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This paper reports direct temperature determination of sympathetically cooled 113 Cd + ions with laser-cooled 24 Mg + in a linear Paul trap. The sympathetically cooled ion species distribute in the outer shell of the large ensembles, which contain up to 3.3 × 10 5 ions. With optimized parameters, the minimum temperature of the sympathetically cooled 113 Cd + ions was measured to be on the order of 10 mK. These results are promising for performance of microwave atomic clocks. The second-order Doppler frequency shift is two orders of magnitudes lower (from 1.88 × 10 −14 to 6.26 × 10 −16 ) and the Dick effect is suppressed.

A novel index-coupled distributed feedback quantum cascade laser emitting at λ ∼ 4.8 μm is demonstrated by a sampled grating. The coupling coefficient can be almost controlled arbitrarily according to the duty cycle of sampled grating. The additional supermodes caused by the sampled grating can be strongly suppressed by choosing a small sampling period, so that the supermodes are shifted apart from the gain curve. Single-mode emission without any significant disadvantages compared with uniform grating is achieved. Especially, this powerful approach presented here can be applied to achieve the performance with high power and low threshold simultaneously.

Quantum measurement using coherent superposition of intrinsic atomic states has the advantage of being absolute measurement and can form metrological standards. One example is the absolute measurement of magnetic field by monitoring the Larmor precession of atomic spins whilst another being the Ramsey type atomic clock. Yet, in almost all coherent quantum measurement, the precision is limited by the coherence time beyond which, the uncertainty decreases only as τ−1/2. Here we show that by non-destructively measuring the phase of the Larmor precession and regenerating the coherence via optical pumping, the self-sustaining Larmor precession signal can persist indefinitely. Consequently, the precision of the magnetometer increases with time following a much faster τ−1 rule. A mean sensitivity of 240  from 1 Hz to 10 Hz is realized, being close to the shot noise level. This method of coherence regeneration may also find important applications in improving the performance of atomic clocks.