Quantum state estimation with unknown measurements

TL;DR

This paper introduces a new experimental method for quantum detector calibration that simplifies the process for complex detectors by limiting the input region, enabling more accurate quantum state estimation.

Contribution

The paper presents the first experimental implementation of a versatile alternative to quantum detector tomography for complex, many-outcome quantum detectors.

Findings

Successful calibration of a quantum detector using the new method

Accurate estimation of non-classical photon number states

Demonstration of method's applicability to complex detectors

Abstract

Improved measurement techniques are central to technological development and foundational scientific exploration. Quantum optics relies upon detectors sensitive to non-classical features of light, enabling precise tests of physical laws and quantum-enhanced technologies such as precision measurement and secure communications. Accurate detector response calibration for quantum-scale inputs is key to future research and development in these cognate areas. To address this requirement quantum detector tomography (QDT) has been recently introduced. However, the QDT approach becomes increasingly challenging as the complexity of the detector response and input space grows. Here we present the first experimental implementation of a versatile alternative characterization technique to address many-outcome quantum detectors by limiting the input calibration region. To demonstrate the applicability of this approach the calibrated detector is subsequently used to estimate non-classical photon number states.