We study isolated core excitation of ultra cold ytterbium Rydberg atoms of high orbital quantum number. Measurements were performed on the $6s_{1/2} 40l \rightarrow 6p_{1/2} 40l $ transition with $l=5-9$. The extracted energy shifts and autoionization rates are in good agreement with a model based on independant electrons, taking into account interactions in a perturbative approach. We reveal a particularly long persistence of the autoionization rates with the orbital quantum number, explained by the strong coupling of the $6p_{1/2}nl$ autoionizing state with the $5d_{3/2}εl'$ continua compared to previously studied divalent atoms.
Long-range dipole-dipole and quadrupole-quadrupole interactions between pairs of Rydberg atoms are calculated perturbatively for calcium, strontium and ytterbium within the Coulomb approximation. Quantum defects, obtained by fitting existing laser spectroscopic data, are provided for all $S$, $P$, $D$ and $F$ series of strontium and for the $^3P_2$ series of calcium. The results show qualitative differences with the alkali metal atoms, including isotropically attractive interactions of the strontium $^1S_0$ states and a greater rarity of Förster resonances. Only two such resonances are identif…
We present an experimental study of the Rydberg $^1S_0$- and $^1P_1$- series of ytterbium for principal quantum numbers in the range of $n=70$ to $90$. The study is performed using trap loss spectroscopy in a magneto-optical trap operating on the $6^1S_0 \rightarrow 6^1P_1$ transition at $399\,\text{nm}$. Compared to the commonly used Rydberg spectroscopy method using field-ionization and ion detection, trap loss spectroscopy is significantly simpler and requires a less sophisticated experimental setup. Using this method we determine relative values of the scalar and tensor electric polarizabi…
Revealing electron-ytterbium interactions through Rydberg molecular spectroscopy
Institute of Applied Physics, University of Bonn（波恩大学应用物理研究所）；Max Planck Institute for the Physics of Complex Systems（马克斯·普朗克复杂系统物理研究所）；Department of Physics and Astronomy, Purdue University（普渡大学物理与天文学系）
We present an experimental system for Rydberg tweezer arrays with ytterbium (Yb) atoms featuring internal state manipulation between the ground ${}^1$S$_0$ and the metastable ${}^3$P$_2$ states, and single-photon excitation from the ${}^3$P$_2$ to Rydberg states. In the experiments, single Yb atoms are trapped in two-dimensional arrays of optical tweezers and are detected by fluorescence imaging with the intercombination ${}^1$S$_0 \leftrightarrow {}^3$P$_1$ transition, and the defect-free single atom arrays are prepared by the rearrangement with the feedaback. We successfully perform high-res…
New measurements of high-lying even parity $6sns\, {}^1 \! S_0$ and $6snd\,{}^{3,1}\!D_2$ levels of neutral $^{174}$Yb are presented in this paper. Spectroscopy is performed by a two-step laser excitation from the ground state $4f^{14}6s^2 \, {}^1 \! S_0$, and the Rydberg levels are detected by using the field ionization method. Additional two-photon microwave spectroscopy is used to improve the relative energy accuracy where possible. The spectroscopic measurements are complemented by a multichannel quantum defect theory (MQDT) analysis for the J=0 and the two-coupled J=2 even parity series. …
Neutral atom qubits with Rydberg-mediated interactions are a leading platform for developing large-scale coherent quantum systems. In the majority of experiments to date, the Rydberg states are not trapped by the same potential that confines ground state atoms, resulting in atom loss and constraints on the achievable interaction time. In this work, we demonstrate that the Rydberg states of an alkaline earth atom, ytterbium, can be stably trapped by the same red-detuned optical tweezer that also confines the ground state, by leveraging the polarizability of the Yb$^+$ ion core. Using the previo…
The fluorescence spectrum resulting from laser excitation of the A^{2}Π_{1/2} - X^{2}Σ^{+} (0,0) band of ytterbium monofluoride, YbF, has been recorded and analyzed to determine the Franck-Condon factors. The measured values are compared with those predicted from Rydberg-Klein-Rees (RKR) potential energy curves. From the fluorescence decay curve the radiative lifetime of the A^{2}Π_{1/2} state is measured to be 28\pm2 ns, and the corresponding transition dipole moment is 4.39\pm0.16 D. The implications for laser cooling YbF are discussed.
