Fig. 4. Experimental mixed-state entanglement.

a, We develop an experimentally measurable proxy that lower-bounds the log negativity, which is a measure of mixed-state entanglement. Here we demonstrate this proxy with error model simulations of RUC and Rydberg evolution. b, The experimental mixed-state entanglement proxy; solid lines are guides to the eye. c, The maximum entanglement proxy for our experiment can be compared against that of literature examples performing global fidelity estimation with digital quantum processors: Sycamore^2,5, Zuchongzhi^3,4 and H2 (ref. ²⁶) (text indicates release year). For literature examples, the x axis is the number of qubits, whereas for our experiment the effective system size is defined as the number of qubits with the same Hilbert space dimension as our experiment under the Rydberg blockade constraint (Supplementary Information) and is, for instance, roughly 42 at n = 60. The data are summarized in Supplementary Table I. 1D, one dimensional; 2D, two dimensional.