scispace - formally typeset
Search or ask a question
Author

H. Alvarez-Martinez

Bio: H. Alvarez-Martinez is an academic researcher from University of Paris. The author has contributed to research in topics: Laser & Spectral hole burning. The author has an hindex of 5, co-authored 14 publications receiving 98 citations. Previous affiliations of H. Alvarez-Martinez include Royal Institute and Observatory of the Spanish Navy.

Papers
More filters
Journal ArticleDOI
TL;DR: In this article, the authors search for coherent variations in the recorded clock frequency comparisons across the network, and significantly improve the constraints on transient variations of the fine structure constant, for example, constraining the variation to |δα/α| ~10^4 km.
Abstract: We search for transient variations of the fine structure constant using data from a European network of fiber-linked optical atomic clocks. By searching for coherent variations in the recorded clock frequency comparisons across the network, we significantly improve the constraints on transient variations of the fine structure constant. For example, we constrain the variation to |δα/α| ~10^4 km) objects.

61 citations

Journal ArticleDOI
TL;DR: In this paper, the authors search for coherent variations in the recorded clock frequency comparisons across the network, and significantly improve the constraints on transient variations of the fine structure constant, for example, constraining the variation in alpha to ~10^4 km.
Abstract: We search for transient variations of the fine structure constant using data from a European network of fiber-linked optical atomic clocks. By searching for coherent variations in the recorded clock frequency comparisons across the network, we significantly improve the constraints on transient variations of the fine structure constant. For example, we constrain the variation in alpha to ~10^4 km) objects.

37 citations

Journal ArticleDOI
20 Apr 2019
TL;DR: In this article, a high-resolution MIR spectrometer traceable to primary frequency standards is presented, which combines a widely tunable ultra-narrow quantum cascade laser (QCL), an optical frequency comb, and a compact multipass cell.
Abstract: There is an increasing demand for precise molecular spectroscopy, in particular in the mid-infrared (MIR) fingerprint window that hosts a considerable number of vibrational signatures, whether it be for modeling our atmosphere, interpreting astrophysical spectra, or testing fundamental physics. We present a high-resolution MIR spectrometer traceable to primary frequency standards. It combines a widely tunable ultra-narrow quantum cascade laser (QCL), an optical frequency comb, and a compact multipass cell. The QCL frequency is stabilized onto a comb controlled with a remote near-infrared ultra-stable laser, transferred through a fiber link. The resulting QCL frequency stability is below 10−15 from 0.1 to 10 s, and its frequency uncertainty of 4×10−14 is given by the remote frequency standards. Continuous tuning over ∼400 MHz is reported. We use the apparatus to perform saturated absorption spectroscopy of methanol in the low-pressure multipass cell and demonstrate a statistical uncertainty at the kilohertz level on transition center frequencies, confirming its potential for driving the next generation technology required for precise spectroscopic measurements.

30 citations

Journal ArticleDOI
TL;DR: In this article, a high-resolution mid-infrared spectrometer traceable to primary frequency standards is presented, which combines a widely tunable ultra-narrow Quantum Cascade Laser (QCL), an optical frequency comb and a compact multipass cell.
Abstract: There is an increasing demand for precise molecular spectroscopy, in particular in the mid-infrared fingerprint window that hosts a considerable number of vibrational signatures, whether it be for modeling our atmosphere, interpreting astrophysical spectra or testing fundamental physics. We present a high-resolution mid-infrared spectrometer traceable to primary frequency standards. It combines a widely tunable ultra-narrow Quantum Cascade Laser (QCL), an optical frequency comb and a compact multipass cell. The QCL frequency is stabilized onto a comb controlled with a remote near-infrared ultra-stable laser, transferred through a fiber link. The resulting QCL frequency stability is below 10-15 from 0.1 to 10s and its frequency uncertainty of 4x10-14 is given by the remote frequency standards. Continuous tuning over ~400 MHz is reported. We use the apparatus to perform saturated absorption spectroscopy of methanol in the low-pressure multipass cell and demonstrate a statistical uncertainty at the kHz level on transition center frequencies, confirming its potential for driving the next generation technology required for precise spectroscopic measurements.

