Absolute calibration of photodiodes with bright twin beams

We present a scheme based on the use of bright entangled twin beams for the calibration of analog photodiodes, providing an extension of the schemes for calibrating photon-counting detectors with photon pairs. Previous proposals for the calibration of analog photodiodes with entangled beams are based on a stimulated parametric process operating in the low-gain regime. We start by showing that in those proposals it is necessary to know the exact value of the gain as any error in estimating it will lead to an error in the calibration of the quantum efficiency. We then introduce a technique that is independent of the gain, thus eliminating the uncertainty introduced from errors in estimating the gain or experimental fluctuations of parameters that affect the gain. A proof of principle implementation of this technique using bright twin beams obtained from a four-wave mixing process in rubidium vapor shows its viability for the calibration of analog photodiodes.