# Physics of information

### From CYPHYNETS

## Physics of Information: Communication, Control and Computation at the Quantum Scale

An important scientific question today is to understand the fundamental limits of information exchange across scales. As devices are being manufactured at smaller and smaller scales, quantum effects are expected to play a prominent role in their design and analysis. These effects are commonly thought of as obstacles or limitations in the continuation of current trends in microelectronics and nanotechnology. However, physicists, computer scientists and mathematicians have recently realized how to exploit these effects to their advantage in future devices and applications [7]. The field of quantum information sciences [8] encompasses many fundamental questions which have excited my interest and I have begun an exploration of these questions in my current postdoctoral work. In particular, I am interested in two broad themes in quantum information sciences: control of quantum mechanical systems and quantum information theory.Quantum control is an emerging technology, driven by investigations into quantum computation, nanotechnology, material synthesis, laser physics and NMR (nuclear magnetic resonance). It concerns the control of those physical systems in which the dominant behavior is quantum mechanical. From practical realizations of quantum computers to error compensation in NMR systems, it is vitally important to understanding all aspects of controlled quantum dynamics. Feedback control not only enables trajectory design for the desired evolution of the system, but is also invaluable for compensation of systematic errors, cancellation of disturbance and suppression of noise. My interest in quantum control concerns the design of pulse sequences for accurate NMR control and quantum gate approximation. The basic idea is to assemble a string of operations chosen from a small set of experimentally realizable primitives to produce arbitrary dynamics.

My other interest in quantum information sciences concerns quantum information theory. This is a relatively young field whose aim is to generalize Shannon’s pioneering work in classical information theory to the quantum setting. Explorations in this area have promised schemes for teleportation, secure communication and cryptography. As with classical information, the main object of study is a (quantum) communication channel over which information is transported in qubits – the quantum analog of bits. The capacities of such channels; coding, compression & modulation schemes and communication security are main themes in this area. Quantum modes of communication, augmented with classical communication schemes give rise to quantum networks. Currently, my interest in quantum information theory concerns the following question: Is there an information theoretic characterization of feedback in quantum controllers and quantum networks? Since this problem has already been studied in recent networked control literature, it is my hope that by re-examining these notions in the quantum setting, several fundamental properties of quantum controllers and quantum networks can be derived.

## References

[7]. Grand Challenges for Engineering by National Academy of Engineering, USA. [1]

[8]. A Quantum Information Science and Technology Roadmap, ARDA, 2004. [2]