Once defined by the predictable swing of a finely-tuned pendulum in the classic era, the most precise clock these days--the atomic clocks--rely on the electron transition frequency to keep track of time.
In the past a couple of months, two new atomic clocks smashed the history of timekeeping yet again. Both designs involve the NIST, or National Institute of Standards and Technology, where the first atomic clock was built in 1948. The proof-of-concept device was less accurate than quartz clocks at the time. However, it inspired the construction of the first modern day master clock (which uses the atomic transition of cesium-133 to keep track of time) in 1955 at UK's National Physical Laboratory.
What are atomic clocks so accurate? They take advantage of the highly consistent resonance frequency of atom. Take cesium-133 for example, all of the same atoms oscillate at exact 9,192,631,770 cycles per second, without variation among them. The remarkably consistent frequency cannot influenced by any environmental factors, unlike quartz crystals which changes their oscillating frequency at different temperatures.
In a recent publication in the journal Nature physicists at NIST described an optical atomic clock that traps a thousand ytterbium atoms using grids of laser beams. It matches the natural frequency with such a small possible error that it would take almost 14 billion years (our universe has existed for less than that) to lose a second. The ytterbium atomic clock set three new world records in "systematic uncertainty, stability, and reproducibility".
In an article published in the journal Science scientists from Joint Institute for Laboratory Astrophysics (JILA), cohosted by NIST, reported another new design: they turned strontium atoms into quantum gas and packed them into a tiny three-dimensional cube at 1,000 times the density of the previous generation of atomic clocks (which are called one-dimensional clock in comparison).
In older atomic clocks each atom existed as a separate quantum particle with their own energy state. JILA's device created a so-called “quantum many-body system,” which arranges the atoms in the way that the collective exists as a whole in the lowest overall energy state. Compared to the group’s previous 1-D clocks, the new 3-D clock can reach the same level of precision more than 20 times faster. Their data show the 3-D clock achieved a precision of just 3.5 parts error in 10 quintillions (10E-19) in about 2 hours, fastest among all atomic clocks.
The science behind time-keeping has come a long way, with the new atomic clock design bringing the accuracy, precision, and stability of time measurement up to whole new levels. Besides tracking time, scientists also hope that one day these highly advanced clocks can help us explore ripples in the spacetime fabrics, or even hunt for the elusive dark matter.