The metastable He atom in its singlet or triplet states is an ideal system to perform tests of ab-initio calculations of two-electron systems that include quantum-electrodynamics and nuclear finite-size effects. The recent determination of the ionization energy of the metastable 2^1S0 state of 4He [1] confirmed a discrepancy between the latest theoretical values of the Lamb shifts in low-lying electronic states of triplet helium [2] and the measured 3 3D ← 2 3S [3] and 3 3D ← 2 3P [4] transition frequencies. This discrepancy could not be resolved in the latest calculations [5,6]. Recently, we developed a new experimental method for the determination of the ionization energy of the 2 3S1 state of 4He via the measurement of transitions from the 2 3S1 state to np Rydberg states. In this talk, we present the the first results on the ionization energy of metastable helium obtained with improved experimental setup and methods, which include (i) the preparation of a cold, supersonic expansion of helium atoms in the 2 3S1 state, (ii) the development and characterization of a laser system for driving the transitions to np Rydberg states, (iii) the implementation of a new sub-Doppler, background-free detection method [7], and (iv) the integration of an interferometer-based retro-reflector canceling the 1st-order Doppler shift to enable Doppler-free spectroscopy. We illustrate its power with a new determination of the ionization energy of 2 3S1 metastable He with a fractional uncertainty in the 10^(−12) range using extrapolation of the np series. The method is extended to measurements on the 3He isotope, as part of an effort to determine the difference between the charge radii of the alpha particle and the helion nuclei.

[1] G. Clausen et al., Phys. Rev. Lett. 127, 093001 (2021).

[2] V. Patkos et al., Phys. Rev. A. 103, 042809 (2021).

[3] C. Dorrer et al., Phys. Rev. Lett. 78, 3658 (1997).

[4] P.-L. Luo et al., Phys. Rev. A. 94, 062507 (2016).

[5] V. A. Yerokhin et al., Eur. Phys. J. D. 76, 142 (2022).

[6] V. A. Yerokhin et al., Phys. Rev. A. 107, 012810 (2023).

[7] G. Clausen et al., Phys. Rev. Lett. 131, 103001 (2023).

We study simultaneous symmetry-breaking in a spontaneous Floquet state, focusing on the specific case of an atomic condensate. We first describe the quantization of the Nambu-Goldstone (NG) modes for a stationary state simultaneously breaking several symmetries of the Hamiltonian by invoking the generalized Gibbs ensemble, which enables a thermodynamical description of the problem. The quantization procedure involves a Berry-Gibbs connection, which depends on the macroscopic conserved charges associated to each broken symmetry and whose curvature is not invariant under generalized gauge transformations. We extend the formalism to Floquet states, where Goldstone theorem translates into the emergence of Floquet-Nambu-Goldstone (FNG) modes with zero quasi-energy. In the case of a spontaneous Floquet state, there is a genuine temporal FNG mode arising from the continuous time-translation symmetry breaking, whose quantum amplitude provides a rare realization of a time operator in Quantum Mechanics. Furthermore, since they conserve energy, spontaneous Floquet states can be shown to possess a conserved Floquet charge. Both the temporal FNG mode and the Floquet charge are distinctive features of a spontaneous Floquet state, absent in conventional, driven systems. Nevertheless, as these operate at fixed frequency, they also admit a thermodynamic description in terms of the Floquet enthalpy, the Legendre transform of the energy with respect to the Floquet charge. We apply our formalism to a particular realization of spontaneous Floquet state, the CES state, which breaks U(1) and time-translation symmetries, representing a time supersolid. We numerically compute its density-density correlations, which are predicted to be dominated by the temporal FNG mode at long times, observing a remarkable agreement between simulation and theory. Based on these results, we propose a feasible experimental scheme to observe the temporal FNG mode of the CES state.

Work done in collaboration with Juan Ramón Muñoz de Nova.

The application of graph theory to networks has resulted in a myriad of classical applications across biology, economics, epidemiology, sociology, and soft condensed matter physics.  Recent quantum information devices allow us access to large, complex quantum states with non-trivial entanglement structure.  In this talk, I will use three case studies to show the ease and usefulness of complex network theory in identifying novel features of known quantum systems and new kinds of quantum states accessible in noisy intermediate-scale quantum (NISQ) scenarios.

