64 research outputs found
Avoiding Aliasing in Allan Variance: an Application to Fiber Link Data Analysis
Optical fiber links are known as the most performing tools to transfer
ultrastable frequency reference signals. However, these signals are affected by
phase noise up to bandwidths of several kilohertz and a careful data processing
strategy is required to properly estimate the uncertainty. This aspect is often
overlooked and a number of approaches have been proposed to implicitly deal
with it. Here, we face this issue in terms of aliasing and show how typical
tools of signal analysis can be adapted to the evaluation of optical fiber
links performance. In this way, it is possible to use the Allan variance as
estimator of stability and there is no need to introduce other estimators. The
general rules we derive can be extended to all optical links. As an example, we
apply this method to the experimental data we obtained on a 1284 km coherent
optical link for frequency dissemination, which we realized in Italy
High-performing vapor-cell frequency standards
Many nowadays scientific and technological applications need very precise time and frequency reference signals. Very often, only atomic clocks can guarantee the high level of accuracy and stability required by these signals. In the current scenario of atomic frequency standards, vapor-cell clocks are particularly suited to be employed in those activities that demand good frequency stability performances joined to compactness, reliability and low power consumption. Recently, due to better-performing laser sources and to innovative techniques to prepare and detect the atoms, several cell-based prototypes exhibiting unprecedented frequency stability have been developed. We review advances in the field of laser-pumped
vapor-cell clocks and we provide an overview of the techniques that allowed to
achieve frequency stabilities in the order of 1×10^−13 at 1 s (short term) and in the range of 10^−15 for the medium-long term. These stabilities are two orders of magnitude better than current commercial Rb clocks. We also prospect the possibility of further improving these results.Many nowadays scientific and technological applications need very precise time and frequency reference signals. Very often, only atomic clocks can guarantee the high level of accuracy and stability required by these signals. In the current scenario of atomic frequency standards, vapor-cell clocks are particularly suited to be employed in those activities that demand good frequency stability performances joined to compactness, reliability and low power consumption. Recently, due to better-performing laser sources and to innovative techniques to prepare and detect the atoms, several cell-based prototypes exhibiting unprecedented frequency stability have been developed. We review advances in the field of laser-pumped vapor-cell clocks and we provide an overview of the techniques that allowed to achieve frequency stabilities in the order of 1 x 10(-13) at is (short term) and in the range of 10(-15) for the medium-long term. These stabilities are two orders of magnitude better than current commercial Rb clocks. We also prospect the possibility of further improving these results
Reducing cavity-pulling shift in Ramsey-operated compact clocks
We describe a method to stabilize the amplitude of the interrogating
microwave field in compact atomic clocks working in a Ramsey approach. In this
technique, we take advantage of the pulsed regime to use the atoms themselves
as microwave amplitude discriminators. Specifically, in addition to the
dependence on the microwave detuning, the atomic signal after the Ramsey
interrogation acquires a dependence on the microwave pulse area (amplitude
times duration) that can be exploited to implement an active stabilization of
the microwave field amplitude, in a similar way in which the Ramsey clock
signal is used to lock the local oscillator frequency to the atomic reference.
