Tuesday, 29 April 2014

Distant Solid State Qubits: New Era of Quantum Networking

The reliable transmission of quantum states between two distinct locations is one of the major challenges of modern science, more specifically physics and engineering studies. The fundamental difficulty of such transmission is that quantum information is pretty fragile stuff. Quantum teleportation always involves creating a qubit, teleporting it and then measuring it immediately after receiving, to check whether the transmission is successful or not.

However, the whole process of measuring has a crucial disadvantage. It completely destroys the information received. So the hard part of developing a quantum router is to keep the information intact. Technically one has to read and write quantum information without destroying it.

The actual process is to read the stored quantum state first and then teleport it and finally store it again to be teleported to the next stage of the transmission unit.

As we know today the most promising candidate for storing qubits is atomic nuclei. That's because Nuclei are not relatively vulnerable to electric or magnetic fields and moreover nuclear spins are also easy to store in crystals unlike slippery photons.

At Delft, Pfaff and Pals have perfected a method of embedding nuclear spin in diamond crystals. Their method allows one to store single atomic memories in a way that can be robustly controlled. They created two quantum memories out of a pair of diamond crystals with single nitrogen atoms embedded in each. Then they stored a qubit in the nuclear spin of the first crystal by microwave pulses. This has turned out to be more promising as the atoms are confined more securely in the lattice and are easy to detect because they fluoresce.

In the operation of teleportation, they made a pair of entangled photons and send one to each crystal. The interaction between stored qubits and entangled photons made it possible to transmit the information from one crystal to another where it ends up stored in the nuclear spin of the nitrogen atom there.

“The source state is successfully teleported in each of the experimental runs”
- say Pfaff and co.

The foremost thing here that the challenge of storing received information without destroying it, is achieved without a doubt. Though there are challenges ahead, of course. In these experiments the crystals were only three meters apart but they will ultimately have to be separated by telecommunication optical fibers. Perhaps we will not have too much longer to wait until we finally get a quantum internet connection for our very own household purpose.