Continuous cloud position spectroscopy using a magneto-optical trap

We extend the technique originally proposed by Honda et al.to measure the\ntemperature of Ytterbium and alkine-earth atoms confined in a Magneto-Optical\nTrap (MOT). The method is based on the analysis of excitation spectra obtained\nby probing the 1S0->3P1 inter-combination line. Thanks to a careful analysis\nand modeling of the effects caused by the MOT light on the probe transition we\novercome the resolution and precision limits encountered in previous works.\nGround state light shift and Rabi broadening are measured and successfully\ncompared with calculated values. This knowledge allows us to properly extract\nthe Doppler contribution to the linewidth, thus obtaining a reliable\nmeasurement of the cloud temperature. We finally show how spectroscopy on\nfree-falling atoms provides an alternative method to determine the sample\ntemperature which resembles the standard time-of-flight technique.\n

Deep laser cooling of atoms, ions, and molecules facilitates the study of fundamental physics as well as applied research. In this work, we report on the narrow-line laser cooling of thulium atoms at the wavelength of 506.2nm with the natural linewidth of 7.8kHz, which widens the limits of atomic cloud parameters control. Temperatures of about 400nK, phase-space density of up to 3.5×10−4 and 2×106 number of trapped atoms were achieved. We have also demonstrated formation of double cloud structure in an optical lattice by adjusting parameters of the 506.2nm magneto-optical trap. These results can be used to improve experiments with BEC, atomic interferometers, and optical clocks.

We present a compact and stable dual-wavelength laser source for onboard atom interferometry with two different atomic species. It is based on frequency-doubled telecom lasers locked on a femtosecond optical frequency comb. We take advantage of the maturity of fiber telecom technology to reduce the number of free-space optical components, which are intrinsically less stable, and to make the setup immune to vibrations and thermal fluctuations. The source provides the frequency agility and phase stability required for atom interferometry and can easily be adapted to other cold atom experiments. We have shown its robustness by achieving the first dual-species K-Rb magneto-optical trap in microgravity during parabolic flights.

We provide an introduction to the experimental physics of quantum gases. At the low densities of ultracold quantum gases, confinement can be understood from single-particle physics, and interactions can be understood from two-body physics. The structure of atoms provides resonances both in the optical domain and in the radio-frequency domain. Atomic structure data is given for the 27 atomic isotopes that had been brought to quantum degeneracy at the time this chapter was written. We discuss the motivations behind choosing among these species. We review how static and oscillatory fields are treated mathematically. An electric dipole moment can be induced in a neutral atom, and is the basis for optical manipulation as well as short-range interactions. Many atoms have permanent magnetic dipole moments, which can be used for trapping or long-range interactions. The Toronto $^{40}$K/$^{87}$Rb lattice experiment provides an illustration of how these tools are combined to create an ultracold, quantum-degenerate gas.

Reconfigurable photonic filters show great promise as a potential solution to meet the evolving needs of future microwave communication systems. By integrating high-performance filters into programmable microwave photonic processors, they can provide significant benefits for signal processing applications. The development of an algorithm that can automatically characterize and reconfigure the filter using a single optical input and output port is essential for this purpose. This paper presents an optimization technique for a fully tunable ring-assisted Mach–Zehnder interferometer filter. The proposed filter design eliminates the need for monitoring components and employs a novel algorithm that operates independently in each ring by switching between the two arms of the filter. In addition, the filter can be configured to implement different filter architectures, allowing for flexible filtering requirements. Measurements were performed using the device as an interleaver, implementing different types of infinite impulse response filters in the optical and radio frequency domains. Side-coupled integrated spaced sequence of resonator filters were also implemented by reconfiguring the same device. These results demonstrate the exceptional reconfigurability of the filter design proposed herein in terms of bandwidth and central frequency.