References:

1.     Marc Andrew Valdez, Daniel Jaschke, David L. Vargas and Lincoln D. Carr, “Quantifying Complexity in Quantum Phase Transitions via Mutual Information Complex Networks,” Phys. Rev. Lett., v. 119, p. 225301 (2017)

2.     Bhuvanesh Sundar, Marc Andrew Valdez, Lincoln D. Carr, and Kaden R. A. Hazzard, “A complex network description of thermal quantum states in the Ising spin chain,” Phys. Rev. A, v. 97, p. 052320 (2018)

3.     Bhuvanesh Sundar, Mattia Walschaers, Valentina Parigi, and Lincoln D Carr, “Response of quantum spin networks to attacks,” J. Phys. Complexity, v.2, p. 035008 (2021)

4.     LE Hillberry, MT Jones, DL Vargas, P Rall, N Yunger Halpern, N Bao, S Notarnicola, S Montangero, LD Carr, “Entangled quantum cellular automata, physical complexity, and Goldilocks rules,” Quantum Science and Technology, v. 6, p. 045017 (2021)

5.     EB Jones, LE Hillberry, MT Jones, M Fasihi, P Roushan, Z Jiang, A Ho, C Neill, E Ostby, P Graf, E Kapit, and LD Carr, “Small-world complex network generation on a digital quantum processor,” Nature Communications v. 13, p. 4483 (2022)

6.     Mattia Walschaers, Nicholas Treps, Bhuvanesh Sundar, Lincoln D Carr, and Valentina Parigi, “Emergent complex quantum networks in continuous-variables non-Gaussian states,” Quantum Science and Technology, v. 8, p. 035009 (2023)

7.     LE Hillberry, M Fasihi, L Piroli, N Yunger Halpern, T Prosen, and LD Carr, “Classical simulability, thermodynamics, and integrability of Goldilocks quantum cellular automata,” Phys. Rev. Lett, under review, arXiv:2404.02994 (2024)

Optical tweezer arrays of neutral atoms have emerged as a promising platform for quantum science. Their geometries are highly configurable, and excitation to Rydberg states allows the atoms to interact. When driven by a laser, the system supports a rich phase diagram containing both a paramagnetic and antiferromagnetic phase. The critical point between these phases belongs to the Ising universality class, allowing our simulator to provide direct measurements of the universal scaling dimensions of the Ising conformal field theory (CFT). We adiabatically prepare the ground state at the critical point in a 1D ring of up to 40 atoms and 2D square of up to 81 atoms, and measure its spatial correlations. In 1D, we are able to extract the CFT sigma field scaling dimension of 0.127(37) by introducing a phenomenological length scale associated with decoherence. In 2D, we extract a scaling dimension of 0.59(9); however, open boundary conditions complicate the reliable extraction of a scaling dimension. In addition, the boundary phase transition supports several distinct universality classes with different critical behavior. In particular, we observe two of these classes: one where the boundary orders with the bulk and one where the boundary orders before the bulk. If time permits, progress towards a dual species optical tweezer array of Na and Cs atoms will be discussed.

The study of non-equilibrium quantum many-body systems presents enduring challenges, as the typical statistical mechanics system for matter at equilibrium is not applicable to such systems. Leveraging engineered Hamiltonians, ultracold quantum gases can simulate a variety of spin-lattice models and provide a powerful and tunable many-body platform to study the out-of-equilibrium dynamics and critical dynamics across quantum phase transitions. In this talk, I will present energy-resolved spin correlation measurements in a weakly interacting Fermi gas, which behaves as a many-body spin lattice in energy space with effective long-range interactions, simulating a model of quantum magnetism. I will discuss how the system magnetization is linked to the localization or spread of spin correlations in energy landscape. The microscopic feature of spin correlation offers an important complement to macroscopic magnetization measurement, enhancing our understanding of the ferromagnetic phase transition. Therefore, we highlight energy-space correlation as an observable in the studies of transition between dynamical phases in quantum simulators accomplished by weakly interacting Fermi gases.

