Washington, August 12 : Scientists at the National Institute of Standards and Technology (NIST) have said that an experimental atomic clock based on ytterbium atoms is about four times more accurate than it was several years ago, giving it a precision comparable to that of the NIST-F1 cesium fountain clock, the civilian time standard of the US.
NIST scientists evaluated the clock by measuring the natural frequency of ytterbium, carefully accounting for all possible deviations such as those caused by collisions between the atoms, and by using NIST-F1 as a 'ruler' for comparison.
The results were good enough to indicate that the ytterbium clock is competitive in some respects with NIST-F1, which has been improving steadily and now keeps time to within 1 second in about 100 million years.
More importantly, the improved ytterbium clock gives the time standards community more options in the ongoing development and comparisons of next-generation clocks, according to NIST physicist Chris Oates.
The NIST ytterbium clock is based on about 30,000 heavy metal atoms that are cooled to 15 microkelvins (close to absolute zero) and trapped in a column of several hundred pancake-shaped wells-an 'optical lattice'-made of laser light.
A laser that 'ticks' 518 trillion times per second induces a transition between two energy levels in the atoms.
The clock's enhanced performance was made possible by improvements in the apparatus and a switch to a different form of ytterbium whose nucleus is slightly magnetic due its 'spin-one half' angular momentum.
This atom is less susceptible to key errors than the 'spin-zero' form of ytterbium used previously.
NIST scientists are developing five versions of next-generation atomic clocks, each using a different atom and offering different advantages.
The experimental clocks all operate at optical (visible light) frequencies, which are higher than the microwave frequencies used in NIST-F1, and thus can divide time into smaller units, thereby yielding more stable clocks.
Additionally, optical clocks could one day lead to time standards up to 100 times more accurate than today's microwave clocks.
Next-generation clocks might lead to new types of gravity sensors for exploring underground natural resources and fundamental studies of the Earth.
NIST scientists evaluated the clock by measuring the natural frequency of ytterbium, carefully accounting for all possible deviations such as those caused by collisions between the atoms, and by using NIST-F1 as a 'ruler' for comparison.
The results were good enough to indicate that the ytterbium clock is competitive in some respects with NIST-F1, which has been improving steadily and now keeps time to within 1 second in about 100 million years.
More importantly, the improved ytterbium clock gives the time standards community more options in the ongoing development and comparisons of next-generation clocks, according to NIST physicist Chris Oates.
The NIST ytterbium clock is based on about 30,000 heavy metal atoms that are cooled to 15 microkelvins (close to absolute zero) and trapped in a column of several hundred pancake-shaped wells-an 'optical lattice'-made of laser light.
A laser that 'ticks' 518 trillion times per second induces a transition between two energy levels in the atoms.
The clock's enhanced performance was made possible by improvements in the apparatus and a switch to a different form of ytterbium whose nucleus is slightly magnetic due its 'spin-one half' angular momentum.
This atom is less susceptible to key errors than the 'spin-zero' form of ytterbium used previously.
NIST scientists are developing five versions of next-generation atomic clocks, each using a different atom and offering different advantages.
The experimental clocks all operate at optical (visible light) frequencies, which are higher than the microwave frequencies used in NIST-F1, and thus can divide time into smaller units, thereby yielding more stable clocks.
Additionally, optical clocks could one day lead to time standards up to 100 times more accurate than today's microwave clocks.
Next-generation clocks might lead to new types of gravity sensors for exploring underground natural resources and fundamental studies of the Earth.
