BEGIN:VCALENDAR VERSION:2.0 PRODID:researchseminars.org CALSCALE:GREGORIAN X-WR-CALNAME:researchseminars.org BEGIN:VEVENT SUMMARY:Ehud Altman (Berkeley) DTSTART:20201109T193000Z DTEND:20201109T203000Z DTSTAMP:20260423T024804Z UID:Kadanoff/15 DESCRIPTION:Title: Symmetry and information flow in quantum circuits with measurements\ nby Ehud Altman (Berkeley) as part of Kadanoff seminars\n\n\nAbstract\nI w ill discuss novel quantum phases and phase transitions that emerge in the dynamics of quantum circuits and represent distinct modes of information f low. I consider a system in which the time evolution by random unitary gat es is occasionally interrupted by local measurements. It was previously fo und that such evolution leads to a phase transition in the entanglement of the wavefunction: at steady state it is characterized by volume law entan glement for small measurement rate\, while it is an area law above a thres hold rate. I will investigate this phase transition by mapping the quantum dynamics into classical statistical mechanics models in equilibrium. Furt hermore\, we show that more phases are possible if we impose symmetries on the dynamics. To identify the phases\, we develop a mapping between the i nformation dynamics in a broad class of circuits to the ground states of e ffective spin Hamiltonians\, which possess a higher symmetry than the orig inal circuit. The different ground state phases admitted by the higher eff ective symmetry correspond to distinct patterns of information flow and sc rambling in the circuit dynamics. We illustrate these ideas with two examp les: (i) a quantum circuit with Z_2 symmetry resulting in non-abelian D_4 symmetry in an effective Hamiltonian and (ii) a quadratic fermionic circui t leading to U(1) symmetry. The latter exhibits Kosterlitz–Thouless tran sition in 1D between a critical phase with log(L) entanglement and "trivia l" area law phases. Our work is a first step toward the classification of information flow in generic quantum circuits.\n LOCATION:https://researchseminars.org/talk/Kadanoff/15/ END:VEVENT END:VCALENDAR