Individual atoms in free space are natural cariers of quantum information:  they are perfectly identical, well isolated from the environment, and easily controlled with optical and rf fields.   While trapped atomic ions have been a leading contender for quantum computing, their neutral cousins have been on the sidelines. This has changed dramatically in the last eight years due to advances in techniques for trapping in optical tweezer arrays and new approaches to creating high-fidelity entangling gates. Still there’s lots to do, with new opportunity for innovation.  In this talk I will consider the unique possibilities of quantum computing with qudits (with d>2 levels), by encoding in the nuclear spins of alkaline earth atoms, such as strontium-87, with d=10  Using quantum control one can implement a universal gate set, including single qudit SU(10) gates, and two-qudit entangling gates. Moreover, by encoding a qubit in a spin-cat qudit, one can design hardware efficient fault-tolerant error correcting codes, analogous to the cat-codes for bosons.  

Recent experiments with quantum simulators and noisy intermediate-scale quantum devices have demonstrated unparalleled capabilities of probing many-body wave functions, via directly probing them at the single quantum level via projective measurements. However, very little is known about to interpret and analyse such huge datasets. This represent a fundamental challenge for theory to understand experimental data, that is also relevant to other fields where similarly large data sets are routinely explored - from classical simulations of gauge theories, to observatory studies of many-body ensembles.

In this talk, I will show how it is possible to provide such characterisation of quantum hardware via a direct and assumption-free data mining. The core idea of this programme is the fact that snapshots of many body systems can be construed as very high-dimensional manifolds. Such a manifolds can be characterised via basic topological concepts, in particular, by their intrinsic dimension, and by advanced theoretical tools from network theory and non-parametric, unsupervised learning.

This new approach to the many-body problem opens up a cornucopia of methods to connect physical properties to a stochastic sampling of the system wave function. I will focus here on two specific applications. Firstly, I will discuss theoretical results for both classical and quantum many-body spin systems that illustrate how data structures undergo structural transitions whenever the underlying physical system does, and display universal (critical) behavior in both classical and quantum mechanical cases. These results pave the way for a systematic understanding of field theory aspects in data space, a topic of current interesting in particle and statistical physics. Secondly, I will discuss how our methods allow to track Kolmogorov complexity in quantum simulators and quantum computers, providing novel insights onto the working of such systems, in terms of both practical and fundamental aspects - including cross-certification of quantum devices, a grand challenge in the field.

An array of radiatively coupled emitters is an exciting new platform for generating, storing, and manipulating quantum light. However, the simultaneous positioning and tuning of multiple lifetime-limited emitters into resonance remains a significant challenge.  We reported the creation of superradiant and subradiant entangled states in pairs of lifetime-limited and sub-wavelength-spaced organic molecules by permanently shifting them into resonance with laser-induced tuning [1]. The molecules are embedded as defects in an organic nanocrystal. The pump light redistributes charges in the nanocrystal and dramatically increases the likelihood of resonant molecules. The frequency spectra, lifetimes, and second-order correlation agree with a simple quantum model. This scalable tuning approach with organic molecules provides a pathway for observing collective quantum phenomena in sub-wavelength arrays of quantum emitters.

[1] C Lange, E Daggett, V Walther, L Huang, and JD Hood, Nature Physics (2024)

Programmable arrays of neutral atoms trapped in optical tweezers and lattices have emerged as a powerful tool for studies of competitive optical atomic clocks, as well as the generation of entangled quantum states with the use of Rydberg interactions and methods from both analog quantum simulation and digital quantum information processing. In this talk, I will discuss our efforts to merge these two capabilities and use Rydberg interactions to generate entanglement that can be applied to optical-frequency measurements on a platform compatible with state-of-the-art frequency precision. First, I will describe work in which we create spin squeezed states with almost 4 dB of metrological gain. We use these states to perform synchronous optical-frequency comparisons between independent ensembles of atoms in our array and realize a fractional-frequency stability of 1.087(1)X10-15 after one second of averaging time. This stability represents a 1.94(1) dB improvement over the theoretically achievable precision for this measurement when performed with the same number of unentangled atoms, known as the standard quantum limit. Second, I will present results on generating Greenberger-Horne-Zeilinger (GHZ) states on the clock transition in strontium. We investigate the possibility of leveraging cascades of GHZ states with different sizes for performing measurements that might outperform comparable classical states, even in the presence of frequency noise that would typically lead to phase excursions beyond the invertible regime for the largest GHZ states.