30 citations

Journal ArticleDOI
TL;DR: In this article , a comparison of two geographically separated lasers over the longest ever reported metrological optical fiber link network, measuring 2220 km in length, at a state-of-the-art fractional-frequency instability of 7 × 10-17 for averaging times between 30 s and 200 s.
Abstract: Ultrastable lasers are essential tools in optical frequency metrology enabling unprecedented measurement precision that impacts on fields such as atomic timekeeping, tests of fundamental physics, and geodesy. To characterise an ultrastable laser it needs to be compared with a laser of similar performance, but a suitable system may not be available locally. Here, we report a comparison of two geographically separated lasers, over the longest ever reported metrological optical fibre link network, measuring 2220 km in length, at a state-of-the-art fractional-frequency instability of 7 × 10-17 for averaging times between 30 s and 200 s. The measurements also allow the short-term instability of the complete optical fibre link network to be directly observed without using a loop-back fibre. Based on the characterisation of the noise in the lasers and optical fibre link network over different timescales, we investigate the potential for disseminating ultrastable light to improve the performance of remote optical clocks.

21 citations


Cited by
More filters
Journal Article
01 Jan 1988-Europace
TL;DR: In this article, the formation, physical properties and cosmological evolution of various topological defects such as vacuum domain walls, strings, walls bounded by strings, and monopoles connected by strings are reviewed.
Abstract: Phase transitions in the early universe can give rise to microscopic topological defects: vacuum domain walls, strings, walls bounded by strings, and monopoles connected by strings. This article reviews the formation, physical properties and the cosmological evolution of various defects. A particular attention is paid to strings and their cosmological consequences, including the string scenario of galaxy formation and possible observational effects of strings.

98 citations

Journal ArticleDOI
TL;DR: In this paper, the authors compared two optical clocks based on the electric quadrupole (E2) and the electric octupole transition (E3) to obtain the most accurate determination of an optical transition frequency to date.
Abstract: We compare two optical clocks based on the ${^{2}S}_{1/2}(F=0)\ensuremath{\rightarrow}{^{2}D}_{3/2}(F=2)$ electric quadrupole (E2) and the ${^{2}S}_{1/2}(F=0)\ensuremath{\rightarrow}{^{2}F}_{7/2}(F=3)$ electric octupole (E3) transition of ${^{171}\mathrm{Yb}}^{+}$ and measure the frequency ratio ${\ensuremath{ u}}_{\mathrm{E}3}/{\ensuremath{ u}}_{\mathrm{E}2}=0.932829404530965376(32)$, improving upon previous measurements by an order of magnitude. Using two caesium fountain clocks, we find ${\ensuremath{ u}}_{E3}=642121496772645.10(8)\text{ }\text{ }\mathrm{Hz}$, the most accurate determination of an optical transition frequency to date. Repeated measurements of both quantities over several years are analyzed for potential violations of local position invariance. We improve by factors of about 20 and 2 the limits for fractional temporal variations of the fine structure constant $\ensuremath{\alpha}$ to $1.0(1.1)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}18}/\mathrm{yr}$ and of the proton-to-electron mass ratio $\ensuremath{\mu}$ to $\ensuremath{-}8(36)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}18}/\mathrm{yr}$. Using the annual variation of the Sun's gravitational potential at Earth $\mathrm{\ensuremath{\Phi}}$, we improve limits for a potential coupling of both constants to gravity, $({c}^{2}/\ensuremath{\alpha})(d\ensuremath{\alpha}/d\mathrm{\ensuremath{\Phi}})=14(11)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}9}$ and $({c}^{2}/\ensuremath{\mu})(d\ensuremath{\mu}/d\mathrm{\ensuremath{\Phi}})=7(45)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}8}$.

