Schrodinger's Machines
Schrodinger's MachinesIt is probably no exaggeration to say that quantum mechanics is the most successful scientific theory in history. However, in spite of the fact that 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 legion.
The reason for this late surge in interest can be traced to the truly weird nature of quantum mechanical ideas; for 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 implications for the nature of reality and the relationship between observer and observed are both subtle and profound.
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 has not understood it.
For decades the sheer weirdness of the quantum world was an obstacle to the theory being known outside the scientific community. Then in the 1970s, 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 mechanical concepts were of a mystical flavor. 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, all the while the practical applications of quantum mechanics were 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 application of quantum mechanical processes. From the humble CD player to the marvels of modern optical fiber communications, from non-drip paint to car brake-lights, from MRI hospital imaging mechanics 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 breath-taking possibilities. The field of nanotechnology sets as its goal the construction of machines of molecular dimensions, with potential applications to medicine, computing, and the fabrication of new and exotic materials. Already quantum technologists can trap and experiment with individual atoms, bounce atoms up and down on cunningly sculpted electromagnetic fields, produce atomic graffiti by displacing single atoms on a material surface, and image the structure of a crystal atom by atom.
These experiments probe the deep quantum regime, where Heisenberg's uncertainty principles and other aspects of quantum weirdness significantly shape the restrictions and possibilities. The common-sense world of Newtonian machines is left far behind. This is the domain of undreamt of possibilities, of microscopic circuits with novel electrical properties, of detectors so sensitive they could pick up 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 envisage 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 unpredictable 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 quietened below the natural background level, opening up the possibility of transmitting or detecting signals with unprecedented sensitivity.
Perhaps the most exciting and most speculative 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 alternative realities simultaneously, and integrate them into a single real-world answer, enabling nothing less than a totally new type of mathematics to be performed.
Indeed, all quantum systems essentially exploit the fact that the quantum microworld has no single, well-defined reality, but is a ghostly amalgam of alternative universes, a hybrid world in which possible realities merge and overlap to produce a final observed actuality. Quantum technology turns this Alice-in-Wonderland realm of mind bending concepts into concrete, practical devices.
Gerard Milburn is a world-renown theorist who works at the forefront of quantum mechanics, quantum field theory, and quantum technology. His current specialism is "atom optics" using the quantum properties of atoms as well as those of lasers to achieve novel states of matter and hitherto unavailable methods of information flow and retrieval.
Milburn shares my excitement about the heady progress being made in laboratories around the world, turning theorists' speculations into reality. Even as Gerard was writing this book, the University of Colorado announced that it had achieved a new state of matter, a so-called Bose condensate, in which atoms of the element rubidium collectively cooperate via quantum effects to behave in some respects like a single, giant atom. Many of these bizarre new properties of matter were predicted over half a century ago by the great founders of quantum physics, such as Albert Einstein, Werner Heisenberg and Niels Bohr, theoretical physicist who developed their ideas using "thought experiments" imaginary situations that are logically possible but which nobody dreamed would ever become a reality. Now those dreams are being put into practice.
The nineteenth century was known as the machine age, the twentieth century will go down in history as the information age. I believe the twenty-first century will be the quantum age. Here to guide you, the reader, into that strange new world, is one of Australia's most skilled and knowledgeable quantum physicists.