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Simplified energy diagram for strontium, including relevant optical transitions and spontaneous decay rates.
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The ESA mission “Space Optical Clock” project aims at operating an optical lattice clock on the ISS in approximately 2023. The scientific goals of the mission are to perform tests of fundamental physics, to enable space-assisted relativistic geodesy and to intercompare optical clocks on the ground using microwave and optical links. The performance...
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The ESA mission "Space Optical Clock" project aims at operating an optical lattice clock on the ISS in approximately 2023. The scientific goals of the mission are to perform tests of fundamental physics, to enable space-assisted relativistic geodesy and to intercompare optical clocks on the ground using microwave and optical links. The performance...
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... The European Space Agency (ESA) has studied plans to launch a sequel mission to the Atomic Clock Ensemble in Space (ACES) in the early 2020s that includes optical atomic clocks and optical links called the Space Optical Clock on the International Space Station (ISS, I-SOC) [87]. ...
We present the white paper developed during the QEYSSat 2.0 study, which was undertaken between June 2021 and March 2022. The study objective was to establish a technology road-map for a Canada-wide quantum network enabled by satellites. We survey the state-of-art in quantum communication technologies, identify the main applications and architectures, review the technical readiness levels and technology bottlenecks and identify a future mission scenario. We report the findings of a dedicated one-day workshop that included Canadian stakeholders from government, industry and academia to gather inputs and insights for the applications and technical road-map. We also provide an overview of the Quantum EncrYption and Science Satellite (QEYSSat) mission expected to launch in 2024-2025 and its anticipated outcomes. One of the main outcomes of this study is that developing the main elements for a Canada-wide quantum internet will have the highest level of impact, which includes Canada-wide entanglement distribution and teleportation. We present and analyze a possible future mission ('QEYSSat 2.0') that would enable a long range quantum teleportation across Canada as an important step towards this vision.
... Longdistance time and frequency links enabling frequency comparisons at the level of 1 × 10 -18 are urgently needed. Such local networks may even be combined by space clocks, as in the ACES [22] or the proposed Space Optical Clock (SOC) [40] missions. Potentially, a space clock can overcome the limitations on the realisation of the SI second and of timescales set by the knowledge of the gravity potential on the ground because the relativistic frequency shift, needed to transform the proper time of the clock to TAI, can be computed more accurately for a space clock than for a ground clock. ...
... Nevertheless, several such systems working with neutral atoms [117][118][119] or single ions [84] have been realised, which already outperform the most accurate microwave standards. These setups are developed for space applications [40], and have been used in a geodetic context [120,121] or to test fundamental aspects of physics [80]. We therefore conclude that the construction and reliable operation of optical clocks with fractional uncertainties of 1 × 10 -17 and below and compact dimensions with volumes 1 m 3 is already possible today [122,123]. ...
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.
... Despite significant progress, the optical clock technology is still insufficiently mature for space applications. There are several proposals aimed at optical clock operation in space, e.g., SAGAS [18], EGE [19] and the ESA's SOC2 project based on Sr and Yb optical lattice clock technologies [20]. At the moment, laboratory tests of the clock modules are being carried out, but the launch is scheduled no earlier than 2038. ...
Optical atomic clocks are currently one of the most sensitive tools making it possible to precisely test the fundamental symmetry properties of spacetime and Einstein’s theory of relativity. At the same time, the extremely high stability and accuracy of compact transportable optical clocks open new perspectives in important fields, such as satellite navigation, relativistic geodesy, and the global time and frequency network. Our project aimed to develop a compact transportable optical clock based on a single ytterbium ion. We present the first prototype of the Yb+ clock (298 kg in 1 m3) and present several solutions aimed to improve the clock’s robustness to approach the demands of a space-qualified system. We present spectroscopic studies of a 435.5 nm quadrupole clock transition with Fourier-limited spectra of 25 Hz. The estimated instability of the output frequency at 1 GHz, which was down-converted with an optical frequency comb (OFC), is at the level of 9×10−15/τ, and the long-term instability and inaccuracy are at the level of 5×10−16. As the next steps, we present a new design for the clock laser and the OFC.
