Stacked quantum Ising systems and quantum Ashkin-Teller model

• URL: http://arxiv.org/abs/2601.18922v1
• Date: Mon, 26 Jan 2026 19:42:32 GMT
• Title: Stacked quantum Ising systems and quantum Ashkin-Teller model
• Authors: Davide Rossini, Ettore Vicari,
• Abstract summary: We analyze an isolated composite system consisting of two stacked quantum Ising (SQI) subsystems.<n>We focus on the quantum correlations of one of the two SQI subsystems, $S$, in the ground state of the global system.<n>For identical SQI subsystems, the global system is equivalent to the quantum Ashkin-Teller model, characterized by an additional $Z$ symmetry between the two subsystem operators.
• Score: 0.0
• License: http://arxiv.org/licenses/nonexclusive-distrib/1.0/
• Abstract: We analyze the quantum states of an isolated composite system consisting of two stacked quantum Ising (SQI) subsystems, coupled by a local Hamiltonian term that preserves the $Z_2$ symmetry of each subsystem. The coupling strength is controlled by an intercoupling parameter $w$, with $w=0$ corresponding to decoupled quantum Ising systems. We focus on the quantum correlations of one of the two SQI subsystems, $S$, in the ground state of the global system, and study their dependence on both the state of the weakly-coupled complementary part $E$ and the intercoupling strength. We concentrate on regimes in which $S$ develops critical long-range correlations. The most interesting physical scenario arises when both SQI subsystems are critical. In particular, for identical SQI subsystems, the global system is equivalent to the quantum Ashkin-Teller model, characterized by an additional $Z_2$ interchange symmetry between the two subsystem operators. In this limit, one-dimensional SQI systems exhibit a peculiar critical line along which the length-scale critical exponent $ν$ varies continuously with $w$, while two-dimensional systems develop quantum multicritical behaviors characterized by an effective enlargement of the symmetry of the critical modes, from the actual $Z_2\oplus Z_2$ symmetry to a continuous O(2) symmetry.

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