Abstract: One of the major open problems in theoretical physics concerns the reconciliation of quantum mechanics with general relativity. In this context, a hallmark problem is the so-called black-hole information paradox, which addresses what happens to information that passes the event horizon. A possible resolution can be sought in information scrambling, which asserts that any information entering a black hole is rapidly and chaotically “scrambled” across the entirety of the event horizon and thus becomes inaccessible to any local observation. This paper analyzes information scrambling in the presence of decoherence, which is the inevitable loss of quantum information due to the interaction with the rest of the universe.

In a recent paper, the authors have shown that scrambling in isolated quantum systems can be quantified by mutual information. In this new study, they further extend the analysis to open quantum systems. In particular, they show that the mutual information can be separated into unique contributions arising from either scrambling or decoherence. This separation of terms lends itself naturally to the further derivation of statements of the second law of thermodynamics for scrambling of information in open systems. The general findings are then illustrated for a variety of models, including the Sachdev-Ye-Kitaev, the Maldacena-Qi, the XXX, the mixed-field Ising, and the Lipkin-Meshkov-Glick model with decoherence in energy or in the computational basis.

This work may have universal applications, from black holes (as their intense gravitational field is a decoherence channel) to ion-trap systems, for which information scrambling has been observed experimentally.

Abstract: We performed combined experimental and theoretical studies of the effect of Cr substitution for Fe on the structural, magnetic, transport, electronic, and mechanical properties of Fe3−xCrxGe (0 ≤ x ≤ 1) intermetallic alloys. Single phase microstructures are observed for x ≤ 0.70. Higher Cr concentrations x > 0.70 are multi-phased. A hexagonal D019 structure is found for all Cr concentrations, with the lattice parameters increasing systematically with an increasing Cr content. All the alloys in the series are found to be ferromagnets with large magnetization values of about 6 Bohr Magneton/fu. and high Curie temperature above room temperature. The low-temperature saturation magnetic moments agree fairly well with our theoretical results and also obey the Slater-Pauling rule. The density functional theory calculation reveals that Cr substitution energetically favours one of the Fe sites in Fe3Ge. The electrical resistivity measured over the temperature range from 5 K to 400 K shows metallic behavior, with a residual resistivity ratio that decreases with Cr content. Vicker’s hardness values are observed to increase with increasing Cr content to approximately 5 GPa.

Abstract: Accretion onto the supermassive black hole in some active galactic nuclei (AGN) drives relativistic jets of plasma, which dissipate a significant fraction of their kinetic energy into gamma-ray radiation. The location of energy dissipation in powerful extragalactic jets is currently unknown, with implications for particle acceleration, jet formation, jet collimation, and energy dissipation. Previous studies have been unable to constrain the location between possibilities ranging from the sub-parsec-scale broad-line region to the parsec-scale molecular torus, and beyond. Here we show using a simple diagnostic that the more distant molecular torus is the dominant location for powerful jets. This diagnostic, called the seed factor, is dependent only on observable quantities, and is unique to the seed photon population at the location of gamma-ray emission. Using 62 multiwavelength, quasi-simultaneous spectral energy distributions of gamma-ray quasars, we find a seed factor distribution which peaks at a value corresponding to the molecular torus, demonstrating that energy dissipation occurs ~1 parsec from the black hole (or ~1e4 Schwarzchild radii for a 1e9 solar mass black hole).