Researchers at Caltech have developed a computer chip that can store quantum information in the form of light, at the nanoscale. The breakthrough is the latest step towards quantum computers and networks, which would allow information to be processed and transmitted faster and with smaller devices.
In traditional computer memory, an individual bit of information is stored as either a 0 or 1. Though still in the experimental phases, quantum computers work on the same basic principle, storing data in quantum bits (qubits). The difference is that thanks to the quirks of quantum mechanics, qubits can not only be either 1 or 0, but both at the same time, allowing them to hold data much more efficiently. Optical quantum devices like the new Caltech chip store and carry that information on photons of light, which are fast and secure because they have no charge or mass.
"This technology not only leads to extreme miniaturization of quantum memory devices, it also enables better control of the interactions between individual photons and atoms," says Tian Zhong, lead author of a study describing the new chip.
The Caltech chip is made up of an array of memory modules, each one measuring 15 microns long and 0.7 microns wide, making them about the size of red blood cells. These modules contain optical cavities made of crystals doped with rare-earth ions that are designed to trap and hold photons. After cooling the modules right down to about 0.5 Kelvin (-272.7° C, -458.8° F), the team used a heavily-filtered laser to beam a single photon into each module, where it was absorbed by the rare-earth ions.
The optical cavities held the photons for 75 nanoseconds before releasing them again, and afterwards the researchers checked the photons to make sure they still carried the same information. The error rate was just 3 percent, according to the team.
To make the chips a practical option in quantum networks designed to transmit information over long distances, they need to be able to store the data for at least one millisecond. That's the goal the team plans to work towards next, as well as developing ways to integrate the chip into other circuits.
"Such a device is an essential component for the future development of optical quantum networks that could be used to transmit quantum information," says Andrei Faraon, corresponding author of the study.
The research was published in the journal Science.