Fig. 1: Experimental concept.
From: Probing entanglement in a 2D hard-core Bose–Hubbard lattice
a, Schematic for an example subsystem X of four qubits within a 16-qubit lattice. The subsystem has a volume of 4 (maroon sites) and an area of 8 (orange lines). b, 2D HCBH lattice emulated by the superconducting quantum circuit. Each site can be occupied by, at most, a single particle. c, Energy E spectrum of the HCBH lattice emulated by our device, shown in the rotating frame resonant with the lattice sites. The energy spectrum is partitioned into distinct sectors defined by the total particle number n. d, Scaling of the entanglement entropy S with subsystem volume V for an eigenstate at the centre of the energy spectrum (orange line, corresponding to the energy eigenstate highlighted by the orange oval in c) and an eigenstate at the edge of the energy spectrum (teal line, corresponding to the energy eigenstate highlighted by the teal oval in c). e, Change in the entanglement behaviour, quantified by the geometric entropy ratio sV/sA, for states with n = 8. f, Schematic for the flip-chip sample consisting of 16 superconducting qubits. g,h, Optical images of the qubit tier (g) and the interposer tier (h) are illustrated with the qubits and the different signal lines false-coloured. Scale bars, 1 mm.
