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Optical and Quantum Sensing and Precision Metrology II

Ultra-low noise laser systems for quantum sensing, computing, and precision metrology

Michele Giunta, Murtaza Ali Khan, Evgeny A. Savelyev, Manuel Brekenfeld, Ivanka Grguraš, Dag Schmidt, Malcolm Simpson, Andreas Fricke, Maurice Lessing, Ronald Holzwarth, M. L. Fischer, Thomas Lompe, Joschua Martinek

Published Mar 8, 2023• 0 citations
Publisher

Abstract

Quantum technologies, spanning from sensing and metrology to simulations and computing, rely upon precise and low noise laser systems. Currently, we are witnessing a paradigm shift, where laboratory-based experiments are engineered such to develop reliable operating devices. The goal of providing continuous operation is key to enable their deployment for, e.g., PNT applications or cloud-based quantum computing services. Ultra-low noise laser systems are becoming integral part of these quantum devices due to their pivotal role in the effective functioning of the physics package. In fact, the performance are fundamentally linked to the noise properties of the driving laser fields, imposing the need of a careful choice of the appropriate sources, their spectral properties, and their stabilization. Here we present some of our recent ultra-stable laser system engineered for enabling several applications, we will describe ultra-stable comb and laser systems for quantum computing using neutral Yb, Sr, Rb, or Cs atoms, electric field sensing with Rydberg Rb atoms, and portable compact comb systems to enable uninterrupted operation of optical clocks in the field. A detailed noise analysis of the systems will be presented.

