What time? \”Science\” to redefine

At present, the timing standards around the world are used to define the second atomic clocks, precision can reach every 20 million years before the error 1 second (20 million years ago, we still ape). Atomic clock is completely different and we normally see the clock looks, no dial, no pointers. The atomic clock is dependent on the atoms. The atomic nucleus and electrons, the energy difference between electrons of different electron shell rotating around the nucleus. When an atom from a high \”energy state\” transition to a low \”energy state\”, it will release the electromagnetic wave. This characteristic frequency electromagnetic wave is discontinuous, i.e. it says that the resonance frequency. An atomic resonance frequency is the same constant – for example, the resonant frequency of the cesium 133 9 192 631 770Hz. Cesium will therefore used as a metronome to maintain highly accurate time.

时间是什么?《Science》来重新定义
atomic photo

However, since the electronic system is not directly counting the optical signal, the optical performance of these clocks can not flex its muscles in the electronics field, the radar, navigation, communications, and basic research are dependent on less stable microwave source. Recently, the American National Standards Institute (NIST) researchers used the technology of the most advanced atomic clocks, advanced optical sensor and one measuring tool called frequency comb, the very stability of atomic clock shift work at optical frequencies microwave frequency, the microwave signal stability increased 100-fold. The microwave signal may be used for stabilization calibration of the electronic device. This marks a step towards a better electronic technology a giant step in order to achieve more accurate timing, improved navigation, more reliable communication and radar astronomy and high-resolution imaging. Microwave signal conversion means. Black rectangle (center) is a high speed semiconductor photodiode, the laser pulse can be converted to the ultra-stable microwave frequency. The diode has a gold-plated around the boundary, embedded inside the electric wire. The copper wire leads are connected to circuitry (top) for extracting the microwave signal. A brass plate against the entire apparatus in order to maintain mechanical stability. In their device, researchers use the \”tick\” of the two ytterbium NIST lattice clock to generate optical pulses, and the frequency comb as gears to accurately convert the frequency into a low frequency microwave signal light pulse. Advanced photodiode converts light into a current pulse, thereby generating a 10 gigahertz (GHz, or 10 per sec.One hundred million cycles) microwave signal, accurate tracking clock ticks, the error is only one of a million cubic (1 followed by 18 zeros) points. This level of performance of the optical clock equivalent to 100 times more stable than the best of the microwave source.

时间是什么?《Science》来重新定义 fraction
Comparative latest source frequency stability

optical wave period is shorter than the microwave, high speed, so that they have different shapes. In converting the light waves into a stable microwave process, researchers tracking phase (the exact time of the wave), to ensure that they are the same, and will not move with each other. Experiment of the phase change, which corresponds to a resolution of only one millionth of a cycle. Lead researcher Frank Quinlan said, some of the components NIST system, such as frequency comb and probe, now ready for field applications. But NIST researchers are still committed to the most advanced optical clock transferred to the mobile platform. Ytterbium clock operating frequency of 518 terahertz (trillion cycles per second), currently occupies a lot of space in a highly controlled laboratory environment. Ultra-stable electronic signal can support a wide range of applications, including electronic clock calibration future. It is to redefine the international time standard – sec IU an important consideration, it is now a conventional microwave frequency clock based on the cesium atomic absorption. The next few years, the international scientific community is expected to select a new time standard based on the frequency of light absorbed by other atoms of ytterbium. Ultra-stable signal of the wireless communication system may be more reliable. The optical signal derived from the electronic imaging system can be made more sensitive. The sensitivity of the radar is now limited by the microwave noise, especially for slow objects, it could be greatly improved. Cooperation by NIST and the University of Virginia production of new photodiode, converts the optical signal into an easier to predict than the previous design, lower noise microwave signal. Furthermore, the microwave signal may also carry long-distance optical clock, navigation and fundamental physics research. Astronomical imaging and measuring the shape of the Earth\’s gravity geodetic relativity, is now based on the receiver detects the microwave signal around the world, and combine to form an image of the object. Calibration of these remote receivers can make a network from the earth into space becomes possible, which will increase the image resolution, to avoid distorting atmospheric observation time limit. For a few hours rather than a few seconds of observation time, researchers can capture more objects. veryMany times, we do not care about the difference between a single minute, but it is not science, researchers \”preoccupied\”, in order to create a better world. Original link:

https://science.sciencemag.org/content/368/6493/889

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