Clock Applications Research Articles

3D printed microwave cavity for atomic clock applications: proof of concept

The authors present the realisation and characterisation of an additively manufactured (AM) microwave resonator cavity for double-resonance (DR) vapour-cell atomic clocks. The design of the compact microwave cavity is based on the loop-gap resonator approach, previously demonstrated for conventionally-machined aluminium components. In the present study, the resonator is fabricated by AM using a metal-coated polymer. A resonance frequency at the desired 6.835 GHz rubidium atomic frequency is obtained. When employed in an atomic clock setup, the AM cavity enables a DR signal of <500 Hz linewidth and of nearly 20% contrast, thus fulfilling the stringent requirements for DR atomic clocks. A clock short-term stability of 1 × 10−12 τ −1/2 is demonstrated, comparable to state-of-the-art clock performances.

Study of additive manufactured microwave cavities for pulsed optically pumped atomic clock applications

Additive manufacturing (AM) of passive microwave components is of high interest for the cost-effective and rapid prototyping or manufacture of devices with complex geometries. Here, we present an experimental study on the properties of recently demonstrated microwave resonator cavities manufactured by AM, in view of their applications to high-performance compact atomic clocks. The microwave cavities employ a loop-gap geometry using six electrodes. The critical electrode structures were manufactured monolithically using two different approaches: Stereolithography (SLA) of a polymer followed by metal coating and Selective Laser Melting (SLM) of aluminum. The tested microwave cavities show the desired TE011-like resonant mode at the Rb clock frequency of ≈6.835 GHz, with a microwave magnetic field highly parallel to the quantization axis across the vapor cell. When operated in an atomic clock setup, the measured atomic Rabi oscillations are comparable to those observed for conventionally manufactured cavities and indicate a good uniformity of the field amplitude across the vapor cell. Employing a time-domain Ramsey scheme on one of the SLA cavities, high-contrast (34%) Ramsey fringes are observed for the Rb clock transition, along with a narrow (166 Hz linewidth) central fringe. The measured clock stability of 2.2 × 10−13 τ−1/2 up to the integration time of 30 s is comparable to the current state-of-the-art stabilities of compact vapor-cell clocks based on conventional microwave cavities and thus demonstrates the feasibility of the approach.

High Performance Clocks and Gravity Field Determination

Time measured by an ideal clock crucially depends on the gravitational potential and velocity of the clock according to general relativity. Technological advances in manufacturing high-precision atomic clocks have rapidly improved their accuracy and stability over the last decade that approached the level of 10$^{-18}$. Based on a fully relativistic description of the background gravitational physics, we discuss the impact of those highly-precise clocks on the realization of reference frames and time scales used in geodesy. We discuss the current definitions of basic geodetic concepts and come to the conclusion that the advances in clocks and other metrological technologies will soon require the re-definition of time scales or, at least, clarification to ensure their continuity and consistent use in practice. The relative frequency shift between two clocks is directly related to the difference in the values of the gravity potential at the points of clock's localization. According to general relativity the relative accuracy of clocks in 10$^{-18}$ is equivalent to measuring the gravitational red shift effect between two clocks with the height difference amounting to 1 cm. We show how clock measurements can provide geopotential numbers for the realization of gravity-field-related height systems and can resolve discrepancies in classically-determined height systems as well as between national height systems. Another application of clocks is the direct use of observed potential differences for the improved recovery of regional gravity field solutions. Finally, clock measurements for space-borne gravimetry are analyzed along with closely-related deficiencies of this method like an extra-ordinary knowledge of the spacecraft velocity, etc. For all these applications besides the near-future prospects, we also discuss the challenges that are related to using those novel clock data in geodesy.

Delay dynamics of neuromorphic optoelectronic nanoscale resonators: Perspectives and applications

With the recent exponential growth of applications using artificial intelligence (AI), the development of efficient and ultrafast brain-like (neuromorphic) systems is crucial for future information and communication technologies. While the implementation of AI systems using computer algorithms of neural networks is emerging rapidly, scientists are just taking the very first steps in the development of the hardware elements of an artificial brain, specifically neuromorphic microchips. In this review article, we present the current state of the art of neuromorphic photonic circuits based on solid-state optoelectronic oscillators formed by nanoscale double barrier quantum well resonant tunneling diodes. We address, both experimentally and theoretically, the key dynamic properties of recently developed artificial solid-state neuron microchips with delayed perturbations and describe their role in the study of neural activity and regenerative memory. This review covers our recent research work on excitable and delay dynamic characteristics of both single and autaptic (delayed) artificial neurons including all-or-none response, spike-based data encoding, storage, signal regeneration and signal healing. Furthermore, the neural responses of these neuromorphic microchips display all the signatures of extended spatio-temporal localized structures (LSs) of light, which are reviewed here in detail. By taking advantage of the dissipative nature of LSs, we demonstrate potential applications in optical data reconfiguration and clock and timing at high-speeds and with short transients. The results reviewed in this article are a key enabler for the development of high-performance optoelectronic devices in future high-speed brain-inspired optical memories and neuromorphic computing.