... The time measurement accuracy of a strontium optical lattice clock (SOLC) has entered the order of 10 −19 ,which is the highest performance index in the world [1] . Due to the microgravity environment of space, performance of the SOLC is expected to be further improved [2,3] . In order to achieve this goal, China is developing a space-based SOLC, which will be launched into the China Space Station (CSS) in late 2022. ...
A hertz-linewidth ultra-stable laser (USL), which will be used to detect the clock transition line, in a strontium optical clock will be launched into the China Space Station (CSS) in late 2022. As the core of the USL, an interference-filter-based external-cavity diode laser (IF-ECDL) was developed. The IF-ECDL has a compact, stable, and environmentally insensitive design. Performances of the IF-ECDL are presented. The developed IF-ECDL can pass the aerospace environmental tests, indicating that the IF-ECDL can be suitable for space missions in the CSS.
... ESA has studied the implementation of a sequel mission to ACES based on an optical atomic clock and optical links concept, Space Optical Clock on the International Space Station (ISS, I-SOC) with a possible implementation in the early 2020s [52]. These experiments clearly show the superior performance of the QT-based optical TFT which have improved the performance at this early stage of development already by three orders of magnitude (two in stability, one in precision) [51]. ...
Recently, the European Commission supported by many European countries has announced large investments towards the commercialization of quantum technology (QT) to address and mitigate some of the biggest challenges facing today’s digital era – e.g. secure communication and computing power. For more than two decades the QT community has been working on the development of QTs, which promise landmark breakthroughs leading to commercialization in various areas. The ambitious goals of the QT community and expectations of EU authorities cannot be met solely by individual initiatives of single countries, and therefore, require a combined European effort of large and unprecedented dimensions comparable only to the Galileo or Copernicus programs. Strong international competition calls for a coordinated European effort towards the development of QT in and for space, including research and development of technology in the areas of communication and sensing. Here, we aim at summarizing the state of the art in the development of quantum technologies which have an impact in the field of space applications. Our goal is to outline a complete framework for the design, development, implementation, and exploitation of quantum technology in space.
... Additional noise of the doubler has already been tested to an instability level of 10 −19 at 1 s [34]. As the cavity mounting is designed to withstand acceleration shocks of up to 55 g an application of the cavity in space missions [35] seems feasible. ...
We present an interrogation laser system for a transportable strontium lattice clock operating at 698 nm, which is based on an ultra-low-expansion glass reference cavity. Transportability is achieved by implementing a rigid, compact, and vibration insensitive mounting of the 12 cm-long reference cavity, sustaining shocks of up to 50 g. The cavity is mounted at optimized support points that independently constrain all degrees of freedom. This mounting concept is especially beneficial for cavities with a ratio of length L over diameter D L/D > 1. Generally, large L helps to reduce thermal noise-induced laser frequency instability while small D leads to small cavity volume. The frequency instability was evaluated, reaching its thermal noise floor of mod σy ≈ 3 × 10⁻¹⁶ for averaging times between 0.5 s and 10 s. The laser system was successfully operated during several field studies.
... While there has been some effort to engineer optical-lattice systems [8,9], in many cases the approach to building robust optical clocks has been to carry out spectroscopy on an atomic beam [10][11][12]. This is because laser technology is arguably the most serious obstacle to robust, continuous operation for an atomic clock (or any other atomic sensor). ...
We have characterized the molecular tellurium (Te$_2$) spectrum in the vicinity of the 423nm $^1S_0-^1P_1$ and the 431nm $^3P_1-^3P_0$ transitions in neutral calcium. These transitions are relevant to optical clocks for atomic-beam characterization and cooling (423nm) and enhanced detection (431nm). The use of a Te$_2$ vapor cell as a frequency reference has many advantages over other laser stabilization techniques, and we discuss an application to measuring the instability due to the second-order Doppler shift in a calcium beam clock.
... A laser system including two laser heads on a compact breadboard with acousto-optical modulators for frequency tuning and intensity modulation, an optical shutter and coupling into three optical fibres. Similar assemblies are used in the transportable optical clocks reported by Koller et al. 2017 andOriglia et al. 2016. As the interrogation or clock laser is only one -though admittedly a very important -part of a complete optical clock, a functional transportable system requires more developments. ...
