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Register a new userMeasuring the evolution of the most stable optical clock G 117-B15A
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We report our measurement of the rate of change of period with time dP/dt for the 215 s periodicity in the pulsating white dwarf G 117-B15A, the most stable optical clock known. After 31 years of observations, we have finally obtained a 4 sigma measurement dP/dt_observed = (4.27 +/- 0.80) x 10^{-15} s/s. Taking into account the proper-motion effect of dP/dt_pm = (7.0 +/- 2.0) x 10^{-16} s/s, we obtain a rate of change of period with time of dP/dt = (3.57 +/- 0.82) x 10^{-15} s/s. This value is consistent with the cooling rate in our white dwarf models only for cores of C or C/O. With the refinement of the models, the observed rate of period change can be used to accurately measure the ratio of C/O in the core of the white dwarf.
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The pulsating hydrogen atmosphere white dwarf star G 117-B15A has been observed since 1974. Its main pulsation period at 215.19738823(63) s, observed in optical light curves, varies by only (5.12+/-0.82)x10^{-15} s/s and shows no glitches, as pulsars do. The observed rate of period change corresponds to a change of the pulsation period by 1 s in 6.2 million years. We demonstrate that this exceptional optical clock can continue to put stringent limits on fundamental physics, such as constraints on interaction from hypothetical dark matter particles, as well as to search for the presence of external substellar companions.
The existence of an internal frequency associated to any elementary particle conjectured by de Broglie is compared with a classical description of the electron, where this internal structure corresponds to the motion of the centre of charge around the centre of mass of the particle. This internal motion has a frequency twice de Broglies frequency, which corresponds to the frequency found by Dirac when analysing the electron structure. To get evidence of this internal electron clock a kind of experiment as the one performed by Gouanere et al. cite{Gouanere} will show a discrete set of momenta at which a resonant scattering effect, appears. The resonant momenta of the electron beam are given by $p_k=161.748/k$ MeV$/c$, $k=1,2,3,...$, where only, the corresponding to $k=2$, was within the range of Gouanere et al. experiment. The extension of the experiment to other values of $p_k$, would show the existence of this phenomenon.
Atomic clocks based on optical transitions are the most stable, and therefore precise, timekeepers available. These clocks operate by alternating intervals of atomic interrogation with dead time required for quantum state preparation and readout. This non-continuous interrogation of the atom system results in the Dick effect, an aliasing of frequency noise of the laser interrogating the atomic transition. Despite recent advances in optical clock stability achieved by improving laser coherence, the Dick effect has continually limited optical clock performance. Here we implement a robust solution to overcome this limitation: a zero-dead-time optical clock based on the interleaved interrogation of two cold-atom ensembles. This clock exhibits vanishingly small Dick noise, thereby achieving an unprecedented fractional frequency instability of $6 times 10^{-17} / sqrt{tau}$ for an averaging time $tau$ in seconds. We also consider alternate dual-atom-ensemble schemes to extend laser coherence and reduce the standard quantum limit of clock stability, achieving a spectroscopy line quality factor $Q> 4 times 10^{15}$.
We demonstrate a precision frequency measurement using a phase-stabilized 120-km optical fiber link over a physical distance of 50 km. The transition frequency of the 87Sr optical lattice clock at the University of Tokyo is measured to be 429228004229874.1(2.4) Hz referenced to international atomic time (TAI). The measured frequency agrees with results obtained in Boulder and Paris at a 6*10^-16 fractional level, which matches the current best evaluations of Cs primary frequency standards. The results demonstrate the excellent functions of the intercity optical fibre link, and the great potential of optical lattice clocks for use in the redefinition of the second.
We explore the feasibility of a compact high-precision Hg atomic clock based on a hollow core optical fiber. We evaluate the sensitivity of the $^1S_0$-$^3P_0$ clock transition in Hg and other divalent atoms to the fiber inner core surface at non-zero temperatures. The Casimir-Polder interaction induced $^1S_0$-$^3P_0$ transition frequency shift is calculated for the atom inside the hollow capillary as a function of atomic position, capillary material, and geometric parameters. For $^{199}mathrm{Hg}$ atoms on the axis of a silica capillary with inner radius $geq 15 ,mu mathrm{m}$ and optimally chosen thickness $dsim 1 ,mu mathrm{m}$, the atom-surface interaction induced $^1S_0$-$^3P_0$ clock transition frequency shift can be kept on the level $delta u/ u_{mathrm{Hg}} sim10^{-19}$. We also estimate the atom loss and heating due to the collisions with the buffer gas, lattice intensity noise induced heating, spontaneous photon scattering, and residual birefringence induced frequency shifts.
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