The ultimate collision: Neutron stars rattle, shine and sparkle 

Towards realizing topological quantum physics in Condensed matter systems

Putting to the test the Standard Model of Particle Physics

Black Holes and the Structure of Spacetime

Black holes are fascinating objects predicted by Einstein's theory of general relativity. Though they were initially viewed as pathological and unphysical solutions, they were later understood to be a solid and generic outcome of the theory. They are objects where the distortion of space and time is so extreme that it defies imagination. Black holes give rise to paradoxes whose resolution requires us to modify our conception of spacetime. We will review how black holes went from being apparently unphysical solutions to a central tool for discovering new perspectives on the nature of spacetime.

Occam's Razor, Boltzmann's Brain, and Wigner's Friend

Vibrations, Quanta & Biology

Conventional wisdom has it that the realisation of quantum technologies requires delicate control employing finest technology and a remarkable degree of isolation of the envisaged quantum device from its environment. Typically, this includes ultrahigh vacuum, ultralow temperatures, stable lasers, shielding against stray fields and so forth. In view of this, the warm, wet and noisy environment that characterises physiology does not seem to be the ideal environment in which to observe quantum dynamics and consider its impact on biological function. In this lecture, however, I would like to reason why I believe that this may not be such an adventurous notion after all. Moreover, I will argue that it is indeed the fruitful interplay between quantum dynamics and the unavoidable noise from the physiological environment that leads to optimal functionality in certain biologically relevant tasks. I will provide simplified theoretical examples and numerical analysis to bring out some basic ideas such as that of noise supported dynamics and present some supporting results from experiment.

Capturing Light on the Nanoscale

Convention has it that light cannot resolve objects much smaller than the wavelength, a 'rule' that was shown to be invalid some years ago. Here we look inside the wavelength and study the properties of plasmonic structures with dimensions of just a few nanometres: a tenth or even a hundredth of the wavelength of visible light, where the ray picture of light fails utterly. We show how the new concept of transformation optics that manipulates electric and magnetic field lines rather than rays can provide an equally intuitive understanding of sub wavelength phenomena and at the level of Maxwell's equations. The new technology brings light into contact with the nanoworld.

How Forces Modulate Cellular Dynamics: From the Immune Response to Gene Expression

Cells need to sense and adaptively respond to their physical environment in diverse biological contexts such as development, cancer and the immune response. In addition to chemical signals and the genetic blueprint, cellular function and dynamics are modulated by the physical properties of their environment such as stiffness and topography. In order to probe and respond to these environmental attributes, cells exert forces on their surroundings and generate appropriate biochemical and genetic responses. These forces arise from the spatiotemporal organization and dynamics of the cell cytoskeleton, a network of entangled biopolymer filaments that is driven out of thermal equilibrium by enzymes that actively convert chemical energy to mechanical energy. Understanding how cells generate forces and sense the mechanical environment (mechanosensing) is an important challenge with implications for physics and biology. We have investigated the principles of cellular force generation, the statistical properties of these forces, and their role in stiffness and topography sensing by immune and cancer cells. We found that transmission of mechanical information from the external environment to biochemical networks inside the cell occurs by adaptive changes in the stability and mechanics of cytoskeletal networks. Using novel imaging methods and physical models, we have revealed that substrate stiffness regulates gene expression by controlling the binding of proteins to DNA. These results have implications for understanding how forces and material properties of the environment are actively transmitted to the nucleus to control cell fate and how mechanosensing is impaired in diseases such as cancer. Our work provides insight into the design principles underlying how biologically active matter controls signaling and gene expression and underscores the importance of physical forces in cellular function.

