back to article Just like knotted-up headphones: Entangled photons stay entwined over record distance

Pairs of entangled photons created on a satellite orbiting Earth have survived the long, perilous trip from space to ground stations. Crucially, they are still linked despite being picked up by receivers over 1,200km (745mi) apart – the longest link ever seen before. “This is a scientific breakthrough,” says Rupert Ursin, a …

  1. Anonymous Coward
    Anonymous Coward

    FTL Comms?

    Can you encode data at one ground station and have it immediately received at the other? There are share dealing companies that would pay a fortune to transport their data faster than their competition.

    1. J4

      Re: FTL Comms?

      IANAQP but I believe it would be possible to transmit stock price info this way. It doesn't break FTL because the initial deployment of the split pair is at light speed.

    2. Destroy All Monsters Silver badge

      Re: FTL Comms?

      Can you encode data at one ground station and have it immediately received at the other?

      No.

      We are talking correlation only, never information transfer.

      1) Arrange to create a single quantum system, from which you can split off two qubits

      2) Transport qubits to where the business ends are: A. B

      3) Extract classical bit from qubit 1 on location A at time T1: cbA. This is a random bit.

      4) Extract classical bit from qubit 2 on location B at time T2: cbB. This is a random bit.

      5) However we have correlation: cbA = ~cbB (so it's "correlation at a distance", not "action at a distance")

      6) If QM is correct, the "single quantum system" effect holds over arbitrarily large distances, and even across time (whatever T1 and T2 are, and they can be exchanged due to special relativity)

    3. Destroy All Monsters Silver badge

      Re: FTL Comms?

      Here is tha article on "correlation across time", the universe is fun (maybe actually a database doing full convolution with itself everywhere anytime, shame about the 3D+1 illusion?):

      Quantum Weirdness Now a Matter of Time

    4. TitterYeNot

      Re: FTL Comms?

      "Can you encode data at one ground station and have it immediately received at the other? "

      In a word, no. This is sending data via a laser, so the time taken for the data to get from orbit to the ground station will be the same as any other optical communication.

      The difference here is that some of the photons sent by the orbital laser are entangled pairs (created in the same event in the laser), and the ground receiver is equipped to be able to identify and read the state of entangled photons.

      My (limited) understanding is that if you consider a particular property of a transmitted entangled pair (e.g. polarisation), while in transit both photons will be in a quantum state, neither polarised in one direction or another. However, once they are detected (i.e. 'observed') by hitting a photoreceptor, they reach a non-quantum state, and become polarised. Depending on the type of entanglement, a pair's photons will have either the same or opposite polarisation as one another.

      This allows detection of an interception attempt. If a pair of received photons have not been intercepted, they will still be entangled when they hit the receiver, and so will always have, for example, opposite polarisation when they leave the quantum state. If one or both of the photons has been intercepted in transit, it/they will have already left the quantum state at some point and will no longer be entangled, so when they hit the ground receiver some will have the same polarisation, and some have different polarisation. That's when you know that someone has potentially fiddled with your data stream and you do not trust it.

      I know it doesn't seem to make much sense, but this is the fun world of quantum mechanics. We know quantum theory is valid due to experiments in the lab and real life examples (i.e. semiconductor technology, and nuclear fusion due to quantum tunnelling in the Sun), just not really why...

  2. J4

    King's speech, 2021

    "And my government will bring forward legislation to ban the evil machinations of quantum physics, and prevent its support for terrorists and their ability to use secure communications"

  3. DougS Silver badge

    May not be useful for communication

    But 1 bps isn't a problem for guaranteed secure key distribution.

  4. Pen-y-gors Silver badge

    Daytime?

    "Next step is to get it working during the day"

    I love it!

  5. frank ly Silver badge

    "(you could think of the direction of a bar magnet)"

    If they're entangled, can they be separated with a big magnet?

    1. Pompous Git Silver badge

      Re: "(you could think of the direction of a bar magnet)"

      "If they're entangled, can they be separated with a big magnet?"
      Wrong part of the Internet to ask that. Try putting the question to Schrödinger's cat/kittens.

  6. Winkypop Silver badge
    Coat

    May and Trump issue Interpol arrest warrant

    Mr A. Einstein for aiding terrorists through unbreakable encryption!

    --> lab jacket

    1. malle-herbert Silver badge
      Coat

      Re: May and Trump issue Interpol arrest warrant

      Einstein was one of the few scientists who actually thought quantum physics was bullsh*it....

      1. Pompous Git Silver badge

        Re: May and Trump issue Interpol arrest warrant

        "Einstein was one of the few scientists who actually thought quantum physics was bullsh*it...."
        Not really. Einstein disagreed with quantum mechanics (Niels Bohr). It was Einstein's work* that gave us quantum physics.

        * And his many predecessors of course.

  7. SkippyBing Silver badge

    I for one

    Demand the government legislate to have a back door put in quantum encryption to keep us safe from the terrorists.

  8. Novex

    Er...

    ...why not put the receiving stations in space as well as the 'transmitter'? Then surely day/night and other interference won't be an issue...?

  9. Peter Fairbrother 1

    Two issues

    First: "The problem is that if you try sending quantum bits through the air or through fiber cables, losses are high"

    That is not what they are doing - they are sending entangled photons, not quantum bits, which are a very different thing.

    Second, this isn't really much use for cryptographic purposes - in order to get even 1 bit per second they need a separate secure channel (which can be hacked), and if that channel hacking is combined with photon emitters the system as a whole can be spoofed into thinking two non-entangled photons created by man-in-the-middle Mallory are an entangled pair.

    However it is interesting as a demonstration of spooky action at a looong distance.

  10. King Jack
    Boffin

    The Wright brothers

    I bet in their time they were laughed at because their machine could only fly a very short distance, and would never be practical. Fast forward 80 years and men were walking on the Moon. Give this Spooky Magic a few years then let the real potential revel itself. My betting is Idiots in power will have a 'book burning' to make it all vanish to keep us all safe. Science must be stopped!!

  11. Axman

    Wait a second!

    Am I the only one here who doesn't understand this?

    They're creating millions of pairs of photons and recording one a second that are 'entangled'!

    How do they know that these,the ones claimed to be entangled, aren't just random associations? I've got to admit I'm entirely baffled by this entire 'technology'.

    1. Pompous Git Silver badge

      Re: Wait a second!

      "Am I the only one here who doesn't understand this?"
      No, understanding quantum entanglement is difficult. As my first year philosophy lecturer put it, "If your brain's not hurting, you're not thinking hard enough". But if you're up for it:

      Quantum Entanglement and Information

  12. John Smith 19 Gold badge
    Unhappy

    Very impressive but a bit sad.

    Yes the FTL aspect sounded quite attractive.

    OTOH the idea of "perfect" reception would also have been quite attractive. Being able to get all of the data off the recent Pluto probe while it continued on out into space, regardless of data rate.

    It's looking like the only viable application for this technology is sending the keys for a private key crypto system in a way that cannot be tapped without showing its been tapped.

    1. Destroy All Monsters Silver badge

      Re: Very impressive but a bit sad.

      Magic is for the movies.

      Now watching STALKER. Now that's magic, and it doesn't even help.

    2. Pompous Git Silver badge
      Facepalm

      Re: Very impressive but a bit sad.

      "It's looking like the only viable application for this technology is sending the keys for a private key crypto system in a way that cannot be tapped without showing its been tapped."
      Cue May, Trump, Turnbull... proposing laws banning quantum entanglement.

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