It is almost exactly 100 years since De-Broglie made public his outrageous hypothesis regarding Wave-Particle Duality (WPD), where the latter plays a key role in interferometry. In parallel, the Stern-Gerlach (SG) effect, found a century ago, has become a paradigm of quantum mechanics. I will describe the realization of a half- [1-3] and full- [4-5] loop SG interferometer for single atoms [6], and show how WPD, or complementarity, manifests itself. I will then use the acquired understanding to show how this setup may be used to realize an interferometer for macroscopic objects doped with a single spin [5], namely, to show that even rocks may reveal themselves as waves. I emphasize decoherence channels which are unique to macroscopic objects such as those relating to phonons [7,8] and rotation [9]. These must be addressed in such a challenging experiment. The realization of such an experiment could open the door to a new era of fundamental probes, including the realization of previously inaccessible tests of the foundations of quantum theory and the interface of quantum mechanics and gravity, including the probing of exotic theories such as the Diosi-Penrose gravitationally induced collapse. Time permitting, and as an anecdote noting also De-Broglie's less popular assertion, namely, that the standard description of QM is lacking, I will also present our recent work on Bohmian mechanics, which is an extension of De-Broglie's ideas concerning the pilot wave [10].

[1] Y. Margalit et al., A self-interfering clock as a "which path" witness, Science 349, 1205 (2015).

[2] Zhifan Zhou et al., Quantum complementarity of clocks in the context of general relativity, Classical and quantum gravity 35, 185003 (2018).

[3] Zhifan Zhou et al., An experimental test of the geodesic rule proposition for the non-cyclic geometric phase, Science advances 6, eaay8345 (2020).

[4] O. Amit et al., T3 Stern-Gerlach matter-wave interferometer, Phys. Rev. Lett. 123, 083601 (2019).

[5] Y. Margalit et al., Realization of a complete Stern-Gerlach interferometer: Towards a test of quantum gravity, Science advances 7, eabg2879 (2021).

[6] M. Keil et al., Stern-Gerlach interferometry with the atom chip, Book in honor of Otto Stern, Springer (2021).

[7] C. Henkel and R. Folman, Internal decoherence in nano-object interferometry due to phonons, AVS Quantum Sci. 4, 025602 (2022) – invited paper for a special issue in honor of Roger Penrose.

[8] C. Henkel and R. Folman, Universal limit on quantum spatial superpositions with massive objects due to phonons, https://arxiv.org/abs/2305.15230 (2023).

[9] Y. Japha and R. Folman, Role of rotations in Stern-Gerlach interferometry with massive objects, Phys. Rev. Lett. 130, 113602 (2023).

[10] G. Amit et al., Countering a fundamental law of attraction with quantum wave-packet engineering, Phys. Rev. Res. 5, 013150 (2023).

The expressive capacity of physical systems employed for learning is limited by the unavoidable presence of noise in their extracted outputs. Although present in biological, analog, and quantum systems, the precise impact of noise on learning is not yet fully understood. Focusing on supervised learning, I will present a mathematical framework for evaluating the resolvable expressive capacity (REC) of general physical systems under finite sampling noise, and provide a methodology for extracting its extrema, the eigentasks. Eigentasks are a native set of functions that a given physical system can approximate with minimal error, and the construction of low-noise eigentasks from measurements provides improved performance for machine learning tasks such as classification, displaying robustness to overfitting. I will then discuss how the REC of a quantum system is limited by the fundamental theory of quantum measurement and how the latter imposes a tight upper bound on the REC of any finitely-sampled physical system. The applicability of these results in practice will be demonstrated with experiments on superconducting quantum processors. I will present analyses suggesting that correlations in the measured quantum system enhance learning capacity by reducing noise in eigentasks and discuss the implications of these results for quantum sensing.

We investigate the collective dynamics of two excited distant two-level atoms coupled to a one-dimensional waveguide in the non-Markovian regime, and analyze the emergence of superradiance decay and stationary entanglement in the system. Our model takes into consideration the delay that appears in the atoms' interactions due to the finite light velocity, turning the dynamics non-Markovian.

