3 ms·

Teleportation is not possible. Quantum teleportation is the transmission of the exact state of a photon from one place to another. Still, even this happens at

Teleportation is not possible. Quantum teleportation is the transmission of the exact state of a photon from one place to another. Still, even this happens at less than the speed of light. Otherwise it would violate causality. The media plays fast and loose with terminology either out of plain ignorance or the desire to sell a story.

danharaj 10y ago
There is nothing else about a photon that could be teleported.
ctrl-j 10y ago
> Teleportation is not possible. Quantum teleportation is the transmission of the exact state of a photon from one place to another. Still, even this happens at less than the speed of light. Otherwise it would violate causality. Maybe I'm remembering my QED special topics class incorrectly, but I thought the state teleportation is believed to be instant. The problem is to extract the state information, the transformation operators still need to be communicated. So you still have to get on the phone to tell your colleague across the planet what to do to see the entangled result. It's been years, so maybe I'm a little off on that? Causality also isn't a hard-and-fast law. We've just never seen it violated before. It's one of those physics problems that is really hard to find evidence to support or discredit it.
- Skunkleton 10y ago
  So many advancements in physics have been the result of a smart person abandoning some "law".
  - jerf 10y ago
    Usually, in the process, discovering a deeper and stronger law. I understand the temptation to think that every "law" is just waiting to be broken, but I can easily read the same data and come to the opposite conclusion about the strength of our current "laws".
josu 10y ago
>this happens at less than the speed of light. Why can't it happen simultaneously? Why is distance relevant in this case?
- tgb 10y ago
  As I always bring up in these threads, quantum teleportation requires the transmission of classical bits, which of course is done slower than the speed of light.
  - jdmichal 10y ago
    As far as I know, ctrl-j [0] is correct. The quantum entangled state transfer may be instantaneous. However, this merely results in a correlation of measurements. In order to determine a correlation, you need to have both measurements to compare. This is the part that must be transferred classically. See my top-level post for more information [1]. [0] https://news.ycombinator.com/item?id=12548712 https://news.ycombinator.com/item?id=12548712 [1] https://news.ycombinator.com/item?id=12548733 https://news.ycombinator.com/item?id=12548733
    - tgb 10y ago
      The second photon that the first's state is being teleported to is constructed by performing certain operations on it and which ones are performed are determined by the two classical bits that are measured from the first photon (hence destroying the firsts's state). So from the first photon being destroyed to the second gaining its state, there must be a speed of light delay as those two classical bits are transmitted.
      - jdmichal 10y ago
        > So from the first photon being destroyed to the second gaining its state, there must be a speed of light delay as those two classical bits are transmitted. This is the part where you are potentially wrong. Entanglement is about correlation. In order to derive the original message, you need the local entangled state, along with data from the remote actor. You could then correlate this information to derive the original remote entangled state -- ie, some message. Of course, this is now useless to you, as they could have simply sent the original message and saved you the correlation step. However, I don't know of any reason that the local quantum state could not be measured prior to the arrival of the data from the remote actor. The math says that the measurable effect should happen instantaneously. But that data alone is not sufficient to derive a message.

danharaj 10y ago

There is nothing else about a photon that could be teleported.

ctrl-j 10y ago

> Teleportation is not possible. Quantum teleportation is the transmission of the exact state of a photon from one place to another. Still, even this happens at less than the speed of light. Otherwise it would violate causality. Maybe I'm remembering my QED special topics class incorrectly, but I thought the state teleportation is believed to be instant. The problem is to extract the state information, the transformation operators still need to be communicated. So you still have to get on the phone to tell your colleague across the planet what to do to see the entangled result. It's been years, so maybe I'm a little off on that? Causality also isn't a hard-and-fast law. We've just never seen it violated before. It's one of those physics problems that is really hard to find evidence to support or discredit it.

Skunkleton 10y ago
So many advancements in physics have been the result of a smart person abandoning some "law".
- jerf 10y ago
  Usually, in the process, discovering a deeper and stronger law. I understand the temptation to think that every "law" is just waiting to be broken, but I can easily read the same data and come to the opposite conclusion about the strength of our current "laws".

josu 10y ago

>this happens at less than the speed of light. Why can't it happen simultaneously? Why is distance relevant in this case?

tgb 10y ago
As I always bring up in these threads, quantum teleportation requires the transmission of classical bits, which of course is done slower than the speed of light.
- jdmichal 10y ago
  As far as I know, ctrl-j [0] is correct. The quantum entangled state transfer may be instantaneous. However, this merely results in a correlation of measurements. In order to determine a correlation, you need to have both measurements to compare. This is the part that must be transferred classically. See my top-level post for more information [1]. [0] https://news.ycombinator.com/item?id=12548712 https://news.ycombinator.com/item?id=12548712 [1] https://news.ycombinator.com/item?id=12548733 https://news.ycombinator.com/item?id=12548733
  - tgb 10y ago
    The second photon that the first's state is being teleported to is constructed by performing certain operations on it and which ones are performed are determined by the two classical bits that are measured from the first photon (hence destroying the firsts's state). So from the first photon being destroyed to the second gaining its state, there must be a speed of light delay as those two classical bits are transmitted.
    - jdmichal 10y ago
      > So from the first photon being destroyed to the second gaining its state, there must be a speed of light delay as those two classical bits are transmitted. This is the part where you are potentially wrong. Entanglement is about correlation. In order to derive the original message, you need the local entangled state, along with data from the remote actor. You could then correlate this information to derive the original remote entangled state -- ie, some message. Of course, this is now useless to you, as they could have simply sent the original message and saved you the correlation step. However, I don't know of any reason that the local quantum state could not be measured prior to the arrival of the data from the remote actor. The math says that the measurable effect should happen instantaneously. But that data alone is not sufficient to derive a message.