In this paper, we report on the mission study and laboratory development for ASTROD. ASTROD mission concept is to use drag-free spacecraft in solar orbits together with a constellation of Earth orbiting satellites to provide high-precision measurement of relativistic effects, better determination of the orbits of major asteroids, improvement in the measurement of G, measurement of solar angular momentum via Lense-Thirring effect and the detection of low-frequency gravitational waves and solar oscillations in a single mission. We present our progress in the mission study on the various aspects for measuring these quantities. As to the laboratory development, after reviewing briefly our progress in long fibre-linked heterodyne interferometer and tunable fibre directional coupler, we present our progress in weak light optical phase locking, fibre delay-line and laser and time metrology.
A Markovian process of a system is defined classically as a process in which the future state of the system is fully determined by only its present state, not by its previous history. There have been several measures of non-Markovianity to quantify the degrees of non-Markovian effect in a process of an open quantum system based on information backflow from the environment to the system. However, the condition for the witness of the system information backflow does not coincide with the classical definition of a Markovian process. Recently, a new measure with a condition that coincides with the classical definition in the relevant limit has been proposed. Here, we focus on the new definition (measure) for quantum non-Markovian processes, and characterize the Markovian condition as a quantum process that has no information backflow through the reduced environment state (IBTRES) and no system-environment correlation effect (SECE). The action of IBTRES produces non-Markovian effects by flowing the information of quantum operations performed by an experimenter at earlier times back to the system through the environment, while the SECE can produce non-Markovian effect without carrying any earlier quantum operation information. We give the necessary and sufficient conditions for no IBTRES and no SECE, respectively, and show that a process is Markovian if and only if it has no IBTRES and no SECE. The quantitative measures and algorithms for calculating non-Markovianity, IBTRES and soly-SECE are explicitly presented.
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