Breakthrough: Transcribing entanglement into and out of quantum memory

We may be getting closer to making quantum communication — communication which, in theory at least, would offer the promise of unbreakable encryption — a reality (but then, readers of the Daily Wire would know that we have made this prognostication before): Scientists at the California Institute of Technology have laid the groundwork for a crucial step in quantum information science. They show how entanglement, an essential property of quantum mechanics, can be generated between beams of light, stored in a quantum memory, and mapped back into light with the push of a button. In the 6 March issue of the journal Nature, Caltech Valentine Professor of Physics H. Jeff Kimble and his colleagues demonstrate for the first time an important capability required for the control of quantum information and quantum networks — the coherent conversion of photonic entanglement into and out of separated quantum memories. Entanglement lies at the heart of quantum physics, and is a state in which parts of a composite system are more strongly correlated than is possible for any classical counterparts regardless of the distance separating them. Entanglement is a critical resource for diverse applications in quantum information science, such as for quantum metrology, computation, and communication. Quantum networks rely on entanglement for the teleportation of quantum states from place to place.

In a quest to turn these abstract ideas into real laboratory systems and to distribute entanglement to remote locations (even on a continental scale), Kimble explains that quantum physicists have studied ways to propagate photonic information into and out of quantum memory using a system called a quantum repeater, invented in 1998 by H. Briegel, J. I. Cirac, and P. Zoller at the University of Innsbruck. Until now, work in Kimble’s group on the realization of a quantum repeater with atomic ensembles relied upon the probabilistic creation of entanglement. In this setting entanglement between two clouds of atoms was generated probabilistically but with an unambiguous heralding event. Such systems hold the potential for scalable quantum networks, but it has been difficult for Kimble’s Quantum Optics Group to apply such schemes to certain protocols necessary for quantum networks, such as entanglement connection. Now, with the new protocol and future improvements, “We can push a button and generate entanglement,” says physics graduate student Kyung Soo Choi, one of four authors of the Caltech experiment.

Entanglement has been traditionally carried out with photons in attempt