Unequivocal security, unlimited devices, potentially unlimited distances, and unimpeded paths make quantum communications for the IoE the next big thing.
The principle of quantum communication (QC) is that it can transfer a quantum state between locations. The significance of that cannot be overstated. This is what we can look to for the delivery of the super-secure communications networks of the future.
This kind of secure communications is made to order for the IoE (and, of course, many other platforms). No matter how simple or complex the IoE object is, it can be secured with a quantum key. Even better, the key doesn’t have to be uber-secure. The fact that any quantum relationship reveals that is has been observed means that even a simple two-bit key is workable for some applications. Most of us don’t really care what simple data a smart sock contains, but we do care if it is compromised and acts as a conduit to critical data.
By putting quantum keys on everything out there, probably the single most fearsome threat in the universe has been rendered moot. That’s simple enough in theory, not so much in practice. We are a long way from deploying even the most basic of quantum cryptography in a ubiquitous fashion, but the theory is sound and discussions around it are exciting – and it will happen.
What is so exciting about QC is that it removes the ability for a hacker to eavesdrop on a system and obtain the “secret” key that secures the communications. No matter how complex or convoluted the key is made, it can be compromised. QC eliminates that issue by what is called quantum key distribution (QKD). QKD security is created when random data is encoding on individual photons quantum state. Then, these photons are transmitted over a quantum channel.
It works like this. Let’s say a hacker tries to take a measurement on a qubit that is in a particular state of superposition. When that attempt is made, the quantum system will be altered, and changed, or reduced to one of the two possible states, by the hacker’s detector. This disruption to the original state will show up as up as an increase in the quantum channel bit error rate (BER), and alert the user that there is a presence on the quantum channel.
While most of the readers of this publication are likely aware of the theories around quantum theory (or mechanics/physics), before we delve into how this works, it might be in order to present a brief discussion on the principles of quantum physics that makes QKD possible.
There are two fundamental quantum theory principles. One is the wave-particle duality theory that presents the concept that quanta exhibit both wave- and particle-like behaviors. Wave-like behaviors are those such as refraction. Particle-like behaviors include such concepts as particles cannot be in two places at once, and they cannot share space with another particle. The duality principle is often debated as to its validity, and is said to exist only when certain things occur, such as when a wave function collapses or two quanta interact.
However, the second principle, the uncertainty principle, is much more valid and relevant to communications. It states that any attempt to measure any attribute, such as velocity, position or spin, will affect a change other attributes. It also involves superposition—the existence of certain relations among states—and observer status. Observation will cause the wave function to collapse to a specific state.
As it turns out, the uncertainty principle is exactly what the doctor ordered for quantum communication security. In a nutshell, if there is any action upon the QKD, it changes the quantum state that the photons that are placed in, which is characterized by the cryptographic key. Any attempt to intercept or view the key alters the quantum state, which immediately points to a security breach and renders the key useless. “This remove this weakest link of the current system”, says Grégoire Ribordy, co-founder and chief executive of ID Quantique.
Quantum communications 101
QC uses quantum physics’ entanglement and other nonlocal characteristics to transfer the quantum state of photons from one location to another. While quantum theory may be the pièce de résistance of secure communications, it is far from being ready for prime time. So far, the only success has been with photons versus atoms or ions, and only in the lab or other experimental environments. It sounds simple enough to send photons as a one or zero, so that if disturbed that state will be altered. But making that actually happen turns out to be not so simple.
The biggest challenge in photon-based schemes is the fact that photons disappear in the quantum channel. If the medium is fiber, they get absorbed or get scattered. In a free space medium, such as lasers, there is no birefringence. The distance is greater, but the photons are still subject to intense backlight, diffusion and absorption, atmospheric turbulence, and decoherence. Until these issue are overcome, space-based quantum communications remains on the test bed.
That doesn’t mean there aren’t successes. They process has been proven to work. At the end of the last decade, there were successes in setting up quantum channels. These experiments have shown that cryptographic keys can be distributed over tens of kilometers, maintaining quantum entanglement, and the observation properties required for secure communications. So we know it can be done. Tens of km is now, tens of thousands is the sweet spot (the top goal is to hit the geostationary satellites just under 36,000 km). Channels have to be able to reach satellites for practical applications. The current record is just over 144 km [see reference 1], which is several years old, and new work being done by both China and the United States that is looking a fiber channels up to 10,000 km in the near future.
Drilling down on challenges
Quantum physics has the unique capability to deliver, from one point to another, strictly correlated strings of bits. These strings come with the explicit assurance that there is no copy of these bits anywhere else in the universe. That is by the laws of nature, and does not rely on mathematical assumptions. This makes it the perfect storm – two strings of correlated bits can offer unequivocally secure keys with 100% guarantee the keys cannot be leaked.