Engineering controllable, strongly interacting many-body quantum systems is at the frontier of quantum simulation and quantum information processing. Arrays of laser-cooled neutral atoms in optical tweezers have emerged as a promising platform, because of their flexibility and the potential for strong interactions via Rydberg states. Existing neutral atom array experiments utilize alkali atoms, but alkaline-earth atoms offer many advantages in terms of coherence and control, and also open the door to new applications in precision measurement and timekeeping. In this work, we present a techniqu…
Neutral alkaline earth(-like) atoms have recently been employed in atomic arrays with individual readout, control, and high-fidelity Rydberg-mediated entanglement. This emerging platform offers a wide range of new quantum science applications that leverage the unique properties of such atoms: ultra-narrow optical "clock" transitions and isolated nuclear spins. Specifically, these properties offer an optical qubit ("o") as well as ground ("g") and metastable ("m") nuclear spin qubits, all within a single atom. We consider experimentally realistic control of this "omg" architecture and its coupl…
New experimental quantum simulation platforms have recently been implemented with divalent atoms trapped in optical tweezer arrays with promising performance. The second valence electron also brings new propects through the so-called Isolated Core Excitation (ICE), however autoionization presents a strong limitation to this use. In this study, we propose and demonstrate a new approach to applying a sizable light shift to a Rydberg state with close-to-resonant ICE while avoiding auto-ionization. In particular, we have investigated ICE of ytterbium atoms in $^1S_0$ Rydberg states. Spectroscopic …
The PairInteraction Toolkit for Modeling Rydberg Physics in Alkali and Alkaline-Earth-Like Atoms
University of Stuttgart（斯图加特大学）；Atom Computing, Inc.（Atom Computing公司）；Universität Tübingen（蒂宾根大学）；University of Bonn（波恩大学）；Universität Heidelberg（海德堡大学）；Max Planck Computing and Data Facility（马克斯·普朗克计算与数据中心）
How do isolated quantum systems approach an equilibrium state? We experimentally and theoretically address this question for a prototypical spin system formed by ultracold atoms prepared in two Rydberg states with different orbital angular momenta. By coupling these states with a resonant microwave driving we realize a dipolar XY spin-1/2 model in an external field. Starting from a spin-polarized state we suddenly switch on the external field and monitor the subsequent many-body dynamics. Our key observation is density dependent relaxation of the total magnetization much faster than typical de…
The structure and photoexcitation dynamics of high lying doubly excited states of the strontium atom with high angular momenta are studied in the vicinity of the Sr$^+(N=5)$ threshold. The spectra recorded using resonant multiphoton isolated core excitation are analyzed with calculations based on configuration interaction with exterior complex scaling, which treats the correlated motion of the two valence electrons of Sr from first principles. The results are rationalized with a model based on multichannel quantum-defect theory and transition dipole moments calculated with a perturbative treat…
We review Rydberg aggregates, assemblies of a few Rydberg atoms exhibiting energy transport through collective eigenstates, considering isolated atoms or assemblies embedded within clouds of cold ground-state atoms. We classify Rydberg aggregates, and provide an overview of their possible applications as quantum simulators for phenomena from chemical or biological physics. Our main focus is on flexible Rydberg aggregates, in which atomic motion is an essential feature. In these, simultaneous control over Rydberg-Rydberg interactions, external trapping and electronic energies, allows Born-Oppen…
We present a new mechanism contributing to the detection of photoassociated long-range Rydberg molecules via pulsed-field ionization: ionic products, created by the decay of a long-range Rydberg molecule, modify the excitation spectrum of surrounding ground-state atoms and facilitate the excitation of further atoms into Rydberg states by the photoassociation light. Such an ion-mediated excitation mechanism has been previously called "Coulomb anti-blockade". Pulsed-field ionisation typically doesn't discriminate between the ionization of a long-range Rydberg molecule and an isolated Rydberg ato…
