arXiv subjects

Erik Weiss

Publications and source records attributed to Erik Weiss.

3 recordsLinked to original sources

arXiv2026

A New Member of the Fast and Furious Family: A Relativistic and Time-Variable UV Outflow in a Luminous Quasar

We report the fastest quasar outflow first detected in the ultraviolet, via variable C IV and Si IV absorption at outflow velocities $-77,000$ km s$^{-1}$ to at least $-90,000$ km s$^{-1}$, in the radio-quiet quasar SDSS J231854.31+243954.2 (J2318). J2318 is a weak-lined quasar in the rest-frame ultraviolet, but Gemini GNIRS spectroscopy reveals an H$\alpha$ redshift of $z=2.6781\pm0.0004$. A twenty-year photometric time series shows peak-to-peak variability of 0.5 mag in the $g$ band. The C IV outflow strengthened monotonically over three epochs spanning $\sim$2.2 rest-frame years. The existence of such a high-velocity outflow implies that models of quasar outflows must be able to either accelerate gas to $0.3c$ while still preserving C IV and Si IV ions, or enable the formation of C IV and Si IV ions in gas which has been accelerated to $0.3c$. Virial estimates reveal a black-hole mass of $1.65\times10^9~M_\odot$, which leads to an Eddington luminosity and Eddington ratio of $2.4\times10^{47}$ erg s$^{-1}$ and $0.45$, respectively. Using very conservative assumptions, the UV-absorbing outflow alone has an estimated mass loss of $>0.82~M_\odot~{\rm yr}^{-1}$ and a kinetic luminosity ratio $L_{kin}/L_{bol}\geq0.75$%. The lower limit is just above the threshold usually cited for significant feedback on the host galaxy. Comparison to PDS 456, the only other known quasar with a UV-absorbing outflow at $0.3c$, suggests that the true $\dot{M}$ and $L_{kin}/L_{bol}$ could be up to two orders of magnitude larger.

astro-ph.GA↗

arXiv2024

Pattern-based quantum functional testing

With the growing number of qubits of quantum information processing devices, the task of fully characterizing these processors becomes increasingly unfeasible. From a practical perspective, one wants to find possible errors in the functioning of the device as quickly as possible, or otherwise establish its correct functioning with high confidence. In response to these challenges, we propose a pattern-based approach inspired by classical memory testing algorithms to evaluate the functionality of a quantum memory, based on plausible failure mechanisms. We demonstrate the method's capability to extract pattern dependencies of important qubit characteristics, such as $T_1$ and $T_2$ times, and to identify and analyze interactions between adjacent qubits. Additionally, our approach enables the detection of different types of crosstalk effects and of signatures indicating non-Markovian dynamics in individual qubits.

quant-ph↗

arXiv2024

Machine learning of quantum channels on NISQ devices

World-wide efforts aim at the realization of advanced quantum simulators and processors. However, despite the development of intricate hardware and pulse control systems, it may still not be generally known which effective quantum dynamics, or channels, are implemented on these devices. To systematically infer those, we propose a neural-network algorithm approximating generic discrete-time dynamics through the repeated action of an effective quantum channel. We test our approach considering time-periodic Lindblad dynamics as well as non-unitary subsystem dynamics in many-body unitary circuits. Moreover, we exploit it to investigate cross-talk effects on the ibmq_ehningen quantum processor, which showcases our method as a practically applicable tool for inferring quantum channels when the exact nature of the underlying dynamics on the physical device is not known a priori. While the present approach is tailored for learning Markovian dynamics, we discuss how it can be adapted to also capture generic non-Markovian discrete-time evolutions.

quant-ph↗