How atomic clocks work (5 photos). The most accurate clock in the world - quantum

When the light suddenly goes off and comes back on a little later, how do you know what time to set the clock? Yes, I'm talking about Digital Watch, which many of us probably have. Have you ever thought about how time is regulated? In this article, we will learn all about the atomic clock and how it makes the whole world tick.

Are atomic clocks radioactive?

Atomic clocks tell time better than any other clock. They show time better than the rotation of the Earth and the movement of the stars. Without atomic clocks, GPS navigation would be impossible, the Internet would not be synchronized, and the positions of the planets would not be known with sufficient accuracy for space probes and vehicles.

Atomic clocks are not radioactive. They do not rely on atomic fission. Moreover, it has a spring, just like a regular watch. The biggest difference between a standard clock and an atomic clock is that oscillations in an atomic clock occur in the nucleus of an atom between the electrons surrounding it. These oscillations are hardly parallel to the balance wheel on a winding watch, but both types of oscillation can be used to track the passage of time. The frequency of vibrations within an atom is determined by the mass of the nucleus, gravity, and the electrostatic “spring” between the positive charge of the nucleus and the cloud of electrons around it.

What types of atomic clocks do we know?

Today there are Various types atomic clocks, but they are built on the same principles. The main difference relates to the element and means of detecting changes in energy levels. Among different types There are the following atomic clocks:

• Cesium atomic clocks using beams of cesium atoms. The clock separates cesium atoms with different energy levels using a magnetic field.
• A hydrogen atomic clock maintains hydrogen atoms at the desired energy level in a container whose walls are made of special material, so the atoms don't lose their high-energy state too quickly.
• Rubidium atomic clocks, the simplest and most compact of all, use a glass cell containing rubidium gas.

The most accurate atomic clocks today use a cesium atom and a conventional magnetic field with detectors. In addition, the cesium atoms are contained by the laser beams, which reduces small changes in frequency due to the Doppler effect.

How do cesium-based atomic clocks work?

Atoms have a characteristic vibration frequency. A familiar example of frequency is the orange glow of sodium in table salt if thrown into the fire. An atom has many different frequencies, some in the radio range, some in the visible spectrum, and some in between. Cesium-133 is most often chosen for atomic clocks.

To cause the cesium atoms to resonate in an atomic clock, one of the transitions, or the resonant frequency, must be accurately measured. This is usually done by locking a crystal oscillator into the fundamental microwave resonance of the cesium atom. This signal is in the microwave range of the radio frequency spectrum and has the same frequency as direct broadcast satellite signals. Engineers know how to create equipment for this spectrum region, in great detail.

To create a clock, cesium is first heated so that the atoms are vaporized and passed through a high-vacuum tube. They first pass through a magnetic field, which selects atoms with the desired energy state; they then pass through an intense microwave field. The frequency of microwave energy jumps back and forth in a narrow range of frequencies so that at a certain point it reaches a frequency of 9,192,631,770 hertz (Hz, or cycles per second). The range of the microwave oscillator is already close to this frequency because it is produced by a precise crystal oscillator. When a cesium atom receives microwave energy of the desired frequency, it changes its energy state.

At the end of the tube, another magnetic field separates atoms that have changed their energy state if the microwave field was of the right frequency. The detector at the end of the tube produces an output signal proportional to the number of cesium atoms that hit it, and peaks when the microwave frequency is sufficiently correct. This peak signal is needed for correction to bring the crystal oscillator, and therefore the microwave field, to the desired frequency. This blocked frequency is then divided by 9,192,631,770 to give the familiar one pulse per second that the real world needs.

When was the atomic clock invented?

In 1945, Columbia University physics professor Isidor Rabi proposed a clock that could be made based on techniques developed in the 1930s. It was called atomic beam magnetic resonance. By 1949, the National Bureau of Standards announced the creation of the world's first atomic clock based on the ammonia molecule, the vibrations of which were read, and by 1952 it created the world's first atomic clock based on cesium atoms, NBS-1.