73 citations

Journal ArticleDOI
TL;DR: Atom interferometers have been developed in the last three decades as new powerful tools to investigate gravity and have been used for measuring the gravity acceleration, the gravity gradient, and the gravity field curvature as mentioned in this paper.
Abstract: Atom interferometers have been developed in the last three decades as new powerful tools to investigate gravity. They were used for measuring the gravity acceleration, the gravity gradient, and the gravity-field curvature, for the determination of the gravitational constant, for the investigation of gravity at microscopic distances, to test the equivalence principle of general relativity and the theories of modified gravity, to probe the interplay between gravitational and quantum physics and to test quantum gravity models, to search for dark matter and dark energy, and they were proposed as new detectors for the observation of gravitational waves. Here I describe past and ongoing experiments with an outlook on what I think are the main prospects in this field and the potential to search for new physics.

68 citations

Journal ArticleDOI
25 Feb 2021
TL;DR: In this article, the authors proposed to use the nuclear resonance frequency, determined by the strong and electromagnetic interactions inside the nucleus, to build a highly precise nuclear clock that will be fundamentally different from all other atomic clocks based on resonant frequencies of the electron shell.
Abstract: The low-energy, long-lived isomer in 229Th, first studied in the 1970s as an exotic feature in nuclear physics, continues to inspire a multidisciplinary community of physicists. It has stimulated innovative ideas and studies that expand the understanding of atomic and nuclear structure of heavy elements and of the interaction of nuclei with bound electrons and coherent light. Using the nuclear resonance frequency, determined by the strong and electromagnetic interactions inside the nucleus, it is possible to build a highly precise nuclear clock that will be fundamentally different from all other atomic clocks based on resonant frequencies of the electron shell. The nuclear clock will open opportunities for highly sensitive tests of fundamental principles of physics, particularly in searches for violations of Einstein’s equivalence principle and for new particles and interactions beyond the standard model. It has been proposed to use the nuclear clock to search for variations of the electromagnetic and strong coupling constants and for dark matter searches. The 229Th nuclear optical clock still represents a major challenge in view of the tremendous gap of nearly 17 orders of magnitude between the present uncertainty in the nuclear transition frequency (about 0.2 eV, corresponding to ∼48 THz) and the natural linewidth (in the mHz range). Significant experimental progress has been achieved in recent years, which will be briefly reviewed. Moreover, a research strategy will be outlined to consolidate our present knowledge about essential 229mTh properties, to determine the nuclear transition frequency with laser spectroscopic precision, realize different types of nuclear clocks and apply them in precision frequency comparisons with optical atomic clocks to test fundamental physics. Two avenues will be discussed: laser-cooled trapped 229Th ions that allow experiments with complete control on the nucleus–electron interaction and minimal systematic frequency shifts, and Th-doped solids enabling experiments at high particle number and in different electronic environments.

51 citations

Journal ArticleDOI
20 Aug 2020
TL;DR: This work disseminates a coherent optical frequency signal to two distant radio telescopes using a 1739-km-long fiber, confirming that the proposed approach is feasible and configures as a novel tool for studying the role of clocks, troposphere, and systematic effects in the ultimate VLBI resolution.
Abstract: Among the most powerful techniques for the exploration of the Universe is very long baseline interferometry (VLBI), which is based on the simultaneous observation of radio sources in the sky with arrays of distant ground-based antennas. One of the effects currently limiting its ultimate sensitivity is the phase-instability of the reference clocks adopted at each antenna. This term can be made negligible delivering the same clock signal to multiple telescope sites using optical fibers. We realized such an infrastructure by disseminating a coherent optical frequency signal to two distant radio telescopes using a 1739-km-long fiber. We performed a 24 h geodetic VLBI campaign in which the same clock reference was used at both telescopes and analyzed it using standard VLBI procedures. The results were consistent with the expectations, confirming that the proposed approach is feasible and configures as a novel tool for studying the role of clocks, troposphere, and systematic effects in the ultimate VLBI resolution.

49 citations