arXiv:2205.06977quant-ph
Hay from the haystack: explicit examples of exponential quantum circuit complexity
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Abstract
The vast majority of quantum states and unitaries have circuit complexity exponential in the number of qubits. In a similar vein, most of them also have exponential minimum description length, which makes it difficult to pinpoint examples of exponential complexity. In this work, we construct examples of constant description length but exponential circuit complexity. We provide infinite families such that each element requires an exponential number of two-qubit gates to be generated exactly from a product and where the same is true for the approximate generation of the vast majority of elements in the family. The results are based on sets of large transcendence degree and discussed for tensor networks, diagonal unitaries, and maximally coherent states.
As an intuition on why many people see this as different. PAC Learning is about compression, KF/EKF is more like Taylor expansion. The specific types of PAC Learning that this paper covers has problems with a simplicity bias, and fairly low sensitivity. While based on UHATs…
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