4 ms·
Everyone here is getting confused by the fact that you cannot control the polarity/polarization of the qubits before/as you send them. This means that one cann
by eoinmurray92 14y ago
Everyone here is getting confused by the fact that you cannot control the polarity/polarization of the qubits before/as you send them.
This means that one cannot send information faster than light.
What is useful however is the fact that when you send entangled qubits very far away, and measure them is the fact that the results of the measurements are always correlated/anti-correlated.
As an example.
Alice has a pair of entangled qubits, they are in a superposition of 1 and 0 (lets say they are an correlated pair, such that when measured both quibits will always agree).
She sends one to Bob.
Bob and Alice now hold one qubit each out of the entangled pair. They both measure their qubits. The measurement is probabilistic, you have a 50/50 chance of getting a 1 or a 0,
but Bobs quibits and Alices quibit will agree everytime.
Since you can't control the outcome of the experiment you cannot decide which bit to send and hence cannot send information.
The useful result is that Alice and Bob have a string of bits which only the two of them know the arrangement of. They can use the string of bits as a one-time pad for encryption.
I have simplified this immensely but I think the point gets across.
Source : I currently undertake research into generating qubits for quantum computation and communication purposes.
- icambron 14y agoCan you explain the one-time pad application a bit more? It seems to me that if Alice and Bob can share a bunch of entangled qbits, they could just as easily share a classical one-time pad. What am I missing?
- eoinmurray92 14y agoThe key is in the no cloning theorem. If Evil Eve intercepts some of the signal that Alice is sending Bob she will resend incorrect information 50% of the time. In a classical bit stream, ie loads of photons in a fiber or a radio wave, Eve can intercept 10% of the signal without Alice or Bob knowing, and she can recreate and send that 10% perfectly. Alice and Bob can publicly announce measurement bases and a few of the bits to see if the line was touched.
- eoinmurray92 14y agoIm not explaining it very well and its difficult to condense, perhaps I'll write a blog post that goes into more detail for a layman reader.
- icambron 14y agoLet me know if you do; I'm certainly interested.