Faulty diamonds could be the key to the quantum internet

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“Imagine trying to connect an Altair, an early personal computer designed in 1974, to the internet via WiFi. It is a difficult but not impossible task. The two technologies speak different languages, so the first step is to help translate,” the researchers said in a media statement.

After noticing this problem, they decided to develop an interface approach to control the diamond-nitrogen vacancy centers in a way that could be directly transferred to quantum devices.

By combining the entangled emission demonstrated in this study with the previously demonstrated quantum teleportation transfer from a photon to a nuclear spin in diamond, the researchers will create quantum teleportation-based quantum entanglement between distant locations. (Picture from Yokohama National University).

“To realize the quantum internet, a quantum interface is required to generate remote quantum entanglement through photons, which is a quantum communication medium,” said Hideo Kosaka, one of the authors of the study.

According to Kosaka, the promised quantum internet is rooted in more than a century of work in which researchers determined that photons are both particles and light waves at the same time – and that their wave state can reveal information about their particle state and vice versa.

“In addition, the two states could influence each other: A pinching of the wave could squeeze the particle, so to speak. Their nature is entangled, even across great distances. The goal is to control entanglement to communicate discrete data instantly and securely,” he said.

The scientist pointed out that previous research has shown that this controlled entanglement can be achieved by applying a magnetic field to the nitrogen vacancy centers, but a non-magnetic field approach is needed to get any closer to realizing the quantum internet.

His team successfully used microwave and light-polarized waves to entangle an emitted photon and leave qubits with left spin, the quantum equivalent of information bits in classical systems. These polarizations are waves traveling perpendicular to the original source, like seismic waves radiating horizontally from a vertical fault shift. In quantum mechanics, the photon’s spin property – either right-handed or left-handed – determines how the polarization moves, meaning it’s predictable and controllable. According to Kosaka, what is crucial is that when entanglement is induced via this property under a non-magnetic field, the connection appears to be stable in relation to other variables.

“The geometric nature of polarization allows us to create distant quantum entanglement that is resilient to noise and timing errors,” Kosaka said.

The researcher and his team now plan to combine this approach with a previously demonstrated quantum information transfer via teleportation to create quantum entanglement and the resulting exchange of information between remote locations. The ultimate goal is to enable an interconnected network of quantum computers to build a quantum internet.

“The realization of a quantum internet will enable quantum cryptography, distributed quantum computing and quantum sensing over long distances of more than 1,000 kilometers,” said the expert.

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