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  • aircraft detection using quantum imaging may be unjammable

    Quantum Imaging Technique Heralds Unjammable Aircraft Detection

    December 14, 2012
    MIT Technology review

    Physicists have exploited the quantum properties of photons to create the first imaging system that is unjammable.

    Jamming radar signals is an increasingly sophisticated affair. There are various techniques such as drowning the radar frequency with noise or dropping chaff to create a false reflection. But the most advanced radar systems can get around these ruses.

    So a more sophisticated idea is to intercept the radar signal and modify it in a way that gives false information about the target before sending it back. That’s much harder to outsmart.

    But today, Mehul Malik and pals at the University of Rochester in New York state demonstrate a way to do it.

    These guys base their technique on the quantum properties of photons and in particular on the fact that any attempt to measure a photon always destroys its quantum properties.

    So their idea is to use polarised photons to detect and image objects. Reflected photons can of course be used to build up an image of the object. But an adversary could intercept these photons and resend them in a way that disguises the object’s shape or makes it look as if it is elsewhere.

    However, such a process would always change the quantum properties of the photons such as their polarisation. And so it should always be possible to detect such interference. “In order to jam our imaging system, the object must disturb the delicate quantum state of the imaging photons, thus introducing statistical errors that reveal its activity,” say Malik and co.

    That’s more or less exactly how quantum key distribution for cryptography works. The idea here is that any eavesdropper would change the quantum properties of the key and so reveal his or her presence. The only difference in the quantum imaging scenario is that the “message” is sent and received by the same person.

    Malik and co have tested their idea by bouncing photons off an aeroplane-shaped target and measuring the polarisation error rate in the return signal. Without any eavesdropping the system easily imaged the aeroplane.

    But when an adversary intercepted the photons and modified them to send back an image of a bird, the interference was easy to spot, say Malik and co.

    That’s an impressive demonstration of the first imaging system that is unjammable thanks to quantum mechanics.

    That’s not to say the technique is perfect. It suffers from the same limitations that plague early quantum cryptographic systems, which are theoretically secure but crackable in practice.

    For example, instead of sending single photons, the quantum imaging system sends photon pulses which contain several photons. One or more of these can easily be siphoned away and analysed by an adversary without anybody else being any the wiser.

    However, there are an increasingly wide range of fixes for these problems for quantum key distribution that could help make this quantum imaging system more secure.

    Perhaps best of all, this kind of system could easily be put to work now. The techniques are well known and widely used in optics labs all over the world. So there’s no reason, this security cannot be added relatively quickly and cheaply to existing imaging systems.

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    Warning, speedsters: you can't fool quantum radar

    by Jacob Aron
    14 December 2012
    New Scientist

    Is it a bird, a plane or a speeding car? Police officers might one day be armed with speed guns that cannot be fooled by even the most determined racers, thanks to a new radar technique based on the laws of quantum mechanics. The ultra-secure system could also be used to counter futuristic military cloaking systems that might disguise a plane as a bird.

    Radar and lidar systems bounce radio or light signals off an object and measure how long they take to return. That information can be used to determine the object's position and shape – identifying it as a war plane, say – or to calculate its speed. But both military and police systems can be fooled by devices that generate photons of the same frequency as in the outgoing beam. This is how the speed gun jammers installed in some cars work.

    To reveal when returning photons have been faked, Mehul Malik and colleagues at the University of Rochester, New York, borrowed a trick from quantum cryptography, polarising each outgoing photon in one of two ways according to a sequence.

    Wrong polarization

    Their radar system also measures the polarisations of the returning photons. That forces someone creating a false beam to polarise their photons too – but they need to know the correct sequence. However, if they try to measure the photons arriving from the radar transmitter, quantum mechanics ensures that many of the true polarisations will get lost. So a false signal will always contain more photons of the wrong polarisations than the true beam.