Wide-range tracking technique for process-variation-robust clock and data recovery applications

A wide-range tracking technique for clock and data recovery (CDR) circuit is presented. Compared to the traditional technique, a digital CDR controller with calibration is adopted to extend the tracking range. Because of the use of digital circuits in the design, CDR is not sensitive to process and power supply variations. To verify the technique, the whole CDR circuit is implemented using 65-nm CMOS technology. Measurements show that the tracking range of CDR is greater than ±6×10−3 at 5 Gb/s. The receiver has good jitter tolerance performance and achieves a bit error rate of <10–12. The re-timed and re-multiplexed serial data has a root-mean-square jitter of 6.7 ps.

Study on a High-frequency Multi-GNSS Real-time Precise Clock Estimation Algorithm and Application in GNSS Augment System

Study on a High-frequency Multi-GNSS Real-time Precise Clock Estimation Algorithm and Application in GNSS Augment System

Microfabricated vapor cells filled with a cesium dispensing paste for miniature atomic clocks

A method for filling alkali vapor cells with cesium from a dispensing paste is proposed and its compliance with miniature atomic clock applications is evaluated. The paste is an organic-inorganic composition of cesium molybdate, zirconium-aluminum powder, and a hybrid organic-inorganic binder. It is compatible with collective deposition processes such as micro-drop dispensing, which can be done under ambient atmosphere at the wafer-level. After deposition and sealing by anodic bonding, cesium is released from the consolidated paste through local heating with a high power laser. Linear absorption signals have been observed over one year in several cells, showing a stable atomic density. For further validation of this technology for clock applications, one cell has been implemented in a coherent population trapping clock setup to monitor its frequency stability. A fractional frequency aging rate around –4.4 × 10−12 per day has been observed, which is compliant with a clock frequency instability below 1 × 10−11 at one day integration time. This filling method can drastically reduce the cost and the complexity of alkali vapor cell fabrication.

Lateral grating DFB AlGaInN laser diodes for optical communications and atomic clocks.

AlGaInN laser diode technology is of considerable interest for telecom applications and next generation atomic optical clocks based on Sr (by using 422nm & 461nm) and Rb at 420.2nm.Very narrow linewidths (<1MHz) are required for such applications. We report lateral gratings on AlGaInN ridge waveguide laser diodes to achieve a single wavelength device with a good side mode suppression ratio (SMSR) that is suitable for atomic clock and telecom applications.

Smart Communication Network design with application of Energy Efficient Digital Clock for Monitoring of Time -To-Live (TTL)

Smart Communication Network design with application of Energy Efficient Digital Clock for Monitoring of Time -To-Live (TTL)

Molecular phylogenetic relationships among Anatolian-Hyrcanian brown frog taxa (Ranidae: Rana)

Although the phylogenetic relationship of Western Palearctic brown frogs has been repeatedly studied, the taxonomic status and phylogenetic relationship of Anatolian-Hyrcanian brown frogs is still not fully resolved. Here, we assess the phylogenetic status of these species among Western Palearctic brown frogs with special emphasize on Iranian populations based on two partial mitochondrial DNA sequences (16S rRNA and cytochrome b genes) and the application of a molecular clock. Our results clearly show that Western Palearctic brown frogs underwent a basal radiation in to two main monophyletic clades, the European brown frogs plus the Asian R. asiatica and the Anatolian-Hyrcanian brown frogs, during Early Miocene ca. 20.2 mya. The Hyrcanian (R. pseudodalmatina) and the Anatolian lineage diverged approximately 16.6 mya. The further diverged into two subclades, R. tavasensis and R. macrocnemis, during the Middle Miocene, 14.5 mya. Our results suggest that diversification within these lineages may be closely linked to the formation of Neotethys and Paratethys and the subsequent uplift of the Turkish-Iranian plateau during the Early Miocene which led to restricted gene flow among brown frogs in these regions. Contrary to previous studies, we conclude that the Plio-Pleistocene epoch seems to be not associated to further significant speciation events within Anatolian-Hyrcanian brown frogs.

