  We propose a new parton theory of the hole-doped cuprates, describing the
evolution from the pseudogap metal with small Fermi surfaces to the
conventional Fermi liquid with a large Fermi surface. We introduce 2 ancilla
qubits per square lattice site, and employ them to obtain a variational
wavefunction of a fractionalized Fermi liquid for the pseudogap metal state. We
propose a multi-layer Hamiltonion for the cuprates, with the electrons residing
in the 'physical' layer, and the ancilla qubits in two 'hidden' layers: the
hidden layers can be decoupled from the physical layer by a canonical
transformation which leaves the hidden layers in a trivial gapped state. This
Hamiltonian yields an emergent gauge theory which describes not only the
fractionalized Fermi liquid, but also the conventional Fermi liquid, and
possible exotic intermediate phases and critical points. The fractionalized
Fermi liquid has hole pockets with quasiparticle weight which is large only on
"Fermi arcs", and fermionic spinon excitations which carry charges of the
emergent gauge fields.
