Atomic clocks rely on a frequency generated by atomic energy level jumps, and this frequency is subject to error during the checking and locking process, resulting in a less precise but more accurate atomic clock; sapphire clocks are another type of clock that is not as accurate as an atomic clock, but is far more precise.
01-Introduction.
Of the seven physical quantities defined by mankind, time is the most accurate; time is measured with a precision that is many orders of magnitude higher than the other physical quantities. Length, for example, is difficult enough to measure down to the nanometer scale. Even at the nanometer scale, it is on the order of 1E-9. However, for the measurement of time and frequency, tens of thousands of dollars of frequency meters can measure up to 1E-12 orders of magnitude. Currently, atomic clocks can measure up to 1E-19 orders of magnitude, which is much higher than the measurement accuracy of other physical quantities.
Due to the high precision of frequency measurement, many high-precision measurements are transferred to the frequency domain for measurement; even the definition of physical quantities are dependent on frequency; for example, the definition of the meter: "the distance that light travels in a vacuum for 1/299 792 458 seconds".
According to the basic principles of quantum physics, an atom absorbs or releases electromagnetic energy according to the energy difference between different electron arrangements in the order in which the electrons are arranged, i.e., the energy difference between the different layers of electrons surrounding the nucleus. Here the electromagnetic energy is discontinuous. When an atom jumps from one "energy state" to a lower "energy state", it releases electromagnetic waves. The characteristic frequency of this electromagnetic wave is discontinuous, which is also known as the resonance frequency. The resonance frequency of the same atom is certain - for example, cesium 133 has a resonance frequency of 9192631770 cycles per second. The caesium atom is therefore used as a metronome to keep highly accurate time.
Many precision measurements in the real world rely on time-frequency measurements, such as satellite navigation systems; to achieve positioning, satellites must ensure that signals are sent synchronously; errors in the time of individual satellites need to be accurately monitored; and satellite master stations have dozens of atomic clocks, whose time is regularly compared with the International Atomic Time.
02-Sapphire Clock
Sapphire clocks
In many cases, however, accuracy is less important than precision. Accuracy, known as "Accuracy" in English, refers to the degree to which the average value of multiple measurements under certain experimental conditions corresponds to the true value, which is used to indicate the size of the error.
Precision is the reproducibility of measurement, known as "Precise", is a prerequisite for accuracy, but high precision does not necessarily guarantee high accuracy. Good precision is a prerequisite for good accuracy. Generally speaking, if the precision of measurement is not good, it is impossible to have good accuracy. Conversely, good precision of measurement does not necessarily lead to good accuracy, a situation that suggests small random errors but large systematic errors in the measurement.
Atomic clocks depend on the frequency generated by atomic energy level jumps, and this frequency is subject to errors in the calibration and locking process, resulting in atomic clocks with low precision but high accuracy.
Sapphire clocks are another type of clock that is less accurate than atomic clocks, but more precise than atomic clocks; sapphire clocks have minimal error in adjacent oscillation cycles and good reproduction consistency. If you use darts as an analogy, atomic clocks are aimed at the bull's-eye, but the error is larger, distributed in a larger piece of the region, as shown in the above figure on the right; sapphire clocks do not aim at the bull's-eye, the darts all fall into a very small range, but each dart is the same, as shown in the above figure on the left;. There are many occasions when accuracy is not required, but precision is required to be extremely high
The sapphire is machined into a cylindrical shape, placed into a clean copper cavity, and injected with a microwave signal, which then travels around the circumference, just as sound reflects off a wall; because this travel loss is minimal, it thus accumulates a large amount of energy at the natural resonant frequency. The world's most sophisticated oscillator can be constructed using this method.
When the sapphire is cooled to absolute zero (-267 degrees Celsius), the loss will drop dramatically and the world's most precise clock can be made. The world's first sapphire oscillator was born at the University of Western Australia in Australia, and is mainly used for gravitational wave detection. This temperature requires liquid helium refrigeration, which is expensive and bulky, making it difficult to promote its use. Sapphire clocks are usually difficult to use at room temperature and need to overcome the effects of temperature changes, vibration and noise. Changsha Sky Dome Electronic Technology Company has solved these problems through years of hard work; it has successfully developed China's first non-low-temperature type super-stable sapphire clock product.
03-Sapphire Clock Application
For meteorological radar, due to the dependence on the signal echo for detection, radar frequency synthesis for the signal frequency accuracy requirements are not high, but the signal frequency precision requirements are extremely high, and the sapphire clock is such a signal frequency precision products. The use of sapphire clock as a radar frequency synthesis reference, can make the transmitter phase noise spectral density reduction, radar improvement factor, significantly improve the detection performance of meteorological radar.
Sapphire clocks can also be widely used in precision physical measurements, such as high-performance atomic clocks using atomic energy level jump to obtain a stable frequency, however, the atomic clock needs a super-stable microwave source for internal excitation, when the sapphire clock as the source of excitation, due to its super-stable performance will reduce the signal synthesis noise, enhance the stability of the output of the atomic clock.
In the field of quantum computing sapphire clocks can improve the stability of quantum bits, thus improving the efficiency of quantum computing. Traditional computers disconnect and turn on the current to produce a binary bit of information that is expressed by 0 or 1; while quantum computers rely on quantum bits, which are a complex superposition of states, and at the same time may be 1 or 0. The effect is a great increase in the information that can be encoded by the quantum bits, but the trouble with quantum bits is that they are instantaneous and unstable; an extremely stable clock is needed to synchronize multiple quantum devices. The sapphire clock will generate a master clock signal at the same frequency as the quantum bits, enabling the computation of quantum bits.
The future broadband communication develops in the direction of high speed and high bandwidth, and the sapphire clock can be used as the frequency reference of broadband communication to reduce the BER due to frequency jitter, solve the bottleneck technology that restricts the increase of broadband communication rate, and improve the performance of broadband communication. Future instrumentation from high-speed analog-to-digital converters and digital-to-analog converters (ADC/DAC) to radar and basic research applications require signals with better frequency stability and spectral purity. Sapphire clocks provide ultra-stable reference sources for analog-to-digital and digital-to-analog conversions in signal analyzers, network analyzers, signal sources and other instruments, significantly reducing sampling noise, improving signal analysis accuracy and precision, and providing technology for high-frequency signal analysis such as 5G, 6G and millimeter wave.
05-About Shoutai Time & Frequency
Changsha Tianqiong Electronics is a professional time and frequency products supplier, "述泰" is the company's registered trademark. The company specializes in low acceleration sensitive frequency control components, high Q resonators and ultra-low phase noise technology. The company is one of the few companies in China that can not only master the technology of high performance crystal oscillators, but also propose a complete set of highly stable signal generation solutions in vibration environments according to the application scenarios and customer needs.