More Like this

1. Measurement of the ratio of the scalar polarizability to the vector polarizability for the $6s{}^{2}S_{1/2}\to 7s{}^{2}S_{1/2}$ transition in cesium

   https://doi.org/10.1103/PhysRevA.109.062809  

   Quirk, Jonah A; Tanner, Carol E; Elliott, D S (June 2024, Physical Review A)

   We report measurements of the ratio of the scalar polarizability $$\alpha$$ to the vector polarizability $$\beta$$ for the $$6s ^2S_{1/2} \rightarrow 7s ^2S_{1/2}$$ transition in atomic cesium. These measurements are motivated by a discrepancy between the values of the vector transition polarizability as determined using two separate methods. In the present measurement, we use a two-pathway, coherent-control technique in which we observe the interference between a two-photon interaction driven by infrared light at 1079 nm and a linear Stark-induced interaction driven by the mutually-coherent second harmonic of this infrared beam at 540 nm. The result of our measurements is $$\alpha/\beta = -9.902 \: (9)$$, in good agreement with the previous determination of this ratio. This measurement, critical to the study of atomic parity violation in cesium, does not reduce the discrepancy between the two methods for the determination of the vector polarizability $$\beta$$ for this transition. 

   more » « less
2. Dissipative Floquet Dynamics: from Steady State to Measurement Induced Criticality in Trapped-ion Chains

   https://doi.org/10.22331/q-2022-02-02-638  

   Sierant, Piotr; Chiriacò, Giuliano; Surace, Federica M.; Sharma, Shraddha; Turkeshi, Xhek; Dalmonte, Marcello; Fazio, Rosario; Pagano, Guido (February 2022, Quantum)

   Quantum systems evolving unitarily and subject to quantum measurements exhibit various types of non-equilibrium phase transitions, arising from the competition between unitary evolution and measurements. Dissipative phase transitions in steady states of time-independent Liouvillians and measurement induced phase transitions at the level of quantum trajectories are two primary examples of such transitions. Investigating a many-body spin system subject to periodic resetting measurements, we argue that many-body dissipative Floquet dynamics provides a natural framework to analyze both types of transitions. We show that a dissipative phase transition between a ferromagnetic ordered phase and a paramagnetic disordered phase emerges for long-range systems as a function of measurement probabilities. A measurement induced transition of the entanglement entropy between volume law scaling and sub-volume law scaling is also present, and is distinct from the ordering transition. The two phases correspond to an error-correcting and a quantum-Zeno regimes, respectively. The ferromagnetic phase is lost for short range interactions, while the volume law phase of the entanglement is enhanced. An analysis of multifractal properties of wave function in Hilbert space provides a common perspective on both types of transitions in the system. Our findings are immediately relevant to trapped ion experiments, for which we detail a blueprint proposal based on currently available platforms. 

   more » « less
3. Atomistic insight into the ferroelastic post-stishovite transition by high-pressure single-crystal X-ray diffraction

   https://doi.org/10.2138/am-2022-8458  

   Zhang, Yanyao; Chariton, Stella; He, Jiaming; Fu, Suyu; Xu, Fang; Prakapenka, Vitali B.; Lin, Jung-Fu (January 2023, American Mineralogist)

   Abstract The post-stishovite transition is a classic pseudo-proper typed ferroelastic transition with a symmetry-breaking spontaneous strain. This transition has been studied using high-pressure spontaneous strains, optic modes, and elastic moduli (Cij) based on the Landau modeling, but its atomistic information and structural distortion remain poorly understood. Here we have conducted synchrotron single-crystal X-ray diffraction measurements on stishovite crystals up to 75.3 GPa in a diamond-anvil cell. Analysis of the data reveals atomic positions, bond lengths, bond angles, and variations of SiO6 octahedra across the transition at high pressure. Our results show that the O coordinates split at ~51.4 GPa, where the apical and equatorial Si-O bond lengths cross over, the SiO6 octahedral distortion vanishes, and the SiO6 octahedra start to rotate about the c axis. Moreover, distortion mode analysis shows that an in-plane stretching distortion (GM1+ mode) occurs in the stishovite structure at high pressure while a rotational distortion (GM2+ mode) becomes dominant in the post-stishovite structure. These results are used to correlate with elastic moduli and Landau parameters (symmetry-breaking strain e1–e2 and order parameter Q) to provide atomistic insight into the ferroelastic transition. When the bond lengths of two Si-O bonds are equal due to the contribution from the GM1+ stretching mode, C11 converges with C12, and the shear wave VS1[110] polarizing along [110] and propagating along [110] vanishes. Values of e1–e2 and Q are proportional to the SiO6 rotation angle from the occurrence of the GM1+ rotational mode in the post-stishovite structure. Our results on the pseudo-proper type transition are also compared with that for the proper type in albite and improper type in CaSiO3 perovskite. The symmetry-breaking strain, in all these types of transitions, arises as the primary effect from the structural angle (such as SiO6 rotation or lattice constant angle) and its relevant distortion mode in the low-symmetry ferroelastic phase. 

   more » « less
4. Measurement of the Static Stark Shift of the $7s{{}^{2}S}_{1/2}$ Level in Atomic Cesium

   https://doi.org/10.1103/PhysRevLett.132.233201  

   Quirk, Jonah A; Jacobsen, Aidan; Damitz, Amy; Tanner, Carol E; Elliott, D S (June 2024, Physical Review Letters)

   We report a new precision measurement of the dc Stark shift of the $$6s\hspace{1mm} ^2S_{1/2} \rightarrow 7s\hspace{1mm}^2S_{1/2}$$ transition in atomic cesium-133. Our result is 0.72246 (29) $$\textrm{Hz}(\textrm{V}/\textrm{cm})^{-2}$$. This result differs from a previous measurement of the Stark shift by $$\sim$$0.5\%, or 4.7$$\sigma$$. We use this value to recalculate the magnitude of the reduced dipole matrix elements $$\langle7s ||r||7p_{j}\rangle$$, as well as the vector transition polarizability for the $$6s \rightarrow 7s$$ transition, $$\tilde{\beta} = 27.043 \: (36) \ a_0^3$$. This determination helps resolve a critical discrepancy between two techniques for determining the vector polarizability. 

   more » « less
5. Excitonic effects at the temperature-dependent E 1 and E 1 + Δ1 critical points of Ge

   https://doi.org/10.1063/5.0276918  

   Armenta, C A; Zollner, S (June 2025, Journal of Applied Physics)

   We investigated excitonic effects in the complex dielectric function of Ge near the E1 and E1+Δ1 critical points as a function of temperature. By employing Tanguy’s theory for two-dimensional excitons [Tanguy, Solid State Commun. 98, 65 (1996)], we fitted the second derivative of the dielectric function to a temperature series of spectroscopic ellipsometry measurements ranging from 4 to 800 K [Emminger et al., J. Vac. Sci. Technol. B 38, 012202 (2020)]. We analyzed the temperature dependence of the effective masses, matrix elements, and exciton binding energies to develop a model for the dielectric function that requires no fitting parameters, apart from energy and broadening. Our calculations not only show a remarkable agreement between theory and experiment, but also provide a model for the absorption by two-dimensional excitons that can be adapted to other applications and materials. 

   more » « less