Hybrid entanglement swapping is a quantum leap in quantum communications
At the level of photons, electrons, and smaller, the descriptions of our physical world provided by classical mechanics cease to apply. Light can behave like a particle. Matter can behave like a wave. And the physical properties of one particle can affect those of another no matter the distance – even miles – between them in a phenomenon Einstein called ‘spooky action at a distance.’ Better known as quantum entanglement, the phenomenon has important implications for quantum information processing and secure quantum communication. With the support of the Marie Skłodowska-Curie programme, the HELIOS project set out to study the newly demonstrated entanglement of particle- and wave-like light, a phenomenon called hybrid entanglement.
A serendipitous quantum leap in quantum communication protocols
Light is perfect for quantum information distribution and processing. It is compatible with most currently existing quantum and classical communication devices and its speed is unsurpassed. Further, its dual particle-wave nature supports a discrete quantum information encoding approach similar to a digital signal as well as a continuous-variable approach similar to an analogue signal. Project fellow Giovanni Guccione set out to demonstrate a hybrid approach combing the two in a quantum version of a digital-to-analogue converter (DAC) exploiting quantum teleportation of light. “Quantum state teleportation effectively transfers the quantum properties of the system from the initial node to the end node without intermediate readings that could compromise quantum information processing,” Guccione explains. It relies on both classical communication and quantum entanglement between the sending and receiving nodes. Although faced with several significant technical obstacles along the way, Guccione created simple yet highly innovative solutions. In the process, HELIOS demonstrated hybrid entanglement of light and made another pioneering discovery. As Guccione recalls, “The improved version also demonstrated the first example of entanglement swapping of a hybrid state of light. This demonstration proved that a particle initially entangled to another particle is susceptible to becoming entangled to an intrinsically different entity without ever directly interacting with it.” Guccione summarises, “From the generation of hybrid entangled states to other fundamental quantum communication protocols, the highlight of the project is the achievement of entanglement swapping involving hybrid entanglement. Since quantum information cannot be replicated or amplified like classical signals, entanglement swapping allows the establishment of quantum repeaters, sort of the quantum equivalent of classical range extenders, across the network.” These findings could be important in future heterogeneous quantum networks, enhancing secure exchange of quantum information and even underlying a quantum internet.
Rushing to meet the future at the speed of light
HELIOS has pushed the frontiers of quantum communication processing and computing. The team has proved that quantum correlations can be established not only between modes that never interacted but also between modes based on otherwise incompatible encodings. Guccione concludes, “While this may represent a single step relative to future advancements, it illustrates how rapidly quantum mechanics is moving from the purely theoretical to practical, real-world applications. ‘Ordinary’ quantum communication might be a reality sooner than expected.” Perhaps the quantum internet is closer than we think, intertwined with and at a short distance ahead of the newly demonstrated hybrid entanglement swapping.
Keywords
HELIOS, quantum, entanglement, communication, hybrid, light, information, particle), quantum information, entanglement swapping, entangled, wave, teleportation, digital-to-analogue converter (DAC), quantum information processing, quantum internet