Classification of one-dimensional gapped phases by boundary-state dimensions

Let Φ0\Phi_0 and Φ1\Phi_1 be two translation-invariant finite-range interactions. For i=0,1i=0,1, suppose there are integers lil_i and rir_i such that

SiZE1,Si(,0]Eri,Si[1,+)Eli.{\mathcal S}^{\mathbb Z}_i\cong{\mathcal E}_1,\qquad {\mathcal S}^{(-\infty,0]}_i\cong{\mathcal E}_{r_i},\qquad {\mathcal S}^{[1,+\infty)}_i\cong{\mathcal E}_{l_i}.

Here SiΓ{\mathcal S}_i^\Gamma denotes the ground-state space on the lattice Γ\Gamma, Ed{\mathcal E}_d is the state space of a dd-dimensional quantum system, ABA\cong B means isomorphism of convex state sets, and S0ΓS1Γ{\mathcal S}_0^\Gamma\sim {\mathcal S}_1^\Gamma means that the two state spaces are related by a quasi-local automorphism. Boundary-state classification conjecture. The following are equivalent: (1) r0=r1r_0=r_1 and l0=l1l_0=l_1; (2) there is a continuously differentiable family of translation-invariant finite-range interactions Φ(s)\Phi(s), s[0,1]s\in[0,1], with Φ(0)=Φ0\Phi(0)=\Phi_0 and Φ(1)=Φ1\Phi(1)=\Phi_1, whose models have a uniform spectral gap γ>0\gamma>0; (3) S0ΓS1Γ{\mathcal S}_0^\Gamma\sim {\mathcal S}_1^\Gamma for Γ=Z,(,0]\Gamma=\mathbb Z,(-\infty,0], and [1,+)[1,+\infty). This conjecture proposes that the dimensions of the half-chain boundary ground-state spaces completely classify these one-dimensional gapped systems, equivalently characterizing connectedness through uniformly gapped paths and quasi-local equivalence of ground states.

Sources & referencesView supporting material

Primary source

Sven Bachmann and Bruno Nachtergaele, “Product vacua with boundary states and the classification of gapped phases”, arXiv:1212.3718 (2013).

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