#atomic clocks

Ytterbium atomic clock could open a new window on fundamental physics

For the first time, an international team of physicists has successfully harnessed a rare orbital transition in atoms of ytterbium to create a new type of atomic clock that is both highly precise and extremely sensitive to fundamental physical effects. Publishing their results in Nature Photonics, the researchers, led by Taiki Ishiyama at Kyoto University, say their approach could pave the way for some of the most stringent tests yet of predictions made by the Standard Model. Underperforming precision To measure the passing of time, an atomic clock excites an electron in confined atoms to a higher energy level, then interrogates the transition frequency of the atoms. Because these oscillations display such little variation, atomic clocks are the most accurate timekeepers ever developed.

A team of international researchers has developed an innovative approach to uncover the secrets of dark matter. In a collaboration between the University of Queensland, Australia, and Germany's metrology institute (Physikalisch-Technische Bundesanstalt, PTB), the team used data from atomic clocks and cavity-stabilized lasers located far apart in space and time to search for forms of dark matter that would have been invisible in previous searches. This technique will allow the researchers to detect signals from dark matter models that interact universally with all atoms, an achievement that has eluded traditional experiments.

Ask Ethan: Where Does Quantum Uncertainty Come From?

“Explain to me what information is gained from the quantum mechanical commutation relation. There's more to it than, "we just can't measure both properties at the same time."”

It’s absolutely true that, in quantum mechanics, there are certain pairs of properties that we simply can’t measure simultaneously. Measure the position of an object really well, and its momentum becomes more uncertain. Measure its energy, and its time becomes more uncertain. And measure its voltage, and the free charge becomes more uncertain. Although this is disconcerting to some, it’s a fundamental part of the quantum nature of the Universe. But there’s also more to it than that! Not only are pairs inherently uncertain, but each component has some built-in uncertainty that you can never take away. Moreover, it arises from a simple fact that isn’t true classically: the order of operations -- whether you measure position or momentum first -- makes a fundamental difference in what you get out. This quantum commutation relation is where so much of the fundamental quantum weirdness in our Universe comes from.

World's most precise clock achieves 19-decimal accuracy with aluminum ion technology

There's a new record holder for the most accurate clock in the world. Researchers at the National Institute of Standards and Technology (NIST) have improved their atomic clock based on a trapped aluminum ion. Part of the latest wave of optical atomic clocks, it can perform timekeeping with 19 decimal places of accuracy. Optical clocks are typically evaluated on two levels—accuracy (how close a clock comes to measuring the ideal "true" time, also known as systematic uncertainty) and stability (how efficiently a clock can measure time, related to statistical uncertainty). This new record in accuracy comes out of 20 years of continuous improvement of the aluminum ion clock. Beyond its world-best accuracy, 41% greater than the previous record, this new clock is also 2.6 times more stable than any other ion clock. Reaching these levels has meant carefully improving every aspect of the clock, from the laser to the trap and the vacuum chamber.

Measuring Time: Atomic Clocks

The most accurate clocks that exist today are atomic clocks, measuring the flow of time based on the resonant frequency of atoms and molecules. This is possible because electrons associated with atoms exist at distinct energy levels, and the transitions between these energy levels can be determined, leading to a consistent resonance when probed. While there are several types of atomic clocks, with different setups and configurations, they all rely on a single substance.

Cesium clocks are the most common, and it is the resonant frequency of cesium (also written caesium) that is used for the current definition of a second. Some atomic clocks also use rubidium, or hydrogen. Less common and more recent is strontium, as well as aluminum, yttrium, and mercury. Historically, ammonia was actually used in the first atomic clock in 1949 before the first cesium clock was built in 1955.

Atomic clocks are used around the world to precisely tell time. Each "tick" of the clock depends on atomic vibrations and their effects on surrounding electromagnetic fields. Standard atomic clocks in use today, based on the atom cesium, tell time by "counting" radio frequencies. These clocks can measure time to a precision of one second per every hundreds of millions of years. Newer atomic clocks that measure optical frequencies of light are even more precise, and may eventually replace the radio-based ones.

Now, researchers at Caltech and the Jet Propulsion Laboratory (JPL), which is managed by Caltech for NASA, have come up with a new design for an optical atomic clock that holds promise to be the most accurate and precise yet (accuracy refers to the ability of the clock to correctly pin down the time, and precision refers to its ability to tell time in fine detail). Nicknamed the "tweezer clock," it employs technology in which so-called laser tweezers are used to manipulate individual atoms.

"One of the goals of physicists is to be able to tell time as precisely as possible," says Manuel Endres, an assistant professor of physics at Caltech who led a new paper describing the results in the journal Physical Review X. Endres explains that while the ultra-precise clocks may not be needed for everyday purposes of counting time, they could lead to advances in fundamental physics research as well as new technologies that are yet to be imagined.

The new clock design builds upon two types of optical atomic clocks already in use. The first type is based on a single trapped charged atom, or ion, while the second uses thousands of neutral atoms trapped in what is called an optical lattice. In the trapped-ion approach, only one atom (the ion) needs to be precisely isolated and controlled, and this improves the accuracy of the clock. On the other hand, the optical lattice approach benefits from having multiple atoms -- with more atoms there are fewer uncertainties that arise due to random quantum fluctuations of individual atoms.

Neglected atom has top properties for atomic clocks

Researchers propose that lutetium clocks could outperform today's timekeepers

Like watchmakers choosing superior materials to build a fine timepiece, physicists at the Centre for Quantum Technologies (CQT) at the National University of Singapore have singled out an atom that could allow us to build better atomic clocks.

The CQT team report in Nature Communications that a previously neglected element -- lutetium -- could improve on today's best clocks. Lutetium (Lu) is a rare earth element with atomic number 71.

"The ultimate performance of a clock comes down to the properties of the atom -- how insensitive the atom is to its environment. I would call lutetium top in its class," says Murray Barrett, who led the research.

Barrett is so confident because data in the team's paper, published 25 April, show Lu to have lower sensitivity to temperature than atoms used in clocks today. These measurements add to earlier results showing lutetium could make a high-performance clock.

Atomic clocks have set the global standard for measuring time for over half a century. But since the second was defined with reference to caesium atoms in the 1960s, there has been world-wide competition to improve the accuracy and stability of atomic clocks.