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April 3, 2011

The future of radar systems : Quantum illumination


Using entangled photons should be possible to improve considerably the data transmission. Raytheon BBN is studying new quantum concepts as quantum illumination for using in remote sensing applications. The development of such concepts would allow Radar, Laser Radar (LADAR), and other remote sensing systems to exceed the performance limits of today’s technology.

Actually traditional methods of data transmission, such as fibre optics or laser-based radar, require 100 photons to transmit a single bit of data. Using quantum illumination should be possible to sent 10 bits on a single photon. This discovery was announced theoretically by Seth Lloyd of the W.M. Keck Center for Extreme Quantum Information Processing (xQIT) 3 years ago. Here after the abstract of his paper Quantum Illumination :

Abstract: The use of entangled light to illuminate objects is shown to provide significant enhancements over unentangled light for detecting and imaging those objects in the presence of high levels of noise and loss. Each signal sent out is entangled with an ancilla, which is retained. Detection takes place via an entangling measurement on the returning signal together with the ancilla. Quantum illumination with e bits of entanglement increases the effective signal-to-noise ratio of detection and imaging by a factor of 2e, an exponential improvement over unentangled illumination.

It's all about entanglement. In this phenomenon when you have a pair of photons the quantum state of one photon is linked to that of another, regardless of how far apart they are. Quantum illumination begins with researchers passing a laser through filters that thin the beam into photons. The filters create identical photons that are linked to each other. Then they split the entangled photons and release one at a target, while the other is keeping near the transmitter. When a photon hits the target, it bounces back towards the source in a process that alters the photon. When it returns to the detector, the altered photon is no longer strictly entangled with its pair, then scientists compare the released photon’s reflection to its unaltered twin. This process is not very different from classical radar, where electromagnetic waves rebound off targets in order to create an image. However the smaller photon delivers far more data far more quickly and efficiently.

As said by researchers at Raytheon BBN, quantum illumination could be used to create hyper-long-distance communications systems where large amounts of information could be sent more quickly (almost instantaneously) and clearly. Some enthusiastic researchers suggest that quantum illumination could lead towards teleportation devices. That's right, but only for information. Star Trek's teleportation of people and objects remains on Science Fiction for the moment...

A definition for quantum illumination which comes from paper Quantum Illumination by Seth Lloyd :

Quantum illumination is a potentially powerful technique for performing detection and imaging, in which signal is entangled with an ancilla, and entangling measurements are made at the detector. Entanglement enhances the effective signal to noise ratio because a noise photon has a d times harder time masquerading as an entangled signal photon, compared with a noise photon masquerading as an unentangled signal photon.
The enhancement of sensitivity and effective signal-to-noise ratio that quantum illumination provides is exponential in the number of bits of initial entanglement, and persists even in the presence of large amounts of noise and loss, when no entanglement survives at the receiver.


Eric Delalonde April 6, 2011 at 12:56 PM  

Bonjour Martin, Congratulations for this article and the blog I discovered at once! I'm afraid not to understand much of it but I appreciate your sense of humor and energy.

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