Shallow data-loading circuits for multivariable functions

Abstract

We construct shallow QROM, diagonal block-encoding, and quantum state preparation oracles for analytic functions on the $D$-dimensional hypercube $[0, 1]^D$. On $n$ qubits and with $2^{- Ω(n/D)}$ error, these circuits have depths of $O \left( \sqrt{\frac{n \log_2 (n)}{D}} \right)$ in the Clifford + $T$ gate set, albeit using $2^{O(\sqrt{nD \log_2 (n)})}$ ancilla qubits. This is a near-quadratic depth reduction compared to known linear-depth methods.