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1. Spectroscopy and Modeling of ${}^{171}\mathrm{Yb}$ Rydberg States for High-Fidelity Two-Qubit Gates

   https://doi.org/10.1103/PhysRevX.15.011009  

   Peper, Michael; Li, Yiyi; Knapp, Daniel Y; Bileska, Mila; Ma, Shuo; Liu, Genyue; Peng, Pai; Zhang, Bichen; Horvath, Sebastian P; Burgers, Alex P; et al (January 2025, Physical Review X)

   Highly excited Rydberg states and their interactions play an important role in quantum computing and simulation. These properties can be predicted accurately for alkali atoms with simple Rydberg level structures. However, an extension of these methods to more complex atoms such as alkaline-earth atoms has not been demonstrated or experimentally validated. Here, we present multichannel quantum defect models for highly excited ${}^{174}\mathrm{Yb}$and ${}^{171}\mathrm{Yb}$Rydberg states with $L\le 2$. The models are developed using a combination of existing literature data and new, high-precision laser and microwave spectroscopy in an atomic beam, and validated by detailed comparison with experimentally measured Stark shifts and magnetic moments. We then use these models to compute interaction potentials between two Yb atoms, and find excellent agreement with direct measurements in an optical tweezer array. From the computed interaction potential, we identify an anomalous Förster resonance that likely degraded the fidelity of previous entangling gates in ${}^{171}\mathrm{Yb}$using $F=3/2$Rydberg states. We then identify a more suitable $F=1/2$state, and achieve a state-of-the-art controlled- gate fidelity of $\mathcal{F}=0.994\left(1\right)$, with the remaining error fully explained by known sources. This work establishes a solid foundation for the continued development of quantum computing, simulation, and entanglement-enhanced metrology with Yb neutral atom arrays. Published by the American Physical Society2025 

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2. Magneto-optical trap of titanium atoms

   https://doi.org/10.1103/PhysRevResearch.7.023025  

   Eustice, Scott; Schrott, Jackson; Stöltzel, Anke; Wolf, Julian; Novoa, Diego; Cassella, Kayleigh; Stamper-Kurn, Dan M (April 2025, Physical Review Research)

   We realize a magneto-optical trap (MOT) of titanium (Ti) atoms, performing laser cooling on the 498 nm transition between the long-lived $3{\mathrm{d}}^3\left({}^4\mathrm{F}\right)4\mathrm{s}{\mathrm{a}}^5{\mathrm{F}}_5$metastable state and the $3{\mathrm{d}}^3\left({}^4\mathrm{F}\right)4\mathrm{p}{\mathrm{y}}^5{\mathrm{G}}_6^{\mathrm{o}}$excited state. Without the addition of any repumping light, we observe MOTs of the three stable, $I=0$bosonic isotopes, ${}^{46}\mathrm{Ti}, {}^{48}\mathrm{Ti}$, and ${}^{50}\mathrm{Ti}$. Up to $8.30\left(26\right)\times {10}^5{}^{48}\mathrm{Ti}$atoms are trapped at a maximum density of $1.3\left(4\right)\times {10}^{11}{\mathrm{cm}}^{-3}$and at a temperature of $90\left(15\right)\mu \mathrm{K}$. By measuring the decay of the MOT, we constrain the leakage branching ratio of the cooling transition ( $\le 2.5\times {10}^{-6}$) and the two-body loss coefficient ( $\le 2\times {10}^{-10}{\mathrm{cm}}^3{\mathrm{s}}^{-1}$). Our approach to laser cooling Ti can be applied to other transition metals, enabling a significant expansion of the elements that can be laser cooled. Published by the American Physical Society2025 

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3. Radiative decay of the ${}^{229m}\mathrm{Th}$ nuclear clock isomer in different host materials

   https://doi.org/10.1103/PhysRevResearch.7.013052  

   Pineda, S V; Chhetri, P; Bara, S; Elskens, Y; Casci, S; Alexandrova, A N; Au, M; Athanasakis-Kaklamanakis, M; Bartokos, M; Beeks, K; et al (January 2025, Physical Review Research)

