Abstract
Abstract Entangled photons are pivotal elements in emerging quantum information technologies. While several schemes are available for the production of entangled photons, they typically require the assistance of cumbersome optical elements to couple them to other components involved in logic operations. Here, we introduce a scheme by which entangled photon pairs are directly generated as guided mode states in optical waveguides. The scheme relies on the intrinsic nonlinearity of the waveguide material, circumventing the use of bulky optical components and their associated phase-matching constraints. Specifically, we consider an optical waveguide under normal illumination, so that photon down-conversion can take place to excite waveguide states with opposite momentum in a spectral region populated by only two accessible modes. By additionally configuring the external illumination to interfere different incident directions, we can produce maximally entangled photon-pair states, directly generated as waveguide modes with conversion efficiencies that are competitive with respect to existing macroscopic schemes. These results should find application in the design of more efficient and compact quantum optics devices.
Highlights
As quantum information processing is reaching a mature state, different platforms that materialize quantum entanglement are being intensely explored [1,2,3,4]
By invoking the reciprocity theorem [30], our analysis effectively describes the fidelity of our proposed spontaneous parametric down-conversion (SPDC) scheme, which can be readily explored in an experimental setting using conventional optical components, and provides a widely accessible source of entangled photon pairs directly generated in an optical waveguide
We propose a straightforward approach to generate entangled photon pairs directly into low-loss dielectric waveguides based on down-conversion of normally impinging light and introduce a theoretical formalism relying on the reciprocity theorem to quantify the efficiency of the process
Summary
As quantum information processing is reaching a mature state, different platforms that materialize quantum entanglement are being intensely explored [1,2,3,4]. The generation of entangled photon pairs via nonlinear light–matter interactions is highly appealing for practical implementation, where photons – being capable of traversing enormous distances at the ultimate speed while interacting weakly with their environment – are ideal carriers of information [5, 6]. In this context, the intrinsically weak interaction of light with matter is both a blessing and a curse, in that propagating photons are less sensitive to decoherence, but are difficult to manipulate because they cannot be brought to interact [7]. Optical metasurfaces capable of generating light in arbitrary spin and OAM states have been employed to produce well-collimated streams of entangled photons [13, 14]
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