An on-demand source of entangled photon pairs for scalable quantum networking

Icarus Quantum Inc and the National Institute of Standards and Technology (NIST) propose to develop an on-demand entangled photon source (O-DEPs) to execute secure quantum communications protocols in a scalable manner. Our O-DEPS is based on Indium Arsenide quantum dots (QDs) coupled to high-quality optical cavities. These QDs are the best sources of on-demand single photons, and can emit a photon upon excitation with >96% quantum efficiency, >93% indistinguishability, and >99.96% purity. Furthermore, if pumped to the biexciton level, these QDs can emit polarization-entangled photon pairs deterministically.  To efficiently extract photons from QDs into a useful mode, optical cavities must be fabricated around them. These QD-cavity sources have emerged as the most efficient sources for single photons, and pervious demonstrations shown single photons coupled to single-mode fiber with 57% efficiency. In this proposal, we will explore the feasibility of a novel cavity structure to efficiently couple to entangled photon pairs emitted from a QD into a single-mode fiber. We will design these cavities using Multiphysics simulations to extract entangled photons with more than 75% efficiency from QD-cavity coupled system and into optical fiber. Our O-DEPS can generate encryption keys that are impossible to break due to their unique properties: It can be verified that the keys are generated freshly in the device (not prerecorded), and that the user is the sole party that possesses the keys (certified quantum randomness). For these purposes, our device will have niche applications in the data encryption market for users with sensitive data. On-demand entangled photons can also be used for secure communications protocols such as quantum key distribution, where two parties can share an encryption key with the ability to detect an eavesdropping attack on the communication channel. Furthermore, on-demand entangled photon sources can be used to distribute entanglement over long distances by using a protocol entanglement swapping, which is to interfere photons from different pairs to entangle photons that have never interacted. Using this method, one can overcome photon loss in fiber-optical quantum networks by using multiple entangled photon sources and interfere them in a chain, resulting in each photon traveling less distance in fibers and hence, experience less loss, known as a quantum repeater process. Proof of principles of this method has been performed using spontaneous entangled photon sources, which due to their spontaneity, are suffer from a dramatic decrease in rates when multiple sources are interfaced together. Our on-demand source offers a scalable approach to interfering multiple photons pairs with each other, extending quantum communications to long distances. Execution of these protocols will lead to a long-range quantum network with security levels impossible to achieve with classical solutions.