Chandra measurements of non-thermal-like X-ray emission from massive, merging, radio-halo clusters

We report the discovery of spatially-extended, non-thermal-like emission components in Chandra X-ray spectra for five of a sample of seven massive, merging galaxy clusters with powerful radio halos. The emission components can be fitted by power-law models with mean photon indices in the range 1.5 < Gamma < 2.0. A control sample of regular, dynamically relaxed clusters, without radio halos but with comparable mean thermal temperatures and luminosities, shows no compelling evidence for similar components. Detailed X-ray spectral mapping reveals the complex thermodynamic states of the radio halo clusters. Our deepest observations, of the Bullet Cluster 1E 0657-56, demonstrate a spatial correlation between the strongest power-law X-ray emission, highest thermal pressure, and brightest 1.34GHz radio halo emission in this cluster. We confirm the presence of a shock front in the 1E 0657-56 and report the discovery of a new, large-scale shock front in Abell 2219. We explore possible origins for the power-law X-ray components. These include inverse Compton scattering of cosmic microwave background photons by relativistic electrons in the clusters; bremsstrahlung from supra-thermal electrons energized by Coulomb collisions with an energetic, nonthermal proton population; and synchrotron emission associated with ultra-relativistic electrons. Interestingly, we show that the power-law signatures may also be due to complex temperature and/or metallicity structure in clusters particularly in the presence of metallicity gradients. In this case, an important distinguishing characteristic between the radio halo clusters and control sample of predominantly cool-core clusters is the relatively low central X-ray surface brightness of the former.Comment: Accepted for publication in MNRAS (24 pages, 13 figures). Improved discussion includes a new, possible explanation for `soft excess' X-ray emission from clusters as an artifact of metallicity/temperature structure and projection effects. Other physical explanations for the observed non-thermal-like X-ray emission also remai

Experimental implementation of fully controlled dephasing dynamics and synthetic spectral densities

Engineering, controlling, and simulating quantum dynamics is a strenuous task. However, these techniques are crucial to develop quantum technologies, preserve quantum properties, and engineer decoherence. Earlier results have demonstrated reservoir engineering, construction of a quantum simulator for Markovian open systems, and controlled transition from Markovian to non-Markovian regime. Dephasing is an ubiquitous mechanism to degrade the performance of quantum computers. However, a fully controllable all-purpose quantum simulator for generic dephasing is still missing. Here we demonstrate full experimental control of dephasing allowing us to implement arbitrary decoherence dynamics of a qubit. As examples, we use a photon to simulate the dynamics of a qubit coupled to an Ising chain in a transverse field and also demonstrate a simulation of non-positive dynamical map. Our platform opens the possibility to simulate dephasing of any physical system and study fundamental questions on open quantum systems.Comment: V2: Added some text and new figur

Quantum control and measurement of atomic spins in polarization spectroscopy

Quantum control and measurement are two sides of the same coin. To affect a dynamical map, well-designed time-dependent control fields must be applied to the system of interest. To read out the quantum state, information about the system must be transferred to a probe field. We study a particular example of this dual action in the context of quantum control and measurement of atomic spins through the light-shift interaction with an off-resonant optical probe. By introducing an irreducible tensor decomposition, we identify the coupling of the Stokes vector of the light field with moments of the atomic spin state. This shows how polarization spectroscopy can be used for continuous weak measurement of atomic observables that evolve as a function of time. Simultaneously, the state-dependent light shift induced by the probe field can drive nonlinear dynamics of the spin, and can be used to generate arbitrary unitary transformations on the atoms. We revisit the derivation of the master equation in order to give a unified description of spin dynamics in the presence of both nonlinear dynamics and photon scattering. Based on this formalism, we review applications to quantum control, including the design of state-to-state mappings, and quantum-state reconstruction via continuous weak measurement on a dynamically controlled ensemble

Interactions and scattering of quantum vortices in a polariton fluid

Quantum vortices, the quantized version of classical vortices, play a prominent role in superfluid and superconductor phase transitions. However, their exploration at a particle level in open quantum systems has gained considerable attention only recently. Here we study vortex pair interactions in a resonant polariton fluid created in a solid-state microcavity. By tracking the vortices on picosecond time scales, we reveal the role of nonlinearity, as well as of density and phase gradients, in driving their rotational dynamics. Such effects are also responsible for the split of composite spin-vortex molecules into elementary half-vortices, when seeding opposite vorticity between the two spinorial components. Remarkably, we also observe that vortices placed in close proximity experience a pull-push scenario leading to unusual scattering-like events that can be described by a tunable effective potential. Understanding vortex interactions can be useful in quantum hydrodynamics and in the development of vortex-based lattices, gyroscopes, and logic devices.Comment: 12 pages, 7 figures, Supplementary Material and 5 movies included in arXi

A Spectral CT Method to Directly Estimate Basis Material Maps From Experimental Photon-Counting Data

The proposed spectral CT method solves the constrained one-step spectral CT reconstruction (cOSSCIR) optimization problem to estimate basis material maps while modeling the nonlinear X-ray detection process and enforcing convex constraints on the basis map images. In order to apply the optimization-based reconstruction approach to experimental data, the presented method empirically estimates the effective energy-window spectra using a calibration procedure. The amplitudes of the estimated spectra were further optimized as part of the reconstruction process to reduce ring artifacts. A validation approach was developed to select constraint parameters. The proposed spectral CT method was evaluated through simulations and experiments with a photon-counting detector. Basis material map images were successfully reconstructed using the presented empirical spectral modeling and cOSSCIR optimization approach. In simulations, the cOSSCIR approach accurately reconstructed the basis map images

Electrically driven photon emission from individual atomic defects in monolayer WS2.

Quantum dot-like single-photon sources in transition metal dichalcogenides (TMDs) exhibit appealing quantum optical properties but lack a well-defined atomic structure and are subject to large spectral variability. Here, we demonstrate electrically stimulated photon emission from individual atomic defects in monolayer WS2 and directly correlate the emission with the local atomic and electronic structure. Radiative transitions are locally excited by sequential inelastic electron tunneling from a metallic tip into selected discrete defect states in the WS2 bandgap. Coupling to the optical far field is mediated by tip plasmons, which transduce the excess energy into a single photon. The applied tip-sample voltage determines the transition energy. Atomically resolved emission maps of individual point defects closely resemble electronic defect orbitals, the final states of the optical transitions. Inelastic charge carrier injection into localized defect states of two-dimensional materials provides a powerful platform for electrically driven, broadly tunable, atomic-scale single-photon sources

Robust concurrent remote entanglement between two superconducting qubits

Entangling two remote quantum systems which never interact directly is an essential primitive in quantum information science and forms the basis for the modular architecture of quantum computing. When protocols to generate these remote entangled pairs rely on using traveling single photon states as carriers of quantum information, they can be made robust to photon losses, unlike schemes that rely on continuous variable states. However, efficiently detecting single photons is challenging in the domain of superconducting quantum circuits because of the low energy of microwave quanta. Here, we report the realization of a robust form of concurrent remote entanglement based on a novel microwave photon detector implemented in the superconducting circuit quantum electrodynamics (cQED) platform of quantum information. Remote entangled pairs with a fidelity of $0.57\pm0.01$ are generated at $200$ Hz. Our experiment opens the way for the implementation of the modular architecture of quantum computation with superconducting qubits.Comment: Main paper: 7 pages, 4 figures; Appendices: 14 pages, 9 figure