Quantum Computing

Quantum Computing

Fury of the Quantum Fist
Quantum mechanics will be our most powerful tool in the world of tomorrow. For those of you that did not know this, quantum mechanics is a physics system or theory using the assumption that energy exists in discrete units. It is probably no exaggeration to say that quantum mechanics is the most successful scientific theory in history. This has been a great success, but in spite of the fact the origins of the quantum theory stretch back nearly a century, it is only in recent years that the general public has become aware of the subject. Indeed, until a few years ago, the very word quantum was almost unknown outside the scientific community. Now books with �quantum' in the title are absurdly numerous.
The reason for this recent surge in interest can be traced to the truly strange nature of quantum mechanical ideas. Quantum physics amounts to much more than a theory of atomic and subatomic processes, it represents nothing less than a complete transformation of our world view. "Its [quantum physics] implications for the nature of reality and the relationship between observer and observed are both subtle and profound. (Barenco)"
A description of the world in which an object can apparently be in more than one place at the same time, in which a particle can penetrate a barrier without breaking it, in which something can be both a wave and a particle, and in which widely separated particles can cooperate in an almost psychic fashion, is bound to be both thrilling and bemusing. Niels Bohr, one of the founders of the theory, once remarked that anybody who is not shocked by quantum mechanics hasn't understood it.
For decades the complexity and incredibility of the quantum world was an obstacle to the theory being known outside the scientific community. Then in the 1970's a number of writers recognized that the deep philosophical implications of quantum mechanics would be of considerable interest to the wider public, especially as some of the quantum mechanics concepts were of a mystical origin. In addition, technological advances enabled certain key ideas of the theory to be tested in the laboratory for the first time, amid considerable publicity.
Although this broader interest was largely stimulated by the philosophical implications of the subject, the practical applications of quantum mechanics had been going from strength to strength. What the public perceived as primarily a set of revolutionary speculations about the nature of reality, professional physicists and engineers regarded as a means to make new devices and handsome profits.
In fact, quantum mechanics has always been a very practical subject. Even in the early years before the Second World War, its principles were applied to the electrical and thermal properties of metals and semiconductors. In the postwar years, the development of the transistor and the laser--two of the best-known quantum devices--heralded the information revolution.
Today we are surrounded by technology that owes its existence, directly or indirectly, to the applications of quantum mechanical processes. Everything from the CD player to non drip paint to car brake-lights, from MRI hospital imaging machines to the scanning tunneling microscope, quantum technology is now a serious money making business.
Looking ahead to the next fifty years, quantum technology offers some breathtaking possibilities. The field of nanotechnology is very promising. The goal of scientists researching nanotechnology is the construction of machines with molecular dimensions. This means that machines utilizing nanotechnology will be very small or microscopic. These machines will have potential applications in many fields such as medicine, computing and the fabrication of new and exotic materials. Quantum technologists can already trap individual atoms and experiment with them. "Quantum technologists can bounce atoms up and down on cunningly sculpted electromagnetic fields, produce atomic graffiti by displacing single atoms on a material surface, and display the structure of a crystal atom by atom. (Benjamin)"
These experiments probe the deep quantum regime, where Heisenberg's uncertainty principle and other aspects of quantum outlandishness significantly shape the restrictions and possibilities. The commonsense world of Newtonian machines is left far behind. This is the domain of undreamt possibilities, of microscopic circuits with novel electrical properties, of detectors so sensitive that they could pick up the equivalent of the drop of a pin on the other side of the earth, of devices to make and break codes that no conventional supercomputer could touch.
Consider, for example, the bizarre properties of the quantum vacuum. Normally we visualize empty space to be just that--a featureless void. But the quantum vacuum, though devoid of ordinary particles, nevertheless seethes with ghostly activity, as so-called virtual particles, spontaneously and unpredictably appear out of nowhere, only to survive fleetingly before disappearing into nothing once more.
This ubiquitous, restless vacuum texture has immense implications. Cosmologists believe it may have been responsible for creating the entire universe. Stephen Hawking believes it will cause black holes to evaporate away into heat radiation. In the laboratory it shows up as slight but measurable shifts in the energy levels of atoms. More importantly, the quantum activity of the vacuum introduces a very fundamental source of noise into many practical devices. To evade this noise requires scientists to develop ways of manipulating the quantum vacuum. Advances with lasers have enabled the vacuum noise to be "squeezed" or quieted below the natural background level, opening up the possibility of transmitting or detecting signals with unprecedented sensitivity.
Perhaps the most exciting and most powerful device on the quantum technology drawing board is the quantum computer, a machine that would be able to perform mathematical manipulations that are impossible, even in principle, on a conventional computer. In effect, a quantum computer could process information in many alternate realities simultaneously, and integrate them into a single real-world answer, enabling nothing less than a totally new type of mathematics at our disposal.
Indeed, all quantum systems essentially exploit the fact that the quantum microworld has no single, well-defined reality, but is a ghostly amalgam of alternate universes, a hybrid world in which possible realities merge and overlap to produce a final observed actuality. Quantum technology turns this unbelievable fantasy realm of mind-bending concepts into concrete, practical devices.
