Temporal Variation Of Fundamental Constants Research Articles

High-Accuracy Optical Frequency Atomic Clock

Frequencies have been the most accurately measured physical quantity since the second was defined in 1967 based on the microwave atomic transition of a Cs atom. Recently, atomic clocks using optical frequency transitions have shown an order of magnitude better accuracy than microwave clocks. Thanks to their high accuracy and resolution, atomic clocks have become a new tool for investigations involving fundamental science and technology, such as the search for dark matter, gravitational wave detection, the temporal variation of fundamental constants, relativistic geodesy, quantum metrology, and the advanced Global Navigation Satellite System (GNSS). In addition, a redefinition of the second based on the optical frequency is expected. In this paper, we review the principles and applications of optical clocks.

Energy of the 229Th nuclear clock transition.

Owing to its low excitation energy and long radiative lifetime, the first excited isomeric state of thorium-229, 229mTh, can be optically controlled by a laser1,2 and is an ideal candidate for the creation of a nuclear optical clock3, which is expected to complement and outperform current electronic-shell-based atomic clocks4. A nuclear clock will have various applications-such as in relativistic geodesy5, dark matter research6 and the observation of potential temporal variations of fundamental constants7-but its development has so far been impeded by the imprecise knowledge of the energy of 229mTh. Here we report a direct measurement of the transition energy of this isomeric state to the ground state with an uncertainty of0.17 electronvolts (one standard deviation) using spectroscopy of the internal conversion electrons emitted in flight during the decay of neutral 229mTh atoms. The energy of the transition between the ground state and the first excited state corresponds to a wavelength of 149.7±3.1 nanometres, which is accessible by laser spectroscopy through high-harmonic generation. Our method combines nuclear and atomic physics measurements to advance precision metrology, and our findings are expected to facilitate the application of high-resolution laser spectroscopy on nuclei and to enable the development of a nuclear optical clock of unprecedented accuracy.

Direct frequency comb spectroscopy in the extreme ultraviolet

The development of the optical frequency comb (a spectrum consisting of a series of evenly spaced lines) has revolutionized metrology and precision spectroscopy owing to its ability to provide a precise and direct link between microwave and optical frequencies. A further advance in frequency comb technology is the generation of frequency combs in the extreme-ultraviolet spectral range by means of high-harmonic generation in a femtosecond enhancement cavity. Until now, combs produced by this method have lacked sufficient power for applications, a drawback that has also hampered efforts to observe phase coherence of the high-repetition-rate pulse train produced by high-harmonic generation, which is an extremely nonlinear process. Here we report the generation of extreme-ultraviolet frequency combs, reaching wavelengths of 40 nanometres, by coupling a high-power near-infrared frequency comb to a robust femtosecond enhancement cavity. These combs are powerful enough for us to observe single-photon spectroscopy signals for both an argon transition at 82 nanometres and a neon transition at 63 nanometres, thus confirming the combs' coherence in the extreme ultraviolet. The absolute frequency of the argon transition has been determined by direct frequency comb spectroscopy. The resolved ten-megahertz linewidth of the transition, which is limited by the temperature of the argon atoms, is unprecedented in this spectral region and places a stringent upper limit on the linewidth of individual comb teeth. Owing to the lack of continuous-wave lasers, extreme-ultraviolet frequency combs are at present the only promising route to extending ultrahigh-precision spectroscopy to the spectral region below 100 nanometres. At such wavelengths there is a wide range of applications, including the spectroscopy of electronic transitions in molecules, experimental tests of bound-state and many-body quantum electrodynamics in singly ionized helium and neutral helium, the development of next-generation 'nuclear' clocks and searches for variation of fundamental constants using the enhanced sensitivity of highly charged ions.

A new approach to relativistic multi-configuration quantum mechanics in titanium

Multiply-ionized atoms in plasmas and astronomical systems are predominantly of intermediate atomic numbers with open electron shells. The spectra seen in laboratory plasmas and astrophysical plasmas are dominated by characteristic K α 1 , 2 photoemission lines. Modelling these transitions requires advanced relativistic frameworks to begin to formulate solutions. We present a new approach to relativistic multi-configuration determination of K α 1 , 2 diagram and satellite energies in titanium to a high level of convergence, allowing accurate fitting of satellite contributions and the first agreement with profile to negligible residuals. These developments also apply to exciting frontiers including temporal variation of fundamental constants, theoretical chemistry and laboratory astrophysics.

Searching for space-time variation of the fine structure constant using QSO spectra: overview and future prospects

Current theories that seek to unify gravity with the other fundamental interactions suggest that spatial and temporal variation of fundamental constants is a possibility, or even a necessity, in an expanding Universe. Several studies have tried to probe the values of constants at earlier stages in the evolution of the Universe, using tools such as big-bang nucleosynthesis, the Oklo natural nuclear reactor, quasar absorption spectra, and atomic clocks (see, e.g. Flambaum & Berengut (2009)).

Enhanced sensitivity to variation of fundamental constants in the narrow nuclear transitions (II)

Several long-lived nuclear isomer states with low energies are proposed to be used for searching the temporal variation of some fundamental constants. Orders of magnitude enhancements of the sensitivity to the fine structure constant, nucleon mass, meson masses and the strong interaction parameter are obtained in the transitions between these isomers and the ground states. The enhancement is mainly due to the low transition energy. The configurations of the states also influence the value of enhancement factor. There are both positive signs of the enhancement factors and negative ones in our results. We suggest to measure the ratio of transition frequencies in two nuclei with opposite signs of the enhancement factors. This could improve the sensitivity to the temporal variation of fundamental constants in experiment.

Constraints on temporal variation of fundamental constants from GRBs

The formation of a strange or hybrid star from a neutron star progenitor is believed to occur when the central stellar density exceeds a critical value. If the transition from hadron to quark matter is of first order, the event has to release a huge amount of energy in a very short time, and we would be able to observe the phenomenon even if it is at cosmological distance far from us. Most likely, such violent quark deconfinement would be associated with at least a fraction of the observed gamma ray bursts. If we allow for temporal variations of fundamental constants like Λ QCD or G N , we can expect that neutron stars with an initial central density just below the critical value can enter into the region where strange or hybrid stars are the true ground state. From the observed rate of long gamma ray bursts, we are able to deduce the constraint G ˙ N / G N ≲ 10 - 17 yr - 1 , which is about 5 orders of magnitude more stringent than the strongest previous bounds on a possible increasing G N .

Dependence of nuclear magnetic moments on quark masses and limits on temporal variation of fundamental constants from atomic clock experiments

We calculate the dependence of the nuclear magnetic moments on the quark masses, including the spin-spin interaction effects, and obtain limits on the variation of the fine structure constant \ensuremath{\alpha} and $({m}_{q}/{\ensuremath{\Lambda}}_{\mathrm{QCD}})$ using recent atomic clock experiments examining hyperfine transitions in H, Rb, Cs, ${\mathrm{Yb}}^{+}$, and ${\mathrm{Hg}}^{+}$ and the optical transition in H, ${\mathrm{Hg}}^{+}$, and ${\mathrm{Yb}}^{+}$.