We demonstrate site-resolved imaging of individual bosonic $^{174}\mathrm{Yb}$ atoms in a Hubbard-regime two-dimensional optical lattice with a short lattice constant of 266 nm. To suppress the heating by probe light with the $^1S_0$-$^1P_1$ transition of the wavelength $λ$ = 399 nm for high-resolution imaging and preserve atoms at the same lattice sites during the fluorescence imaging, we simultaneously cool atoms by additionally applying narrow-line optical molasses with the $^1S_0$-$^3P_1$ transition of the wavelength $λ$ = 556 nm. We achieve a low temperature of $T = 7.4(1.3)\ μ\mathrm{K}$…
We present a mechanism that permits the parallel execution of multiple quantum gate operations within a single long linear ion chain. Our approach is based on large coherent forces that occur when ions are electronically excited to long-lived Rydberg states. The presence of Rydberg ions drastically affects the vibrational mode structure of the ion crystal giving rise to modes that are spatially localized on isolated sub-crystals which can be individually and independently manipulated. We theoretically discuss this Rydberg mode shaping in an experimentally realistic setup and illustrate its pow…
Fast Quantum Interconnects via Neutral Atom Ensembles
Institute of Theoretical Physics, TU Wien（维也纳工业大学理论物理研究所）；Institute of Quantum Electronics, Department of Physics, ETH Zürich（苏黎世联邦理工学院物理系量子电子学研究所）；Quantum Center, ETH Zürich（苏黎世联邦理工学院量子中心）；Laboratory for Nano and Quantum Technologies, Paul Scherrer Institut（保罗谢尔研究所纳米与量子技术实验室）
Controlling strongly interacting many-body systems enables the creation of tailored quantum matter, with properties transcending those based solely on single particle physics. Atomic ensembles which are optically driven to a Rydberg state provide many examples of this, such as atom-atom entanglement, many-body Rabi oscillations, strong photon-photon interaction and spatial pair correlations. In its most basic form, Rydberg quantum matter consists of an isolated ensemble of strongly interacting atoms spatially confined to the blockade volume - a so-called superatom. Here we demonstrate the cont…
In the laser excitation of ultracold atoms to Rydberg states, we observe a dramatic suppression caused by van der Waals interactions. This behavior is interpreted as a local excitation blockade: Rydberg atoms strongly inhibit excitation of their neighbors. We measure suppression, relative to isolated atom excitation, by up to a factor of 6.4. The dependence of this suppression on both laser irradiance and atomic density are in good agreement with a mean-field model. These results are an important step towards using ultracold Rydberg atoms in quantum information processing.
Generating quantum entanglement in large systems on time scales much shorter than the coherence time is key to powerful quantum simulation and computation. Trapped ions are among the most accurately controlled and best isolated quantum systems with low-error entanglement gates operated via the vibrational motion of a few-ion crystal within tens of microseconds. To exceed the level of complexity tractable by classical computers the main challenge is to realise fast entanglement operations in large ion crystals. The strong dipole-dipole interactions in polar molecule and Rydberg atom systems all…
We propose a simple three-body model of an atom in which one electron on a circular Rydberg orbit is treated as an independent particle and the remaining core electrons are collectively described as a single object. Within this model we predict the existence of stable deformed states of atoms. The deformation is generated by a bootstrap mechanism. The atomic core is polarized by the excited electron and the induced dipole moment keeps this electron localized. The deformed stable states of the atom are similar to the Trojan states observed in recent experiments. However, in the present case the…
We report on the direct measurement of the van der Waals interaction between two isolated, single Rydberg atoms separated by a controlled distance of a few micrometers. By working in a regime where the single-atom Rabi frequency of the laser used for excitation to the Rydberg state is comparable to the interaction energy, we observe a \emph{partial} Rydberg blockade, whereby the time-dependent populations of the various two-atom states exhibit coherent oscillations with several frequencies. A quantitative comparison of the data with a simple model based on the optical Bloch equations allows us…
Spontaneous avalanche to plasma splits the core of an ellipsoidal Rydberg gas of nitric oxide. Ambipolar expansion first quenches the electron temperature of this core plasma. Then, long-range, resonant charge transfer from ballistic ions to frozen Rydberg molecules in the wings of the ellipsoid quenches the centre-of-mass ion/Rydberg molecule velocity distribution. This sequence of steps gives rise to a remarkable mechanics of self-assembly, in which the kinetic energy of initially formed hot electrons and ions drives an observed separation of plasma volumes. These dynamics adiabatically sequ…
