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Atomic clocks come in various configurations, set their tickers based on different atoms

NIST Timekeepers At A Glance Atomic clocks come in various configurations, set their tickers based on different atoms Strontium lattice optical clock Aluminum ion logic clock Cesium fountain clock This experimental clock resides in a basement at the University of Colorado, Boulder. Credit: Ye Group & Baxley/JILA Clocks like this one have demonstrated that time speeds up at higher altitudes. Credit: Burrus/NIST NIST defines the second using two fountain clocks. The F2, shown here, is its most accurate. Credit: NIST Accuracy (variation from perfect time) No more than 1 second in 5 billion years No more than 1 second in 3.5 billion years No more than 1 second in 300 million yearsa Atomic Transition Probed Electric quadrupole transition, 1S0 ---> 3P0 Electric quadrupole transition, 1S0 ---> 3P0 Ground state (2S1/2) hyperfine transition, F=3 ---> F=4 How It Works A network of lasers traps ultracold strontium atoms in a lattice of light. Scientists probe the clock's ticking by tuning a red probe laser to match the frequency at which the strontium atoms flip their “spins.” A tiny electromagnetic trap constrains a single aluminum ion. A helper ion with a more accessible energy transition—magnesium or beryllium—also sits in the trap. Scientists measure the clock's ticking by tuning a laser pulse to the frequency at which Al moves from a low energy state to a high energy state. They do so by observing light emission from the helper. Six lasers cool a ball of cesium atoms in a vacuum chamber. Two other lasers launch the cesium ball upward through the chamber, where it passes through a microwave cavity. Scientists probe the clock's ticking by tuning the microwaves to match the frequency at which the cesium atoms flip their "spins." This animation describes the inner workings of a strontium lattice clock. Credit: Greg Kuebler/JILA This is the electromagnetic trap that captures the aluminum and helper ion in a logic clock. Credit: J. Koelemeij/NIST This animation goes inside a cesium fountain clock to reveal how it ticks. Credit: Trent Schindler/NIST a = Value for NIST's F2 cesium clock SOURCES: NIST, aluminum ion (Phys. Rev. Lett. 2010, DOI: 10.1103/PhysRevLett.104.070802); cesium fountain (Metrologia 2014, DOI: 10.1088/0026-1394/51/3/174); strontium lattice (Nature 2014, DOI: 10.1038/nature12941).

Credit: Ye Group & Baxley/JILA

NIST Timekeepers At A Glance

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The inner workings of a strontium lattice clock.  Credit: Greg Kuebler/JILA

Credit: Burrus/NIST

The electromagnetic trap that captures the aluminum and helper ion in a logic clock.  Credit: J. Koelemeij/NIST

Credit: NIST

Go inside a cesium fountain clock to reveal how it ticks. Credit: Trent Schindler/NIST