arXiv subjects

A. Auerbach

Publications and source records attributed to A. Auerbach.

6 recordsLinked to original sources

arXiv2022

Lindblad evolutions, Born rule, Heralding and cloning

We discuss an apparent difficulty in computing the radiation emitted by a system undergoing Lindblad evolution. The difficulty is resolved by viewing the problem as Born rule for conserved currents defined by the appropriate terms in the adjoint Lindbladian. In Heralding Alice prepares Bob's system in a state that mirrors her test. We show that heralding is consistent with no-cloning. This follows from the observation that heralding is not a completely positive map.

quant-ph↗

arXiv2021

Expert-Augmented Machine Learning

Machine Learning is proving invaluable across disciplines. However, its success is often limited by the quality and quantity of available data, while its adoption by the level of trust that models afford users. Human vs. machine performance is commonly compared empirically to decide whether a certain task should be performed by a computer or an expert. In reality, the optimal learning strategy may involve combining the complementary strengths of man and machine. Here we present Expert-Augmented Machine Learning (EAML), an automated method that guides the extraction of expert knowledge and its integration into machine-learned models. We use a large dataset of intensive care patient data to predict mortality and show that we can extract expert knowledge using an online platform, help reveal hidden confounders, improve generalizability on a different population and learn using less data. EAML presents a novel framework for high performance and dependable machine learning in critical applications.

stat.ML↗

arXiv2007

Quantum vortex tunneling in $YBa_2Cu_3O_{7-δ}$ thin films

Cuprate films offer a unique opportunity to observe vortex tunneling effects, due to their unusually low superfluid density and short coherence length. Here, we measure the magnetoresistance (\textit{MR}) due to vortex motion of a long meander line of a superconducting film made of underdoped $YBa_2Cu_3O_{7-δ}$. At low temperatures (\textit{T}), the \textit{MR} shows a significant deviation from Arrhenius activation. The data is consistent with two dimensional Variable Range Hopping (VRH) of single vortices, i.e. $MR\propto exp[-(T_0/T)^{1/3}]$. The VRH temperature scale $T_0$ depends on the vortex tunneling rates between pinning sites. We discuss its magnitude with respect to estimated parameters of the meander thin film.

cond-mat.supr-con↗

arXiv2000

Appearance of spontaneous macroscopic magnetization at the superconducting transition of YBCO

We report the observation of a weak spontaneous magnetic field appearing at the transition temperature of $\rm YBa_2Cu_3O_{7-δ}$ into the superconducting state. The effect is observed in 14 out of 15 epitaxial films grown on different substrates and by two distinct techniques. The average magnetic field sensed by the SQUID magnetometer is of the order of 10$^{-5}$ G. The effect indicates a breaking of both parity and time reversal symmetries in the superconductor. We consider two different interpretations: (i) The condensate carries an intrinsic magnetic moment. At T=0, this moment is between $\rm 10^{-2} μ_B$ and $\rm 10^{-4} μ_B$ per plaquette, depending whether the width of the unscreened region near the edge of the film is the coherence length or the penetration length. (ii) $π$ junctions which may exist near the edges produce circulating supercurrents and magnetic flux. Constraints imposed on these scenarios by temperature and geometry dependence of the data are discussed.

cond-mat.supr-con↗

arXiv1998

Quantum Magnetism Approaches to Strongly Correlated Electrons

Problems of strongly interacting electrons can be greatly simplified by reducing them to effective quantum spin models. The initial step is renormalization of the Hamiltonian into a lower energy subspace. The positive and negative U Hubbard models are explicitely transformed into the Heisenberg and -x-xz models respectively. Basic tools of quantum magnetism are introduced and used: spin coherent states path integral, spin wave theory, and continuum theory of rotators.The last lecture concerns pseudospin approaches to superconductivity and superfluidity. The SO(3) rotator theory for the -x-xz model describes a charge density wave to superconductor transition. Analogously, Zhang's SO(5) rotator theory describes the antiferromagnet to d-wave superconductor transition in high Tc cuprates. Finally the Magnus force on the two dimensional vortices and their momentum, are derived from the Berry phase of the spin path integral.

cond-mat.str-el↗

arXiv1996

Even-odd correlations in capacitance fluctuations of quantum dots

We investigate effects of short range interactions on the addition spectra of quantum dots using a disordered Hubbard model. A correlation function \cS(q) is defined on the inverse compressibility versus filling data, and computed numerically for small lattices. Two regimes of interaction strength are identified: the even/odd fluctuations regime typical of Fermi liquid ground states, and a regime of structureless $\cS(q)$ at strong interactions. We propose to understand the latter regime in terms of magnetically correlated localized spins.

cond-mat↗