APS Global Physics Summit student talks: Shruti Shirol, Yating Zhang, and Cheng-Han Li

Four-Photon Dissipative Stabilization of Binomial Kitten Code

Speaker:  Shruti Shirol

Authors:  Shruti Shirol, Sean van Geldern, and Chen Wang

The logical qubits encoded in rotation symmetric bosonic codes such as mod-4 cat, binomial or pair-cat codes, require stabilization mechanisms in both modulo photon numbers and modulo oscillator phases in order to preserve the logical information. There are experiments showing parity corrections for these codes that realize stabilization with respect to the modulo photon number. However, no experiment has yet demonstrated a sufficiently effective mechanism for stabilizing the conjugate modulo phase, which requires at least a four-photon stabilization process. In this talk, we report experimental progress in realizing a four-photon driven-dissipative process that stabilizes a binomial code in a superconducting microwave cavity. The process operates alongside our previously implemented autonomous parity-selective photon-addition scheme for correction of single-photon loss. This together achieves a complete first-order protection of a logical qubit using fully passive, continuous quantum error correction

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Spatial Gradients in Stokesian Sedimentation

Speaker:  Yating Zhang

Authors:  Yating Zhang and Narayanan Menon

We report spatially-resolved measurements of spatial density gradients in sedimenting suspensions of spheres and discs using x-ray absorption methods. We prepare the suspension with a homogeneously distributed global volume fraction \Phi, and then measure the time-resolved evolution of the local volume fraction \phi during sedimentation, revealing that the suspension develops a density gradient along the height of the container. The density profile evolves with time: every band of fixed local volume fraction (\phi) settles at a steady velocity that depends both on its local volume fraction and the global volume fraction \Phi. As is well known, the typical sedimentation speed decreases as the global volume fraction is increased, but for a given global volume fraction, we find surprisingly, that higher local densities correspond to faster settling velocities. This suggests that the dynamics of hindered settling are not local: settling dynamics are determined by the global and local value of the volume fraction.
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Swelling Equilibria, Dynamics, and Rheology of Charged Coacervate Gels

Speaker:  Cheng-Han Li

Authors:  Cheng-Han Li, Kuo Chen, and Murugappan Muthukumar

We have investigated swelling and dynamic properties of the composite hydrogel composed of anionic poly (acrylamide-r-sodium acrylate) gel matrix and linear polycationic poly(allylamine) hydrochloride. We have quantified the role of added salt concentration on the extent of volume shrinkage and enhancement of shear modulus arising from electrostatic complexation between the guest polymer and the host gel. In tandem, the dynamics of the guest polymer, as monitored using FCS and FRET, exhibits diffusive–subdiffusive–diffusive behavior depending on the time scale. At intermediate time scales, the degree of anomalous diffusion increases as the salt concentration is decreased. Our results show design rules to tune the mechanical properties of composite hydrogels using concentration of added salt.