IQSE - Institute for Quantum Science and Engineering - Harvard University

About IQSE

A number of intellectual and technical advances point to the start of a fundamentally new era for the physical sciences and engineering in which some of the more subtle and counterintuitive principles quantum mechanics have moved from the realm of philosophical debate to the laboratory and even the marketplace, offering potentially revolutionary technological capabilities.

Fig. 1 The miniaturization of information processing devices is represented in these four images, from the mechanical age, to the age of microfabrication, to quantum devices, and ultimately to the scale of molecules, atoms, and even atomic nuclei as the place where bits of information reside.

On the fundamental side, there has been rapid development at the intersection of mathematics, computer science and physics that demonstrating that quantum mechanics provides a yet untapped resource allowing secure communication and rapid computation. The capabilities are revolutionary: as an example, the problem of finding the prime factors of a number — a task whose difficulty forms the basis of internet security — can be speed up exponentially by taking advantage of the quantum laws. Problems that would literally take the age of the universe to solve on a classical computer become rapid calculations for a corresponding quantum computer. These stunning results are purely mathematical at this point, and the job of actually building such a machine is for now beyond technological reach, though a number of proposals are being pursued in labs around the world. Even at the theoretical level, understanding the connections between information theory and quantum physics is a field in its infancy.

In the area of communications, quantum mechanics offers the possibility of completely secure communications through the generation and transmission of quantum-entangled pairs of photons. With such a device, any eavesdropper would be immediately revealed. Success in this area will require fundamental advances such as entirely new light emitting devices capable of generating non classical states of light as well as system advances in areas such as coding and quantum cryptography.

On the technical side, developments in nanotechnology have brought together the world of the atom — a world ruled by quantum laws — with the world of microelectronics and micromachines. Nanoscience is itself under rapid development. In the last year alone we have seen the analogs of atom-photon interaction played out with purely electronic circuits nanofabricated from superconductors and cooled to near absolute zero. Equally remarkable are developments in material science, with ultrapure semiconductor material, carbon nanotubes, and nanowires made of composite semiconductors. These materials will form the basis of realizing the quantum world on a chip. A number of other technological advances, such as efficient sources of non-classical (“squeezed”) light, optical lattices for holding particles in free space using light forces, and the realization of Bose-Einstein condensates, also facilitate a coming together of information, quantum physics, and nanoscience.

In areas such as optical communication and chemical sensing, quantum devices have already revolutionized the field. For instance, the majority of high-speed fiber optic links on land or under the ocean now use quantum well lasers to transmit information. A low-noise transistor based on a two-dimensional quantum gas of electrons is a key element of modern cell phones. Quantum cascade lasers are revolutionizing chemical sensing and trace gas analysis for a wide range of applications.

Such new developments in quantum devices, including transistors and lasers that use the spin of electrons to achieve new functionalities not achievable with conventional charge based electronic and photonics, are on the horizon. As these and other quantum technologies develop, new applications ranging from compact coherent solid state sources analogous to lasers, but operating at a few terahertz (1 THz =10¹² Hz) to circuits for applications in quantum computing will likely appear.

Although some companies have already appeared, large-scale practical application of the ideas in the emerging field of quantum information processing is probably years in the future. Quantum cryptography is of potential interest for ultra-secure optical communication systems. These could be either short spans in metropolitan networks or much longer spans in long-haul systems. For the long-haul systems major advances need to be made in order to preserve the integrity of the quantum information over long distances where losses can degrade the signals to the level that they are not adequate for secure coding. Optical quantum repeaters are a research topic of great interest at present. Major advances in understanding quantum channel capacities are being made in the regime of small photon count per bit of information.

From the engineering side, the demonstration of compact quantum devices operating at near room temperature is a major technological challenge that will have to be met to create widespread practical impact of quantum information technology.