    In lab tests, photons reflected from a cut-out of a stealth bomber had an error rate of less than 1 per cent, while over half the photons created on the fly to mimic the shape of a bird had the wrong polarisation. In quantum cryptography, the same principle reveals if photons encoding a secret key have been intercepted.

    "If it works in practice, it would be super-cool," says Vadim Makarov of the University of Waterloo, Canada. But he warns that reflected photons are more likely to change polarisation outside a laboratory setting.

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    Is there such a thing as unjammable radar?
    Quantum imaging radar seems so.

    by Tibi Puiu
    Mon, Dec 17, 2012
    ZME Science

    Detecting a potential threat before it occurs is the first step to preventing any aggression. In today’s wars, the scales favor the party that controls the air. Dominate the battle in the air, and you’ll dominate the battlefield ground side as well. It’s no secret to anyone that impressive aircraft detection systems have been developed and deployed in the years past, however, every time, a counter was found. Recently, physicists at University of Rochester in New York have unveiled a novel technique based on quantum imaging that is potentially unjammable, making the detection of any object possible.



    The first radar prototype came in 1936 and soon showed its value in the second World War, when it became an invaluable asset to the RAF, and a complete nightmare to the Lufftwaffe during the heavy battles over Britain. Initially radars were based on the clever principle that all metals reflect back radiowaves. For every weapon however, there’s an anti-weapon, and much in the same manner, anti-detection measures were employed and evolved along with radars. This includes drowning radar signals or launching false signals to trick the radars. One modern and highly effective anti-radar technique involves intercepting radar waves, modifying them and sending them back in such a manner that the information presented doesn’t catch the threat.

    Now, Mehul Malik and colleagues believe they’ve developed a system that is able to detect aircraft without the other being capable of countering monitoring. Their technique harnesses the power of quantum imaging. Once a photon is measured, it instantly looses its quantum properties. Research in the field has been used particularly in data encryption, however the Rochester University researchers harnessed these properties in radar imaging as well.

    A radar that can not be fooledBasically, the system works by using polarized photons to detect and image objects. Once they meet an object in the air, they bounce back to form an image. If the aircraft makes an attempt to intercept these photons and change the information it conveys, then inevitably a disruption occurs and this can be registered. It’s pretty clear then for the radar system that something’s out there. The process is irreversible, so the technique is basically unjammable.

    “In order to jam our imaging system, the object must disturb the delicate quantum state of the imaging photons, thus introducing statistical errors that reveal its activity,” say Malik and co.
    Malik and co have tested their idea by bouncing photons off an aeroplane-shaped target and measuring the polarization error rate in the return signal. Without any eavesdropping the system easily imaged the aeroplane, however when the other end tried to alter the signal to send back the image of a bird, the interference was easy to spot.

    It sounds perfect, but it’s not. Since it’s based on the same principles as quantum encryption, which has been around for some time and is still in its incipient age, one can infer the same advantages and disadvantages. It too, like this novel radar system, is uncrackable in theory – in practice not so much. Still this is highly interesting, and armed with such a sophisticated means of detection, countries could protect their boarder a lot better.

    The quantum imaging radar was described in the [1212.2605]Journal Applied Physical Letters.

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    In doing a Google search on this subject, I also saw the book below advertised on Amazon. I don't have a copy, have not read it, am merely posting the link here in case anybody might be interested.

    Last edited by JRT; 18 Dec 12,, 18:42.
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  • #2
    Wow - good read, thanks for posting this.

    I'll need to read this a lot slower as time permits to let it really soak in - it sounds too much like science fiction.
    "Bother", said Poo, chambering another round.

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    • #3
      I remember reading all about quantum cryptography about 10 years ago in Simon Singh's "The Code Book". Amazing stuff, and Simon Singh is an all around excellent non-fiction writer
      Meddle not in the affairs of dragons, for you are crunchy and taste good with ketchup.

      Abusing Yellow is meant to be a labor of love, not something you sell to the highest bidder.

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