The linear frequency swept light source is a critical device for several sensing applications, including FMCW LiDAR, with which the maximum sensing distance is determined by the coherence length of the light source and the spatial resolution is limited by the frequency scan nonlinearity. Here, we report what we believe to be a novel approach to generate highly coherent optical linear frequency sweeps (LFS) with a Fourier domain mode-locked (FDML) opto-electronic oscillator (OEO) deploying carrier suppressed single sideband (CS-SSB) modulation enabled by a dual-parallel Mach-Zehnder modulator (DP-MZM), with the coherence length determined by the fixed frequency laser used in the OEO, without the need of an expensive high-speed arbitrary waveform generator (AWG). Concurrently, a radio frequency (RF) LFS synchronized with the optical LFS is also generated with the FDML OEO. We obtained a nearly ideal optical LFS around 1550 nm with a side-mode suppression ratio of 27.4 dB, by controlling the bias point and the RF power feeding back to the DP-MZM in the OEO loop. The resulting dual optical and RF LFS' achieved a chirp rate of 27.27 MHz/µs and a frequency tuning range of 0.6 GHz, which can be extended to 142 MHz/µs and 2.0 GHz, respectively by reducing the size of the tunable ring filter circuit inside the OEO loop. By using pre-distortion method, the residual nonlinearity is reduced to 1.9881 × 10-5, and the root mean square (RMS) value of the frequency swept nonlinearity is less than 0.764 MHz. Our dual optical and RF LFS generation with a CS-SSB FDML-OEO has the advantages of long coherence length, high tuning speed, excellent frequency tuning linearity and repeatability, and potentially low cost, which can be used to make a dual optical and RF FMCW ranging system (LiDAR and RADAR) and are attractive for many applications, such as 3D sensing and autonomous driving, as well as optical frequency domain reflectometer (OFDR), and other applications requiring fast and reliable linear frequency sweeps in either optical and RF domains.

We present a scheme to enhance the atom number in magneto-optical traps of strontium atoms operating on the 461-nm transition. This scheme consists of resonantly driving the ${}^{1}{\mathrm{S}}_{0}\ensuremath{\rightarrow}{}^{3}{\mathrm{P}}_{1}$ intercombination line at 689 nm, which continuously populates a short-lived reservoir state and, as expected from a theoretical model, partially shields the atomic cloud from losses arising in the 461-nm cooling cycle. We show a factor of 2 enhancement in the atom number for the bosonic isotopes ${}^{88}\mathrm{Sr}$ and ${}^{84}\mathrm{Sr}$, and the fermionic isotope ${}^{87}\mathrm{Sr}$, in good agreement with our model. Our scheme can be applied in the majority of strontium experiments without increasing the experimental complexity of the apparatus, since the employed 689-nm transition is commonly used for further cooling. Our method should thus be beneficial to a broad range of quantum science and technology applications exploiting cold strontium atoms, and could be extended to other atomic species.

We report the direct excitation of the highly forbidden (6s2) 1S0 <--> (6s6p) 3P0 optical transition in two odd isotopes of neutral ytterbium. As the excitation laser frequency is scanned, absorption is detected by monitoring the depletion from an atomic cloud at approximately 70 microK in a magneto-optical trap. The measured frequency in 171Yb (F=1/2) is 518,295,836,591.6 +/- 4.4 kHz. The measured frequency in 173Yb (F=5/2) is 518,294,576,847.6 +/- 4.4 kHz. Measurements are made with a femtosecond-laser frequency comb calibrated by the National Institute of Standards and Technology cesium fountain clock and represent nearly a 10(6)-fold reduction in uncertainty. The natural linewidth of these J=0 to J=0 transitions is calculated to be approximately 10 mHz, making them well suited to support a new generation of optical atomic clocks based on confinement in an optical lattice.

The spectra of three-photon laser excitation (according to the 5S1/2 → 5P3/2 → 6S1/2 → 37P3/2 scheme) of mesoscopic ensembles of cold Rb Rydberg atoms in a magneto-optical trap, using cw single-frequency lasers in each stage, have been investigated. The ensembles consisted of 1 to 5 atoms, and their presence was recorded by the selective field ionisation method with postselection according to the number of atoms. The dependence of the spectral shape on the excitation laser pulse duration has been studied. For 2-μs pulses, the minimum spectral width was found to be 1.3 MHz; it was determined by the laser linewidth and the spectral width of laser pulse. For pulses shorter than 0.5 μs, additional spectral broadening and occurrence of Rabi oscillations in the wings of three-photon resonances have been observed, a fact indicative of implementation of coherent three-photon laser excitation of Rydberg atoms. An analysis of the spectra within the four-level theoretical model based on optical Bloch equations showed good agreement between the experimental and theoretical results. The dependence of the shape of three-photon excitation spectrum on the number of recorded atoms was also studied. An increase in the average number of atoms leads to the occurrence of a dip in the single-atom excitation spectra; this dip is due to the specificity of the excitation and detection statistics of Rydberg atoms. The results obtained are important for applications of Rydberg atoms in quantum informatics.

