The Need for Advances

Quantum Algorithms

Quantum Communications

Quantum Control

xQIT: The Pressing Need for Advances in Extreme Quantum Infomation Theory

Over the last half century, the components of computers have gotten smaller by a factor of two every 18 months, a phenomenon known as Moore's law. In state-of-the-art computers, the smallest wires and transistors are approaching 100 nm feature size, which is approximately 1000x the diameter of an atom. Quantum mechanics is the theory of physics that describes the behavior of matter and energy in extreme conditions, such as short times and tiny distances. As transistors and wires become smaller and smaller, they inevitably begin to behave in intrinsically quantum mechanical ways. Thus, whereas the quantum mechanics of semiconductor band theory has given us the microprocessors and laser diodes that have fueled our information ageís computers and communication systems, these technologies have not exhibited macroscopically quantum-mechanical effects. This will no longer be true as we drive forward to ever smaller and faster devices, and so it becomes essential to address information science in a fully quantum mechanical setting, viz., we need quantum computers and quantum communications.

Quantum computers and quantum communication systems operate at the level of individual quanta—atoms, photons, and electrons. They store, process, and transmit information at the smallest possible scales, and using the minimum possible energy. Even if Moore's law persists, commercial quantum computers are not yet due on the shelves for another few decades; nonetheless, prototype quantum computers consisting of a small number of atoms and quantum communication systems that use single photons have been built and operated. Quantum mechanics is famously counterintuitive. (Einstein, despite making great contributions to quantum mechanics, never fully accepted it.) Quantum computers and communication systems exploit quantum weirdness to do things that classical information technologies cannot. A quantum computer could search databases and break codes that no classical computer could search or break. Quantum communication systems allow the creation of unbreakable codes, and could be used to teleport the state of matter from one place to another. Quantum enhancements to the Global Positioning System (GPS) could greatly enhance its accuracy.

What more could quantum computers and quantum communication systems do? Might quantum computers be able to solve harder problems than code breaking? Could quantum communication channels convey information at much higher rates than conventional radio frequency or optical communication channels? What are the ultimate attainable accuraciesóbased on the laws of physicsóof measurement and sensing systems such as GPS? Despite much productive research into the theory of quantum computation and quantum communication, the answers to these questions are not known. The ultimate capabilities of quantum computers and quantum communication systems, pressed to their extremes, remain to be discovered. Our efforts to meet these challenges will focus on three areas:

• Algorithms to Solve Average-Case NP-Hard Problems
  
  
• Capacities and Coding for Quantum Communication Channels
  
  
• Fundamental Limits on Quantum Sensing and Control