Spontaneous parametric downconversion is an important process for providing pairs of photons for quantum optics. We discuss a scheme for eliminating undesired inter-photon correlations inherent in this process, and an efficient characterization of spectral correlations.
Nonlinear spectroscopy with quantum entangled photons is an emerging field of research that holds the promise to achieve superior signal-to-noise ratio and effectively isolate many-body interactions. Photon sources used for this purpose, however, lack the frequency tunability and spectral bandwidth demanded by contemporary molecular materials. Here, we present design strategies for efficient spontaneous parametric downconversion to generate biphoton states with adequate spectral bandwidth and at visible wavelengths. Importantly, we demonstrate, by suitable design of the nonlinear optical interaction, the scope to engineer the degree of spectral correlations between the photons of the pair. We also present an experimental methodology to effectively characterize such spectral correlations. Importantly, we believe that such a characterization tool can be effectively adapted as a spectroscopy platform to optically probe system-bath interactions in materials.
The generation of high purity single photons and entangled photon pairs is a crucial first step in many quantum optics experiments, including those that require quantum teleportation [1], entanglement swapping [2], and the generation of multi-photon entanglement [3]. The most widely used and established approach for creating photon pairs is spontaneous parametric down conversion (SPDC) - where pump photons undergo a non-linear optical process to create a down-converted photon pair [4]. Traditionally, the generation of high-purity heralded single photons required severe spectral filtering, introducing additional loss. However, through careful engineering of spectral correlations of the down-converted photon pairs one can circumvent the need for filtering and avoid the accompanying reduction in heralding efficiency.
The eventual success of optical quantum information (QI) processing depends critically on the available technologies. Photons produced via the nonlinear process of spontaneous parametric downconversion (SPDC) have now been used in a vast array of experiments in optical quantum computing and long-distance quantum communication. However, almost no source to date has been fully optimized. Here, we describe our progress in engineering an ideal photon-pair source for optical quantum information processing – polarization-entangled photons made indistinguishable by engineering spatio-spectral unentanglement at the source. We present solutions for several key challenges encountered in the development of the indistinguishable source. We expect such a source to directly translate into significantly enhanced QI protocols with higher rates, fidelities and efficiencies.