Precise phase control of ultra-wide-bandwidth optical frequency combs has produced remarkable and unexpected progress in precision metrology and ultrafast science. The combination of the ability to do completely arbitrary, optical, waveform synthesis with recently developed optical pulse measurement techniques is analogous to the development of oscilloscopes and waveform generators in the early 20th century. The development of ultra-stable optical frequency standards into optical atomic clocks and optical frequency synthesizers again complement and rival the similar technologies developed in the radio frequency domain. I will cover a range of key advances that have been enabled by this revolutionary merge between the ultrafast and ultra-precision fields, including direct optical frequency measurement, carrier-envelope phase control, alloptical atomic clocks, optical frequency synthesizers, coherent pulse synthesis and distribution, and nonlinear spectroscopy.

The most radical evolution in recent mobile communication technology is imminent in the coming years. The fronthaul network architecture is part of this evolution and is expected to support dense deployment of infrastructure to provide increased bandwidth and ultra-low latency for 5th generation (5G) networks in a cost-effective manner. The new fronthaul architecture called cloud radio access network (C-RAN) has been introduced over the last years to increase scalability, manageability, and flexibility of mobile systems. In this context, this paper addresses the principal technology enablers of the C-RAN 5G fronthaul architecture, namely radio-over-fiber, ribbon optical fibers, wavelength-division multiplexing, and millimeter wave (mmWave) frequencies. The convergence of optical fiber networks and mmWave radio pave the way towards a truly efficient fronthaul infrastructure for 5G mobile communications with seamless connectivity for millions of devices and quality-of-service guarantees in terms of latency for the first time ever. We perceive a network scenario with seamless starting and ending interfaces by exploiting space diversity in both radio frequency and optical domains with efficient integrated photonics technology. Furthermore, we introduce the ongoing developments of the Eindhoven-based 5G Brainport testbed towards an open environment for validation and test of end-to-end emerging applications benefitting from the 5G key-performance indicators.

In this paper, we propose an integrated method for windowing and matched filtering in the analog domain based on microwave photonic technology, which utilizes dispersion regulation of optical waveguide to achieve the windowing processing of broadband signals in the optical domain and the surface acoustic wave filter (SAWF) to achieve the following matched filtering processing in the radio frequency (RF) domain, thus realizing their integration processing in the analog domain. The proposed method is validated by simulation and experiment, in which the integrated processing of matched filtering and windowing in the analog domain for a linear frequency modulation (LFM) signal with a bandwidth of 1 GHz is carried out and the peak to sidelobe ratio (PSLR) of the output signal is -19.55 dB and the mainlobe width (MLW) broadens to 0.16 ns with the maximum achievable dispersion value. The proposed method can significantly reduce the pressure of signal processing at the back-end of the radar system and improve the response speed of the broadband radar system in detecting the targets.

We experimentally demonstrate four-wave-mixing (FWM) spectroscopy using frequency combs. The experiment uses a geometry where excitation pulses and FWM signals generated by a sample co-propagate. We separate them in the radio frequency domain by heterodyne detection with a local oscillator comb that has a different repetition frequency.

We propose and experimentally demonstrate a nondestructive method to monitor chromatic dispersion (CD) and polarization-mode dispersion (PMD) in traffic-carrying wavelength-division-multiplexing optical systems. Coherent heterodyne detection is used to down convert the spectrum of digitally modulated signal from optical domain into radio-frequency (RF) domain. By analyzing group delay difference and polarization walkoff between different frequency components through proper RF signal processing, both CD and PMD can be precisely determined. Good agreement between experimental results and theoretical values has been obtained.

We introduce a new method of simultaneously implementing frequency stabilization and frequency shift for semiconductor lasers. We name this method the frequency tunable modulation transfer spectroscopy (FTMTS). To realize a stable output of 780 nm semiconductor laser, an FTMTS optical heterodyne frequency stabilization system is constructed. Before entering into the frequency stabilization system, the probe laser passes through an acousto-optical modulator (AOM) twice in advance to achieve tunable frequency while keeping the light path stable. According to the experimental results, the frequency changes from 120 MHz to 190 MHz after the double-pass AOM, and the intensity of laser entering into the system is greatly changed, but there is almost no change in the error signal of the FTMTS spectrum. Using this signal to lock the laser frequency, we can ensure that the frequency of the laser changes with the amount of AOM shift. Therefore, the magneto-optical trap (MOT)-molasses process can be implemented smoothly.