A brief history of the appearance of atomic instruments for measuring time. The most accurate clock in the world - quantum
The atomic clock is a device for very precise time measurement. They got their name from the principle of their work, since natural vibrations of molecules or atoms are used as a period. Atomic clocks have been widely used in navigation, in the space industry, in satellite positioning, in the military, in aircraft detection, and in telecommunications.
As you can see, there are a lot of areas of application, but why do they all need such accuracy, because today the error of ordinary atomic clocks is only 1 second in 30 million years? But there is even more precise. Everything is understandable, because time is used to calculate distances, and there a small error can lead to hundreds of meters, or even kilometers, if we take cosmic distances. For example, let's take the American GPS navigation system, when using a conventional electronic clock in the receiver, the error in measuring coordinates will be quite significant, which can affect all other calculations, and this can lead to consequences when it comes to space technologies. Naturally, for GPS receivers in mobile devices and other gadgets, greater accuracy is not at all important.
The most accurate time in Moscow and the world can be found on the official website - "server of the exact current time" www.timeserver.ru
What are atomic clocks made of?
An atomic clock consists of several main parts: a quartz oscillator, a quantum discriminator, and electronics blocks. The main reference setting is a quartz oscillator, which is built on quartz crystals and, as a rule, produces a standard frequency of 10, 5, 2.5 MHz. Since the stable operation of quartz without error is rather small, it must be constantly adjusted.
The quantum discriminator fixes the frequency of the atomic line, and it is compared in the frequency-phase comparator with the frequency of the quartz oscillator. The comparator has feedback to the crystal oscillator to adjust it in case of frequency mismatch.
Atomic clocks can not be built on all atoms. The most optimal is the cesium atom. It refers to the primary against which all other suitable materials are compared, such as, for example: strontium, rubidium, calcium. The primary standard is absolutely suitable for measuring exact time, which is why it is called primary.
The most accurate atomic clock in the world
To date most accurate atomic clock are in the UK (officially accepted). Their error is only 1 second in 138 million years. They are the standard for the national time standards of many countries, including the United States, and also determine the international atomic time. But in the kingdom there are not the most accurate clocks on Earth.
most accurate atomic clock photo
The US claimed to have developed an experimental type of precision clock based on cesium atoms, with an error of 1 second in almost 1.5 billion years. Science in this area does not stand still and develops at a rapid pace.
Firstly, the clock uses humanity as a means of program-time control.
Secondly, today the measurement of time is also the most accurate type of measurement of all conducted: the accuracy of time measurement is now determined by an incredibly error of the order of 1 10-11%, or 1 s in 300 thousand years.
And modern people achieved such accuracy when they began to use atoms, which, as a result of their oscillations, are the regulator of the atomic clock. Cesium atoms are in the two energy states we need (+) and (-). Electromagnetic radiation with a frequency of 9,192,631,770 hertz is produced when atoms move from the state (+) to (-), creating a precise constant periodic process - the controller of the atomic clock code.
In order for atomic clocks to work accurately, cesium must be evaporated in a furnace, as a result of which its atoms are ejected. Behind the furnace is a sorting magnet, which has the capacity of atoms in the (+) state, and in it, due to irradiation in a microwave field, the atoms go into the (-) state. The second magnet directs atoms that have changed state (+) to (-) to the receiving device. Many atoms that have changed their state are obtained only if the frequency of the microwave emitter coincides exactly with the frequency of vibrations of cesium 9 192 631 770 hertz. Otherwise, the number of atoms (-) in the receiver decreases.
Instruments constantly monitor and adjust the constancy of the frequency 9 192 631 770 hertz. So, the dream of watch designers came true, an absolutely constant periodic process was found: a frequency of 9,192,631,770 hertz, which regulates the course of atomic clocks.
Today, as a result of international agreement, the second is defined as the radiation period multiplied by 9,192,631,770, corresponding to the transition between two hyperfine structural levels of the ground state of the cesium atom (cesium-133 isotope).
