Quantum memory device

First on-chip quantum memory device developed

Image credit: Ella Maru Studio

The smallest ever optical quantum memory device has been developed by an international team of engineers based at California Institute of Technology (Caltech). This could, in future, form the basis of an optical quantum network.

Quantum memory requires the storage of information on individual particles of light (photons). This allows for the device to harness the common sense defying properties of quantum particles, such as superposition (by which a particle can exist in multiple states (0 and 1) at once) and entanglement (whereby multiple particles are connected such that their states are interdependent).

These properties allow for data to be stored far more efficiently and securely than in classical computers.

The computer chip developed by the Caltech-based team is a means of storage for quantum networks using photons: optical quantum networks. As photons are massless and electrically neutral, they can be transmitted reliably along fibre optic network with minimal interactions with other particles.

“Such a device is an essential component for the future development of optical quantum networks that could be used to transmit quantum information,” said Professor Andrei Faraon, corresponding author of the Science paper detailing the development of the chip.

Due to their potential in improving the reliability and security of data transmission and in accelerating quantum computing technology, physicists and engineers have long worked towards the development of optical quantum memory devices that could be used in a practical quantum network.

Like a traditional memory chip, the Caltech chip stores information in binary code. However, while in a classical chip, information is stored by flipping billions of miniaturised electronic switches to “on” or “off” (1 or 0), the quantum memory chip stores information using the quantum properties of photons. A quantum bit (qubit) can represent a 1 and a 0 at once, due to the quantum phenomenon of superposition.

Professor Faraon and his team used optical cavities made from crystals doped with rare-earth ions as the basis for their memory modules. The modules were cooled to just above absolute zero, then a tightly controlled laser pumped individual photons into the modules.

The photons were absorbed by the rare-earth ions, with the help of the cavities. 75 nanoseconds later, they were released, and the researchers found that 97 per cent of the time, they retained the information recorded.

“This technology not only leads to extreme miniaturisation of quantum memory devices, it also enables better control of the interactions between individual photons and atoms,” said Professor Tian Zhong, lead author and molecular engineer at the University of Chicago.

The international team will continue to develop the technology, aiming to extend the amount of time the memory chip can store information; to form the basis of a quantum network, the device will need to store data for at least one millisecond.

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