Bo Yang - Verifiable blind observable estimation

Wed, 15 Oct 2025 00:00:00 +0000

Ce séminaire, donné par Bo Yang, aura lieu le 15 October 2025, à 12:0. Il aura lieu en salle 25-26/105.

Vous trouverez un plan du campus ici.

Résumé

The rapid advance of quantum hardware is spotlighting pre-fault-tolerant tasks that may no longer be efficiently validated by classical means and are likely to run on potentially untrusted remote quantum servers. This motivates problem-independent verification protocols with rigorous guarantees. The Verifiable Blind Quantum Computation (VBQC) protocol provides delegated computation where the composable security spans the confidentiality and integrity of the computation.However, the success of these cryptographic protocols, especially their low space overhead, is unfortunately confined to problems that admit an algorithm whose output can be amplified through majority voting toward the correct solution. This leaves various notable near-term applications relying on observable estimation without efficient verification protocols.To address these needs, we introduce a protocol implementing Secure Delegated Observable Estimation (SDOE), which efficiently verifies observable estimation performed on an untrusted quantum machine. More precisely, it guarantees that the computed estimate is within some ϵ>0 of the true expectation value or else it aborts. The required overhead is limited to adding test rounds that are not more complex than the unprotected computation that needs to be performed to implement the desired measurement on a given fiducial state; and in addition, the security error is negligible in the total number of rounds of the protocol.

Quantum Error Suppression with Subgroup Stabilisation

Mon, 09 Sep 2024 00:00:00 +0000

Quantum state purification is the functionality that, given multiple copies of an unknown state, outputs a state with increased purity. This will be an essential building block for near- and middle-term quantum ecosystems before the availability of full fault tolerance, where one may want to suppress errors not only in expectation values but also in quantum states. We propose an effective state purification gadget with a moderate quantum overhead by projecting $M$ noisy quantum inputs to their symmetric subspace defined by a set of projectors forming a symmetric subgroup with order $M$. Our method, applied in every short evolution over $M$ redundant copies of noisy states, can suppress both coherent and stochastic errors by a factor of $1/M$, respectively. This reduces the circuit implementation cost $M$ times smaller than the state projection to the full symmetric subspace proposed by Barenco et al. more than two decades ago. We also show that our gadget purifies the depolarised inputs with probability $p$ to asymptotically $O\left(p^{2}\right)$ with an optimal choice of $M$ when $p$ is small. The sampling cost scales $O\left(p^{-1}\right)$ for small $p$, which is also shown to be asymptotically optimal. Our method provides flexible choices of state purification depending on the hardware restrictions before fully fault-tolerant computation is available.

Bo Yang | LIP6 - Équipe QI

Bo Yang - Verifiable blind observable estimation

Verifiable blind observable estimation

Résumé

Quantum Error Suppression with Subgroup Stabilisation