Clock atomic transition

FIGURE 11.21 An example of a clock atomic transition. The excitation probability of the clock transition (the atomic oscillator) is measured through the quantum jump number vs. the laser tuning of the local oscillator. Each probe pulse is of 90 ms duration, and twenty probe cycles were performed for each value of the detuning. (Reproduced with the permission of the Physikalisch-Technisehe Bundesanstalt.)... 

All atomic clocks are based on the same servo-loop scheme (Figure 11.1). An internal atomic oscillator at cOai is used to lock an external or local atomic oscillator at frequency (Dq- The local oscillator is used to probe the atomic transition at (0, and... 

FIGU RE 11.1 A schematic diagram of an atomic clock. The atomic reference (0) 1) i provided by an atomic transition of an atom or a molecule. The fluorescence of the transition is detected by the oscillator (the local oscillator), which excites the atomic system at CBo. Before each interrogation, to make cOq a close as possible to cOac the servo loop adjusts the CBo fluorescence signal. A part of the signal of the local oscillator at cOo delivers the clock signal. 

Since the first Cesium-atomic clock based on an atomic beam, different approaches have been developed, justified by the need to reduce the global uncertainty of the system. The search for an appropriate atomic transition is guided by seeking its potentiality to have the narrowest spectral transition possible. Atomic calculations have assisted in making this choice. At the beginning of the atomic time era. 

The considerable Doppler shift in all collinear-beam experiments has opened up a few general applications beyond the spectroscopy of particular atomic or molecular systems. The scope of such applications ranges from simple beam velocity analyses to precision experiments related to metrology or problems of fundamental physics. These latter include the calibration of high voltages and measurements of the relativistic Doppler effect, for which the atomic transition frequency provides an intrinsic clock. 

A. H. Zewail If we solve for the molecular Hamiltonian, we will be theorists I do, of course, understand the point by Prof. Quack and the answer comes from the nature of the system and the experimental approach. For example, in elementary systems studied by femtosecond transition-state spectroscopy one can actually clock the motion and deduce the potentials. In complex systems we utilize a variety of template-state detection to examine the dynamics, and, like every other approach, you/we use a variety of input to reach the final answer. Solving the structure of a protein by X-ray diffraction may appear impossible, but by using a number of variant diffractions, such as the heavy atom, one obtains the final answer. 

The black body shifts are not confined to Rydberg atoms, but also alter the frequency of atomic clock transitions. Itano et al. have shown that the Cs 9 GHz ground state hyperfine interval, the definition of the second, is increased by one part in 1014 when the temperature is raised from 0 K to 300 K.29. 

We wish to point out, that by use of a suitable fiber which further broadens the spectrum, this fs laser frequency measurement technique has now been simplified to a setup with a single laser, as described elsewhere in this volume [6]. With the technique of Fig. 6, the 15 — 25 transition frequency was measured twice, first with a GPS referenced commercial Cs clock [29], and second with a transportable Cs atomic fountain clock constructed by A. Clairon and coworkers in Paris [30]. A total of 614 spectral lines was recorded in the latter measurement during ten days, and fitted with the described line shape model [13]. After adding a correction of 310 712 233(13) Hz to account for the hyperfine splitting of the 15 and 25 levels, we obtain for the hyperfine centroid [28] ... 

Abstract. A suitable femtosecond (fs) laser system can provide a broad band comb of stable optical frequencies and thus can serve as an rf/optical coherent link. In this way we have performed a direct comparison of the IS — 2S transition in atomic hydrogen at 121 nm with a cesium fountain clock, built at the LPTF/Paris, to reach an accuracy of 1.9 x 10-14. The same comb-line counting technique was exploited to determine and recalibrate several important optical frequency standards. In particular, the improved measurement of the Cesium Di line is necessary for a more precise determination of the fine structure constant. In addition, several of the best-known optical frequency standards have been recalibrated via the fs method. By creating an octave-spanning frequency comb a single-laser frequency chain has been realized and tested. 

The atom exhibits very regular, hyperfine energy-level transitions and it is possible to count these cycles of energy. In 1967 the General Conference accepted 9,192,631,770 cycles of cesium-133 as the measurement of one second, making the atomic clock the true international timekeeper. The cesium clock is maintained in Boulder, Colorado, in the offices of the National Institute of Standards and Technology (formally the National Bureau of Standards). Its accuracy is one part in 1,000,000,000,000 (10 12). It will not gain or lose a second in 6000 years. 

This particular quantum transition later rose to stardom in the world of physics. It was the same transition that Rabi and his students, shortly after the war, found to be at odds with Dirac theory, and it was this transition that led to a new value for the electron s magnetic moment. By 1947, this transition had gained prominence from an experiment on earthbound hydrogen atoms soon this same transition would assume galactic significance. Also, this same transition would become the basis for the most accurate atomic clock, which was developed in the late 1950s (discussed in Chapter 18). 

When an atom makes a transition from a high-energy quantum state to a lower energy state, electromagnetic radiation with a definite frequency and a definite period is emitted. When properly detected, this frequency, or period, becomes the ticking of an atomic clock, just as the crystal vibration frequency and the swinging frequency are the inaudible ticks of a quartz clock and a pendulum clock. The frequency emanating from the atom, however, is much less influenced by environmental factors such as temperature, pressure, humidity, and acceleration than are the frequencies from quartz crystals or pendula. Thus, atomic clocks hold inherently the potential for reproducibility, stability, and accuracy. 

Microwave technology is robnst. Highly stable solid state devices are commercially available that operate from 1-18 GHz. These devices can be locked to atomic clocks or global positioning systems to achieve frequency stability that far exceeds the natural linewidth of the measured rotational transitions. The result is a frequency generation system that requires little to no maintenance over long time periods (months to years), a featnre that is currently impossible to achieve with broadly tunable laser systems. These stand-alone microwave systems, which can be remotely controlled, are technically feasible and can be operated with pnsh-bntton control. ... 

In 1993, the National Institute of Standards and Technology (NIST) brought into use a caesium-based atomic clock called NIST-7 which kept international standard time to within one second in 10 years the system depends upon repeated transitions from the ground to a specific excited state of atomic Cs, and the monitoring of the frequency of the electromagnetic radiation emitted. 

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