Quantum phase transitions (QPTs) involve transformations between different states of matter that are driven by quantum fluctuations. These fluctuations play a dominant role in the quantum critical region surrounding the transition point, where the dynamics are governed by the universal properties associated with the QPT. While time-dependent phenomena associated with classical, thermally driven phase transitions have been extensively studied in systems ranging from the early universe to Bose Einstein Condensates, understanding critical real-time dynamics in isolated, non-equilibrium quantum sy…
Isolated attosecond pulses (IAP) generated by high-order harmonic generation are valuable tools that enable dynamics to be studied on the attosecond time scale. The applicability of these IAP would be widened drastically by increasing their energy. Here we analyze the potential of using multi-colour driving pulses for temporally gating the attosecond pulse generation process. We devise how this approach can enable the generation of IAP with the available high-energy kHz-repetition-rate Ytterbium-based laser amplifiers (delivering 180-fs, 1030-nm pulses). We show theoretically that this require…
A two-level quantum system coherently driven by a resonant electromagnetic field oscillates sinusoidally between the two levels at frequency $Ω$ which is proportional to the field amplitude [1]. This phenomenon, known as the Rabi oscillation, has been at the heart of atomic, molecular and optical physics since the seminal work of its namesake and coauthors [2]. Notably, Rabi oscillations in isolated single atoms or dilute gases form the basis for metrological applications such as atomic clocks and precision measurements of physical constants [3]. Both inhomogeneous distribution of coupling str…
We present a study of even parity Rydberg exciton states in cuprous oxide using time-resolved second harmonic generation (SHG). Excitonic states with principal quantum number n = 5 - 12 were excited by nanosecond pulses around 1143 nm. Using time-resolved single-photon counting, the coherently generated second harmonic was isolated both temporally and spectroscopically from inelastic emission due to lower-lying free and bound excitonic states, which included narrow resonances at 1.99 eV associated with an exceptional lifetime of 641 $\pm$ 7 $μ$s. The near transform-limited excitation bandwidth…
We present the results of experiments demonstrating the spectroscopic detection of Förster resonance energy transfer from NH$_3$ in the $X\,^1A_1$ ground electronic state to helium atoms in 1s$n$s\,$^3$S$_1$ Rydberg levels, where $n=37$ and $n=40$. For these values of $n$ the 1s$n$s\,$^3$S$_1\rightarrow$1s$n$p\,$^3$P$_J$ transitions in helium lie close to resonance with the ground-state inversion transitions in NH$_3$, and can be tuned through resonance using electric fields of less than 10~V/cm. In the experiments, energy transfer was detected by direct state-selective electric field ionizati…
Understanding the dynamics of strongly interacting disordered quantum systems is one of the most challenging problems in modern science, due to features such as the breakdown of thermalization and the emergence of glassy phases of matter. We report on the observation of anomalous relaxation dynamics in an isolated XXZ quantum spin system realized by an ultracold gas of atoms initially prepared in a superposition of two-different Rydberg states. The total magnetization is found to exhibit sub-exponential relaxation analogous to classical glassy dynamics, but in the quantum case this relaxation …
We analyze a method for preparing low-entropy many-body states in isolated quantum optical systems of atoms, ions and molecules. Our approach is based upon shifting entropy between different regions of a system by spatially modulating the magnitude of the effective Hamiltonian. We conduct two case studies, on a topological spin chain and the spinful fermionic Hubbard model, focusing on the key question: can a "conformal cooling quench" remove sufficient entropy within experimentally accessible timescales? Finite temperature, time-dependent matrix product state calculations reveal that even mod…
To advance quantum information science a constant pursuit is the search for physical systems that meet the stringent requirements for creating and preserving quantum entanglement. In atomic physics, robust two-qubit entanglement is typically achieved by strong, long-range interactions in the form of Coulomb interactions between ions or dipolar interactions between Rydberg atoms. While these interactions allow fast gates, atoms subject to these interactions must overcome the associated coupling to the environment and cross-talk among qubits. Local interactions, such as those requiring significa…
