Correlated Photon Based Metrology Without Absolute Standards

Michael A. Gruntman

Alan L. Migdall

Just like human twins who evoke amazement and a ense of mystery by reporting empathetic experiences across great distances, photons born in pairs also astonish us by their quantum-correlated behavior.

Alan L. Migdall

G. Brida, Marco Genovese, Marco Gramegna

The aim of this review paper is to enlighten some recent progresses in quantum optical metrology in the part of quantum efficiency measurements of photo-detectors performed with bi-photon states. The intrinsic correlated nature of entangled photons from Spontaneous Parametric Down Conversion phenomenon has opened wide horizons to a new approach for the absolute measurement of photo-detector quantum efficiency, outgoing the requirement for conventional standards of optical radiation; in particular the simultaneous feature of the creation of conjugated photons led to a well known technique of coincidence measurement, deeply understood and implemented for standard uses. On the other hand, based on manipulation of entanglement developed for Quantum Information protocols implementations, a new method has been proposed for quantum efficiency measurement, exploiting polarisation entanglement in addition to energy-momentum and time ones, that is based on conditioned polarisation state manipulation. In this review, after a general discussion on absolute photo-detector calibration, we compare these different methods, in order to give an accurate operational sketch of the absolute quantum efficiency measurement state of the art.

Xia Maopeng, Jianjun Li, Gao Dongyang +4 more

Absolute calibration can be realized by means of correlation photon which is generated by the parametric down conversion. The main difficulty lies in obtaining correlation information about photon flux when this method is applied to analog detector calibration process. A novel method of processing the photocurrent on the basis of detecting multimode spatial correlation is proposed. By converting the charge quantity contained in the photocurrent detected in a certain time interval into the photon counting, and by using double channels balance detection and measuring mean photon counts of each model to correct the dual channels fluctuations, the high accuracy calibration of quantum efficiency can be achieved. The photon fluxes of two channels are balanced by inserting an adjustable attenuator in one optical path. The cross section of pumping beam is comparable to the detection area to ensure three-wave colinearity, and the coherent area of the correlation photons is obtained by measuring pump beam waist and lens focus length. With the known detection area, coherence time and coherence area, the average photon number of each mode is computed. This process should be performed under the average photon number of each mode as a reference which could be used for the proportional scaling of equivalent photons of two channels. Based on this new approach, the absolute power responsivity of an InSb detector is calibrated at 3390 nm with correlated photon pairs at 631 and 3390 nm. The calibration procedure and experiments are described and the uncertainty of this method is analyzed. The results show a relative combination uncertainty of about 7.785% for this calibration method, which agrees well with the result independently obtained in the national photoelectronic metrology laboratory within a relative difference of about 3.6%. This result verifies that the quantum efficiency of an analog detector can be calibrated by the correlated photon method, which has potential applications in highly accurate radiometric calibration without external standards.

Dániel Oszetzky