In 1955, the National Physical Laboratory in England built the first clock using a cesium beam as a calibration source. Over the next decade, more advanced watches were created. In 1967, during the 13th General Conference on Weights and Measures, the SI second was determined based on vibrations in the cesium atom. There was no timekeeping system in the world more precise definitions than this. NBS-4, the world's most stable cesium clock, was completed in 1968 and was in use until 1990.

Atomic clocks are the most accurate time measuring instruments that exist today and are becoming increasingly higher value with development and complexity modern technologies.

Principle of operation

Atomic clocks keep accurate time not thanks to radioactive decay, as their name might suggest, but using vibrations of nuclei and the electrons surrounding them. Their frequency is determined by the mass of the nucleus, gravity and the electrostatic “balancer” between the positively charged nucleus and electrons. This does not quite correspond to a regular watch movement. Atomic clocks are more reliable time keepers because their oscillations do not change depending on such factors environment, such as humidity, temperature or pressure.

Evolution of atomic clocks

Over the years, scientists have realized that atoms have resonant frequencies related to each's ability to absorb and emit electromagnetic radiation. In the 1930s and 1940s, high-frequency communications and radar equipment was developed that could interface with the resonance frequencies of atoms and molecules. This contributed to the idea of ​​a watch.

The first examples were built in 1949 by the National Institute of Standards and Technology (NIST). Ammonia was used as a vibration source. However, they were not much more accurate than the existing time standard, and cesium was used in the next generation.

New standard

The change in the precision of time measurement was so great that in 1967 the General Conference on Weights and Measures defined the SI second as 9,192,631,770 vibrations of a cesium atom at its resonant frequency. This meant that time was no longer related to the movement of the Earth. The world's most stable atomic clock was created in 1968 and was used as part of the NIST timekeeping system until the 1990s.

Improvement car

One of the latest advances in this area is laser cooling. This improved the signal-to-noise ratio and reduced the uncertainty in the clock signal. Housing this cooling system and other equipment used to improve cesium clocks would require space the size of a railroad car, although commercial versions could fit in a suitcase. One of these laboratory installations keeps time in Boulder, Colorado, and is the most accurate clock on Earth. They are only wrong by 2 nanoseconds per day, or 1 second per 1.4 million years.

Complex technology

This enormous precision is the result of complex technological process. First, liquid cesium is placed in a furnace and heated until it turns into a gas. The metal atoms exit at high speed through a small opening in the furnace. Electromagnets cause them to split into separate beams with different energies. The required beam passes through a U-shaped hole, and the atoms are irradiated with microwave energy with a frequency of 9,192,631,770 Hz. Thanks to this, they are excited and move into a different energy state. The magnetic field then filters out other energy states of the atoms.

The detector reacts to cesium and shows a maximum at correct value frequencies. This is necessary to configure the quartz oscillator that controls the clock mechanism. Dividing its frequency by 9.192.631.770 gives one pulse per second.

Not just cesium

Although the most common atomic clocks use the properties of cesium, there are other types. They differ in the element used and the means for determining changes in energy level. Other materials are hydrogen and rubidium. Hydrogen atomic clocks function similarly to cesium clocks, but require a container with walls made of a special material that prevents the atoms from losing energy too quickly. Rubidium watches are the simplest and most compact. In them, a glass cell filled with rubidium gas changes the absorption of light when exposed to ultrahigh frequency.

Who needs accurate time?

Today, time can be measured with extreme precision, but why is this important? This is necessary in systems such as Cell phones, Internet, GPS, aviation programs and digital television. At first glance this is not obvious.

An example of how precise time is used is in packet synchronization. Thousands of telephone calls pass through the average communication line. This is only possible because the conversation is not transmitted completely. The telecommunications company splits it into small packets and even skips some of the information. They then pass through the line along with packets of other conversations and are restored at the other end without mixing. The telephone exchange's clocking system can determine which packets belong to a given conversation by the exact time the information was sent.

GPS

Another implementation of precise time is a global positioning system. It consists of 24 satellites that transmit their coordinates and time. Any GPS receiver can connect to them and compare broadcast times. The difference allows the user to determine their location. If these clocks were not very accurate, then the GPS system would be impractical and unreliable.

