Quantum hard drives on the horizon

PORTLAND, Ore. -- The California Institute of Technology has demonstrated that quantum entanglement can simultaneously transfer whole blocks of quantum information, providing a proof-of-concept for future quantum HDs.

The Caltech team claimed that its device is the harbinger of quantum HDs that someday may challenge traditional storage technologies with optical memories that use entanglement for access. In its demonstration, the team transfered the state of four quantum memories to an optical signal and back again, claiming that the principle could be extended to any number of parallel transfers into and out of future quantum HDs.

"We have shown four quantum memories talking to four quantum channels that can be coherently absorbed by virtue of electromagnetic transparency, which slows down the light to zero for storage," said Kyung Soo Cho, a doctoral candidate at Caltech

Electromagnetically-induced transparency is a coherent optical nonlinearity which renders a medium transparent, enabling light encoded with quantum states to be stopped within a quantum memory device. 

Caltech's entanglement technique used lasers to cool the four quantum memories--each a collection of 1 million cesium atoms magnetically separated by 1 millimeter. The magnetic spin of each atom in the quantum memory spins either up or down, collectively describing a spin-wave that represents the whole ensemble. By simultaneously irradiating the quantum memories with laser beam encoding, the spin waves of the four quantum memories were identically entangled. This technique, called "measurement induced entanglement," was first achieved at Caltech five years ago, but only for two ensembles. Caltech has now demonstrated theoretically that the technique can be extended to any number of nodes.

The Caltech group also characterized the decay of the entangled quantum states among the separate nodes, showing how the system decays from a complex quantum state into classical memory values in what they claims is a predictable, repeatable manner.

Next, the researchers want to study the dynamics of entanglement decay as applied to entangled spin waves in quantum magnetic memories. They also want to expand quantum "metrology" whereby quantum states can be generated, stored and transferred using measurements of the ordinarily fragile states of quantum memories.

Research funding was provided by the National Science Foundation, the Defense Department and Northrop Grumman Corp., among others.