This stabilization results in a reduced sensitivity of the clock frequency to
microwave amplitude fluctuations that are transferred to the atoms through the
cavity-pulling effect. The proposed technique is then effective to improve the
clock stability and drift on medium and long term. We demonstrate the method
for a vapor-cell clock working with a hot sample of atoms but it can be
extended to cold-atom compact clocks.Comment: Accepted for publication by IEEE UFFC on April 16th 201
Phase Noise and Frequency Stability of the Red-Pitaya Internal PLL
partially_open5sìIn field-programmable gate array platforms, the main clock is generally a low-cost quartz oscillator whose stability is of the order of 10-9 to 10-10 in the short term and 10-7 to 10-8 in the medium term, with the uncertainty of tens of ppm. Better stability is achieved by feeding an external reference into the internal phase-locked loop (PLL). We report the noise characterization of the internal PLL of Red-Pitaya platform, an open-source embedded system architected around the Zynq 7010 System on Chip, with analog-to-digital and digital-to-analog converters. Our experiments show that, providing an external 10-MHz reference, the PLL exhibits a residual frequency stability of 1.2×10-12 at 1 s and 1.3×10-15 at 4000 s, Allan deviation in 5-Hz bandwidth. These results help to predict the PLL stability as a function of frequency and power of the external reference, and provide guidelines for the design of precision instrumentation, chiefly intended for time and frequency metrology.partially_openCardenas Olaya, Andrea Carolina; Calosso, Claudio Eligio; Friedt, Jean-Michel; Micalizio, Salvatore; Rubiola, EnricoCardenas Olaya, Andrea Carolina; Calosso, Claudio Eligio; Friedt, Jean-Michel; Micalizio, Salvatore; Rubiola, Enric
Measurement of the Blackbody Radiation Shift of the 133Cs Hyperfine Transition in an Atomic Fountain
We used a Cs atomic fountain frequency standard to measure the Stark shift on
the ground state hyperfine transiton frequency in cesium (9.2 GHz) due to the
electric field generated by the blackbody radiation. The measures relative
shift at 300 K is -1.43(11)e-14 and agrees with our theoretical evaluation
-1.49(07)e-14. This value differs from the currently accepted one
-1.69(04)e-14. The difference has a significant implication on the accuracy of
frequency standards, in clocks comparison, and in a variety of high precision
physics tests such as the time stability of fundamental constants.Comment: 4 pages, 2 figures, 2 table
Loaded microwave cavity for compact vapor-cell clocks
Vapor-cell devices based on microwave interrogation provide a stable
frequency reference with a compact and robust setup. Further miniaturization
must focus on optimizing the physics package, containing the microwave cavity
and atomic reservoir. In this paper we present a compact cavity-cell assembly
based on a dielectric-loaded cylindrical resonator. The structure accommodates
a clock cell with inner volume and has an outer volume
of only . The proposed design aims at strongly reducing
the core of the atomic clock, maintaining at the same time high-performing
short-term stability (
standard Allan deviation). The proposed structure is characterized in terms of
magnetic field uniformity and atom-field coupling with the aid of
finite-elements calculations. The thermal sensitivity is also analyzed and
experimentally characterized. We present preliminary spectroscopy results by
integrating the compact cavity within a rubidium clock setup based on the
pulsed optically pumping technique. The obtained clock signals are compatible
with the targeted performances. The loaded-cavity approach is thus a viable
design option for miniaturized microwave clocks.Comment: Submitted to IEEE-UFF
Frequency noise characterization of diode lasers for vapor-cell clock applications
The knowledge of the frequency noise spectrum of a diode laser is of interest in several high-resolution experiments. Specifically, in laser-pumped vapor-cell clocks, it is well-established that the laser frequency noise plays a role in affecting clock performances. It is then relevant to characterize the frequency noise of a diode laser since such measurements are rarely found in the literature and hardly ever provided by vendors. In this article, we describe a technique based on a frequency-to-voltage (f/V) converter that transforms the laser frequency fluctuations into voltage fluctuations. In this way, it is possible to characterize the laser frequency noise power spectral density (PSD) in a wide range of Fourier frequencies, as required in cell clock applications
Cold atoms in space: community workshop summary and proposed road-map
We summarise the discussions at a virtual Community Workshop on Cold Atoms in Space concerning the status of cold atom technologies, the prospective scientific and societal opportunities offered by their deployment in space, and the developments needed before cold atoms could be operated in space. The cold atom technologies discussed include atomic clocks, quantum gravimeters and accelerometers, and atom interferometers. Prospective applications include metrology, geodesy and measurement of terrestrial mass change due to, e.g., climate change, and fundamental science experiments such as tests of the equivalence principle, searches for dark matter, measurements of gravitational waves and tests of quantum mechanics. We review the current status of cold atom technologies and outline the requirements for their space qualification, including the development paths and the corresponding technical milestones, and identifying possible pathfinder missions to pave the way for missions to exploit the full potential of cold atoms in space. Finally, we present a first draft of a possible road-map for achieving these goals, that we propose for discussion by the interested cold atom, Earth Observation, fundamental physics and other prospective scientific user communities, together with the European Space Agency (ESA) and national space and research funding agencies.publishedVersio
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