The efficient characterization of photonic quantum sources enables precise source engineering for quantum information applications. I present our demonstrations of the stimulated emission tomography technique to efficiently characterize sources in multiple degrees of freedom.
Using stimulated emission tomography, we characterize an entangled photon-pair source in the energy and polarization degrees of freedom, with a precision far exceeding what could be obtained by quantum state tomography. Through this multidimensional tomography we find that energy-polarization correlations are a cause of polarization-entanglement degradation, demonstrating that this technique provides useful information for source engineering and can accelerate the development of quantum information processing systems dependent on many degrees of freedom.
We perform a multidimensional characterization of a polarization-entangled photon-pair source using stimulated emission tomography (SET). We measure the frequency-resolved polarization density matrix, which is composed of thousands of individual polarization density matrices, each corresponding to a different frequency pair. The measurement exhibits detailed information about correlations that would be difficult to observe using traditional quantum state tomography. This demonstration exhibits the power of SET to characterize a source of quantum states with multi-dimensional correlations and hyper-entanglement. The SET technique can be applied to a variety of photon-pair-based sources for the optimization and engineering of quantum states.
We identify a relation between the number of photon pairs generated by parametric fluorescence, through either spontaneous parametric down-conversion (SPDC) or spontaneous four-wave mixing, and the number generated by the corresponding stimulated process, respectively, either difference-frequency generation or stimulated four-wave mixing. On the basis of this very general result, we show that the characterization of SPDC sources of two-photon states in a given system can be performed solely by studying stimulated emission. We call this technique stimulated emission tomography (SET). We show that the number of photons detected in SET can be 9 orders of magnitude larger than the average number of coincidence counts in two-photon quantum state tomography. These results open the way to the study of sources of quantum-correlated photon pairs with unprecedented precision and unparalleled resolution.