Scrambling Transition in a Radiative Random Unitary Circuit.

We study quantum information scrambling in a random unitary circuit that exchanges qubits with an environment at a rate p. As a result, initially localized quantum information not only spreads within the system, but also spills into the environment. Using the out-of-time-order correlator (OTOC) to characterize scrambling, we find a nonequilibrium phase transition in the directed percolation universality class at a critical swap rate p_{c}: for pp_{c} the OTOC fails to percolate within the system and vanishes uniformly within a finite timescale, indicating that all local operators are rapidly swapped into the environment. To elucidate its information-theoretic consequences, we demonstrate that the transition in operator spreading coincides with a transition in an observer's ability to decode the system's initial quantum information from the swapped-out, or "radiated," qubits. We present a simple decoding scheme which recovers the system's initial information with perfect fidelity in the nonpercolating phase, and with continuously decreasing fidelity with decreasing swap rate in the percolating phase. Depending on the initial state of the swapped-in qubits, we further observe a corresponding entanglement transition in the coherent information from the system into the radiated qubits.

Effect of Active Photons on Dynamical Frustration in Cavity QED.

We study the far-from-equilibrium dynamical regimes of a many-body spin-boson model with disordered couplings relevant for cavity QED and trapped ion experiments, using the discrete truncated Wigner approximation. We focus on the dynamics of spin observables upon varying the disorder strength and the frequency of the photons, finding that the latter can considerably alter the structure of the system's dynamical responses. When the photons evolve at a similar rate as the spins, they can induce qualitatively distinct frustrated dynamics characterized by either logarithmic or algebraically slow relaxation. The latter illustrates resilience of glassylike dynamics in the presence of active photonic degrees of freedom, suggesting that disordered quantum many-body systems with resonant photons or phonons can display a rich diagram of nonequilibrium responses, with near future applications for quantum information science.

Both the autophagy and proteasomal pathways facilitate the Ubp3p-dependent depletion of a subset of translation and RNA turnover factors during nitrogen starvation in Saccharomyces cerevisiae.

Protein turnover is an important regulatory mechanism that facilitates cellular adaptation to changing environmental conditions. Previous studies have shown that ribosome abundance is reduced during nitrogen starvation by a selective autophagy mechanism termed ribophagy, which is dependent upon the deubiquitinase Ubp3p. In this study, we asked whether the abundance of various translation and RNA turnover factors are reduced following the onset of nitrogen starvation in Saccharomyces cerevisiae. We found distinct differences in the abundance of the proteins tested following nitrogen starvation: (1) The level of some did not change; (2) others were reduced with kinetics similar to ribophagy, and (3) a few proteins were rapidly depleted. Furthermore, different pathways differentially degraded the various proteins upon nitrogen starvation. The translation factors eRF3 and eIF4GI, and the decapping enhancer Pat1p, required an intact autophagy pathway for their depletion. In contrast, the deadenylase subunit Pop2p and the decapping enzyme Dcp2p were rapidly depleted by a proteasome-dependent mechanism. The proteasome-dependent depletion of Dcp2p and Pop2p was also induced by rapamycin, suggesting that the TOR1 pathway influences this pathway. Like ribophagy, depletion of eIF4GI, eRF3, Dcp2p, and Pop2p was dependent upon Ubp3p to varying extents. Together, our results suggest that the autophagy and proteasomal pathways degrade distinct translation and RNA turnover factors in a Ubp3p-dependent manner during nitrogen starvation. While ribophagy is thought to mediate the reutilization of scarce resources during nutrient limitation, our results suggest that the selective degradation of specific proteins could also facilitate a broader reprogramming of the post-transcriptional control of gene expression.

Saccadic eye movements smear spatial working memory.

Why do saccades interfere with spatial working memory? One possibility is that attention and saccades are tightly coupled, and performing a saccade momentarily removes attention from spatial working memory, degrading the memory representation. This cannot be the entire explanation, because saccades cause greater interference than do covert attentional shifts (Lawrence, Myerson, & Abrams, 2004). In addition, this saccadic degradation is limited to spatial but not object, configural, or verbal representations. We propose that saccadic remapping is partially responsible for this increased interference. To test this, we used a spatial change detection task, and during the retention interval, participants either performed a central task, a peripheral task without an eye movement, or a peripheral task that required a saccade. Using the method of constant stimuli allowed us to fit psychophysical functions in which we derived measures of spatial memory precision, guessing, and response bias. It is important that we found a directionally specific loss of memory precision, such that memory representations were less precise along the axis of the saccade. This was beyond the general loss of precision we found for covert shifts, suggesting that part of the effect is because of remapping. Saccades also increased guessing, but unlike the loss of precision, the effect was nondirectional. (PsycINFO Database Record (c) 2019 APA, all rights reserved).

Hand proximity differentially affects visual working memory for color and orientation in a binding task.

Observers determined whether two sequentially presented arrays of six lines were the same or different. Differences, when present, involved either a swap in the color of two lines or a swap in the orientation of two lines. Thus, accurate change detection required the binding of color and orientation information for each line within visual working memory. Holding viewing distance constant, the proximity of the arrays to the hands was manipulated. Placing the hands near the to-be-remembered array decreased participants' ability to remember color information, but increased their ability to remember orientation information. This pair of results indicates that hand proximity differentially affects the processing of various types of visual information, a conclusion broadly consistent with functional and anatomical differences in the magnocellular and parvocellular pathways. It further indicates that hand proximity affects the likelihood that various object features will be encoded into integrated object files.