renormalization group (DMRG), we calculate both the direct and indirect resonant inelastic x-ray scattering (RIXS) spectra for the trimer spin chain. To interpret the observed features in the RIXS spectra, we perform a theoretical perturbative analysis to compute the energy dispersions, which are then utilized to determine the density of states (DOS) for both the single-particle and the two-particle excitation spectra. Our results show that the single-particle continua of the direct RIXS spectrum align with the energy levels observed in the DOS spectra of spinon, doublon, and quarton excitations. Furthermore, the two-particle continua are revealed in the indirect RIXS process, where all possible single-particle excitations combine to form the various two-particle excitations of the trimer spin chain. Based on our calculations, we propose the RIXS mechanism of generating the fractionalized (spinon) and collective (doublon and quarton) excitations in the trimer spin chain at both the LLL edge and the KKK edge, including discussing the interplay of these excitations in the RIXS spectrum for various trimer coupling strength. The computed energy range of the excitations suggest the possibility of experimental detection at both the LLL edge and the KKK edge within the current capabilities of RIXS instrumentation resolution.
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Resonant inelastic x-ray scattering (RIXS) has proven a powerful tool to investigate dynamic magnetic correlations, yielding complementary insights compared to neutron scattering. A key issue is the interpretation of spectroscopic measurements in terms of quasi-particle excitations. In this paper we study the spin-conserving channel of RIXS spectra for two-leg quantum spin ladders using continuous unitary transformations. We find that multi-triplon continua and bound states are the leading contribution, opening new venues for observing and characterizing multi-triplons in quantum spin systems.
Recent work has demonstrated that quantum Fisher information (QFI), a witness of multipartite entanglement, and magnetic Van Hove correlations G(r,t)G(r,t)G(r,t), a probe of local real-space real-time spin dynamics, can be successfully extracted from inelastic neutron scattering on spin systems through accurate measurements of the dynamical spin structure factor $S(k,\ensuremath{\omega})$. Here we apply theoretically these ideas to the half-filled Hubbard chain with nearest-neighbor hopping, away from the strong-coupling limit. This model has nontrivial redistribution of spectral weight in $S(k,\ensuremath{\omega})$ going from the noninteracting limit (U=0U=0U=0) to strong coupling ($U\ensuremath{\rightarrow}\ensuremath{\infty}$), where it reduces to the Heisenberg quantum spin chain. We use the density matrix renormalization group to find $S(k,\ensuremath{\omega})$, from which QFI is then calculated. We find that QFI grows with UUU. With realistic energy resolution it becomes capable of witnessing bipartite entanglement above U=2.5U=2.5U=2.5 (in units of the hopping), where it also changes slope. This point is also proximate to slope changes of the bandwidth W(U)W(U)W(U) and the half-chain von Neumann entanglement entropy. We compute G(r,t)G(r,t)G(r,t) by Fourier transforming $S(k,\ensuremath{\omega})$. The results indicate a crossover in the short-time short-distance dynamics at low UUU characterized by ferromagnetic light-cone wavefronts, to a Heisenberg-type behavior at large UUU featuring antiferromagnetic light cones and spatially period-doubled antiferromagnetism. We find this crossover has largely been completed by U=3U=3U=3. Our results thus provide evidence that, in several aspects, the strong-coupling limit of the Hubbard chain is reached qualitatively already at a relatively modest interaction strength. We discuss experimental candidates for observing the G(r,t)G(r,t)G(r,t) dynamics found at low UUU.
We calculate the resonant inelastic x-ray scattering (RIXS) response of the Kitaev honeycomb model, an exactly solvable quantum-spin-liquid model with fractionalized Majorana and flux excitations. We find that the fundamental RIXS channels, the spin-conserving (SC) and the non-spin-conserving (NSC) ones, do not interfere and give completely different responses. SC RIXS picks up exclusively the Majorana sector with a pronounced momentum dispersion, whereas NSC RIXS also creates immobile fluxes, thereby rendering the response only weakly momentum dependent, as in the spin structure factor measured by inelastic neutron scattering. RIXS can, therefore, pick up the fractionalized excitations of the Kitaev spin liquid separately, making it a sensitive probe to detect spin-liquid character in potential material incarnations of the Kitaev honeycomb model.