From Quantum Theory to Technology through Characterization and Control of Quantum Devices

Quantum technology has enormous potential to revolutionize many areas of science and technology from computing and communication, to chemical engineering and material science. For instance, quantum computers could perform certain tasks much faster than ordinary computers, quantum communication systems such a quantum internet could guarantee secure communication, and quantum control of chemical reactions might lead to the discovery of new drugs or materials, to mention only a few promising applications. As for any device, whether this be a car, computer or toaster, control is essential to ensure that the device functions as intended, and optimizing the device performance by optimizing our control of the device is usually a non-trivial problem. However, control of quantum devices is particularly challenging. One reason for this is quantum coherence, a special property of quantum systems that all quantum devices exploit. Unfortunately, quantum coherence is very fragile, easily destroyed through uncontrolled interactions of the system with its environment, and not easy to control in general. One of the main objectives of this project is to address this problem and find optimal ways to control quantum devices coherently. In addition to the fragile nature of quantum coherence, realizing this aim is complicated by the fact that no manufactured device will ever be perfect, and device imperfections such as small variations in size and shape of a particular element, can be very detrimental to our ability to control the system effectively. Hence, another important aspect of the project is to look at the sensitivity of various control strategies (and ways of encoding information in quantum systems) to device imperfections. It is hoped that understanding the effect of device imperfections will allow us to design more robust strategies, which is essential if we are to build quantum devices that work in the real world.Finally, the variations of manufactured devices mean that before we can actually hope to control the operation of the device, we must first identify experimentally what the effect of certain control influences on the system is. A simple example is a toaster with a control knob to adjust how long we wish the bread to be toasted. If it is a new toaster some experimentation with the position of the knob may be required to find the right position of the knob for perfect toast. For a simple calibration problem such as this, trial and error is usually sufficient to achieve satisfactory results after a few trials. For complex devices, and especially quantum devices, more efficient and systematic ways to experimentally characterize the device and its interaction with the control apparatus are required. This is essential before we can optimize the control to achieve robust operation of the device, and is another key objective of the project.