Semi-device-dependent blind quantum tomography

TL;DR

This paper introduces a scalable blind quantum tomography method that relaxes the need for precisely calibrated measurement devices by leveraging the low-rank and sparse structures of quantum states and calibrations, supported by theoretical guarantees and numerical demonstrations.

Contribution

It presents a novel blind quantum tomography scheme that reduces calibration dependence using low-rank and sparse matrix techniques, with provable recovery guarantees and practical validation.

Findings

The scheme recovers low-rank quantum states with near-optimal measurement settings.

It relaxes calibration requirements by exploiting state and calibration structures.

Numerical results demonstrate robustness in practical ion-trap quantum systems.

Abstract

Extracting tomographic information about quantum states is a crucial task in the quest towards devising high-precision quantum devices. Current schemes typically require measurement devices for tomography that are a priori calibrated to high precision. Ironically, the accuracy of the measurement calibration is fundamentally limited by the accuracy of state preparation, establishing a vicious cycle. Here, we prove that this cycle can be broken and the dependence on the measurement device's calibration significantly relaxed. We show that exploiting the natural low-rank structure of quantum states of interest suffices to arrive at a highly scalable `blind' tomography scheme with a classically efficient post-processing algorithm. We further improve the efficiency of our scheme by making use of the sparse structure of the calibrations. This is achieved by relaxing the blind quantum tomography problem to the de-mixing of a sparse sum of low-rank matrices. We prove that the proposed algorithm recovers a low-rank quantum state and the calibration provided that the measurement model exhibits a restricted isometry property. For generic measurements, we show that it requires a close-to-optimal number of measurement settings. Complementing these conceptual and mathematical insights, we numerically demonstrate that robust blind quantum tomography is possible in a practical setting inspired by an implementation of trapped ions.