Deviation from maximal entanglement for mid-spectrum eigenstates of local Hamiltonians

• URL: http://arxiv.org/abs/2202.01173v2
• Date: Mon, 11 Dec 2023 09:26:16 GMT
• Title: Deviation from maximal entanglement for mid-spectrum eigenstates of local Hamiltonians
• Authors: Yichen Huang
• Abstract summary: In a spin chain governed by a local Hamiltonian, we consider a microcanonical ensemble in the middle of the energy spectrum and a contiguous subsystem whose length is a constant fraction of the system size. We prove that if the bandwidth of the ensemble is greater than a certain constant, then the average entanglement entropy of eigenstates in the ensemble deviates from the maximum entropy by at least a positive constant.
• Score: 6.907555940790131
• License: http://arxiv.org/licenses/nonexclusive-distrib/1.0/
• Abstract: In a spin chain governed by a local Hamiltonian, we consider a microcanonical ensemble in the middle of the energy spectrum and a contiguous subsystem whose length is a constant fraction of the system size. We prove that if the bandwidth of the ensemble is greater than a certain constant, then the average entanglement entropy (between the subsystem and the rest of the system) of eigenstates in the ensemble deviates from the maximum entropy by at least a positive constant. This result highlights the difference between the entanglement entropy of mid-spectrum eigenstates of (chaotic) local Hamiltonians and that of random states. We also prove that the former deviates from the thermodynamic entropy at the same energy by at least a positive constant.

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