ABSTRACT – We have built an imaging system that uses a photon’s position or time-of-flight information to image an object, while using the photon’s polarization for security. This ability allows us to obtain an image which is secure against an attack in which the object being imaged intercepts and resends the imaging photons with modified information. Popularly known as “jamming,” this type of attack is commonly directed at active imaging systems such as radar. 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
In conclusion, we have implemented an active imaging scheme that uses quantum mechanical principles to ensure security against intercept-resend jamming attacks. We have also proposed a quantum-secured optical ranging technique. We should point out that our proposed schemes have certain limitations. Our experimental implementation used weak coherent pulses, which makes it susceptible to a photon-number splitting attack, where the jammer splits one or more photons from pulses containing more than one photon. This would allow the jammer to measure these photons in both polarization bases and perfectly replicate the querying pulses. It may be possible to use decoy states to defeat such an attack, as has been demonstrated in QKD. Further, a sophisticated jammer may use quantum teleportation to teleport the polarization state of our querying photons onto photons carrying false position or time information. In practice, however, this would prove extremely challenging, as quantum teleportation involves Bell state measurements, which can only be performed probabilistically in a linear optical scheme. Finally, our protocol does not provide security against attacks that preserve a photon’s polarization state. For example, metamaterials and slow-light techniques can be used to hide an object in space and time without disturbing the polarization of any querying photons. However, these methods are currently in their infancy and only work in extremely limiting cases. On the other hand, given the current state of QKD technology our quantum-secured protocol can easily be realized and integrated into modern optical ranging and imaging systems. Also, the possibility of using other degrees of freedom of a photon such as its orbital angular momentum in a quantum-secured channel may open up exciting avenues for future research.
SOURCES : Arxiv, Technology Review