The transmissivity of the beam splitter and quantum efficiency of the heralding detector are key concerns for accurate assessment of generated non-classical states. An experimentally feasible in situ scheme simultaneously estimates both parameters using solely measurement data obtained during device operation. The protocol combines click statistics from an on/off heralding detector with homodyne measurements performed on the transmitted mode of the beam splitter when supplied by a displaced squeezed state. Classical multi-parameter estimation theory derives the c.

Improved characterisation of quantum devices via simultaneous parameter estimation

A five-fold reduction in parameter uncertainty has occurred during the simultaneous estimation of beam splitter transmissivity and detector quantum efficiency. Previously, accurate characterisation necessitated complex calibrations impractical for routine use. The new technique employs readily available measurement data from heralding counts alongside homodyne detection, offering an in situ method applicable directly during device operation instead of relying on external calibration procedures.

This breakthrough enables more precise control over non-Gaussian optical states important for advanced quantum technologies such as computation and metrology; these states are notoriously difficult to create and maintain. Homodyne detection, a technique measuring light’s amplitude and phase, when used with heralding counts yielded a substantial improvement in parameter estimation precision. Researchers quantified sloppiness using the determinant of the Fisher information matrix as a figure of merit for quantifying parameter degeneracy.

Careful selection of the measurement angle sharply reduces ambiguity when estimating both beam splitter transmissivity and detector efficiency simultaneously, consistently outperforming strategies reliant on sequential determination across various experimental conditions relevant to quantum technologies. However, calculations assume ideal Gaussian states alongside perfect knowledge of initial squeezing parameters, control of which remains challenging within real-world photonic circuits before widespread practical application is possible.

In-situ parameter estimation improves photon subtraction fidelity for quantum technologies

Advances in secure communication and ultra-sensitive sensing fuel demand for reliable non-classical light sources; photon subtraction offers a promising route towards creating these essential resources. Current models rely on idealised conditions, perfectly squeezed initial states notoriously difficult to achieve consistently in practice. This simplification introduces uncertainty because imperfections in optical components or fluctuations during operation cause real photonic circuits to inevitably deviate from theoretical perfection.

Estimating beam splitter transmissivity and detector efficiency simultaneously during device operation provides a valuable tool for calibration and optimisation, moving beyond the need for pre-characterisation of often imprecise components. Analysis of parameter ‘sloppiness’, measuring how easily researchers identify different variables within a statistical model, revealed that careful selection of measurement settings minimises ambiguity when estimating both properties at once. The developed technique allows simultaneous determination of beam splitter transmissivity (τ) and detector efficiency across experimentally relevant values such as 0.9 and 0.99, key parameters governing photon subtraction devices used in advanced quantum technologies; these tools remain vital for advances in secure communication.

The research demonstrated an experimental method to simultaneously estimate beam splitter transmissivity and heralding detector efficiency during the operation of a photon-subtraction device. This is important because accurate knowledge of these parameters improves the quality of non-classical states generated for use in quantum information processing and metrology.

By analysing measurement data from homodyne detection combined with click statistics, researchers found that selecting appropriate settings reduces ambiguity when determining both values at once, across transmissivities such as 0.9 and 0.99. The authors suggest this technique could be used to calibrate devices without relying on pre-characterisation of components.

👉 More information
🗞 In situ characterization of a photon-subtraction device via heralding counts and homodyne detection
✍️ Priyanka Sharma, Matteo G. A. Paris and Stefano Olivares
🧠 ArXiv: https://arxiv.org/abs/2609.10100

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