A quantum network is constrained by two nasty facts of quantum life.
The No-cloning theorem states that it is impossible to create an identical copy of an arbitrary unknown quantum state. This no-go theorem of quantum mechanics was articulated by James Park in proving the impossibility of a simple perfect non-disturbing measurement scheme, [...] It has profound implications in quantum computing and related fields.[...] No well-defined state can be attributed to a subsystem of an entangled state.
Holevo's theorem proves that given n qubits, although they can "carry" a larger amount of (classical) information (thanks to quantum superposition), the amount of classical information that can be retrieved, i.e. accessed, can be only up to n classical (non-quantum encoded) bits. This is surprising, for two reasons: (1) quantum computing is so often more powerful than classical computing, that results which show it to be only as good or inferior to conventional techniques are unusual, and (2) because it takes 2^n complex numbers to encode the qubits that represent a mere n bits.
Other quantum characteristics should also be considered:
- Bell's theorem
- Gottesman-Knill theorem
- Margolus-Levitin theorem
- No-broadcast theorem
- No-communication theorem
- No-deleting theorem
- No-hiding theorem
- No-teleportation theorem
- PBR theorem
- Quantum threshold theorem
Within this incredibly complex system of constraints, it appears quantum networks will have two specialized applications:
1. computation Networked quantum computing or distributed quantum computing works by linking multiple quantum processors through a quantum network by sending qubits in-between them. Doing this creates a quantum computing cluster and therefore creates more computing potential. Less powerful computers can be linked in this way to create one more powerful processor. This is analogous to connecting several classical computers to form a computer cluster in classical computing. Like classical computing this system is scale-able by adding more and more quantum computers to the network. Currently quantum processors are only separated by short distances.
2. communication In the realm of quantum communication, one wants to send qubits from one quantum processor to another over long distances. This way local quantum networks can be intra connected into a quantum internet. A quantum internet supports many applications, which derive their power from the fact that by creating quantum entangled qubits, https://en.wikipedia.org/wiki/Quantum_entanglement
information can be transmitted between the remote quantum processors.