The JILA strontium lattice clock is about 50 percent more precise than the record holder of the past few years, NIST’s quantum logic clock. Precision refers to how closely the clock approaches the true resonant frequency at which its reference atoms oscillate between two electronic energy levels. The new strontium clock is so precise it would neither gain nor lose one second in about 5 billion years, if it could operate that long. (This time period is longer than the age of the Earth, an estimated 4.5 billion years old.)
The next-generation atomic clock that tops previous records for accuracy in clocks based on neutral atoms has been demonstrated by physicists at JILA, a joint institute of the Commerce Department’s National Institute of Standards and Technology (NIST) and the University of Colorado at Boulder. The new clock, based on thousands of strontium atoms trapped in grids of laser light, surpasses the accuracy of the current U.S. time standard based on a “fountain” of cesium atoms.
The strontium clock’s stability—the extent to which each tick matches the duration of every other tick—is about the same as NIST’s ytterbium atomic clock, another world leader in stability unveiled in August 2013. Stability determines in part how long an atomic clock must run to achieve its best performance through continual averaging. The strontium and ytterbium lattice clocks are so stable that in just a few seconds of averaging they outperform other types of atomic clocks that have been averaged for hours or days.
“We already have plans to push the performance even more,” said NIST/JILA Fellow and group leader Jun Ye, who is also an adjoint professor of physics at CU-Boulder. “So in this sense, even this new Nature paper represents only a ‘mid-term’ report. You can expect more new breakthroughs in our clocks in the next 5 to 10 years.”
In JILA’s world-leading clock, a few thousand atoms of strontium are held in a column of about 100 pancake-shaped traps called an optical lattice formed by intense laser light. JILA scientists detect strontium’s “ticks” (430 trillion per second) by bathing the atoms in very stable red laser light at the exact frequency that prompts the switch between energy levels.
Recent technical advances enabling the strontium clocks’ record performance include the development of ultrastable lasers and precise measurements of key effects—atom collisions and environmental heating—that cause tiny changes in the clock’s ticking rate.
Progress in atomic, optical and quantum science has led to rapid improvements in atomic clocks. At the same time, atomic clock research has helped to advance the frontiers of science, affecting both fundamental and applied research. The ability to control quantum states of individual atoms and photons is central to quantum information science and precision measurement, and optical clocks based on single ions have achieved the lowest systematic uncertainty of any frequency standard. Although many-atom lattice clocks have shown advantages in measurement precision over trapped-ion clocks their accuracy has remained 16 times worse. Here we demonstrate a many-atom system that achieves an accuracy of 6.4 × 10^−18, which is not only better than a single-ion-based clock, but also reduces the required measurement time by two orders of magnitude. By systematically evaluating all known sources of uncertainty, including in situ monitoring of the blackbody radiation environment, we improve the accuracy of optical lattice clocks by a factor of 22. This single clock has simultaneously achieved the best known performance in the key characteristics necessary for consideration as a primary standard—stability and accuracy. More stable and accurate atomic clocks will benefit a wide range of fields, such as the realization and distribution of SI units, the search for time variation of fundamental constants, clock-based geodesy and other precision tests of the fundamental laws of nature. This work also connects to the development of quantum sensors and many-body quantum state engineering (such as spin squeezing) to advance measurement precision beyond the standard quantum limit.
SOURCES – University of Colorado, Nature
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