Boffins bring us one step closer to a quantum network

Researchers claim to have demonstrated how it is possible to move quantum information from individual sets of multi-partite entangled atoms to four entangled beams of light (previously they had only managed with two). In simple terms, this a a big step forward in information science because it paves the way toward quantum networks.

A quantum network is a "web" composed of many interconnected quantum nodes (which work like hard drives), each of which is capable of basic quantum logic operations (Caltech says this is similar to the "AND" and "OR" gates in computers). The operations take place using "quantum transistors" and the resulting quantum states are stored in quantum memories.

Four Caltech researchers demonstrated this by mapping the transfer of the entangled photons out of and into a system of four distinct collections of atoms.

Those of you who are familiar with physics know that matter on a quantum level often contains several simultaneous possibilities. An entangled system is no different. It contains multiple possibilities for its properties.

As particles decay over time into other kinds of particles, pairs of particles can come into being which are said to be entangled with one having an "up" spin direction and the other a "down" spin direction. The members of such entangled pairs must be in the state they are in - and measuring the state of one "alters" the state of the other. The two particles are separated over distance by the way and they can spin the same way or different ways.

How they did it

The starting points were four sets of approximately one million Caesium atoms, with each set separated from the others by 1mm and confined within a magnetic field. The four were cooled to just a few hundred millionths of a degree above absolute zero, using lasers apparently. Caesium is a metal that is in a near-liquid state at room temperature; presumably it would be more solid than a rock when cooled this much.

Each set or ensemble of these atoms has atoms in it with an up or down spin direction with a spin wave concept describing the overall spin characteristics of each set. The Caltech researchers entangled these spin waves among the four sets. So now we have information, in a sense, stored in the four sets and the researchers shone four lasers into the four entangled ensembles to detect this.

The read laser lights were altered because "the coherent arrangement of excitation amplitudes for the atoms in the ensembles, described by spin waves, enhances the matter–light interaction through a phenomenon known as super-radiant emission."

Akihisa Goban, one of the Caltech researchers and co-author of a paper in Nature about their work, said: "The emitted light from each atom in an ensemble constructively interferes with the light from other atoms in the forward direction, allowing us to transfer the spin wave excitations of the ensembles to single photons."

Caltech's press release stated:

"The researchers were therefore able to coherently move the quantum information from the individual sets of multi-partite entangled atoms to four entangled beams of light, forming the bridge between matter and light that is necessary for quantum networks."

Caltech graduate student researcher Kyung Soo Choi, the lead author of the Nature paper, cast more light on the subject, saying: "In the zoology of entangled states, our experiment illustrates how multi-partite entangled spin waves can evolve into various subsets of the entangled systems over time, and sheds light on the intricacy and fragility of quantum entanglement in open quantum systems."

Choi added: "Our work introduces new sets of experimental capabilities to generate, store, and transfer multi-partite entanglement from matter to light in quantum networks."

Unable to stop because of his super-excited state, Choi carried on. "It signifies the ever-increasing degree of exquisite quantum control to study and manipulate entangled states of matter and light."

If your cranial supercomputer is still functioning at this point you can read a little bit more here. ®