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arXiv:1812.00327 · Physical Review A

Spin squeezing and many-body dipolar dynamics in optical lattice clocks

Chunlei Qu, Ana María Rey

Published Oct 10, 2019• 35 citations
arXivHTMLPDF

Abstract

The recent experimental realization of a three-dimensional (3D) optical lattice clock not only reduces the influence of collisional interactions on the clock's accuracy but also provides a promising platform for studying dipolar many-body quantum physics. Here, by solving the governing master equation, we investigate the role of both elastic and dissipative long-range interactions in the clock's dynamics and study its dependence on lattice spacing, dimensionality, and dipolar orientation. For small lattice spacing, i.e., ${k}_{0}a\ensuremath{\ll}1$, where $a$ is the lattice constant and ${k}_{0}$ is the transition wave number, a sizable spin squeezing appears in the transient state which is favored in a head-to-tail dipolar configuration in 1D systems and a side-by-side configuration in 2D systems, respectively. For large lattice spacing, i.e., ${k}_{0}a\ensuremath{\gg}1$, the single atomic decay rate can be effectively suppressed due to the destructive dissipative emission of neighboring atoms in both 1D and 2D. Our results will not only aid in the design of the future generation of ultraprecise atomic clocks but also illuminates the rich many-body physics exhibited by radiating dipolar system.

