A research team led by The Hong Kong University of Science and Technology (HKUST) has achieved a groundbreaking quantum simulation of the non-Hermitian skin effect in two dimensions using ultracold fermions, marking a significant advance in quantum physics research.
Quantum mechanics, which typically considers a well-isolated system from its environment, describes ubiquitous phenomena ranging from electron behavior in solids to information processing in quantum devices. This description typically requires a real-valued observable—specifically, a Hermitian model (Hamiltonian).
The Hermiticity of the model, which guarantees conserved energy with real eigenvalues, breaks down when a quantum system exchanges particles and energy with its environment. Such an open quantum system can be effectively described by a non-Hermitian Hamiltonian, providing crucial insights into quantum information processing, curved space, non-trivial topological phases, and even black holes. Nevertheless, many questions about non-Hermitian quantum dynamics remain unanswered, especially in higher dimensions.
In collaboration with Peking University (PKU), physicists from the two universities have simulated one such intriguing phenomenon—the non-Hermitian skin effect (NHSE)—which involves the accumulation of eigenstates at the boundary of an open system. This successful demonstration marks a crucial advancement, as previous experimental realizations of the non-Hermitian skin effect were limited to lower dimensions or classical systems rather than quantum systems.
This finding is published in Nature on January 8, 2025. The research created a two-dimensional non-Hermitian topological band for ultracold fermions in spin-orbit-coupled optical lattices with tunable dissipation, unveiling the non-Hermitian skin effect, says Prof. JO Gyu-Boong, Professor of Physics at HKUST leading the study.
"Our work unveils an intriguing system that allows us to explore how non-Hermiticity plays with symmetry and topology," said Prof. Jo. "Our experiment naturally sets a quantum many-body system instead of classical systems, opening up avenues to investigate non-Hermitian quantum dynamics using ultracold fermions with dissipation."
Prof. LIU Xiong-jun, Professor at PKU and the other leader of the team added, "The interplay of higher-dimensional non-Hermitian skin effect with fundamental Hermitian scenarios, such as curved spaces, black holes, quantum information, and higher-order topological phases, necessitates exploration in many-body systems beyond a one-dimensional system. The high degree of control in our system positions it as a versatile platform for exploring high-dimensional non-Hermitian phenomena, offering insights into exotic quantum physics beyond the realms of condensed matter and ultracold atoms."
The team emphasized that a complete understanding of the NHSE remains elusive, with key questions still unanswered: "Is there a general topological explanation for NHSE?" and "How much does topology determine its presence or absence?" "This reported work sets the stage for exploring such questions," Prof. Jo added.
