Question

If, in the Alice and Bob scenario illustrating superdense coding, Alice would be on earth and Bob in another star system, could Bob receive the entangled qubit and would the quantum communication still work like in the original scenario?

Answer 1

In the superdense coding protocol, the standard scenario involves Alice and Bob being in close proximity and sharing an entangled pair of qubits. However, if Alice and Bob are in separate star systems, the practical implementation of superdense coding becomes more challenging due to the constraints of quantum communication and the distance between them.

In the original scenario, Alice and Bob share an entangled pair of qubits, with Alice having one qubit and Bob the other. By applying specific quantum operations on her qubit, Alice can encode two classical bits of information and transmit her qubit to Bob. Bob, upon receiving the qubit, can perform measurements on his qubit along with the one he received from Alice to decode the information she encoded.

In the scenario you mentioned, where Alice is on Earth and Bob is in another star system, several factors come into play:

1. Distance and Quantum Communication: The separation between Earth and another star system introduces significant challenges for quantum communication. Quantum systems are delicate and prone to decoherence and loss of entanglement when transmitted over long distances. Currently, quantum communication over such interstellar distances is not feasible with our current technology.

2. Entanglement Preservation: To perform superdense coding, Alice and Bob require a shared entangled pair of qubits. However, maintaining the entanglement of the qubits over such long distances would be extremely challenging due to environmental noise, interference, and the inability to perform real-time error correction. The entangled state is highly fragile and susceptible to disturbances.

3. Time Delay: The vast distances between the star systems would introduce significant time delays in the communication. This delay could disrupt the sequential operations required for superdense coding, as the quantum operations performed by Alice would need to be coordinated with Bob's measurements. The time delay would also increase the vulnerability to decoherence and loss of entanglement.

In summary, while the concept of superdense coding remains valid in theory, the practical implementation becomes extremely challenging over vast interstellar distances. The constraints of quantum communication, entanglement preservation, and time delay make it currently infeasible to achieve superdense coding between Alice on Earth and Bob in another star system.