Resources for flexible quantum information processing

Over the past two decades, quantum technologies for computation, communication and sensing have progressed from theoretical proposals to experimental reality. Although these technologies are widely expected to outperform their classical counterparts in the future, present day state-of-the-art setups operating in the quantum domain cannot compete with currently available classical devices such as smart phones or laptop computers. This is, in part, due to the difficulties in controlling and precisely manipulating the required quantum systems such as trapped atoms or quanta of light (so-called photons). Consequently, modern prototypes for quantum computers operate with only a handful of information carrying systems called qubits, the quantum equivalents of classical bits. In the proposed research project entitled Resources for flexible quantum information processing we therefore intend to investigate how the scarce quantum resources such as the available qubits can be used most efficiently to perform desired tasks such as running computations on a quantum computer. In particular, a novel aspect of this theoretical research project will be the focus on developing flexible multi-purpose devices for quantum-enhanced sensing and computation. That is, if resources are very limited and costly, it is desirable to design gadgets that are able to perform several tasks of interest using the same basic resources. The project is in this sense inspired by the technological miniaturization and functional integration that has taken place for modern smart phones. In our quest to develop flexible integrated quantum devices, we will hence study how resources for quantum computation and quantum communication can be converted and used most efficiently to perform also other tasks such as the precise measurement and estimation of unknown parameters. Apart from the conversion of information-theoretic resources into each other, we will also consider the exchange with physical resources such as the available energy. To achieve this, our research of computational and communicational tasks will be embedded in the context of physical theories such as quantum thermodynamics (e.g., to study the exchange and extraction of energy from systems with some temperature) and quantum optics (the interaction of light and matter in the quantum domain). Using these techniques, we will investigate, for example, how energy may be traded for information gain in the estimation of an unknown quantity, and how such tasks may be influenced by practical and fundamental limitations. The multi-facetted interdisciplinary character of this project will bring about many interesting new insights into the relation of resources for different quantum-enhanced devices, and contribute to bridging the gap between computational and physical aspects of quantum information science.

Over the past two decades, quantum technologies for computation, communication and sensing have progressed from theoretical proposals to experimental reality. Although these technologies are widely expected to outperform their classical counterparts in the future, present day state-of-the-art setups operating in the quantum domain cannot compete with currently available classical devices such as smart phones or laptop computers. This is, in part, due to the difficulties in controlling and precisely manipulating the required quantum systems such as trapped atoms or quanta of light (so-called photons) in the presence of disturbance from their environment. Consequently, modern prototypes for quantum computers operate with small numbers of information carrying systems such as so-called "qubits", the quantum equivalents of classical bits, yet require complex control mechanism, energy for cooling and other resources for their operation. In this research project entitled "Resources for flexible quantum information processing" we have therefore followed a dual approach: On the one hand, we have investigated how the available scarce quantum resources can be used most efficiently for tasks such as running computations on a quantum computer or distributing quantum systems for quantum communication. Among the key results of this approach were the development of a machine learning algorithm that can protect quantum computations by dynamically adapting its error correction routine to changing environmental conditions, as well as the design of procedures for improving the distribution of quantum states among multiple users by tapping into information about noise that is encoded in otherwise discarded systems. On the other hand, the project has aimed to provide fundamental theoretical insight into the resources needed to establish these quantum resources to begin with. In this second approach we have addressed the question of how time, energy, and precise control over the internal structure and interaction of complex quantum systems allow us to perform measurements, cool quantum systems to the required temperatures, store and estimate useable energy, and create correlations. The multi-facetted interdisciplinary character of this project has brought about many interesting new insights into the relation of resources for different quantum-enhanced devices and contributed to bridging the gap between computational and physical aspects of quantum information science.