- Quantum Internet to Communicate by Entanglement
- Secure eavesdrop-proof communications using quantum-key distribution are already available over optical gateways between two parties, but now a possible new quantum Internet could be enabled by teleporting the same information to multiple nodes using entanglement—what Einstein called "spooky action at a distance"—thereby allowing secure broadcasts to copy identical information to multiple nodes on a future quantum Internet.
The realization of a quantum Internet got one step closer when entanglement was recently demonstrated as a viable method to broadcast or copy information to many other network nodes—or users—simultaneously.
Previously, quantum entanglement had only been demonstrated between a single sender and single receiver using optical gateways made by ID Quantique (Geneva) and MagiQ Technologies (New York). Quantum teleportation uses entanglement to inextricably lock the state of a quantum memory at one location to the state of a second memory device, despite their being separated by nearly any distance. Now Caltech researchers have demonstrated that not just two, but any number of quantum memory devices can be entangled, potentially solving the problem of how to broadcast and copy quantum information among the nodes, or users, of a quantum version of the Internet.
"In a future 'quantum Internet' we could rely on entanglement for the teleportation of quantum states from place to place—a technique could interconnect a cloud of quantum computers," said Kyung Soo Cho, doctoral candidate at Caltech working in the laboratory of Caltech professor Jeff Kimble. "By converting entangled states to an optical signal to propagate we could send secret messages to the whole Internet."
Secret messages that are eavesdrop-proof have already been demonstrated between two nodes—called bipartite entanglement—but by entangling more than two nodes—called multipartite entanglement—the researchers have demonstrated the principle of broadcasting or copying eavesdrop-proof messages to any number of quantum Internet nodes simultaneously.
Massive hardware cools and isolates the nodes of Caltech's seminal quantum network (source: Nara Cavalcanti).
In particular, Caltech scientists used lasers to entangle four memory cells composed of cesium atoms, then later read out the quantum state of the atoms with a second laser—demonstrating that the quantum states of any number of quantum network nodes could be simultaneously transferred. Such techniques will need to be perfected in order to broadcast information on future quantum Internet connections.
Each quantum memory device consisted of 1,000 supercooled cesium atoms, which are confined by a magnetic field and written-to and read-out using a multiple lasers. The specially prepared photons from the communications lasers were able to entangle all four quantum memory devices simultaneously, proving that coherent control of entanglement could be extended to any number of spatially separated quantum nodes of a future quantum Internet.