Holographic classical shadow tomography

We introduce ``holographic shadows,'' a new class of randomized measurement schemes for classical shadow tomography that achieves the optimal scaling of sample complexity for learning geometrically local Pauli operators at any lengthscale, without the need for fine-tuning protocol parameters such as circuit depth or measurement rate. Our approach utilizes hierarchical quantum circuits, such as tree quantum circuits or holographic random tensor networks. Measurements within the holographic bulk correspond to measurements at different scales on the boundary (i.e., the physical system of interests), facilitating efficient quantum state estimation across observable at all scales. Considering the task of estimating stringlike Pauli observables supported on contiguous intervals of $k$ sites in a one-dimensional system, our method achieves an optimal sample complexity scaling of $\ensuremath{\sim}{d}^k\mathrm{poly}(k)$, with $d$ the local Hilbert space dimension. We present a holographic minimal cut framework to demonstrate the universality of this sample complexity scaling and validate it with numerical simulations, illustrating the efficacy of holographic shadows in enhancing quantum state learning capabilities.