Curator's Take
This theoretical work reveals a fascinating new pathway to quantum entanglement that leverages non-Hermitian physics rather than traditional magnetic field control, potentially opening up novel approaches for quantum state engineering in future devices. The discovery that non-Hermiticity alone can drive a system to maximal entanglement represents a significant departure from conventional quantum mechanics, where Hermitian operators have dominated our understanding of quantum systems. What makes this particularly intriguing is the identification of a sharp phase transition that occurs through energy gap closure rather than at exceptional points, suggesting fundamentally different physics at play that could inspire new quantum hardware designs. While still theoretical, this work contributes to the growing recognition that non-Hermitian quantum systems may offer unexplored advantages for quantum information processing applications.
— Mark Eatherly
Summary
Theoretical analysis of a prototypical two-qubit effective non-Hermitian system characterized by asymmetric Heisenberg $XY$ interactions in the absence of external magnetic fields demonstrates that maximal bipartite entanglement and quantum phase transitions can be induced exclusively through non-Hermiticity. At thermal equilibrium as $T\rightarrow 0$, the system attains maximal entanglement ${C}=1$ for values of the non-Hermiticity parameter greater than a critical value $γ>γ_c=J\sqrt{(1-δ^2)}$, where $J$ denotes the exchange interaction and $δ$ represents the anisotropy of the system; conversely, for $γ< γ_c$, entanglement is nonmaximal and given by ${C} = \sqrt{(1 - (γ/J)^2)}$. The entanglement undergoes a discontinuous transition to zero precisely at $γ= γ_c$. This phase transition originates from the closing of the energy gap at a non-Hermiticity-driven ground state degeneracy, which is fundamentally different from an exceptional point. This work suggests the use of singular-value-decomposition generalized density matrix for the computation of entanglement in bi-orthogonal systems.