A new device uses optical fibers to measure light from individual ions. Since these charged atoms store quantum information, this ion trap could allow us to build practical quantum computers and to link light and matter at the quantum level.

The real stumbling block for quantum computers is finding something that can practically be used to house a qubit, the building blocks of quantum information. This ion trap makes the electrically charged atoms a genuine possibility by isolating each one and making possible the extraction of individual qubits of information. In fact, the researchers were able to use them in some very rudimentary experimental quantum computing.


So how does it work? The device is just one square millimeter in size and has a built-in optical fiber. Tiny electrodes are used to trap the ions that pass through it within 30 to 50 micrometers below the surface of the device. The ion is then within reading distance of the optical fiber, which detects the ion's fluorescence signals and uses that data to figure out the ion's quantum information content.

Previous attempts to read the fluorescence of ions have depended on external lenses located about 5 centimeters away. That may not sound like much, but it's a full 500 times further away from the ions than the fiber needs to be, which means the detection system can be miniaturized and packed in on a level never before imagined. A huge number of these fibers could be put on a single quantum computer chip, which just wouldn't be possible with the older lens system. The fiber method isn't as efficient as its lens counterpart, although its developers are confident they can improve the light absorption of the device. Either way, since ions give off millions of photos per second, they are plenty bright enough for the fibers to detect and read.


For this particular trap design, the researchers ultimately hope to pair individual photons with individual ions. That would allow information to be swapped from matter qubits to photon qubits. Matter qubits, like those using ions, are currently the preferred foundation of quantum computers, while photon qubits are used for quantum communications, which is thought to be the most secure form of communication possible. By linking data between the two types of qubits, the developers could set up a system that would bring together quantum computers and quantum communications networks.

[Physical Review Letters]