Quantum State Preparation without Coherent Arithmetic
Sam McArdle, András Gilyén, Mario Berta
Abstract
We introduce a versatile method for preparing a quantum state whose amplitudes are given by some known function. Unlike existing approaches, our method does not require handcrafted reversible arithmetic circuits, or quantum table reads, to encode the function values. Instead, we use a template quantum eigenvalue transformation circuit to convert a low-cost block encoding of the sine function into the desired function. Our method uses only four ancilla qubits (three if the approximating polynomial has definite parity), providing order-of-magnitude qubit count reductions compared to state-of-the-art approaches, while using a similar number of gates if the function can be well represented by a polynomial or Fourier approximation. We demonstrate the algorithmic utility of our method, including preparing Gaussian and Kaiser window states.