But to get this ready for prime time means overcoming some huge challenges. One is isolation of the propagation channel. If quantum objects interact with the environment, they lose their quantumness, and revert to becoming classical objects.
Earth’s atmosphere will absorb most of the photons transmitted from the ground. The further the distance, the more absorption occurs. One experiment, which was done to see if longer distances can be achieved, used the theory that each pulse will have a precise number of photons. This number would be such that, on average, only a single photon would reach the satellite and be reflected back to Earth. The gotcha is “on average.” To make this reliable would mean that a methodology would have to be devised to make the reliability much higher, not just N number of pluses and catch a single photon every now and then. Still, it proved that it can be done.
Another challenge is distance, not just from Earth to a satellite, but from point to point on Earth. This can be overcome with the use of repeaters, and free-space optics (FSO) over which the entanglement can be teleported. While this might be practical for terrestrial links, it won’t work for the space-based distances.
How it might work
Optical fibers and free space are the two media through which photons can propagate. For optical fiber the frequencies are 1300 and 1550nm, while for free space the most desired are 800nm or longer wavelengths from 4 to 10 microns (4,000 to 10,000nm).
One particular experiment used a pair of telescopes set up in a binocular fashion. They were pointed at an orbiting satellite about 400 km away. In this particular case a satellite was chosen that could bounce a laser beam back to Earth to its original positon. Then one telescope was used to shoot a pulse at the satellite while the second was used to observe the reflection.
Simple in theory, but as was discussed earlier, it turns out the majority of the pulses are lost. Here each pulse was beamed out with about 1 billion photons and only one, if any, started the return journey. Not only are most of the photons lost leaving the earth, but reciprocally, just as many would be lost on atmospheric re-entry.
So the ensuing work turns up some inserting metrics. It seems that it takes several billion pulses per second to get a respectable return. According to Jian-Wei and Co., one of the experimenters, it takes that many outgoing pulses to get about 600 returning photons per second. And, says Wei, “These results are sufﬁcient to set up an unconditionally secure QKD link between satellite and earth, technically.” However, this is all still on paper and nothing has been actually developed to support these results.
The relationship between QC and entanglement
One of the most interesting phenomenon is entanglement and how it enables QKD. Quantum entanglement is a physical phenomenon that says that certain generated groups or pairs of particles can be bound in such a way that the individual particles cannot be described independently. The only way to describe them is to give them what is called a “quantum state,” which describes the makeup of the systems or groups/pairs of, in this case, photons. The various properties of entangled particles – spin, momentum, polarization and position— are expressly correlated with each of the individual particle.
For example, say a pair of photons is entangled in such a way that one of the properties, spin, is known to be zero. That means that they are axial opposites. If the spin of one of the particles is clockwise, the other must be counterclockwise.
In QKD, such a system can be used to define a bit within a cryptograph key. This process is simply repeated for however many bits are desired. And, as was discussed earlier, any attempt to view this entanglement will “act” upon the particle and collapse the state. Voila! Unbreakable cryptography.
As was noted by Bruce Potter, CTO of the KEYW Corp., “quantum cryptology (and its crypto components) is a mind-bending concept that baffles even the most experienced scientists. Those who try to understand what’s going on are stymied by the diversity, age and code complexity of the various software components. And, while cryptographic core algorithms have been well studied, other components in enterprise cryptosystems are less understood. It’s no wonder this field of science incites so much controversy.”
What else holds so much promise and excitement as quantum anything? It has the potential to revolutionize and secure communications, and that is only a small vector.
In the future it will be possible to send totally secure, hack-proof messages around the planet. This has tremendous implications for governments, the military, commercial organizations such as bank, and, the next great enabler, the IoE. And, such communications can be totally independent of the Internet.
And this is just the tip of the iceberg. Researchers in quantum entanglements are looking at elements such at time and energy as entanglement options as well as polarization.
What all this will look like 10 years from now is hard to predict. But once there are some real-world working applications, the sky will be the limit and you’ll be able to freely give out your credit card data.
Reference 1. R. Ursin, F. Tiefenbacher, T. Schmitt-Manderbach, H. Weier, T. Scheidl, M. Lindenthal, B. Blauensteiner, T. Jennewein, J. Perdigues, P. Trojek, B. Oemer, M. Fuerst, M. Meyenburg, J. Rarity, Z. Sodnik, C. Barbieri, H. Weinfurter, A. Zeilinger, Free-space distribution of entanglement and single photons over 144 km, Nat. Phys. 3, pp. 481, 2006.