The limit of perfection

With the development of technology and atomic clocks, the inaccuracies of the Universe became noticeable. The earth moves unevenly, causing random variations in the length of years and days. In the past, these changes would have gone unnoticed because the tools for measuring time were too imprecise. However, much to the frustration of researchers and scientists, the time of atomic clocks has to be adjusted to compensate for anomalies real world. They are amazing tools that help advance modern technology, but their excellence is limited by the limits set by nature itself.

These are devices for measuring time, the operating principle of which is based on atomic physics. Thanks to the properties chemical elements used in the design, the error of these watches is minimal. For example, devices based on thorium-229 will lag by a tenth of a second in about 14 billion years.

How do atomic clocks work?

If in quartz watch The reference frequency for determining the second is the number of vibrations of a quartz crystal, then in atomic ones it is taken to be the frequency of transitions of electrons in the atoms of certain chemical elements from one energy level to another.

1 - Electronic component (chip)

2 - Nuclear source

3 - Photodetector

4 - Upper heater

5 - Resonant cell

6 - Wave plate

7 - Bottom heater

8 - Vertical emitting laser

Here's the point: atoms have electrons. They have energy. When absorbing or releasing energy, electrons jump from one energy level to another, absorbing or emitting electromagnetic waves, the frequency of which is always the same. This phenomenon can be controlled: when an atom is exposed to microwave radiation, it responds with a certain number of vibrations.

This property is used to improve the accuracy of time measurements. Thus, it is recognized that a second is the duration of 9192631770 radiation cycles. This frequency corresponds to the transition between two energy levels of the cesium-133 atom. By comparing the oscillation frequency of a quartz oscillator with the transition frequency of the element’s atoms, the slightest deviations are recorded. If there are deviations, the quartz vibrations are adjusted.

Cesium is not the only material used in atomic clocks. Devices based on chemical elements are appearing that can provide even greater precision: ytterbium, thorium-229, strontium.

Why are atomic clocks accurate?

The vibration frequency of the chemical element is the same, and this minimizes the possibility of error. In addition, unlike a quartz crystal, the atoms do not wear out or lose their Chemical properties with time.

Other names for atomic clocks: quantum, molecular.

A new impetus in the development of devices for measuring time was given by atomic physicists.

In 1949, the first atomic clock was built, where the source of oscillations was not a pendulum or a quartz oscillator, but signals associated with the quantum transition of an electron between two energy levels of an atom.

In practice, such clocks turned out to be not very accurate, moreover, they were bulky and expensive and were not widely used. Then it was decided to turn to the chemical element cesium. And in 1955, the first atomic clocks based on cesium atoms appeared.

In 1967, it was decided to switch to the atomic time standard, since the rotation of the Earth is slowing down and the magnitude of this slowdown is not constant. This made the work of astronomers and time keepers much more difficult.

The Earth currently rotates at a rate of about 2 milliseconds per 100 years.

Fluctuations in the length of the day also reach thousandths of a second. Therefore, the accuracy of Greenwich Mean Time (generally accepted as a global standard since 1884) has become insufficient. In 1967, the transition to the atomic time standard took place.

Today, a second is a period of time exactly equal to 9,192,631,770 periods of radiation, which corresponds to the transition between two hyperfine levels of the ground state of the Cesium 133 atom.

Currently, Coordinated Universal Time is used as the time scale. It is formed by the International Bureau of Weights and Measures by combining data from time storage laboratories various countries, as well as data from the International Earth Rotation Service. Its accuracy is almost a million times higher than astronomical Greenwich Mean Time.

A technology has been developed that will radically reduce the size and cost of ultra-precise atomic clocks, which will make it possible to widely use them in mobile devices himself for various purposes. Scientists were able to create an atomic time standard of ultra-small size. Such atomic clocks consume less than 0.075 W and have an error of no more than one second in 300 years.

A US research group has succeeded in creating an ultra-compact atomic standard. It has become possible to power atomic clocks from ordinary AA batteries. Ultra-precise atomic clocks, usually at least a meter high, were placed in a volume of 1.5x1.5x4 mm

An experimental atomic clock based on a single mercury ion has been developed in the USA. They are five times more accurate than cesium, which is accepted as the international standard. Cesium clocks are so accurate that it will take 70 million years for a discrepancy of one second to be achieved, while for mercury clocks this period will be 400 million years.