DOI
10.1117/12.2650719

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Quantum technologies, spanning from sensing and metrology to simulations and computing, rely upon precise and low noise laser systems. Currently, we are witnessing a paradigm shift, where laboratory-based experiments are engineered such to develop reliable operating devices. The goal of providing continuous operation is key to enable their deployment for, e.g., PNT applications or cloud-based quantum computing services. Ultra-low noise laser systems are becoming integral part of these quantum devices due to their pivotal role in the effective functioning of the physics package. In fact, the performance are fundamentally linked to the noise properties of the driving laser fields, imposing the need of a careful choice of the appropriate sources, their spectral properties, and their stabilization. Here we present some of our recent ultra-stable laser system engineered for enabling several applications, we will describe ultra-stable comb and laser systems for quantum computing using neutral Yb, Sr, Rb, or Cs atoms, electric field sensing with Rydberg Rb atoms, and portable compact comb systems to enable uninterrupted operation of optical clocks in the field. A detailed noise analysis of the systems will be presented.
Quantum technologies are nowadays emerging as enabling tools for practical applications, such as quantum sensing, quantum computing and quantum metrology. Lasers play a central role in many of these technological platforms, e.g. for atomic clocks, ion-based or neutral atom-based quantum computers or atom interferometers. Here we present a complete laser system to cool, trap and control strontium atoms in an optical lattice or in tweezer arrays. A sub-Hz linewidth master laser, locked to a high-finesse optical cavity provides the frequency reference for an ultra-low noise comb. The rack-mounted laser system consists of all cooling, repumping, and clock lasers stabilized to the optical frequency comb. Each of the involved laser frequencies can therefore be tuned and mapped in the frequency domain with a high degree of stability. The system is controlled via a software interface, allowing to operate the cold-atom-based physics package autonomously. The system is tailored for the operation of 88Sr or 87Sr optical lattice clocks, or for quantum computing applications, but other sub-Hz lasers could be obtained by phase locking additional clock laser frequencies to the ultra-stable comb, enabling convenient and accurate optical frequency ratio measurements. The laser system architecture and the relevant characterization measurements will be presented, proposing some user-cases such as quantum computing and atom interferometry on strontium atoms. This represents a technological leap for quantum optics, allowing to explore further applications of quantum sensors outside a traditional lab.
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Recent progress in Rydberg atoms has enabled a wide range of applications in quantum sensing and quantum computation. In these applications, ultra-stable optical reference systems are essential to meet the requirements of a narrow linewidth and low technical noise. However, most existing systems are confined to laboratory settings and are not suitable for measurement-site-independent applications, such as external electric field sensors. This paper presents a transportable ultra-stable optical reference system for Rydberg excitation. The system is based on a 10 cm long ultra-low-expansion glass optical cavity, and it achieves finesse values of 410 k (at 1018 nm) and 200 k (at 852 nm). After being assembled in the experimental environment, it can still operate with only minor adjustments even after being transported over 400 km. Thanks to its vibration-insensitive design, two-stage temperature control, and hybrid locking unit, the system can maintain its locking status for up to 2 h.
For the past 15 years, tremendous progress within the fields of laser stabilization, optical frequency combs and atom cooling and trapping have allowed the realization of optical atomic clocks with unrivaled performances. These instruments can perform frequency comparisons with fractional uncertainties well below 10-17, finding applications in fundamental physics tests, relativistic geodesy and time and frequency metrology. Even though most optical clocks are currently laboratory setups, several proposals for using these clocks for field measurements or within an optical clock network have been published, and most of time and frequency metrology institutes have started to develop transportable optical clocks. For the purpose of this special issue, we chose to focus on trapped-ion optical clocks. Even though their short-term fractional frequency stability is impaired by a lower signal-to-noise ratio, they offer a high potential for compactness: trapped ions demand low optical powers and simple loading schemes, and can be trapped in small vacuum chambers. We review recent advances on the clock key components, including ion trap and ultra-stable optical cavity, as well as existing projects and experiments which draw the picture of what future transportable, single-ion optical clocks may resemble.
Atoms cooled and trapped using laser light have become the backbone of modern quantum physics research. Various new applications based on laser-cooled atoms are in active development. The work described in this dissertation is dedicated to this endeavor. I present experimental and numerical investigations on several fundamental properties of the laser-cooled atoms in different quantum states and how they may translate into applications within several emerging atom-based technologies. First, I describe the precision measurements of the dynamic polarizability and photo-ionization cross-section at 1064-nm light of the 5D3/25D_{3/2}5D3/2​ state in rubidium, which is of interest for the portable atomic clocks. Two different spectroscopic methods are implemented to extract the polarizability from the experimental data. The results are statistically equivalent: -524(17) [-499(59)] atomic units from the first [second] method. The photo-ionization cross section of the 5D3/25D_{3/2}5D3/2​ state at 1064~nm is measured to be 44(1) Mb. The aforementioned photo-ionization cross section is suitable for efficient ion generation and the subsequent application in cold-atom-based ion sources. This is demonstrated in the second study presented here. The ion source employs a novel method to monitor the electric microfields of the ions using the Stark effect of the highly-excited (Rydberg) atoms seeded within the origin of the ion source. Rydberg atoms are extremely sensitive to electric fields and serve as an embedded real-time sensor and tracker of the ion-source performance because of their quasicontinuous creation and detection. The principles of such ion-microfield sensing are discussed and analyzed in detail and can be utilized in any cold-atom-based focused-ion-beam source. The hyperfine structure of the 4D3/24D_{3/2}4D3/2​ state in rubidium is investigated next. The measurement utilizes two-photon optical absorption spectroscopy and a detailed analysis of light shifts. All four hyperfine components are resolved in the experimental data. The magnetic-dipole and electric-quadrupole hyperfine constants are obtained to be 7.419(45) MHz and 4.19(19) MHz, respectively. Future applications of the 4D3/24D_{3/2}4D3/2​ state in optical atomic clocks and Rydberg-atom physics are discussed. Next, I investigate a Rydberg-atom-ion molecule bound by long-range multipolar forces. The molecule is the first example of a bound state between a Rydberg atom and an ion. Strong interactions between these two particles lead to large molecular binding energy (reaching a few GHz) and large binding length (exceeding 1 mumumum). The Born-Oppenheimer approximation does not hold for the Rydberg-atom-ion molecule because the motion of the Rydberg-atom nucleus is on the same timescale as the dynamics of the ion. The Born-Huang theory is utilized to investigate the resultant nonadiabatic dynamics of the molecule and to make the first fully quantum predictions of its lifetime as a function of the vibrational state and quantum principal number of the Rydberg atom. Lastly, I present a novel technique for atom interferometry that employs uninterrupted three-dimensional confinement and manipulation during the interferometric protocol. The atoms in the existing apparatuses have to follow several-meter-long trajectories along which various detrimental effects such as wave-packet dispersion erase useful phase information. ``Tractor atom interferometry" presented here promises to suppress the harmful effects and improve the interferometers’ sensitivity; provide flexible control over the atomic trajectories; and significantly reduce the experimental footprint. The suitability of this approach for measuring background acceleration (such as due to the gravitational field) is demonstrated. The sensitivity estimations, experimental considerations, and initial laboratory work are discussed.