Ultracold polar molecules are an exciting platform for quantum science and technology. The combination of rich internal structure of vibration and rotation, controllable long-range dipole-dipole interactions and strong coupling to applied electric and microwave fields has inspired many applications. These include quantum simulation of strongly interacting many-body systems, the study of quantum magnetism, quantum metrology and molecular clocks, quantum computation, precision tests of fundamental physics and the exploration of ultracold chemistry. Many of these applications require full quantum control of both the internal and motional degrees of freedom of the molecule at the single particle level.

In Durham, we study ultracold ground-state RbCs molecules formed by associating Rb and Cs atoms using a combination of magnetoassociation and stimulated Raman adiabatic passage [1]. This talk will report our work on the development of full quantum control of the molecules. Specifically, I will explain how we have mastered the ac Stark shift due to the trapping light [2] to demonstrate robust storage qubits in the molecule [3] and will describe the development of magic traps [4] that support second-scale rotational coherences giving access to controllable dipole-dipole interactions [5]. I will also report on new experiments that produce single molecules in optical tweezers starting from a single Rb and a single Cs atom [6]. Using this platform, we prepare the molecules in the motional ground state of the trap and can perform addressing and detection of single molecules [7]. Finally, we demonstrate a new hybrid platform that combines single ultracold molecules with single Rydberg atoms [8], opening a myriad of possibilities.

[1]  P.K.Molony et al., “Creation of Ultracold RbCs Molecules in the Rovibrational Ground State”, Phys. Rev. Lett. 113, 255301 (2014).

[2]  P.D.Gregory et al., “ac Stark effect in ultracold polar RbCs molecules”, Phys. Rev. A 96, 021402(R) (2017).

[3]  P.D.Gregory et al., “Robust storage qubits in ultracold polar molecules”, Nature Physics 17, 1149-1153 (2021).

[4]  Q.Guan et al., “Magic conditions for multiple rotational states of bialkali molecules in optical lattices”, Phys. Rev. A 103, 043311 (2021).

[5]  P.D.Gregory et al., “Second-scale rotational coherence and dipolar interactions in a gas of ultracold polar Molecules” arXiv:2306.02991

[6]  R.V.Brooks et al., “Preparation of one Rb and one Cs atom in a single optical tweezer”, New J. Physics 23, 065002 (2021).

[7]  D.K.Ruttley, A.Guttridge et al., “Formation of ultracold molecules by merging optical tweezers”, Phys. Rev. Lett. 130, 223401 (2023).

[8]  A.Guttridge, D.K.Ruttley et al., “Observation of Rydberg blockade due to the charge-dipole interaction between an atom and a polar molecule”,
Phys. Rev. Lett. 131, 013401 (2023).

In this talk, I will give a general introduction of APS journals, their history and current scopes, especially, Physical Review X, an online-only, fully open access journal that places a high value on innovation, quality, and long-term impact in the science it publishes. I will try to explain how PRX editors apply these principles in practice, and so determine which few of the many excellent research submissions that we receive make it through to publication.

The creation of a matter-wave interferometer can be achieved by loading Bose-Einstein condensed atoms  into an optical lattice. By shaking the lattice via either phase or frequency modulation, the traditional steps of interferometry; effectively splitting, propagating, reflecting, again propagating and then recombining the atomic wavefunction, can be implemented, allowing for the sensing of inertial signals. This approach is interesting, since the atoms can be supported against external forces and perturbations, and the system can be completely reconfigurable on-the-fly for a new design goal. I will report on theoretical and experimental results in which atoms are cooled into a dipole trap and subsequently loaded into an optical lattice.  Shaking protocols for obtaining interferometry steps are derived via machine learning and quantum optimal control methods. We demonstrate  progress in realizing a shaken lattice interferometer and its sensitivity to an applied acceleration signal and discuss the possibility of tailoring the signal to specific scenarios. 

The quantization of gravity is widely believed to result in gravitons -- particles of discrete energy that form  gravitational waves. But their detection has so far been considered impossible. Inspired by a quantum optics approach, here we show that signatures of single-graviton-exchange can be observed in laboratory experiments. We show that stimulated and spontaneous single-graviton  processes can become relevant for massive quantum acoustic resonators and that stimulated absorption can be resolved through continuous sensing of quantum jumps. We analyze the feasibility of observing the exchange of single energy quanta between matter and gravitational waves. Our results show that single graviton signatures are within reach of experiments. In analogy to the discovery of the photo-electric effect for photons, such signatures can provide the first experimental evidence of the quantization of gravity.