DOI
10.1103/physreva.100.041602

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The recent experimental realization of a three-dimensional (3D) optical lattice clock not only reduces the influence of collisional interactions on the clock's accuracy but also provides a promising platform for studying dipolar many-body quantum physics. Here, by solving the governing master equation, we investigate the role of both elastic and dissipative long-range interactions in the clock's dynamics and study its dependence on lattice spacing, dimensionality, and dipolar orientation. For small lattice spacing, i.e., k0a\ensuremath≪1{k}_{0}a\ensuremath{\ll}1k0​a\ensuremath≪1, where aaa is the lattice constant and k0{k}_{0}k0​ is the transition wave number, a sizable spin squeezing appears in the transient state which is favored in a head-to-tail dipolar configuration in 1D systems and a side-by-side configuration in 2D systems, respectively. For large lattice spacing, i.e., k0a\ensuremath≫1{k}_{0}a\ensuremath{\gg}1k0​a\ensuremath≫1, the single atomic decay rate can be effectively suppressed due to the destructive dissipative emission of neighboring atoms in both 1D and 2D. Our results will not only aid in the design of the future generation of ultraprecise atomic clocks but also illuminates the rich many-body physics exhibited by radiating dipolar system.
In this work we study the effect of interactions in an optical lattice clock based on fermionic Sr atoms. In current one-dimensional lattice clocks nuclear spin-polarized atoms are known to have contact interactions of p-wave character and collective in nature. Here we focus on interactions that will influence the design of future optical lattice clocks. We study the case where atoms are no longer confined to a single nuclear spin state. By using samples of atoms with different distributions among the ten nuclear spin states of Sr we show that these interactions are SU(N) symmetric up to a 3% uncertainty in our measurements. Through these measurements we are also able to determine all the s-wave and p-wave scattering lengths.\nWe also study the case of nuclear spin-polarized interacting atoms that are allowed to tunnel between different lattice sites where the electronic spin and the motion of these atoms become coupled. We observe spectroscopically the precession of the collective magnetization and evolution of spin locking effects arising from the interplay between p-wave interactions and interactions induced by the spin-orbit coupling. The many-body dynamics are captured by a spin model that describes a broad class of condensed matter systems ranging from superconductors to quantum magnets.\nBy loading a dense sample of atoms into a magneto-optical trap we are able to observe long-range dipole-dipole interactions between our Sr atoms. These interactions will be important for atomic clocks based on a three dimensional lattice, such as the one recently demonstrated in our lab. In these clocks it is possible to remove the contact interactions between the atoms by loading only one atom per lattice site. In this case the dominant interactions will be from the long-range dipole-dipole interactions that will take place between the atoms.
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Entanglement can improve the measurement precision of quantum sensors beyond the shot noise limit. Neutral atoms, the basis of some of the most precise and accurate optical clocks and interferometers, do not naturally exhibit the all-to-all interactions traditionally used to generate such entangled states. On the other hand, these systems exhibit exceedingly high degrees of experimental control over parameters such as temperature, spatial entropy, and itinerancy. In this work, we investigate spin squeezing in a highly coherent itinerant system of neutral atoms with magnetic dipole-dipole interactions. We achieve 7.1 dB of metrologically useful squeezing using finite-range spin-exchange interactions in an erbium quantum gas microscope, and we demonstrate that introducing atomic motion, realizing a dipolar t − J model, protects the spin sector coherence at low fillings, significantly improving the achievable spin squeezing in a 2D dipolar system. This work’s protocol can be implemented with most neutral atoms, opening the door to quantum-enhanced metrology in other itinerant dipolar systems, such as molecules or optical lattice clocks, and serves as a novel method for studying itinerant quantum magnetism with long-range interactions.
Strontium optical lattice clocks at JILA recently demonstrated record-high accuracy and stability. These advances were enabled by an ultrastable laser with fractional frequency stability of 1x10-16 at 1 second. This laser allows us to study systematic shifts of the 1S0 to 3P0 clock transition with unprecedented precision. Density-dependent frequency shifts represent an unavoidable perturbation for clocks based on many atoms. Our studies of atomic interactions in an optical lattice clock system uncover the nature of these interactions and reveal important many-body atomic correlation effects in this open quantum system. By extending our measurements to all ten nuclear-spin sublevels of the clock states, we observe the first direct evidence of SU(N) symmetric interactions in alkaline earth(-like) atoms. Using the techniques we developed in these studies, we also demonstrate a novel technique for measuring the frequency noise spectrum of an ultrastable laser. We discuss designs for the future direction of our experiment which will place 87Sr atoms within a high finesse cavity that is resonant on the 1S0 to 3P1 transition. We will use this system to study collective effects in cavity quantum electrodynamics. Most notably, strong atom-cavity coupling can enhance the spectroscopic sensitivity of our clock by creating spin-squeezed states via quantum non-demolition measurements. As a precursor to future work studying cavity-mediated collective behavior, we use the unique atomic structure of 88Sr to investigate free-space retarded dipolar coupling in an optically thick sample of atoms.
Optical lattice clocks have set records in clock precision and accuracy. Continuing to advance their performance, via probing as many atoms as possible for the longest interrogation time affordable, requires experimentally and theoretically studying a many-body lattice system. Motivated by recent experimental results on a Fermi-degenerate three-dimensional optical lattice clock [W. R. Milner et al., Science 388, 503 (2025)], we present a theoretical overview of Ramsey and Rabi spectroscopy in one-dimensional chains. At realistic experimental temperatures and confinement conditions, atoms are spatially localized into small chains of approximately one to five atoms. We show that in the presence of spin-orbit coupling induced by the clock laser, the spectroscopy observables are modified by superexchange interactions within each chain, and depend strongly on the length of the chain. The thermal distribution of chain lengths thus plays a key role in the spectroscopy measurements. Our results offer insight into observable many-body effects in state-of-the-art lattice clocks and suggest new directions for optimizing clock performance.
Atoms deeply trapped in magic wavelength optical lattices provide a Doppler- and collision-free dense ensemble of quantum emitters ideal for high-precision spectroscopy and they are the basis of some of the best optical atomic clocks to date. However, despite their minute optical dipole moments the inherent long-range dipole-dipole interactions in such lattices still generate line shifts, dephasing and modified decay. We show that in a perfectly filled lattice line shifts and decay are resonantly enhanced depending on the lattice constant and geometry. Potentially, this yields clock shifts of many atomic linewidths and reduces the measurement by optimizing the lattice geometry. Such collective effects can be tailored to yield zero effective shifts and prolong dipole lifetimes beyond the single-atom decay. In particular, we identify dense 2D hexagonal or square lattices as the most promising configurations for an accuracy and precision well below the independent ensemble limit. This geometry should also be an ideal basis for related applications such as superradiant lasers, precision magnetometry or long-lived quantum memories.