Replica manipulation of the ground state in one-dimensional quantum spin systems
裕太 熊野
In the last decade it has become evident that information-theoretic quantities, which quantify a quantum entanglement encoded in a quantum state, are extremely useful to analyze a state of mane-body systems.Celebrated examples are the entanglement entropy and the Shannon entropy, which extract universal information of the underlying field theory of the system.Furthermore, a significant concept, the entanglement spectrum, has been proposed recently.It contains more complete information than the entanglement entropy.They have achieved a considerable success in characterizing exotic quantum phases that are beyond conventional descriptions.Inspired by these developments, we propose a new state, which we name a Rényified state, as follows: for a given quantum state |Ψ⟩ = ∑ i ψ i |i⟩ and the basis states |i⟩, the Rényified state is defined by raising the wave-function coefficients ψ i to the power of n (and normalized).The Shannon entropy can be obtained from the Rényified state.Moreover, the latter contains more information than the former.We study the Rényified state starting from a Tomonaga-Luttinger liquids (TLL), which is an important universality class of one-dimensional quantum systems.A TLL is characterized by a TLL parameter K, and described by the free boson field theory with a central charge c = 1 in the conformal field theory (CFT) context.We will show, using numerical calculations, that the Rényified state behaves as a TLL described by a modified TLL parameter K = K/n for small n.For larger n, the Rényified state behaves in a different way: the longitudinal correlation has long-range order while the transverse one remains algebraic.Based on the numerical results, we apply a replica field theory formulation to an analysis of the Rényified state.It suggests that the Rényified state is also a TLL described by a modified TLL parameter K = K/n, when n < 4K.The field theoretical analysis indicates that the TLL description breaks down at n = 4K, which is related to a phase transition in the Rényi-Shannon entropy.Beyond the transition, n > 4K, it suggests that the Rényified state is no longer a TLL since the longitudinal correlation has long-range order while the transverse one remains i algebraic.This exceptional behavior is unlikely to be realized in the ground state of a Hamiltonian with only short-range interactions.This indicates that the Rényified state beyond the transition belongs to a new class of exotic quantum phase.We explain an origin of the exotic behavior by constructing a particular conformal invariant boundary state of a two-component massless free boson.The relationship between the Rényified state and the Rényi-Shannon entropy is also elucidated in boundary CFT formalism.
•Mar 24, 2015•1 citation