Pictures of the Future      Spring 2005

Powered by Einstein

Was Einstein a genius in an ivory tower? This cliché is as widespread as it is wrong. On the contrary, rather than being abstractions, many of Einstein’s ideas can be found in everyday technology, including quite a number of Siemens products. These range from navigation systems—soon to be accurate to within centimeters, thanks to Einstein—to blue laser diodes, which are set to usher in the next generation of data-storage media.

This year, people around the world are commemorating the 100th anniversary of a publication date that stands out in human history. In 1905, Albert Einstein published five works that radically changed our understanding of space, time, energy and matter (see  box). More than anything, it was his theory of relativity that made him one of the strangest of 20th-century icons—a man celebrated for ideas that most of us find incomprehensible. Yet the image of a man married to abstract ideas distorts the picture of a scientist who also had a strong practical bent. Einstein held many down-to-earth patents, among them his invention of a marine gyrocompass, which provided him with a lucrative source of extra income. Moreover, as the man behind the theory of relativity and a pioneer of quantum physics, Einstein has had a profound impact on everyday technology.

Relative Positions. "Take GPS, the Global Positioning System," says IT specialist Torsten Mosis, who develops software for automotive navigation systems at Siemens VDO in Regensburg, Germany. "Through a receiver, it gives your current position, in terms of latitude, longitude and altitude." But a dash of Einstein’s thinking is included in the calculations. Of the 24 satellites in the GPS fleet, the onboard receiver can "see" at most a dozen at any one time. Each of these sends an accurate time signal. The navigation system is therefore able to calculate its distance from a satellite on the basis of the delay that elapses before the signal is received by the car. The information derived from at least four to five satellite signals can then be superimposed to reveal the system’s position to an accuracy of around 20 m.

With the launch of the planned European satellite navigation system, this level of error will decrease to a few meters—and perhaps to as little as 10 cm, if additional equipment is used. However, in line with Einstein’s general theory of relativity, time on board the GPS satellites passes faster than in the receiver on the ground. This is because the latter is situated some 20,000 km deeper in the Earth’s gravitational field. Furthermore, because a GPS satellite orbits the Earth at a speed of around 14,000 km/h, its onboard clock moves marginally slower than the one in the GPS receiver—at least as far as an observer on the ground is concerned. As these two relativistic effects do not absolutely cancel one another out, a GPS satellite’s onboard clock gains almost 40 ms a day. That might not sound like much. But without relativistic correction, it is enough to limit positioning accuracy to 30 m at best.

Onboard GPS systems also run into problems when satellite signals are blocked by road tunnels or corrupted by reflections from high buildings. In such cases, a good car navigation system will fall back on other sensors. The tachometer, for example, measures the distance covered, the transmission reports forward or reverse motion, and a gyroscope signals a change in direction. Using this information, the system can bridge a temporary loss of satellite signal. However, this can introduce new errors. One problem, says Torsten Mosis, is that the tachometer is sensitive to fluctuations in tire pressure. To recognize such deviations, the system has to compare the sensor data with a digital road atlas stored in its memory in a process known as "map matching." However, this too can cause problems, because even the best maps contain inaccuracies.

How, then, can the system still determine what is right? Engineers employ a range of solutions. For example, they equip the navigation system with memory, so that it can remember the most recent vehicle movements and continuously compare them with the map. If the tachometer is off by 10 %, the system recalibrates it. Such sophisticated technology makes fully integrated onboard systems more reliable than retrofitted terminals that can only process satellite signals.

"To build a laser, you basically need a lasing medium, a resonator with mirrors and an energy source," says Dr. Ulrich Steegmüller, a physicist and project manager at Osram Opto Semiconductors, a Siemens subsidiary, in Regens­burg, Germany. His job is to develop lasers from semiconductor crystals, an application that makes practical use of quantum physics. Such crystals only emit light quanta of a particular spectral region. To turn these into a laser beam, the semiconductor must be placed inside an optical resonator consisting essentially of a tube with inward-facing mirrors at either end. The light emitted when electrical voltage is applied to the semiconductor is then reflected back and forth along the tube until it is amplified to the requisite intensity—similar to the howl produced in acoustic feedback.

The two key considerations in the development of semiconductor light emitting diodes (LEDs) are the color of the light and the efficiency with which it is generated. These dictate the nature and composition of the materials to be used. The first LEDs of the 1970s and ‘80s, which were made of gallium arsenide or gallium arsenide-phosphide, produced either red or infrared light. This meant they were only suitable for niche applications. Subsequent increases in the phosphorus content then spawned yellow and green LEDs.

