Quantum networks are closer to reality

When the photon interacts with the quantum memory, it becomes entangled with memory – which means that the measurements made are on the photon Or memory would provide information about (and thus modify) the state of the other.

However, instead of measuring the photon (and therefore extracting the information), the photon undergoes a quantum frequency conversion from the visible frequency (where quantum memory operates) to the telecommunications frequency (where losses in the fiber optical are minimized). The photon (now the telecommunications frequency) then travels back and forth through an underground fiber network before returning to Harvard, where it is converted back to the visible frequency.

Once this journey is complete, the photon bounces onto a different quantum memory in a different laboratory, thus transferring the entanglement of the photon to this second memory. Finally, the photon, after bouncing off the second memory, is then routed to a detector which notes the presence of a photon, but does not reveal any of the underlying quantum information contained in the light. It is entangled in memory, meaning that measuring either the photon or the memory changes the state of the other. The photon then converts from a visible frequency to a telecommunication frequency, which then bounces back to another laboratory, completing the journey.