Giant gain from spontaneously generated coherence in Y-type double quantum dot structure

A theoretical model was presented for linear susceptibility using density matrix theory for Y-configuration of double quantum dots (QDs) system including spontaneously generated coherence (SGC). Two SGC components are included for this system: V, and Λ subsystems. It is shown that at high V-component, the system have a giga gain. At low Λ-system component; it is possible to controls the light speed between superluminal and subluminal using one parameter by increasing SGC component of the V-system. This have applications in quantum information storage and spatially-varying temporal clock.

Impact of multi-constellation products and ambiguity resolution in Precise Point Positioning for real-time measurements

Abstract Precise Point Positioning (PPP) has revolutionized Global Navigation Satellite Systems (GNSS) processing. This computation method achieves precise positioning with a single receiver and un-differenced observations. Its conceptual basis consists of solving the position with pseudo-range and carrier-phase GNSS measurements, with the application of external clock and orbit satellite corrections, previously estimated signal biases and atmospheric models computed in the International GNSS Service or Analysis Centers. However, in the case study of real-time PPP, the computation engine requires continuous streams of products that must meet certain availability requirements. In a case study of real-time measurements the technique is very sensitive to outliers in products and changes in the constellation geometry. As a result, there are long initialization periods, losses of convergence and a lack of accuracy in the results. This study shows how multi-constellation approaches for external products reduce loss of convergence and outliers in the real-time PPP solutions and also highlights the impact that ambiguity resolution has.

Thorium-229 quantified in historical Thorium-228 capsules

Thorium-229 is a valuable, but scarce, radionuclide for nuclear clock applications or targeted alpha therapy. While it is mostly produced by the decay of 233U, 229Th can also be produced by neutron irradiation of 226Ra. At SCK•CEN, capsules containing mainly 228Th (by-product of 226Ra irradiation) were characterized to quantify the present amounts of 229Th, 228Th, 227Ac, 226Ra with high resolution gamma spectroscopy, after a decay period of 40 years in which 228Th has decayed. High purity 229Th was quantified, and after recovery using radiochemical separation processes, it can be used to support ongoing research.

Characterization of commercially available vertical-cavity surface-emitting lasers tuned on Cs D1 line at 894.6 nm for miniature atomic clocks.

We report on the metrological characterization of novel commercially available 894.6nm vertical-cavity surface-emitting lasers (VCSELs), dedicated to Cs D1 line spectroscopy experiments. The thermal behavior of the VCSELs is reported, highlighting the existence of a minimum threshold current and maximum output power in the 55°C-60°C range. The laser relative intensity noise, measured to be -108 dB/Hz at 10Hz Fourier frequency f for a laser power of 25μW, is reduced with increased power. The VCSELs frequency noise is 108 Hz2/Hz at f=100 Hz. The spectral linewidth of the VCSELs is about 30MHz. VCSELs injection current can be directly modulated at 4.596GHz with microwave power in the range of -10 to +0 dBm to generate optical sidebands. A VCSEL was used in a microcell-based Cs atomic clock based on coherent population trapping. A preliminary clock short-term fractional frequency stability of 8×10-11τ-1/2 up to about 100s is reported, demonstrating the suitability of these VCSELs for miniature atomic clock applications.

Providing Cost Save by Using Electronic Meters in Residental Areas

In our country, the demand for electrical energy, which is a development indicator, is increasing day by day. Due to the limited energy resources to meet this growing demand for energy it is not only able to meet the increasing production. Therefore, the current system of electricity generation, transmission and distribution used more efficiently that is electrical energy saving has become very important today. F or energy saving, advanced clock application and use of electronic meter such administrative precaution and the correction of power factor such technical precaution. The most important administrative precaution to reduce the use of energy at the most consumed period and hours is to apply a higher price rate at these hours. Thus, by shifting the cosumption at these hours to other suitable hours, a balanced energy consumption may be obtained. The measurement and billing of electric energy used within the day at different times are done by means of electronic meters. In this study, it explained how to achieve saving through the use of electronic meter and suggestions were made.

Coherent population trapping with polarization modulation

Coherent population trapping (CPT) is extensively studied for future vapor cell clocks of high frequency stability. In the constructive polarization modulation CPT scheme, a bichromatic laser field with polarization and phase synchronously modulated is applied on an atomic medium. A high contrast CPT signal is observed in this so-called double-modulation configuration, due to the fact that the atomic population does not leak to the extreme Zeeman states, and that the two CPT dark states, which are produced successively by the alternate polarizations, add constructively. Here, we experimentally investigate CPT signal dynamics first in the usual configuration, a single circular polarization. The double-modulation scheme is then addressed in both cases: one pulse Rabi interaction and two pulses Ramsey interaction. The impact and the optimization of the experimental parameters involved in the time sequence are reviewed. We show that a simple seven-level model explains the experimental observations. The double-modulation scheme yields a high contrast similar to the one of other high contrast configurations like push-pull optical pumping or crossed linear polarization scheme, with a setup allowing a higher compactness. The constructive polarization modulation is attractive for atomic clock, atomic magnetometer, and high precision spectroscopy applications.

