OPTICAL-FREQUENCY COMBS

1. WWVB (Fort Collins, Colorado) This low frequency (LF) radio station broadcasts a time code that is widely used to set clocks and watches throughout the country. The so-called ‘Atomic Clocks’ available through many retail outlets actually contain radio receivers that receive the WWVB time code and set the time and date. The number of WWVB radio controlled clocks is believed to exceed 50 million as of 2009. WWV & WWVH These shortwave radio stations, WWV (to the right) in Fort Collins, Colorado) and WWVH (above) in Kauai, broadcast time and frequency signals that are received throughout the United States and in many other countries. The stations also broadcast marine storm warnings, geophysical alerts and GPS Status Announcements. TIME ON THE WEB The national web clock, time.gov, provides accurate time that can be adjusted to all United States time zones. This NIST-operated site also displays a world map that shows the regions of the world that are currently in light and darkness, and provides links to related timekeeping information. AUTOMATED COMPUTER TIME SERVICE (ACTS) This service was designed by NIST to set computer clocks before the advent of the Internet. It still provides more accurate synchronization than the Internet service, because it measures and compensates for telephone line delay. INTERNET TIME SERVICE NIST operates over 20 Internet Time Servers at 16 locations throughout the United States. This service is accessed nearly three billion times per day. Accurate time distributed through this and other NIST time services is critical to many activities. including the time stamping of financial transactions, which must be placed in time/date order to assure equity in trading. FREQUENCY MEASUREMENT AND ANALYIS SERVICE (FMAS) This service provides industrial and government calibration laboratories around the nation with continuous access to accurate frequency. It automates their frequency measurements and allows them to establish measurement traceability through NIST to the international system of units (SI) maintained by the International Bureau of Weights and Measures (BIPM) 100 GHZ REFERENCE SYNTHESIZER This NIST-designed system can provide reference frequency outputs at 40 different frequencies in the 100 GHz region. It is used for measurements of phase and amplitude noise, which are important to applications in the telecommunications and aerospace industries. TIME MEASUREMENT AND ANALYSIS SERVICE (TMAS) The NIST TMAS allows subscribers such as defense laboratories and research facilities to continuously compare their time standard to the UTC(NIST) time scale. Measurement results are available via the Internet and are updated every 10 minutes. The measurement uncertainty is roughly 10 nanoseconds for time, and about 5 parts in 1014 for frequency. INTERNATIONAL TIME COORDINATION Coordinated Universal Time (UTC) is a worldwide time maintained through regular comparisons of atomic clocks in more than 60 countries around the globe. NIST contributes to UTC by participating in comparisons involving the exchange of signals through communication satellites and through common-view observation of signals from GPS satellites. SEMINARS NIST staff members teach time and frequency metrology at annual seminars held in Boulder, Colorado and at other locations. The comprehensive training provided by NIST covers subject matter not available at any college or university, and has benefitted hundreds of scientists, engineers and technicians worldwide. SISTEMA INTERAMERICANO DE METROLOGIA (SIM) TIME NETWORK The SIM time network extends throughout the Americas and the Caribbean. It coordinates timekeeping within this region of the world by using GPS links to intercompare the standards of all participating countries. Designed by NIST, the SIM TN provides efficient and inexpensive access to accurate time to even the smallest countries, and makes its measurement results available in near real-time via the Internet. Time and Frequency Division PHYSICS LABORATORY Timing Services for America Research for the Future NIST TIME SCALE NIST TIME SCALE The NIST Time Scale is central to most activities in the Time and Frequency Division. It provides the reference for all broadcast and measurement services and the basis for research on advanced atomic clocks. The output of the Time Scale is the weighted average of the outputs of an ensemble of commercial cesium beam and hydrogen-maser clocks. OTHER DIVISION RESEARCH QUANTUM-LOGIC CLOCK This experimental optical clock is based on a single aluminum ion. It and another single-ion clock based on mercury are the two most accurate clocks in the world as of 2009. The error achieved in comparison of the two, using the optical-frequency comb, is approximately 2 parts in 1017. NEUTRAL-ATOM CLOCK This graphical representation is of an experimental optical clock based on neutral ytterbium atoms. This NIST clock has been demonstrated to be accurate to 1 part in 1016. This clock as well as similar NIST clocks based on calcium atoms exhibits extremely high stability for short time intervals making them useful for optical-frequency measurements. QUANTUM-LOGIC RESEARCH An outgrowth of research aimed at developing improved atomic clocks, this research is a world-leading effort to develop logic-circuitry that is radically different and more powerful than that found in today’s digital computers. The elements in this approach to quantum computing, called qubits, are made up of single ions trapped by electric fields in the gap at the center of this chip. This particular device was designed to demonstrate teleportation of qubits. CHIP-SCALE ATOMIC CLOCKS AND SENSORS The device shown here is a highly sensitive magnetometer, but it can also be configured as an atomic clock. No bigger than a grain of rice, atomic clocks of this sort offer performance well beyond that of quartz crystal oscillators. These NIST-engineered devices are now being developed for commercial applications. The chip-scale atomic clocks should find applications in areas such as telecommunications and GPS navigation. OPTICAL-FREQUENCY COMBS These devices provide the means for nearly perfect comparisons of the frequencies of both microwave and optical clocks. The error introduced in making comparisons with this device has been demonstrated to be as small as one part in 1019. Beyond their utility in making clock comparisons, NIST is developing variations that should be useful for applications such as chemical sensing and astronomical observations. US PRIMARY FREQUENCY STANDARD NIST-F1 is the primary frequency standard for the United States, serving to define the length of the second for the Country. This is a cesium-fountain standard, wherein atoms are tossed vertically about 1 meter and their resonance frequency is determined during their approximate one-second transit up and down the vertical tube. It is accurate to about 3 parts in 1016.