Researchers in the School of Mathematical Sciences have managed to pull off an article hat-trick, with three accepted for publication in the same prestigious journal 'Physical Review Letters'. All three researchers are from the Quantum Information group and their papers are available to read in full by clicking on the underlined titles below..
Gerardo Adesso:
Quantum information technology is empowered by the realisation that stronger forms of correlations, such as quantum entanglement, exist between elementary systems like atoms and photons, which can be exploited for better and more secure information processing compared to conventional classical electronics. Recently, it has been realised that more general nonclassical features of correlations, sometimes referred to as quantum discord, are retrievable between noisy quantum systems and can give rise to an improved computational power. Accessing and quantifying these correlations in laboratory is important to assess the usefulness of realistic systems for information processing tasks, but it remains an elusive task, as quantum correlations cannot be observed directly. In a joint venture between theory (Mathematical Sciences at Nottingham) and nuclear magnetic resonance experiments (Institute of Physics at Sao Carlos, Brazil), the authors demonstrate a method to quantitatively estimate the amount of general quantum correlations in bipartite systems without the need for a full reconstruction of their quantum state. This provides a direct confirmation that highly noisy systems, even in absence of entanglement, have a distinct quantum character which can be exploited as a resource for robust quantum technologies.
Ivette Fuentes:
How do motion and gravity affect quantum information tasks? In 2012 a teleportation protocol was successfully performed across 143km between two Canary Islands by A. Zeilinger’s group. In this experiment, time and positions were determined accurately employing the Global Positioning System (GPS), which is a system of satellites used for time dissemination and navigation. It is well known that GPS takes into account Einstein's theory of relativity to achieve the required precision. However, relativistic effects over the basic resource of the experiment -quantum entanglement- were not considered. Motivated by the success of this kind of tests, space agencies are investing resources for the implementation of space-based quantum communications. At these regimes, relativistic effects can no longer be ignored. In our Letter, we show that relativistic motion and gravity have observable effects in the quantum teleportation protocol. Indeed they can decrease its efficiency; however, we explain how the errors can be corrected. We propose a physical implementation of our relativistic teleportation protocol, which is well within reach of cutting-edge technology using superconducting circuits. The realization of this low-cost tabletop experiment, demonstrating for the first time the effects of relativity on quantum information tasks, will inform expensive space-based programs.
Madalin Guta:
The theory of phase transitions is essential for understanding fundamental physical phenomena such as magnetism, superconductivity and superfluidity. This paper investigates phase transitions occurring in quantum systems such as atoms, optical cavities and quantum spin chains. Since the state of a quantum system cannot be observed directly without disturbing it, the system is monitored indirectly through its imprint on the environment, e.g. in the form of emitted photons. The authors investigate dynamical phase transitions which are manifest in the time record of measurement trajectories, for instance through alternating periods of high activity (many emitted photons) and low activity (few emitted photons). The emerging theoretical framework is based on the analogy between quantum trajectories and configurations of thermodynamical systems, and the mathematical theory of large deviations.
Posted on Monday 15th April 2013