A Caltech-led team of engineers have for the very first time developed a on-chip nanoscale optical quantum memory device.
Guided by assistant professor Andrei Faraon, the team’s quantum memory device is the smallest till date, and comes with the potential of being scaled up for commercial use.
Quantum memory stores information in a similar fashion to the way traditional computer memory does, but on individual quantum particles that are basically photons of light. This allows it to take advantage of the peculiar features of quantum mechanics – such as superposition, in which a quantum element can exist in two distinct states simultaneously – to store data more efficiently and securely.
According to the researchers, the new quantum memory chip is analogous to a traditional memory chip in a computer. Both store information in a binary code.
With traditional memory, information is stored by flipping billions of tiny electronic switches either on or off, representing either a 1 or a 0. That 1 or 0 is known as a bit.
In contrast, quantum memory stores information via the quantum properties of individual elementary particles. A fundamental characteristic of those quantum properties is that they can exist in multiple states at the same time. This means that a quantum bit (known as a qubit) can represent a 1 and a 0 at the same time.
To store photons, Faraon’s team created memory modules using optical cavities made from crystals doped with rare-earth ions. Each memory module is like a miniature racetrack, measuring just 700 nanometers wide by 15 microns long – on the scale of a red blood cell.
Each module was cooled to about 0.5 Kelvin – just above Absolute Zero (0 Kelvin, or -273.15 Celsius) – and then a heavily filtered laser pumped single photons into the modules. Each photon was absorbed efficiently by the rare-earth ions with the help of the cavity.
The photons were released 75 nanoseconds later, and checked to see whether they had faithfully retained the information recorded on them. Ninety-seven percent of the time, they had, Faraon says.
The team now plans to extend the time that the memory can store information, as well as its efficiency.
Image credits and content: Ella Maru Studio/Caltech