Neutral atom quantum computing is a rapidly developing field. Exploring new atomic species, such as alkaline earth atoms, provides additional opportunities for cooling and trapping, measurement, qubit manipulation, high-fidelity gates and quantum error correction. In this talk, I will present recent results from our group on implementing high-fidelity gates on nuclear spins encoded in metastable 171Yb atoms, including mid-circuit detection of gate errors that give rise to leakage out of the qubit space, using erasure conversion. I will conclude by discussing several new directions including spectroscopy and modeling of 171Yb Rydberg states and interactions, and the construction of high-speed modulators for local gate addressing.

This talk will present our effort to control and use the dipole-dipole interactions between cold atoms in order to implement spin Hamiltonians useful for quantum simulation of condensed matter or quantum optics situations. We trap atoms in arrays of optical tweezers separated by a few micrometers. We create almost arbitrary geometries of the atomic arrays in two and three dimensions up to about 200 atoms. To make the atoms interact, we either excite them to Rydberg states or induce optical dipoles with a near-resonance laser. Using this platform, we have in particular explored quantum magnetism, topological synthetic quantum matter, and observe a non-equilibrium phase transition resulting from the interplay between collective decay and laser drive.

Arrays of transmons have proven to be a viable medium for quantum information science and quantum simulations. Despite their popularity and success as qubit arrays, there remains yet untapped potential beyond the two-level approximation. Being experimentally controllable with high fidelity, the higher excited states provide an important resource for hardware-efficient many-body quantum simulations, quantum error correction, and quantum information protocols.

In this talk, I will first present an theoretical and numerical framework for describing the effective unitary dynamics of highly excited states based on degenerate perturbation theory. This allows us to describe various collective phenomena—such as bosons stacked onto a single site behaving as a single particle, edge localization, and effective longer-range interactions—in a unified, compact, and accurate manner. In the second part, I will discuss transmons in a waveguide and show how their bosonic statistics enhances collective sub/superradiance compared to that of qubit array. Together with the long-lived coherence times and versatile engineering possibilities, superconducting quantum devices provide an exciting platform to explore and deepen understanding on open many-body quantum dynamics.

Atoms made of a particle and an antiparticle are unstable, usually surviving less than a microsecond. Antihydrogen, the bound state of an antiproton and a positron, is made entirely of antiparticles and is believed to be stable. It is this longevity that holds the promise of precision studies of matter-antimatter symmetry. I will give an overview of the ALPHA experiment (with an emphasis on the physical processes involved in the measurements) which has succeeded in trapping antihydrogen in a cryogenic Penning trap for times up to 15 minutes and has successfully performed precision measurements of several properties of antihydrogen. For example, we have measured the 1S-2S frequency to about one part in a trillion. I will conclude with prospects for future precision measurements.  

This is an exciting time for quantum computing where early-stage quantum computers become available at your fingertips through clouds. The conventional design of quantum algorithms is centered around the abstraction of quantum circuits and relies on a digital mindset for application design and implementation. While serving as an elegant mathematical interface, circuit-based digital abstraction usually fails to capture the native programmability of quantum devices, and incurs large overheads, which significantly restricts its near-term feasibility where the quantum computing resource is the major limitation. 

We propose to use quantum Hamiltonian evolution as the central object in end-to-end quantum application design, i.e. the so-called Hamiltonian-oriented paradigm, based on the observation that Hamiltonian evolution is a native abstraction for both low-level hardware control and high-level quantum applications. We illustrate that the Hamiltonian-oriented design not only allows more efficient implementation of existing quantum algorithms but also inspires novel quantum algorithms, especially in optimization and scientific computing, which are hard to perceive in the circuit model. We also develop a programming infrastructure called SIMUQ (SIMUlation language for Quantum) for easy implementation of Hamiltonian-based quantum applications for domain experts on heterogeneous quantum devices.