Molecular diversity and phylogeography of Andricus curtisii (Hymenoptera, Cynipidae) in Turkey

A 433-bp fragment of the mitochondrial cytochrome b gene and the entire nuclear ITS2 region were sequenced in an oak gall wasp species, Andricus curtisii, which represents 21 populations across its range in Turkey. Forty cytochrome b haplotypes and 63 ITS2 alleles were discovered among the 161 individuals studied. Remarkable genetic variation was detected in the species, with an average haplotype diversity (h) of 0.72 and 0.76 and an average nucleotide diversity (π) of 0.06 and 0.01 for the cyt b gene and the ITS region, respectively. Most populations were genetically distinct, possessing unique cytochrome b haplotypes. Maximum likelihood and Bayesian phylogenetic analyses and application of the haplotype network to both datasets revealed that the most basally located haplotypes/alleles were from the eastern part of Turkey. The detection of older sequences in the phylogenetic trees of the easterly located populations implied an eastern origin of the species. The application of a conventional insect mitochondrial DNA clock to the dataset suggested a splitting of ingroup haplotypes from the outgroup lineages predating the Pleistocene epoch and the formation of two major haplogroups that coincided with the oscillation of the early Pleistocene glaciations.

Mitochondrial DNA analyses revealed low genetic diversity in the endangered Indian wild ass Equus hemionus khur

The Indian wild ass Equus hemionus khur, belonging to ass-like equid branch, inhabits the dry and arid desert of the Little Rann of Kutch, Gujarat. The E. h. khur is the sole survivor of Asiatic wild ass species/subspecies in South Asia. To provide first ever insights into the genetic diversity, phylogeny, and demography of the endangered Indian wild ass, we sampled 52 free-ranging individuals from the Little Rann of Kutch by using a non-invasive methodology. The sequencing of 230 bp in cytochrome b (Cyt b) and displacement loop (D-loop) region revealed that current ∼4000 extant population of Indian wild ass harbours low genetic diversity. Phylogenetic analyses confirmed that E. h. khur, E. h. onager, and E. h. kulan belong to a single strict monophyletic clade. Therefore, we suggest the delimitation of the five E. hemionus subspecies in vogue to a single species E. hemionus. The application of molecular clock confirmed that the Asiatic wild ass had undergone diversification 0.65 Million years ago. Demographic measurements assessed using a Bayesian skyline plot demonstrated decline in the maternal effective population size of the Indian wild ass during different periods; these periods coincided with the origin and rise of the Indus civilization in the northwest of the Indian subcontinent during the Neolithic. In conclusion, maintaining high genetic diversity in the existing isolated population of 4000 Indian wild asses inhabiting the wild ass sanctuary is important compared with subspecies preservation alone.

Dating placentalia: Morphological clocks fail to close the molecular fossil gap.

Dating the origin of Placentalia has been a contentious issue for biologists and paleontologists. Although it is likely that crown‐group placentals originated in the Late Cretaceous, nearly all molecular clock estimates point to a deeper Cretaceous origin. An approach with the potential to reconcile this discrepancy could be the application of a morphological clock. This would permit the direct incorporation of fossil data in node dating, and would break long internal branches of the tree, so leading to improved estimates of node ages. Here, we use a large morphological dataset and the tip‐calibration approach of MrBayes. We find that the estimated date for the origin of crown mammals is much older, ∼130–145 million years ago (Ma), than fossil and molecular clock data (∼80–90 Ma). Our results suggest that tip calibration may result in estimated dates that are more ancient than those obtained from other sources of data. This can be partially overcome by constraining the ages of internal nodes on the tree; however, when this was applied to our dataset, the estimated dates were still substantially more ancient than expected. We recommend that results obtained using tip calibration, and possibly morphological dating more generally, should be treated with caution.

Effect of atomic diffusion on the Raman–Ramsey coherent population trapping resonances

We experimentally investigated the characteristics of two-photon transmission resonances in Rb vapor cells with different amount of buffer gas under the conditions of steady-state coherent population trapping (CPT) and pulsed Raman-Ramsey (RR-) CPT interrogation scheme. We particularly focused on the influence of the Rb atoms diffusing in and out of the laser beam. We showed that this effect modifies the shape of both CPT and Raman-Ramsey resonances, as well as their projected performance for CPT clock applications. In particular we found that at moderate buffer gas pressures RR-CPT did not improved the projected atomic clock stability compare to the regular steady-state CPT resonance.