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 2^e, 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.

Read more...

Teleportation becomes a little more real…

Ok, they (Monroe's research group at Joint Quantum Institute) didn’t teleported captain Kirk or Spock, but quantum information of ions, and they did it over 1 meter!! A major implication for future quantum computation and quantum communication... and maybe more if we broke some technological barriers.

As indicated in paper “Quantum Teleportation Between Distant Matter Qubits” [1], Christopher Monroe and his team of the Joint Quantum Institute (JQI) in Maryland, reported the teleportation of quantum information between atomic quantum memories separated by 1 meter. A quantum bit (qubit) stored in a single trapped ytterbium ion (Yb+) is teleported to a second Yb+ atom with a measured average teleportation fidelity of 90% +/- 2% over a replete set of states. The teleportation protocol is based on the heralded entanglement of the atoms through interference and detection of photons emitted from each atom and guided through optical fibers.

Let me reminds you some basic concepts in order to continue.

What’s a Qubit? Just as a bit is a basic unit of information in the digital world, a qubit is a unit of information in the quantum world. You know very well that a bit ca be either a 0 or a 1. Qubit can be both 0 and 1 at he same time (superposition property).

© www.spectrum.ieee.org

What’s about quantum entanglement? Quantum entanglement is a quantum mechanical phenomenon in which the quantum states of two or more quantum particles (photons of light or atoms, for example) are linked together so that one object can no longer be adequately described without full mention of its counterpart (even though the individual objects may be spatially separated). You can then separate them as far as you like, and a change in one is instantly reflected in the other.

In the Monroe's experience, two ytterbium ions were trapped in two different cavities separated 1 meter away. The first has a qubit of information and then, thanks to a laser pulse, it was entangled with the second ion present in the other remote ion trap.

Looking at the first ion, a superposition state is destroyed, causing the emission of a photon which can have two possible states of energy. The information carried by the first ion is then destroyed, but because of the entanglement of this ion with the second, the status of the second ion is changed in order to registers the information found in the first ion.

Depending on the photon energy emitted by the first ion, we know what kind of operations can be subjected to the second one to return information about the first ion. The researchers found that there had been teleportation of quantum state of the ion on the first second.

A similar experiment was already conducted in 2004 with ions but teleportation had been made on microscopic distances. Teleportation of quantum states had already been implemented, too many years ago, over long distances but with photons. It is therefore the first time a teleportation of quantum states with the matter on macroscopic distances has been conducted.

If we talk about the applications of entanglement and quantum teleportation, we could imagine (1) teleporting quantum information instantaneously at any distance (quantum communication faster than light), (2) to achieve the exponential processing speed-up promised by quantum computation, (3) to conceive unbreakable encryption.

You noted that I didn't mentioned the quantum teleportation of non living objects or living beings. The quantum teleportation has been done for microscopic distances with large molecules, similar in size to a bacterium, so it’s possible that we could teleport something living. Someones says that it won’t work with something as big as a person. You would have to scan every single molecule in the body and reassemble at the other end, which doesn’t look like it’s every going to be practical [3].

Factually, the teleportation as we know popularly from Star Trek will not be possible (at least in the short run). Teleportating a human being would require an enormous calculation capacity: in a human body of 70 kg there're ~7 x 10^27 atoms, that's seven billion billion billion atoms, that's a 7 followed by 27 zeros! [4]. Today's fastest parallel computing operations are capable of teraflop speeds (as the computer used for lattice QCD computations). So for a computer that can handle 200 teraflops (that's 1 x 10^12 operations per second) to simply pass this much information would require a little more than 1 million years (1109843 years). Another problem, storing and retrieving data : assuming that 1 atom implies 1 byte, even with the best hard disks (2 Tera-byte of capacity) we would need 3,5 x 10^15 hard disks !!

Finally, if we broke these technological barriers in the future, maybe the teleportation of human beings will be possible. As Michio Kaku writes in his book "Physics of the Impossible", applying the process of quantum entanglement to larger objects like people is just a scientific "engineering problem", that is likely to be solved in time.


References:

[1] Quantum Teleportation Between Distant Matter Qubits, S. Olmschenk, D. N. Matsukevitch, P. Maunz, D. Hayes, L-M. Duan, C. Monroe. Paper available at http://www.iontrap.umd.edu and publied in SCIENCE (www.sciencemag.org) 23 january 2009 (Vol. 323).

[2] JQI News. Available in http://www.jqi.umd.edu

[3] Interview to Brian Clegg (The God Effect : Quantum Entanglement, Science’s Strangest Phenomenon) at http://calitreview.com/51

[4] Nanomedicine, by Robert A. Freitas Jr (1998). Available at http://www.foresight.org/Nanomedicine/Ch03_1.html

Read more...