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We report a high-performance transportable microwave frequency standard scheme based on sympathetically cooled 113Cd+ ions using 40Ca+ as coolant ions. A transportable physical package (1.4 m3) with high-performance magnetic shielding (radial shielding coefficient 460 000) has been built. In experiments, more than 105 113Cd+ ions were sympathetically cooled to 90 mK in a Paul trap and the ion-loss time constant extends to 84 hours. Without direct cooling procedures, the Dick effect-limited Allan deviation due to the deadtimes is reduced to 1.8×10−14/τ. Under our scheme, the uncertainties in the main frequency shifts such as those from second-order Zeeman and second-order Doppler terms were reduced below the order of 10−15. The relevant ac Stark shifts uncertainties were estimated to be below 5×10−18. Minor shifts further reflect the superiority of coolant ions 40Ca+ for 113Cd+. These results indicate that a microwave clock based on this sympathetic cooling scheme shows potential in establishing a vehicle transportable ground-based time-frequency reference for navigation systems.

We measured the ground-state hyperfine splitting of trapped 113 C d + ions to be 15199862855.02799(27) Hz with a fractional uncertainty of 1.8 × 10 − 14 . The ions were trapped and laser-cooled in a linear quadrupole Paul trap. The fractional frequency stability was measured to be 4.2 × 10 − 13 / τ , obtained from Ramsey fringes of high signal-to-noise ratios and taken over a measurement time of nearly 5 h, which is close to the short-term stability limit estimated from the Dick effect. Our result is consistent with previously reported values, but the measurement precision is four times better than the best result obtained to date.

Intelligent agents (IA) are autonomous entities which observe through sensors and act upon an environment using actuators to adjust their activities towards achieving certain goals. The architectures of agents have enormous potentials when they are applied into critical systems, where agents choose actions between working with their own and cooperating with others. Rational utility-based agents choose actions to maximize their expected utilities. Rational secure multi-party computing (RSMPC) means secure multi-party computing (SMPC) in the presence of rational utility-based agents. Here, we call them rational parties. In this paper certain goals of rational parties are maximizing their utilities. The introduction of rational parties considers the incentives in executing protocols. The security definitions under rational framework can better demonstrate the executing environment of real protocols. Furthermore, rational two-party computing removes some impossibility in traditional two-party computing, such as fairness. This paper represents the research status of RSMPC and some typical protocols. The advantages and disadvantages of previous rational SMPC protocols are discussed here. As an emerging field, there are still lots of open problems in RSMPC, such as communication channels, utility assumptions and equilibrium notions etc.

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