Researchers have managed to entangle ten billion pairs of particles at once, according to a letter in Nature this week. The group of scientists used phosphorus-doped silicon, a microwave pulse, and a radio pulse to achieve the record number of simultaneous entanglements. The process worked on 98 percent of the possible pairs and, while control over their states is still somewhat limited, the authors note that mass entanglement could be an important step for quantum computing.

The experiment took place in a cube of silicon spiked with phosphorus ions, with the phosphorus's nuclei serving as one half of the entangled pair and one of the phosphorus' electrons (donated in a bond to a silicon atom) as the other half. The phosphorus donors were ideal for this, because materials doped into semicondunctors like silicon are able to hold particles in entangled states for seconds at a time. Other entangling materials, like photons, see the entanglement decay within a few thousandths of a second or less. The researchers needed all the extra time they could get to herd all of the particles into behaving in a similar way.

The researchers pulsed the particles with a microwave to set their wavefunctions to a particular state, and then sent a second radio frequency pulse to entangle the pairs. When they went to extract the particles' final state, they found that 98 percent of the attempted pairs had entangled, and the process worked on up to ten billion pairs at once.

Of course, creating the entanglements is only the first step—it's reading and writing to the entangled particles that will allow them to serve as quantum bits, or qubits, in quantum computers. Still, the ability to create all these pairs—the storage equivalent of 2.5 gigabytes—will be something future quantum computers will probably need to do.

Nature, 2011. DOI: 10.1038/nature09696 (About DOIs).