Demonstration of blind quantum computing

Quantum computers, besides offering substantial computational speedups, are also expected to preserve the privacy of a computation. We present an experimental demonstration of blind quantum computing in which the input, computation, and output all remain unknown to the computer. We exploit the conceptual framework of measurement-based quantum computation that enables a client to delegate a computation to a quantum server. Various blind delegated computations, including one- and two-qubit gates and the Deutsch and Grover quantum algorithms, are demonstrated. The client only needs to be able to prepare and transmit individual photonic qubits. Our demonstration is crucial for unconditionally secure quantum cloud computing and might become a key ingredient for real-life applications, especially when considering the challenges of making powerful quantum computers widely available.     

Effect of livestock manure on the chemical quality of groundwater

In Germany groundwater represents the main source for the water supply. Up to the present the nitrogen surplus due to agricultural production has increased to about 100 kg N/ha and year. This surplus reaches other, mainly aquatic ecosystems, transported by water and trough the air. The impact of the long-term load through nutrients on groundwater is exemplified here in the case of Lower Saxony. In karst and rock aquifers the transport velocities are usually relatively high. After nutrients have left the root zone of the soil there remains in this kind of aquifer little opportunity for nitrate decomposition. Therefore rising nitrate values can soon be observed in pumpage wells. Intensive cattle production is especially widespread in the northern parts of Lower Saxony. In these areas of sandy aquifers the period of substance transport between the input into the system and reaching pumpage wells may cover years or even decades. Therefore there is a greater chance for nitrate decomposition. Nonetheless many upper aquifers are severely contaminated with nitrates, for instance. In many cases a reductive chemical environment can be observed, which causes an increase in substances such as iron or trace elements like nickel. This leads to considerable problems for water supply and treatment. In order to protect the quality and decomposition capacity of the groundwater for the next generation it is urgently necessary to minimise nutrient surpluses in the field of agricultural production.     

Long-distance free-space distribution of quantum entanglement

We demonstrate the distribution of quantum entanglement via optical free-space links to independent receivers separated by 600 m, with no line of sight between each other. A Bell inequality between those receivers is violated by more than four standard deviations, confirming the quality of the entanglement. This outdoor experiment represents a step toward satellite-based distributed quantum entanglement.