To measure the exact time, you can also use vibrations of other atoms and molecules, such as atoms of calcium, rubidium, cesium, strontium, hydrogen molecules, iodine, methane, etc. However, the radiation of the cesium atom is recognized as the frequency standard. In order to compare the vibrations of different atoms with a standard (cesium), a titanium-sapphire laser was created that generates a wide frequency range in the range from 400 to 1000 nm.
The first creator of quartz and atomic clocks was an English experimental physicist Essen Lewis (1908-1997). In 1955, he created the first atomic frequency (time) standard on a beam of cesium atoms. As a result of this work, 3 years later (1958) a time service emerged based on the atomic frequency standard.
In the USSR, Academician Nikolai Gennadievich Basov put forward his ideas for creating atomic clocks.
So, atomic clock, one of the exact types of clocks is a device for measuring time, where the natural oscillations of atoms or molecules are used as a pendulum. The stability of atomic clocks is the best among all existing types of clocks, which is the key to the highest accuracy. The atomic clock generator produces more than 32,768 pulses per second, unlike conventional clocks. Oscillations of atoms do not depend on air temperature, vibrations, humidity and many other external factors.
In the modern world, when navigation is simply indispensable, atomic clocks have become indispensable assistants. They are able to determine the location of a spacecraft, satellite, ballistic missile, aircraft, submarine, car automatically via satellite communications.
Thus, for the last 50 years, atomic clocks, or rather cesium clocks, have been considered the most accurate. They have long been used by timekeeping services, and time signals are also broadcast by some radio stations.
The atomic clock device includes 3 parts: 
quantum Discriminator,
quartz oscillator,
electronics complex.
A quartz oscillator generates a frequency (5 or 10 MHz). The oscillator is an RC radio generator, in which the piezoelectric modes of a quartz crystal are used as a resonant element, where the atoms that have changed the state (+) to (-) are compared. To increase stability, its frequency is constantly compared with the vibrations of the quantum discriminator (atoms or molecules) . When there is a difference in oscillations, the electronics adjusts the frequency of the quartz oscillator to zero, thereby increasing the stability and accuracy of the clock to the desired level.
In today's world, atomic clocks can be made in any country in the world for use in everyday life. They are very small in size and beautiful. The size of the latest novelty of atomic clocks is no more than a matchbox and their low power consumption is less than 1 watt. And this is not the limit, perhaps in the future technological progress will reach mobile phones. In the meantime, compact atomic clocks are installed only on strategic missiles to increase the accuracy of navigation many times over.
Today, men's and women's atomic watches for every taste and budget can be bought in online stores.
In 2011, the world's smallest atomic clock was created by Symmetricom and the Sandia National Laboratory. This watch is 100 times more compact than previous commercially available versions. The size of an atomic chronometer is no larger than a matchbox. It needs 100 mW of power to operate, which is 100 times less than its predecessors.
It was possible to reduce the size of the clock by installing instead of springs and gears a mechanism that operates on the principle of determining the frequency of electromagnetic waves emitted by cesium atoms under the influence of a laser beam of negligible power.
Such watches are used in navigation, as well as in the work of miners, divers, where it is necessary to accurately synchronize time with colleagues on the surface, as well as accurate time services, because the error of atomic clocks is less than 0.000001 fractions of a second per day. The cost of the record-breaking small Symmetricom atomic clock was about $1,500.
When the light suddenly goes out and comes back on a little later, how do you know what time the clock needs to be set? Yes, I'm talking about electronic watches, which many of us probably have. Have you ever thought about how time is regulated? In this article, we will learn all about atomic clocks and how they make the whole world tick.
Are atomic clocks radioactive?
Atomic clocks tell time better than any other clock. They tell the 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 position of the planets would not be known with sufficient accuracy for space probes and vehicles.
Atomic clocks are not radioactive. They don't rely on atomic decay. Moreover, they have a spring, just like regular watches. The biggest difference between standard clocks and atomic clocks is that oscillations in atomic clocks occur in the nucleus of an atom between the surrounding electrons. These oscillations can hardly be called parallel to the balance wheel in a winding watch, but both types of oscillation can be used to keep track of the passing time. The oscillation frequency 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 different types of atomic clocks, but they are built on the same principles. The main difference is related to the element and means of detecting changes in the energy level. Among the different types of atomic clocks, there are the following:
- Cesium atomic clocks using beams of cesium atoms. The clock separates cesium atoms with different energy levels by a magnetic field.
