Colloquium Schedule

Fall 2024

Networking Quantum Computers

Abram Falk ('03), IBM Watson Research Center
Friday, September 20, at 12:45

As the quantum computing industry continues its rapid growth, the need to distribute quantum information across networks is becoming increasingly pressing. However, the fragility of quantum states makes quantum networking a challenging problem, especially when the quantum bits (qubits) comprise microwave photons, which rapidly thermalize at ambient conditions. In this colloquium, I will introduce quantum computing, superconducting quantum qubits, and strategies for networking qubits using quantum transducers, which are devices that can convert the frequency of individual photons in a single-photon basis. Although these devices invariably lead to the transmission of imperfect quantum states, there is nonetheless a possibility for high quality quantum networks via techniques such as entanglement heralding and distillation.

Grain-scale dynamics and force transmission in sticking and slipping granular materials: effects of friction and grain shape

Ryan Kozlowski, College of the Holy Cross
Friday, October 4, at 12:45

Granular materials are ubiquitous in nature, from household table salt to mountainside boulders, silty river beds, and distant  protoplanetary disks. Despite their prevalence in daily life and countless industries like agriculture and pharmaceuticals, the stability, flow, and responses of these materials to external perturbations are all active areas of physics research: unlike conventional solids or liquids, they often exist in non-equilibrium states, interact dissipatively, and have constituent particles of infinite variety in size, shape, and frictional properties. In this talk, I will present experiments specifically probing how grain shape and friction with boundaries influence the stick-slip dynamics of driven granular materials. In stick-slip dynamics, the granular material transitions back and forth between stable sticking periods and rapid, energy-releasing slip events, like the destructive sliding between tectonic plates that generates earthquakes. I begin by analyzing macroscopic stick-slip of driven granular materials and then connect these observations with grain-scale flow and interparticle stresses, demonstrating that grain-scale interactions indeed influence bulk granular material stability and yielding. In particular, I show that friction between grains and a substrate dramatically stabilizes the material against an intruding load, and that strongly angular grains exhibit both greater stability in sticking periods and more energetic slip events than less angular grains.

Neutron Scattering and Quantum Materials Research at the Spallation Neutron Source

Matthew Stone, Oak Ridge National Laboratory
Friday, November 1, at 12:45

The 1933 Nobel Prize in Physics was awarded for the discovery of the neutron. Less than 20 years later, the Graphite Reactor at Oak Ridge National Lab pioneered the use of neutron beams to investigate the fundamental properties and behaviors of energy and materials at the atomic scale. In 2024, there are more than 20 neutron sources worldwide producing neutrons for scientific investigations. One of the most powerful of these sources is the Spallation Neutron Source at Oak Ridge. This facility currently houses 20 instruments. This presentation will take you on a guided tour of the components that are common across the diverse instrument suite of the SNS facility. We will examine how neutron guides, neutron choppers, sample environments, and neutron detectors all work together to allow these instruments to perform approximately 800 experiments annually. One current focus of neutron scattering measurements is to examine the excitations in quantum materials. I will present some recent studies of quantum materials and describe how neutron scattering is used to understand these systems.

Design of Chiral Particles Moving in Fluids

Greg Voth, Wesleyan University
Friday, November 15, at 12:45

How can we design particle shapes to optimize the coupling of translation to rotation in fluid flow? This chiral design problem has a rich history with connections to the chiroptical response of molecules and metamaterials, chiral phases in crystals and nematics, and many applications of particle motion in fluids including locomotion of micro-organisms and robots. Experiments on sedimentation in highly viscous fluids provide a familiar and concrete context in which to unlearn some oversimplification about handedness as a binary or scalar property of particles and replace them with adequate tools for quantifying translation-rotation coupling. The talk will particularly focus on helical ribbons. Even in Stokes flow, their dynamics are non-linear and we observe a sequence of bifurcations as we change their length and center of mass. In certain cases their dynamics can be very simple, and we can continuously modify them to approach the maximum complexity of sedimenting particles.