Certified randomness has a long history in quantum information, with many potential applications. Recently Aaronson (Aaronson , 2020 proposed a novel certified randomness protocol based on existing random circuit sampling (RCS) experiments -placing this application within the reach of near-term quantum devices. The security of his protocol, however, relies on non-standard complexity-theoretic conjectures which were not previously studied in the literature. In this work we provide strong complexity-theoretic evidence in support of these conjectures. In particular we prove two versions of Aaronson's conjectures unconditionally in a black-box Fourier sampling setting. This mirrors earlier complexity-theoretic evidence for quantum advantage, bringing the security of Aaronson's protocol up to the same level of evidence we have for quantum advantage from heavy output generation.

Quantum secret sharing is a method for sharing a secret quantum state among a number of individuals such that certain authorized subsets of participants can recover the secret shared state by collaboration and other subsets cannot. In this paper, we first propose a method for sharing a quantum secret in a basic (2, 3) threshold scheme, only by using qubits and the 7-qubit CSS code. Based on this (2, 3) scheme, we propose a new (n, n) scheme and we also construct a quantum secret sharing scheme for any quantum access structure by induction. Secondly, based on the techniques of performing quantum computation on 7-qubit CSS codes, we introduce a method that authorized subsets can perform universal quantum computation on this shared state, without the need for recovering it. This generalizes recent attempts for doing quantum computation on (n, n) threshold schemes.

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