Special Seminar: “Ancilla theory of the pseudogap, and of the cuprate phase diagram” (Prof. Subir Sachdev)

The pseudogap is mysterious metallic state of electrons which appears above the critical temperature of correlated electron superconductors, most prominently in the lightly-hole-doped cuprates. I argue that the pseudogap is best understood as the finite temperature realization of a metallic ground state with a spin liquid character, andpresent a theory using a bi-layer of ancilla qubits. This theory leads to a variational wavefunction for the pseudogap state, to gauge theories for transitions and crossovers out of the pseudogap, and to a unifying perspective on the cuprate phase diagram.