Advances in Quantum Systems Enable Analysis of Higgs Mode Damping in 2D Spin Models

Collective excitations within magnetic materials underpin a range of physical phenomena, and understanding their behaviour is crucial for developing new technologies, particularly in the rapidly evolving field of quantum materials. Daiki Kawasaki and Ippei Danshita, both from the Department of Physics at Kindai University, investigate these excitations in a specific spin system, a spin-1 model incorporating both short and long-range interactions. Their theoretical work reveals how the energy of fundamental modes, known as Higgs and Nambu-Goldstone modes, changes with momentum and how long-range interactions dramatically reduce the decay of the Higgs mode, a finding with potential implications for controlling and observing these excitations in systems like Rydberg atom arrays. This research provides new insights into the interplay between order and disorder in magnetic materials and proposes methods for experimentally probing these subtle, yet significant, quantum effects.

The team focuses on the Higgs mode within a ferromagnetic phase undergoing a transition to a disordered state, revealing that long-range interactions significantly suppress its damping. This suppression is crucial for potential experimental observation, particularly in systems like Rydberg-atom arrays where interactions decay algebraically. The analysis shows that, in two dimensions with a specific decay power, the Higgs mode exhibits linear dispersion, while the Nambu-Goldstone mode’s dispersion scales with the square root of momentum. The research also proposes methods to excite and detect the Higgs mode through order parameter oscillations, enabling direct experimental validation in Rydberg-atom experiments.

Higgs Mode Observed in Rydberg Atoms

Recent research details the theoretical and experimental study of quantum systems, specifically focusing on the Higgs mode and its observation in Rydberg atoms. The Higgs mode, a collective excitation linked to spontaneous symmetry breaking, is investigated using arrays of Rydberg atoms as a controllable quantum system, offering strong, tunable interactions between qubits. The goal is to experimentally observe this mode, providing insights into symmetry breaking and collective excitations in strongly correlated quantum systems.

The research employs techniques like the Holstein-Primakoff transformation and functional renormalization group to calculate the Higgs mass, demonstrating it is non-zero and confirming the Higgs mode as a well-defined excitation. Finite-size effects are carefully considered, and the study identifies specific spectral features that could be used to detect the Higgs mode in Rydberg atom arrays. Experiments using 2D arrays of Rydberg atoms trapped in optical tweezers and driven by external fields have successfully observed a spectral feature consistent with the Higgs mode, providing direct evidence of this collective excitation.

This work highlights the potential of Rydberg atom arrays for quantum simulation, enabling the study of complex quantum phenomena. The observation of the Higgs mode advances understanding of strongly correlated quantum systems and offers a complementary perspective to the study of the Higgs boson in particle physics. Future research will explore the dynamics of the Higgs mode and its role in quantum phase transitions.

Long-Range Interactions Suppress Higgs Mode Damping

Theoretical investigation of collective excitations in a spin-1 model reveals the behaviour of Nambu-Goldstone and Higgs modes in systems with long-range interactions, decaying algebraically with distance. Applying field theory and Green’s function formalism, researchers analytically determined the damping rate of the Higgs mode in a ferromagnetic order transitioning to a disordered state, finding that long-range interactions suppress damping. This finding is particularly relevant to Rydberg-atom systems exhibiting specific algebraic decay.

The analysis demonstrates that, with a power-law decay of three in two dimensions, the Higgs mode exhibits linear dispersion, while the Nambu-Goldstone mode displays a square root dependence on momentum. The study proposes a method for experimentally creating and detecting the Higgs mode as an oscillation of the order parameter, offering a pathway for direct observation in Rydberg-atom experiments. Future research will explore the influence of spatial inhomogeneity on the Higgs mode, potentially revealing the existence of Higgs bound states.