- A hydrogen atomic clock keeps the hydrogen atoms at the right energy level in a container whose walls are made of a 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 filled with rubidium gas.
The most accurate atomic clocks today use a cesium atom and a conventional magnetic field with detectors. In addition, cesium atoms are held back by laser beams, which reduces small frequency changes due to the Doppler effect.
How do cesium-based atomic clocks work?
Atoms have a characteristic vibrational frequency. A familiar example of frequency is the orange glow of sodium in table salt when thrown into a fire. The 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.
In order to cause the resonance of cesium atoms in an atomic clock, one of the transitions, or the resonant frequency, must be accurately measured. This is usually done by blocking the crystal oscillator in 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 the signals from direct broadcast satellites. Engineers know how to create equipment for this region of the spectrum, down to the smallest detail.
To create a clock, cesium is first heated so that the atoms vaporize and pass through a high vacuum tube. First, they pass through a magnetic field, which selects atoms with the desired energy state; then they pass through an intense microwave field. The frequency of microwave energy jumps back and forth in a narrow band of frequencies, so that at some 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, since 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 the atoms, which have changed their energy state if the microwave field was at the right frequency. The detector at the end of the tube gives an output proportional to the number of cesium atoms that hit it, and peaks when the microwave frequency is sufficiently true. This peak signal is needed for correction in order to bring the crystal oscillator, and hence the microwave field, to the desired frequency. This locked 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 Isidore Rabi proposed a clock that could be made using techniques developed in the 1930s. It was called the magnetic resonance atomic beam. 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 had 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 better definition in the world timekeeping system than this. NBS-4, the world's most stable cesium clock, was completed in 1968 and was in use until 1990.
High-precision atomic clocks that make an error of one second in 300 million years. This clock, which replaced an old model that had a one-second error in a hundred million years, now sets the standard for American civil time. Lenta.ru decided to recall the history of the creation of atomic clocks.
First atom
In order to create a clock, it is enough to use any periodic process. And the history of the emergence of time measuring instruments is partly the history of the emergence of either new energy sources or new oscillatory systems used in watches. The simplest clock is probably the sun clock, requiring only the sun and an object to cast a shadow to operate. The disadvantages of this method of determining the time are obvious. Water and hourglasses are no better either: they are suitable only for measuring relatively short periods of time.
The oldest mechanical clock was found in 1901 near the island of Antikythera on a sunken ship in the Aegean Sea. They contain about 30 bronze gears in a wooden case measuring 33 by 18 by 10 centimeters and date back to around 100 BC.
For almost two thousand years, mechanical watches have been the most accurate and reliable. The appearance in 1657 of the classic work of Christian Huygens "Pendulum Clock" ("Horologium oscillatorium, sive de motu pendulorum an horologia aptato demonstrationes geometrica") with a description of a time reference device with a pendulum as an oscillating system, was probably the apogee in the history of the development of mechanical devices of this type.
However, astronomers and navigators still used the starry sky and maps to determine their location and exact time. The first electric clock was invented in 1814 by Francis Ronalds. However, the first such instrument was inaccurate due to its sensitivity to temperature changes.
The further history of watches is connected with the use of different oscillatory systems in devices. Introduced in 1927 by employees of Bell Labs, quartz watches used the piezoelectric properties of a quartz crystal: when an electric current is applied to it, the crystal begins to shrink. Modern quartz chronometers can achieve an accuracy of up to 0.3 seconds per month. However, since quartz is subject to aging, over time the watch becomes less accurate.
With the development of atomic physics, scientists proposed using particles of matter as oscillatory systems. This is how the first atomic clock appeared. The idea of using atomic vibrations of hydrogen to measure time was suggested back in 1879 by the English physicist Lord Kelvin, but this became possible only by the middle of the 20th century.
