Xingjian Zhang, Zhaokai Pan, Guoding Liu (Feb 20 2024).
Abstract: Quantum theory promises computation speed-ups than classical means. The full power is believed to reside in “magic” states, or equivalently non-Clifford operations – the secret sauce to establish universal quantum computing. Despite the celebrated Gottesman-Knill Theorem stating that magic-free computation can be efficiently simulated by a classical computer, it is still questionable whether “magic” is really magical. Indeed, all the existing results establish its supremacy for efficient computation upon unproven complexity assumptions or queries to black-box oracles. In this work, we show that the magic advantage can be unconditionally established, at least in a shallow circuit with a constant depth. For this purpose, we first construct a specific nonlocal game inspired by the linear binary constraint system, which requires the magic resource to generate the desired nonlocal statistics or quantum “pseudo telepathy.” For a relation problem targeting generating such correlations between arbitrary nonlocal computation sites, we construct a shallow circuit with bounded fan-in gates that takes the strategy for quantum pseudo telepathy as a sub-routine to solve the problem with certainty. In contrast, magic-free counterparts inevitably require a logarithmic circuit depth to the input size, and the separation is proven optimal. As by-products, we prove that the nonlocal game we construct has non-unique perfect winning strategies, answering an open problem in quantum self-testing. We also provide an efficient algorithm to aid the search for potential magic-requiring nonlocal games similar to the current one. We anticipate our results to enlighten the ultimate establishment of the unconditional advantage of universal quantum computation.