Magic Angle Graphene: a New Platform for Strongly Correlated Physics

The understanding of strongly-correlated quantum matter has challenged physicists for decades. Such difficulties have stimulated new research paradigms, such as ultra-cold atom lattices for simulating quantum materials. In this talk I will present a new platform to investigate strongly correlated physics, based on graphene moiré superlattices. In particular, I will show that when two graphene sheets are twisted by an angle close to the theoretically predicted ‘magic angle’, the resulting flat band structure near the Dirac point gives rise to a strongly-correlated electronic system. These flat bands exhibit half-filling insulating phases at zero magnetic field, which we show to be a correlated insulator arising from electrons localized in the moiré superlattice. Moreover, upon doping, we find electrically tunable superconductivity in this system, with many characteristics similar to high-temperature cuprates superconductivity. These unique properties of magic-angle twisted bilayer graphene open up a new playground for exotic many-body quantum phases in a 2D platform made of pure carbon and without magnetic field. The easy accessibility of the flat bands, the electrical tunability, and the bandwidth tunability though twist angle may pave the way towards more exotic correlated systems, such as quantum spin liquids or correlated topological insulators.

Emerging Phenomena at a Quantum Phase Transition: the Magnetic Field-Tuned Superconductor to Insulator Transition

The magnetic-field tuned superconductor-to-insulator transition (H-SIT), along with the quantum-Hall liquid-to- insulator transitions (QHIT) are paradigmatic quantum phase transitions and among the best experimentally studied ones. While evidence continue to mount to the fact that these two phenomena are in the same universality class, key results in the QHIT were not previously identified in the case of H-SIT. Tuning the disorder of two-dimensional superconducting films, and studying the full resistivity tensor, our results show a stark difference between films exhibiting weak vs. strong disorder. In weakly disordered films, the superconducting state gives way to an "anomalous metallic phase" with a resistivity that extrapolates to a non-zero value, but with a vanishing Hall resistance. In the strong disorder limit a "true" H-SIT is observed, characterized by an emerging self-duality at the H-SIT, and the proximate insulating phase is fundamentally distinct from a conventional "Anderson insulator" in that the Hall resistance, rather than diverging, tends to a finite value as the temperature approaches zero [1]. That these features are analogous to behaviors previously documented near the QHIT supports the existence of the correspondence between the two problems implied by the composite boson theory. [1] N.P. Breznay, M.A. Steiner, S.A. Kivelson, A. Kapitulnik, Proceedings of the National Academy of Sciences 113 (2016), 280. Hosted by Brian Swingle/Victor Galitski

Are We Quantum Computers, or Merely Clever Robots?

Of course quantum information processing is not possible in the warm wet brain. There is, however, one “loophole” - offered by nuclear spins - that must be closed before acknowledging that we are merely clever robots. Putative neural quantum processing with nuclear spins seemingly requires fulfillment of many unrealizable conditions: for example, a common biological element with a very isolated nuclear spin to serve as a qubit, a mechanism for quantum entangling qubits, a mechanism for quantum memory storage and processing, a quantum to biochemical transduction that modulates neuron firing rates, among others. My strategy, guided by these requirements, is one of reverse engineering seeking to identify the bio-chemical substrate and mechanisms hosting such putative quantum processing. Remarkably, a specific neural qubit and a unique collection of ions, molecules and enzymes is identified, illuminating an apparently single path towards nuclear spin quantum processing in the brain. 

Neutrino Astronomy at the South Pole with Ice Cube

The Universe has been studied using light since the dawn of astronomy, when starlight captured the human eye. The IceCube Neutrino Observatory, located at the geographic South Pole, observes the Universe in a different and unique way: in high-energy neutrinos. IceCube's discovery in 2013 of a diffuse flux of astrophysical neutrinos, in other words, isotropic high-energy neutrinos from beyond the solar system, started an era of neutrino astronomy. This year, spectacular multiwavelength observations were made that indicate the first astronomical source to emit such astrophysical neutrinos being identified. I will motivate why neutrinos are a necessary messenger in high-energy astronomy, and review what these milestones mean. I will try to reconcile other IceCube analysis results to draw a coherent picture that is the state of neutrino astronomy.

Completing Our Picture of the Neutrino

Science Journalism:  Reporting and Writing for Physics Today