The nineteenth century was known as the machine age, and the twentieth century will go down in history as the information age. Unless we develop something better than quantum mechanics, however unlikely, the twenty-first century will be the quantum age. We must acknowledge the great benefit that quantum devices will bring, no matter what the cost.
Imagine a computer whose memory is exponentially larger than its apparent physical size; a computer that can manipulate an exponential set of inputs simultaneously; a computer that sets itself apart from our classical examples of a computer. The computer you imagine is a quantum computer. It has immense capabilities and enormous power. This computer would be able to solve many of our problems, including many problems that had not even surfaced yet. We must endeavor to overcome the obstacles that lie before us and construct our solution to everything.
One of the many obstacles that stand in our way presently is the Shor algorithm. The Shor algorithm involves factorizing very large integers. It's not that our computers can't factor integers, it's because it would take many years for even our best supercomputers to factor these large integers. We've tested how capable our computers are at large integers before:
"For instance, in 1994 a 129-digit number (known as RSA129 ) was successfully factored using this algorithm on approximately 1600 workstations scattered around the world; the entire factorization took eight months. Using this to estimate the prefactor of the above exponential scaling, we find that it would take roughly 800,000 years to factor a 250-digit number with the same computer power; similarly, a 1000 digit number would require years (significantly longer than the age of the universe). (Steane)"
Numbers as large as these can be used to calculate the amount of fuel needed for a mission to Mars or predict the amount of electrons in a gallon of water. Remarkably, quantum computing would be able to solve the Shor algorithm. If we had a quantum computer, we could solve mathematical problems non-linearly. This result is of considerable commercial and military interest as one of the most common data encryption systems is based on the supposed computational difficulty of factoring large numbers. " . . . [This] astonished the community by describing an algorithm which was not only efficient on a quantum computer, but also addressed a central problem in computer science: that of factorizing large integers. (Hoffman 63)" The first problem in making a quantum computer is that the quantum interference effects, which permit algorithms such as Shor's, are extremely fragile: the quantum computer would be ultra-sensitive to experimental noise and impression. Scientists are developing ways to dampen the noise level around a possible quantum computer using lasers. Although unbelievably complex and far from my grasp of understanding, scientists will be able to eventually unlock the secret to this puzzle with enough research.
Quantum computers process information non-linearly. A quantum computer can follow all computational paths simultaneously. So, instead of doing one task at a time and doing everything step by step, a quantum computer will begin working on all steps at the same time. "If the fastest computer we have takes more than 24 hours just to run the calculation through for 1 output alone, then we are sunk, and can do nothing. If we have a quantum computer, we can prepare the input in coherent superposition of the two inputs and do both calculations simultaneously in 24 hours. (Milburn 164) " This demonstrates how completely different and new the quantum computer will be compared to every other computer ever built. It won't just solve our current problems, it will find problems that we couldn't have even predicted. We'll be able to process information in ways only thought of in a science fiction novel.
Quantum computation works on a completely subatomic level, therefore allowing enormous speed without the heat. "Classic computers (the ones we have today) are getting smaller and smaller and soon physics will limit our technological leaps and bounds. (Petru 91)" We simply won't be able to make our current computers too much smaller. Quantum computers will be the answer to this problem. The quantum computer will hardly take up any space at all. Using quantum technology will allow us to maximize computational power and physical space. This is mostly because of the fact that quantum computers would process information using single photons. The crucial problem would be to get it to work with single photons, mostly because this requires large optical non-linearities. Optical non-linearities tend not to stay in a unitary state due to their tendency to absorb light. Even so, there are advantages when processing information with single photons instead of a stream of electrons in a computer. With single photons the chips won't melt and cause a breakdown. The photons will not generate any heat, therefore eliminating the problem that we currently have with our classical computers.
Quantum computing will and must be allowed to change our lives. Solving the Shor Algorithm, computing non-linearly, and finding a way around the heat dissipation problem in today's computers are all problems that must be faced eventually, and quantum computing is the answer. We just need to put forth the effort, time, and money to construct the answer. The result will be computational power which makes today's most advanced supercomputer look like an abacus. If we don't take the chance then we are denying our future.

Works Consulted Page
Barenco, A. "A short introduction to quantum computation" Centre for Quantum Computation

Benjamin, Simon and Ekert, Artur . "Towards Quantum Information Technology" Centre for Quantum Computation http://www.qubit.org/intros/nano/nano.html

Hoffman, K.H. and Schreiber M. Computational Physics New York: Springer, 1996

Milburn, J. Gerard. Schrodinger's Machines : The Quantum Technology Reshaping Everyday Life New York: W.H. Freeman and Company, 1997

Petru, Zygmunt, Przystawa, Jerzy, and Rapcewicz, Krzysztof. From Quantum Mechanics to Technology New York: Springer, 1996

Steane, Andrew, "Quantum Computing" Centre for Quantum Computation Reports on Progress in Physics, vol 61, pp 117-173 (1998). http://www.qubit.org/intros/compSteane/qcintro.html