In order to build a quantum internet – a network that is faster
and more secure than the current internet – the key is the
ability to transmit quantum information between remote quantum
computers (i.e., nodes). The most familiar approach involves
entangling the links between nodes and then using quantum
repeaters at intermediate locations to provide entanglement
swapping, extending the range of entanglement across km-long
networks. In such a system, the performance is inherently
limited by the time it takes to establish entanglement between
nodes. This time is at best the classical signaling time between
the nodes, but with many schemes it is even longer, and
increases as network size increases. Since the qubits that store
the quantum information are unstable and quickly decohere,
quantum memories are required to store quantum information for
milliseconds or longer while they wait for entanglement. The
result is a theoretical limitation on speed due to the system's
design and the need for additional component