A giant leap for quantum computing

A long-cherished dream for a portable quantum computer came close to reality in the week of World Quantum Day, celebrated on April 14.

Tech giants around the world, including Google and IBM, are in a race to achieve quantum supremacy – the capacity for a quantum computer to solve problems that are beyond the capabilities of classical computers. However, quantum computers are still limited to working in lab conditions; they are also bulky and noise-prone. Now, a quantum photonics group led by Michael Kues and Raktim Haldar from Leibniz University Hannover in Germany has built a chip smaller than a five-rupee coin that works at room temperature using light particles or photons (go.nature.com/416H6di).

"We used photons because they are less interactive to the world, and so less noise-prone," says Haldar. Within a tiny space, the chip can create many entangled photons, the basic building blocks of quantum computation that lead to making a portable quantum computer. Quantum computation using light is another approach to achieving quantum supremacy. On the other hand, most companies and start-ups use superconducting atoms as qubits (quantum bits) that run at -273^°C for their quantum computer.

Quantum entanglement is a curious phenomenon in the subatomic world where two particles with the same origin are everlastingly drawn to each other. They can sense and influence each other instantly, even if they are apart. A sceptical Einstein, however, described it as a "spooky action at a distance." Entangled particles are the basis for quantum computation. The Leibniz researchers generated entangled photons in a single chip. They inserted the indium phosphide laser source in the chip using hybrid technology. The integrated micro rings and an interferometer, thinner than a human hair, help to generate entangled photons.

QuiX Quantum, a photonic quantum technology start-up, and scientist Klaus-Jochen Boller of the University of Twente, in the Netherlands, helped fabricate the photonic chip designed by the Leibniz researchers.

"Fabricating all the parts... in a tiny chip was the real challenge for us," recalls Haldar. "The chip could be in every future photonic quantum computer." It will not only be a source for quantum computation but could also be useful for any kind of quantum information processing and communication such as quantum internet and cryptography. The research team is now looking forward to making a cluster of such photonic chips for robust quantum architecture. The chip will also help generate random quantum numbers, which is critical for data security and communication.

Shailendra K. Varshney, a quantum photonic expert from the Indian Institute of Technology Kharagpur, says: "This discovery will open up a new path in quantum computation and will inspire the younger generation to explore realistic quantum computers."