The first atomic clock, which used resonant frequencies of atoms to maintain accuracy in time measurement, was born at Britain's National Physical Laboratories.
A device for precise measurement of time, which controls all aspects of our daily lives, the atomic clock, is celebrating a jubilee.
The first atomic clock, which used resonant frequencies of atoms to maintain accuracy in time measurement, was born at Britain's National Physical Laboratories. The atomic clock was designed to produce a standard for Coordinated Universal Time (UTC), which is used to legally measure time all over the world. The clock is essential for a variety of technologies such as global positioning satellites (GPS) and television signal timing.
The fine precision of time measurement is also essential for other synchronized events, such as, for example, the distribution and management of electricity, as well as money transfers all over the world. Even Big Ben in London relies on an atomic clock to maintain accuracy.
The first accurate cesium clock was developed at the National Physical Laboratories (NPL) in Great Britain in 1955, by Dr. Louis Essen. However, the idea was first proposed by Lord Calvin in 1879. He said that measuring time based on the way atoms behave would be a better way to measure the time intervals between anything else.
"Until the development of the atomic clock, the definition of time was based on the rotation of the earth," explains Prof. Patrick Gill, a senior colleague at the laboratory. "Although it sounds logical, the movement of the Earth shows variation, and the reason for using the atomic clock is that the frequency that responds to changes in the energy of the basic state of atoms is used - and this is much more accurate than any astronomical arrangement."
Atomic clocks are still much more constant than any other method of measuring time, although they are sensitive, albeit slightly, to changes in the electric and magnetic fields.
The development of the atomic clock was aided to some extent by the technological developments of World War II, including the radar. In the fifty years that have passed since the atomic clock started ticking, the accuracy of these devices has increased a hundred thousand times.
Atomic time is also very important for the congestion of the communication and computing applications, such as, for example, the coordination of sending data packets through the network, the GPS satellites and mobile phones. When the network splits the information streams and reassembles them, the timing must be precise at the point of reunification. If it is not accurate, and it doesn't matter what the data is sent, a VoIP package of an Internet phone, for example - they will reach the other side mixed up.
Modern and precise atomic clocks now use cesium 133 atoms, created in a special type of furnace, which can measure time to the nearest tenth of a billionth of a second per day. They do this by measuring a time base in the way that cooled cesium atoms bounce back and forth between different energy levels.
These jumps appear in the microwave frequency ranges, with close to 9.2 billion jumps making up the time interval known as one second. Atoms are cooled to reduce the width of that "frequency resonance". The narrower this bandwidth is, the greater the time measurement accuracy.
"Essen's initial idea was to use a horizontal beam of uncooled cesium atoms, moving about a meter across. He followed this up by measuring the microwave signals at two points along the way," explains Prof. Gil.
The atomic clocks still use this method, but in a slightly different form, known as an "atomic fountain".
"At the bottom of the fountain there is a cloud of a million atoms, cooled by lasers - usually to temperatures very close to absolute zero. "We give them a little push from below, and they jump about a meter high and fall back down. So we measure the microwaves and track them on their way up and down. From the double measurement we can reach a narrow frequency". said.
There are 5-6 international standard laboratories that use the atomic fountain method and all contribute to the UTC. There are also many commercial atomic clocks operating around the world, some of which also contribute to UTC, but they are not as accurate as the clocks in those laboratories, Prof Gill said.
Know your place
The next step, according to Prof. Gil and his team - and several other groups around the world - is the development of replacement microwaves with a lower wavelength of laser light. These optical clocks are still in the development stages and they operate at high frequencies, and therefore will allow greater accuracy of time measurement. It is also possible that the optical clocks will replace the microwave clocks as the main ones responsible for measuring time in about a decade.
Optical atomic clocks have the potential to improve the performance of GPS systems in the area of less than one meter, says Prof. Gil. "The technology that uses the most precision is the GPS systems," says Prof. Gil.
"GPS satellites have radium and cesium clocks. These satellites, which provide the basis for the triangulation required to obtain the exact position on the ground, are also monitored by ground systems. "These stations have more accurate clocks than inside the satellites. This allows an accuracy of nanoseconds and causes a deviation of a few meters. An optical clock will appear first in the ground stations and then also in the next generations of satellites, and this means an accuracy in position of less than a meter, even when the object or person is in motion.
This opens up many possibilities for military applications that rely heavily on GPS, as well as more everyday uses, such as civilian transportation and tracking activities. "There is even talk of inserting receivers into mobile phone devices and even tiny atomic clocks inside the mobile devices," said Prof. Gil.
They will not be as accurate as the cesium fountain systems, but they will be small and will be able to give local time for periods when the receiver does not see satellites.
In September 2004, the US National Institute of Standards (NIST) will use computer chip manufacturing techniques to produce small atomic clocks.
In the final development we will see systems based on electric batteries the size of a tiny night lamp.