... The activities of the "Space Optical Clock" consortium (SOC) are coordinated by the University of Düsseldorf (Bongs et al. 2015). Originally following the development of both Sr and Yb lattice clocks it focusses now on a very compact Sr system (Bongs et al. 2015;Origlia et al. 2016). So far, spectroscopy of the 698 nm clock transition on 88 Sr has been demonstrated with an apparatus that houses all laser systems (figure 6.9) and vacuum components necessary for the clock excluding electronics and the clock laser in a volume of less than 1 m 3 . ...
We review experimental progress on optical atomic clocks and frequency transfer, and consider the prospects of using these technologies for geodetic measurements. Today, optical atomic frequency standards have reached relative frequency inaccuracies below 10-17, opening new fields of fundamental and applied research. The dependence of atomic frequencies on the gravitational potential makes atomic clocks ideal candidates for the search for deviations in the predictions of Einstein's general relativity, tests of modern unifying theories and the development of new gravity field sensors. In this review, we introduce the concepts of optical atomic clocks and present the status of international clock development and comparison. Besides further improvement in stability and accuracy of today's best clocks, a large effort is put into increasing the reliability and technological readiness for applications outside of specialized laboratories with compact, portable devices. With relative frequency uncertainties of 10-18, comparisons of optical frequency standards are foreseen to contribute together with satellite and terrestrial data to the precise determination of fundamental height reference systems in geodesy with a resolution at the cm-level. The long-term stability of atomic standards will deliver excellent long-term height references for geodetic measurements and for the modelling and understanding of our Earth.
... The lattice clock apparatus with its cooling and manip- ulation lasers is described in [26,27]. Atoms are cooled and trapped in a 1D vertically oriented optical lattice (magic wavelength: 813 nm, ⇠ 40 µm waist radius). ...
Optical lattice clocks with uncertainty and instability in the $10^{-17}$-range and below have so far been demonstrated exclusively using fermions. Here, we demonstrate a bosonic optical lattice clock with $3\times 10^{-18}$ instability and $2.0\times 10^{-17}$ accuracy, both values improving on previous work by a factor 30. This was enabled by probing the clock transition with an ultra-long interrogation time of 4 s, using the long coherence time provided by a cryogenic silicon resonator, by careful stabilization of relevant operating parameters, and by operating at low atom density. This work demonstrates that bosonic clocks, in combination with highly coherent interrogation lasers, are suitable for high-accuracy applications with particular requirements, such as high reliability, transportability, operation in space, or suitability for particular fundamental physics topics. As an example, we determine the $^{88}\textrm{Sr} - ^{87}$Sr isotope shift with 12 mHz uncertainty.
... Recent progress in the development of quantum sensors has led to systems outperforming classical devices, such as quantum gravimeters, 4,5 and clocks exceeding 10 17 accuracy. 2,6,7 New applications such as relativistic geodesy 8 using transportable optical clocks [9][10][11] or taking advantage of the long interaction times in atom interferometry experiments in a microgravity or even space environment [12][13][14] have emerged. For these applications, quantum optics experiments need to be operated outside highly specialized laboratories, increasing the demands in terms of mechanical robustness of the optical setups. ...
We present a highly stable bow-tie power enhancement cavity for critical second harmonic generation (SHG) into the UV using a Brewster-cut β-BaB2O4 (BBO) nonlinear crystal. The cavity geometry is suitable for all UV wavelengths reachable with BBO and can be modified to accommodate anti-reflection coated crystals, extending its applicability to the entire wavelength range accessible with non-linear frequency conversion. The cavity is length-stabilized using a fast general purpose digital PI controller based on the open source STEMlab 125-14 (formerly Red Pitaya) system acting on a mirror mounted on a fast piezo actuator. We observe 130 h uninterrupted operation without decay in output power at 313 nm. The robustness of the system has been confirmed by exposing it to accelerations of up to 1 g with less than 10% in-lock output power variations. Furthermore, the cavity can withstand 30 min of acceleration exposure at a level of 3 grms without substantial change in the SHG output power, demonstrating that the design is suitable for transportable setups.