   A comparative vacuum ultraviolet spectroscopy study conducted at ISOLDE-CERN of the radiative decay of the ${}^{229m}\mathrm{Th}$nuclear clock isomer embedded in different host materials is reported. The ratio of the number of radiative decay photons and the number of ${}^{229m}\mathrm{Th}$embedded are determined for single crystalline ${\mathrm{CaF}}_2, {\mathrm{MgF}}_2, {\mathrm{LiSrAlF}}_6$, AlN, and amorphous ${\mathrm{SiO}}_2$. For the latter two materials, no radiative decay signal was observed and an upper limit of the ratio is reported. The radiative decay wavelength was determined in ${\mathrm{LiSrAlF}}_6$and ${\mathrm{CaF}}_2$, reducing its uncertainty by a factor of 2.5 relative to our previous measurement. This value is in agreement with the recently reported improved values from laser excitation. Published by the American Physical Society2025 

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4. Proton emission in ultraperipheral Pb-Pb collisions at $\sqrt{s_{NN}}=5.02$ TeV

   https://doi.org/10.1103/PhysRevC.111.054906  

   Acharya, S; Agarwal, A; Aglieri_Rinella, G; Aglietta, L; Agnello, M; Agrawal, N; Ahammed, Z; Ahmad, S; Ahn, S U; Ahuja, I; et al (May 2025, Physical Review C)

   The first measurements of proton emission accompanied by neutron emission in the electromagnetic dissociation (EMD) of ${}^{208}\mathrm{Pb}$nuclei in the ALICE experiment at the Large Hadron Collider are presented. The EMD protons and neutrons emitted at very forward rapidities are detected by the proton and neutron zero degree calorimeters of the ALICE experiment. The emission cross sections of zero, one, two, and three protons accompanied by at least one neutron were measured in ultraperipheral ${}^{208}\mathrm{Pb}\text{−}{}^{208}\mathrm{Pb}$collisions at a center-of-mass energy per nucleon pair $\sqrt{s_{NN}}=5.02\mathrm{TeV}$. The 0p and 3p cross sections are described by the RELDIS model within their measurement uncertainties, while the 1p and 2p cross sections are underestimated by the model by 17–25%. According to this model, these 0p, 1p, 2p, and 3p cross sections are associated, respectively, with the production of various isotopes of Pb, Tl, Hg, and Au in the EMD of ${}^{208}\mathrm{Pb}$. The cross sections of the emission of a single proton accompanied by the emission of one, two, or three neutrons in EMD were also measured. The data are significantly overestimated by the RELDIS model, which predicts that the (1p,1n), (1p,2n), and (1p,3n) cross sections are very similar to the cross sections for the production of the thallium isotopes ${}^{206,205,204}\mathrm{Tl}$. ©2025 CERN, for the ALICE Collaboration2025CERN 

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5. Chiral Superfluid Helium-3 in the Quasi-Two-Dimensional Limit

   https://doi.org/10.1103/PhysRevLett.134.136001  

   Heikkinen, Petri J; Levitin, Lev V; Rojas, Xavier; Singh, Angadjit; Eng, Nathan; Casey, Andrew; Saunders, John; Vorontsov, Anton; Zhelev, Nikolay; Sebastian, Abhilash Thanniyil; et al (March 2025, Physical Review Letters)

   Anisotropic pair breaking close to surfaces favors the chiral $A$phase of the superfluid ${}^3\mathrm{He}$over the time-reversal invariant $B$phase. Confining the superfluid ${}^3\mathrm{He}$into a cavity of height $D$of the order of the Cooper pair size characterized by the coherence length ${\xi }_0$—ranging between 16 nm (34 bar) and 77 nm (0 bar)—extends the surface effects over the whole sample volume, thus allowing stabilization of the $A$phase at pressures $P$and temperatures $T$where otherwise the $B$phase would be stable. In this Letter, the surfaces of such a confined sample are covered with a superfluid ${}^4\mathrm{He}$film to create specular quasiparticle scattering boundary conditions, preventing the suppression of the superfluid order parameter. We show that the chiral $A$phase is the stable superfluid phase under strong confinement over the full $P\text{−}T$phase diagram down to a quasi-two-dimensional limit $D/{\xi }_0=1$, where $D=80\mathrm{nm}$. The planar phase, which is degenerate with the chiral $A$phase in the weak-coupling limit, is not observed. The gap inferred from measurements over the wide pressure range from 0.2 to 21.0 bar leads to an empirical ansatz for temperature-dependent strong-coupling effects. We discuss how these results pave the way for the realization of the fully gapped two-dimensional $p_x+i{p}_y$superfluid under more extreme confinement. Published by the American Physical Society2025 

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