Can quantum entanglement be used to transmit information between two distant points?
The short answer is no, you cannot send usable (classical) information simply by measuring one half of an entangled pair—at least not in a way that circumvents normal communication channels. Although entangled particles have correlations in their measurement outcomes, these correlations alone cannot be used to transmit messages faster than light or in the absence of a classical signal.
Below is a bit more detail on why:
1. Quantum Entanglement in a Nutshell
- Entanglement is a quantum-mechanical phenomenon where the quantum states of two (or more) particles become linked.
- Measuring one entangled particle appears to “instantaneously” affect the state of the other, no matter the distance between them.
Despite this “spooky” nature, entanglement by itself does not allow you to send classical information (i.e., readable messages) faster than light.
2. The No-Communication Theorem
The no-communication theorem in quantum mechanics states that measurements on one part of an entangled system cannot, on their own, be used to convey information to someone measuring the other part. Here’s why:
Randomness of Outcomes:
- When you measure an entangled particle, the outcome is inherently probabilistic (e.g., spin-up or spin-down).
- You cannot control which specific outcome appears on your side.
Correlations Require Comparison:
- The correlated results between the two entangled particles only become apparent once both parties compare their measurement outcomes (usually via a normal, slower-than-light communication channel).
- Prior to that comparison, each measurement looks random in isolation.
No Faster-Than-Light Signal:
- Since you need a classical channel (e.g., phone, internet, etc.) to compare notes and make any sense of the measurement statistics, the speed of information transfer is limited by conventional communication speeds.
3. Quantum Teleportation vs. “Sending Information”
Quantum Teleportation:
- A process by which you can transfer the quantum state of one particle onto another distant particle.
- This requires both entangled particles and a classical communication channel to work (so it’s still limited by the speed of light for the classical bits).
Entanglement-Based Cryptography:
- Quantum key distribution (QKD) can use entangled states to detect eavesdroppers and secure communication.
- Even so, the actual message is still sent using classical (light-speed-limited) communication, with entanglement ensuring security rather than allowing faster-than-light or no-channel-required messaging.
4. Conclusion
While quantum entanglement allows for fascinating and non-intuitive correlations, it does not enable “instant” or “channel-free” transfer of information. All physically meaningful communication, even in quantum protocols (like quantum teleportation), still relies on a classical signal, and thus remains limited by the speed of light.
disclaimer: this text results from a partnership between the blog author and ChatGPT
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