Reproduction of a painting by Hubert von Herkomer (1907)
In the 1930s, the American physicist and discoverer of nuclear magnetic resonance, Isidore Rabi, began working on cesium-133 atomic clocks, but the outbreak of war prevented him. Already after the war, in 1949, the first molecular clock using ammonia molecules was created at the US National Committee of Standards with the participation of Harold Lyonson. But the first such instruments for measuring time were not as accurate as modern atomic clocks.
The relatively low accuracy was due to the fact that due to the interaction of ammonia molecules with each other and with the walls of the container in which this substance was located, the energy of the molecules changed and their spectral lines broadened. This effect is very similar to the friction in a mechanical watch.
Later, in 1955, Louis Esssen of the UK's National Physical Laboratory introduced the first caesium-133 atomic clock. This clock accumulated an error of one second in a million years. The device was named NBS-1 and began to be considered a cesium frequency standard.
The circuit diagram of an atomic clock consists of a crystal oscillator controlled by a feedback discriminator. The oscillator uses the piezoelectric properties of quartz, while the discriminator uses the energy vibrations of atoms, so that the vibrations of quartz are tracked by signals from transitions from different energy levels in atoms or molecules. Between the generator and the discriminator there is a compensator tuned to the frequency of atomic vibrations and comparing it with the vibration frequency of the crystal.
The atoms used in the clock must provide stable vibrations. Each frequency of electromagnetic radiation has its own atoms: calcium, strontium, rubidium, cesium, hydrogen. Or even molecules of ammonia and iodine.
time standard
With the advent of atomic time measuring instruments, it became possible to use them as a universal standard for determining the second. Since 1884, Greenwich time, considered the world standard, has given way to the standard of atomic clocks. In 1967, by decision of the 12th General Conference of Weights and Measures, one second was defined as the duration of 9192631770 periods of radiation corresponding to the transition between two hyperfine levels of the ground state of the cesium-133 atom. This definition of a second does not depend on astronomical parameters and can be reproduced anywhere on the planet. Cesium-133, used in the standard atomic clock, is the only stable isotope of cesium with 100% abundance on Earth.
Atomic clocks are also used in the satellite navigation system; they are necessary to determine the exact time and coordinates of the satellite. Thus, each satellite of the GPS system has four sets of such clocks: two rubidium and two cesium, which provide a signal transmission accuracy of 50 nanoseconds. The Russian satellites of the GLONASS system also have cesium and rubidium atomic time measuring instruments, and the satellites of the unfolding European geopositioning system Galileo are equipped with hydrogen and rubidium ones.
The accuracy of hydrogen clocks is the highest. It is 0.45 nanoseconds in 12 hours. Apparently, the use of such accurate clocks by Galileo will bring this navigation system to the fore in 2015, when its 18 satellites will be in orbit.
Compact atomic clock
Hewlett-Packard was the first company to develop a compact atomic clock. In 1964, she created the HP 5060A cesium instrument, the size of a large suitcase. The company continued to develop this direction, but since 2005 it has sold its atomic clock division to Symmetricom.
In 2011, Draper Laboratories and Sandia National Laboratories developed and Symmetricom released the first Quantum miniature atomic clock. At the time of release, they cost about 15 thousand dollars, were enclosed in a sealed case measuring 40 by 35 by 11 millimeters and weighed 35 grams. The power consumption of the watch was less than 120 milliwatts. Initially, they were developed by order of the Pentagon and were intended to serve navigation systems that function independently of GPS systems, for example, deep under water or land.
Already at the end of 2013, the American company Bathys Hawaii introduced the first "wrist" atomic clock. They use the SA.45s chip manufactured by Symmetricom as the main component. Inside the chip is a capsule with cesium-133. The design of the watch also includes photocells and a low-power laser. The latter provides heating of gaseous cesium, as a result of which its atoms begin to move from one energy level to another. The measurement of time is just made by fixing such a transition. The cost of the new device is about 12 thousand dollars.
Trends towards miniaturization, autonomy and accuracy will lead to the fact that in the near future there will be new devices using atomic clocks in all areas of human life, from space research on orbiting satellites and stations to domestic applications in indoor and wrist systems.