In 1982, in a dispute between the astronomical definition of the Time standard and those who defeated it atomic clock a new astronomical object intervened - a millisecond pulsar. These signals are as stable as the best atomic clocks

Did you know?

The first clocks in Rus'

In 1412 in Moscow, a clock was placed in the courtyard of the Grand Duke behind the Church of the Annunciation, and it was made by Lazar, a Serbian monk who came from the Serbian land. Unfortunately, no description of these first clocks in Rus' has been preserved.

How did the chiming clock appear on the Spasskaya Tower of the Moscow Kremlin?

In the 17th century, the Englishman Christopher Galloway made chimes for the Spasskaya Tower: the hour circle was divided into 17 sectors, the only clock hand was stationary, directed downwards and pointed at some number on the dial, but the dial itself rotated.

We often hear the phrase that atomic clocks always show the exact time. But from their name it is difficult to understand why atomic clocks are the most accurate or how they work.

Just because the name contains the word “atomic” does not mean that the watch poses a danger to life, even if thoughts of atomic bomb or nuclear power plant. In this case, we are just talking about the principle of operation of the watch. If in normal mechanical watch oscillatory movements are performed by gears and their movements are counted, then in an atomic clock the oscillations of electrons inside atoms are counted. To better understand the principle of operation, let's remember the physics of elementary particles.

All substances in our world are made of atoms. Atoms consist of protons, neutrons and electrons. Protons and neutrons combine with each other to form a nucleus, which is also called a nucleon. Electrons move around the nucleus, which can be at different energy levels. The most interesting thing is that when absorbing or releasing energy, an electron can move from its energy level to a higher or lower one. An electron can obtain energy from electromagnetic radiation, absorbing or emitting electromagnetic radiation of a certain frequency with each transition.

Most often there are watches in which atoms of the element Cesium -133 are used for change. If in 1 second the pendulum regular watch makes 1 oscillatory motion, then the electrons in atomic clocks based on Cesium-133, when transitioning from one energy level to another, they emit electromagnetic radiation with a frequency of 9192631770 Hz. It turns out that one second is divided into exactly this number of intervals if it is calculated in atomic clocks. This value was officially adopted by the international community in 1967. Imagine a huge dial with not 60, but 9192631770 divisions, which make up only 1 second. It is not surprising that atomic clocks are so accurate and have a number of advantages: atoms are not subject to aging, do not wear out, and the oscillation frequency will always be the same for one chemical element, thanks to which it is possible to synchronously compare, for example, the readings of atomic clocks far in space and on Earth, without fear of errors.

Thanks to atomic clocks, humanity was able to test in practice the correctness of the theory of relativity and make sure that it is better than on Earth. Atomic clocks are installed on many satellites and spacecraft, they are used for telecommunications needs, for mobile communications, and they are used to compare the exact time on the entire planet. Without exaggeration, it was thanks to the invention of atomic clocks that humanity was able to enter the era of high technology.

How do atomic clocks work?

Cesium-133 is heated by evaporating cesium atoms, which are passed through a magnetic field, where atoms with the desired energy states are selected.

The selected atoms then pass through a magnetic field with a frequency close to 9192631770 Hz, which is created by a quartz oscillator. Under the influence of the field, cesium atoms again change energy states and fall on a detector, which records when greatest number the incoming atoms will have the “correct” energy state. Maximum amount atoms with a changed energy state indicates that the frequency of the microwave field is selected correctly, and then its value is fed into an electronic device - a frequency divider, which, reducing the frequency by an integer number of times, receives the number 1, which is the reference second.

Thus, cesium atoms are used to check the correctness of the frequency magnetic field, created by a crystal oscillator, helping to maintain it at a constant value.

This is interesting: Although the current atomic clocks are unprecedentedly accurate and can run for millions of years without errors, physicists are not going to stop there. Using atoms of various chemical elements, they are constantly working to improve the accuracy of atomic clocks. Among the latest inventions is the atomic clock strontium, which are three times more accurate than their cesium counterpart. To lag behind just a second, they will need 15 billion years - time exceeding the age of our Universe...

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