We introduce and demonstrate a hybrid optically-pumped magnetometer (hOPM) that simultaneously measures one dc field component and one rf field component quadrature with a single atomic spin ensemble. The hOPM achieves sub-pT/√Hz sensitivity for both dc and rf fields, and is limited in sensitivity by measurement back-action and spin projection noise at low frequencies, and by photon shot noise at high frequencies. We demonstrate with the hOPM a new application of multi-parameter quantum sensing: background-cancelling spread spectrum magnetic communication. The combination of high sensitivity, quantum-noise-limited performance, and real-world application potential makes the hOPM an ideal system in which to study high-performance multi-parameter quantum sensing.

While dissipation is in general perceived as a destructive feature of a quantum system, it can also be utilized to engineer nontrivial states, often in conjunction with pushing a system out of equilibrium. We study various non-equilibrium phases in an ultracold quantum gas coupled to a high-finesse optical cavity. We utilize both effective models, such as the three-level Dicke model, and numerical methods to characterize the emerging phases ranging from time crystals to dark states. We put forth the first experimental realization of a limit cycle in an atom-cavity system and explain its origin using bifurcation theory, which also enables us to understand the system's route to aperiodic dynamics. Finally, we propose to use the atom-cavity system to create a quantum rotational sensor not only for static high precision frequency measurements but also for inertial measurements and navigation.

Taken out of equilibrium, a collisional gas is known to rethermalize as follows from the second law of thermodynamics. The trajectory by which a gas takes to do so, however, may well be complicated by the nature of collisions and the rate at which they occur. In particular, ultracold, but not yet quantum degenerate, gases of dipolar particles experience wildly anisotropic scattering as the dominant two-body interaction. In this talk, we will explore how dipolar collisions affect collective gas dynamics en route to equilibrium. Along the way, motivations for understanding such processes will be discussed, along with applications of its theoretical modeling to experimental measurements.          

To realize a high-accuracy optical clock, the 2S1/2 ↔ 2F7/2 electric octupole (E3) transition in 171Yb+ is well-suited. The same ion also features an electric quadrupole (E2) transition. Because the two transitions have a large differential sensitivity to the fine structure constant α, tight limits on its possible variations can be obtained by comparing their frequencies at various positions in spacetime. These limits can then be used to constrain models predicting such variations. In particular, the couplings of so-called ultralight bosonic dark matter (m << 1 eV/c^2) to standard model particles would lead to coherent oscillations of constants, with an oscillation frequency corresponding to the Compton frequency of the dark matter mass. We conduct a broadband dark-matter search by comparing the frequency of the E3 transition to that of the E2 transition, and to that of the 1S0 ↔ 3P0 transition in 87Sr. We find no indication for significant oscillations in our experimental data, and improve existing bounds on the scalar coupling of ultralight dark matter to photons for dark-matter masses of about 1E−24 to 1E−17 eV/c^2. As recently shown, couplings to quarks and gluons can also be investigated with our optical frequency ratio measurements by considering the effect an oscillating nuclear charge radius would have on electronic transitions. Alternatively, an optical frequency can be compared to a microwave clock based on a hyperfine transition, such as a Cs fountain clock.

In recent years, advancements in optically levitated nanoparticles have enabled the cooling of their center-of-mass motion to the quantum ground state. As a result, a nanoparticle, which comprises billions of atoms, becomes delocalized over picometer scales. This talk aims to explore the challenges and requirements of achieving a macroscopic quantum superposition of a nanoparticle, in which the center-of-mass position is delocalized over orders of magnitude larger scales. We will discuss an experimentaly feasible approach that employs fast quantum dynamics in nonharmonic potentials to meet the stringent requirements imposed by environmentally-induced decoherence. The generation of such macroscopic quantum states would test quantum mechanics at unprecedented scales, develop highly sensitive detectors of external signals, and address fundamental questions, such as the nature of the gravitational field generated by a delocalized mass source.

I will present how ab initio electronic structure and multichannel scattering calculations can propose, guide, and explain ultracold quantum physics experiments. I will start with our theoretical predictions of the scattering lengths for ultracold collisions without any adjustment to experimental data, which were possible by including high-level-correlation, relativistic, QED, and adiabatic corrections. I will conclude with our theoretical explanations of quantum resonances measured in ultracold atom-ion and atom-molecule collisions, where the quantum regime of cold collisions and their quantum control with an external magnetic field have been recently reached for the first time.

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