Engineering Quantum Entanglement

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Quantum technologies are becoming the engine of innovations in the 21st century. A key component in quantum technologies is the quantum entanglement source, which produces entangled particles, typically, entangled photons. These photons exhibit strong correlations that cannot be mimicked by classical particles. For example, for polarization-entangled photon pairs, the measurement of one photon’s polarization state reveals that of its partner, even when they are physically far away from each other—a phenomenon once described by Einstein as “spooky action at a distance”. It is this “spookiness”, or non-intuitiveness, that inspired the unconventional usage of quantum entanglement. Entanglement-based quantum cryptography, for example, utilizes the correlation of the photons sent to two remote parties and allows them to share a common set of random cryptographic keys. It guarantees the security of the keys since any eavesdropping attempt would result in a detectable deterioration of correlation. The quantum entanglement can also be harnessed to perform other functions impossible to achieve classically, such as efficient quantum computing algorithms and ultra-high resolution in quantum imaging.