Japanese researchers caused a major sensation in 1993 when they developed a brilliant blue LED made of gallium nitride and then followed it up in 1995 with the world’s first blue laser diode. "Before 1993, we thought that gallium nitride couldn’t be controlled in this kind of environment," says Dr. Norbert Stath, Head of Innovation Management at Osram Opto Semi­conductors. In the ensuing race to close the technology gap, Osram has gained ground. "We’re now one of the leaders in gallium nitride technology, which also plays a key role in white LEDs," says Stath, adding that "We have played a pioneering role in the development of the white LED."

In cooperation with the Fraunhofer Institute for Applied Solid-State Physics in Freiburg and the Universities of Stuttgart, Braunschweig and Ulm, Osram has also been developing blue laser diodes from indium-gallium nitride for several years. The latest prototype can operate for more than 600 hours at 10 mW. While there is also an enormous market potential for normal LEDs, this new type of laser diode is poised to play a key role in the IT industry, where it will greatly enhance the capacity of optical memory media. Compared to the DVD, which uses a red laser diode, the shorter wavelength of the light produced by the new laser diode will make it possible to pack much more data onto a disc. "Everyone agrees that blue-based data media are on the way," says Steeg­müller. "In fact, the first products for professional applications are already here, and mass-market products will follow after 2006. The exact time of market launch depends less on the technical properties of laser diodes and more on commercial aspects such as the development of the DVD market."

Quantum Cryptography. Personal data needs to be confidential. In online banking, for example, information is encrypted with a code before being trans­mitted. Unfortunately, most cryptographic codes can in principle be cracked, albeit with great effort. Quantum cryptography, on the other hand, generates a code that is protected against eavesdropping by the laws of physics. This is because it exploits a special property of quanta by which they can be "entangled" to form a new quantum system. Any attempt to manipulate one of the photons in such a system is immediately registered by all the other entangled parts. This works regardless of how far apart the photons are from one another. Einstein was the first person to identify this amazing consequence of quantum theory.

For him, this also demonstrated the incompleteness of a theory that he never felt at home with. The idea of particles being able to "communicate" with one another over cosmic distances without any delay contradicted his picture of physical reality. Einstein formulated his reservations in 1935 in the form of a famous thought experiment together with physicists Boris Podolsky and Nathan Rosen.

This paradox was to inspire laser physicists for years to come. Finally, at the start of the 1980s, physicists succeeded in actually making a similar experi­ment work. This showed that the mysterious phenomenon that Einstein called "eerie action at a distance" exists and that quantum theory is thus right—contrary to Einstein’s expectations. On the basis of this knowledge, it is now possible to transfer information through a fiber-optic network, using entangled pairs of photons, to a distance of around 100 km. Any attempt to eavesdrop on the data immediately destroys the entanglement and is therefore automatically revealed. A small Geneva-based company is already marketing a commercial system based on this technology. In other words, Einstein’s mistake has borne unexpected fruit.

Computing with Quanta. However, as Dr. Markus Dichtl makes clear, this fruit does not yet include broad-based applications. Dichtl, a mathematician and cryptologist at Siemens Corporate Technology in Munich, takes a keen interest in developments in the field of quantum cryptography and quantum computing. The so-called quantum computer exploits the fact that entangled quantum systems can represent not only the values 0 and 1—as used by conventional computers—but also values in between. If researchers succeed in developing a quantum computer, it will be possible to accelerate the speed of many calculations by a factor of millions. Although such a processor would be unsuitable as a replacement for today’s PCs, it could be used to crack conventionally encrypted codes or search databases at lightning speed. To date, however, physicists have only managed to build very small systems comprising just a few "quantum bits." According to Dichtl, these don’t even "attain the power of an abacus." He therefore doesn’t expect any applications based on this technology to emerge within the next ten years.

Dichtl has identified a fundamental problem of quantum cryptography. Although it offers perfect control over the actual transfer of data, it doesn’t guarantee the authenticity of the sender and the recipient. This only happens when they have a special key that is unavailable to others. But how can this key be securely transferred? While cryptographic protocols could be used to transmit such a key, these function differently from quantum cryptography and are therefore incapable of providing absolutely secure data transfers. This key distribution problem therefore continues to pose a real headache for cryptographers.

Similarly, the physical principle behind quantum cryptography also raises technical issues that are as yet unresolved. For example, individual photons must be able to transfer information undisturbed over long distances. "But 100 to 200 km of optical fiber is about the maximum here," says Dichtl. Transfer over greater distances will require some form of amplification along the way. As yet, however, "repeaters" capable of copying the entangled quantum states and dispatching them on the next stage of their journey don’t exist. In fact, the only solution involves very powerful quantum computers. After all, if normal repeaters were used to decrypt and then re-encrypt the data, the latter would no longer be secure against eavesdropping. It is thus still unclear if and when these two quantum technologies might find their way into everyday applications. Notwithstanding such provisos, an amazing amount of modern technology could still legitimately bear the label "Powered by Einstein."
                                                                                                    Roland Wengenmayr