Abstract: The Dark Energy Spectroscopic Instrument (DESI) collaboration is conducting a 5 year redshift survey of 40 million extra-galactic sources over 14,000 square degrees of the northern sky. One of its primary goals is to measure the cosmic expansion history with baryon acoustic oscillations (BAO). I will present the measurement of BAO in galaxy, quasar and Lyman-alpha forest tracers from the first year of observation. With 5.7 million galaxy and quasar redshifts in the range 0.1 < z < 2.1, and 420,000 Lyman-alpha forest quasars at higher redshift, the aggregate precision on BAO is of 0.52% at z<2.1 and 1.1% at an effective redshift z=2.3, surpassing in a year two decades of observations with the SDSS. I will present some of the numerous validation tests performed with simulations and blinded data. I will then highlight the main cosmological results, with improved constraints on the dark energy equation of state, the Hubble parameter, spatial curvature, and the sum of neutrino masses.

Abstract: 

Abstract: The 1+1 dimensional gauge theories have served as useful models of quark confinement. I will revisit the classic Schwinger model and its lattice Hamiltonian formulation, where it can be reduced to a model of qubits with long-range interactions. A mass shift between the lattice and continuum definitions of mass, which is motivated by chiral symmetry, is shown to lead to improved results. I will also present the zero-temperature phase diagram of the two-flavor Schwinger model at theta=pi, which exhibits dimensional transmutation and spontaneous breaking of charge conjugation. Finally, I will discuss Adjoint QCD2, which is the 2D SU(N) gauge theory coupled to an adjoint multiplet of Majorana fermions. This model has a rich topological structure. I will introduce a Hamiltonian lattice gauge theory approach to Adjoint QCD2, in which one can compute its low-lying spectrum, the string tensions, and other observables.

Abstract: Biogenic emissions contribute significantly to the composition and chemistry of the troposphere, with vegetation being the main source of volatile alkenes. For example, isoprene is emitted by plants during photosynthesis and is one of the most abundant organic compounds released into the atmosphere: around 500 Tg of isoprene is emitted annually and forms the largest fraction of non-methane hydrocarbon emissions. The dominant mechanisms for the atmospheric removal of alkenes are reactions with the OH radical and ozone. Alkenes is their reaction with ozone, leads to the formation of zwitterionic reactive intermediates named carbonyl oxides, more commonly known as Criegee intermediates (CIs, RCR’OO). Since the advent of photolytic methods to directly generate the smallest CI, CH2OO, direct experiments by researchers across the world have revealed the reactivity of these elusive species to be much more varied and complex than previously anticipated based on ozonolysis experiments. These direct studies have revealed that many CI reactions are faster than previously anticipated. For example, the reaction of CH2OO with SO2 is ~10,000 times faster than previously deduced from ozonolysis experiments.

Recent work has indicated the potentially important role of CIs in particulate formation. For example, the fast reaction of CIs with SO2 is estimated to contribute up to 50% of atmospheric H2SO4 formation – a critical precursor to sulfate aerosols. Additionally, recent work, has shown many bimolecular reactions of CI, such as reaction with hydroperoxides (ROOHs), lead to the formation of higher molecular weight, highly oxygenated reaction products. These species have been implicated in the formation of secondary organic aerosol (SOA). Theoretical work has also indicated that the reactions of CI + ROO reactions might proceed rapidly, via a mechanism involving the addition of the terminal oxygen of ROO to the O-bound carbon of the CI - regenerating the ROO -OO functional group for subsequent reaction. 

In this work we have utilized novel photolytic precursors to generate select CIs and investigate their role in oligomizeration reactions. The talk will focus on the use of flash photolysis multi pass broad band UV-vis spectrometry and multiplexed photoionization mass spectrometry to investigate the reactions of Criegee intermediates. We will focus on the impact of water on reactivity and the that helps drive tropospheric composition changes including contribution to SOA mass. 
Suggested Reading

Welz et al., (2012) Reaction of CH2I with O2 forms Criegee Intermediate: Direct Measurements of CH2OO Kinetics, Science, 335, 204-207.
Caravan et al., (2024) Observational evidence for Criegee intermediate oligomerization reactions relevant to aerosol formation in the troposphere. Nat. Geosci. 17, 219–226.
Chao et al., (2024) Chemical Kinetic Study of the Reaction of CH2OO with CH3O2. J. Phys. Chem. Letts.  15 (13), 3690-3697
 

Abstract: Empirical evidence for a gap between the computational powers of classical and quantum computers has been provided by experiments that sample the output distributions of two-dimensional quantum circuits. Many attempts to close this gap have utilized classical simulations based on tensor network techniques, and their limitations shed light on the improvements to quantum hardware required to frustrate classical simulability. In particular, quantum computers having in excess of ∼50 qubits are primarily vulnerable to classical simulation due to restrictions on their gate fidelity and their connectivity, the latter determining how many gates are required (and therefore how much infidelity is suffered) in generating highly-entangled states. Here, we describe recent hardware upgrades to Quantinuum's H2 quantum computer enabling it to operate on up to 56 qubits with arbitrary connectivity and 99.843(5)% two-qubit gate fidelity. Utilizing the flexible connectivity of H2, we present data from random circuit sampling in highly connected geometries, doing so at unprecedented fidelities and a scale that appears to be beyond the capabilities of state-of-the-art classical algorithms. The considerable difficulty of classically simulating H2 is likely limited only by qubit number, demonstrating the promise and scalability of the QCCD architecture as continued progress is made towards building larger machines.

==========

All seminars are held in the CASE Auditorium. Light refreshments will be served starting at 3:30 p.m. Talk begins at 4 p.m.
This seminar series is sponsored by CUbit with generous support of the Caruso Foundation.

Abstract: From its initial proposal, Quantum Computing (QC) has had captivating potential, and scientists have worked on advancing toward that potential. With well-known algorithms as motivation, and increasingly capable hardware devices, QC has now reached an interesting and important inflection point. The Algorithms-to-Devices gap in QC refers to the orders of magnitude difference between the quantity and quality of resources needed by QC algorithms, and what has been successfully built today. Computer science and engineering research can help QC systems close this gap, by develop the crucial intermediate tool flows and hybrid classical-quantum techniques that can move towards practical quantum utility. My talk will offer some recent advances in these topic areas. More broadly, I will advocate for the role that computer scientists and engineers must play in order for QC to reach its full potential.

Forthcoming

Abstract: Empirical evidence for a gap between the computational powers of classical and quantum computers has been provided by experiments that sample the output distributions of two-dimensional quantum circuits. Many attempts to close this gap have utilized classical simulations based on tensor network techniques, and their limitations shed light on the improvements to quantum hardware required to frustrate classical simulability. In particular, quantum computers having in excess of ∼50 qubits are primarily vulnerable to classical simulation due to restrictions on their gate fidelity and their connectivity, the latter determining how many gates are required (and therefore how much infidelity is suffered) in generating highly-entangled states. Here, we describe recent hardware upgrades to Quantinuum's H2 quantum computer enabling it to operate on up to 56 qubits with arbitrary connectivity and 99.843(5)% two-qubit gate fidelity. Utilizing the flexible connectivity of H2, we present data from random circuit sampling in highly connected geometries, doing so at unprecedented fidelities and a scale that appears to be beyond the capabilities of state-of-the-art classical algorithms. The considerable difficulty of classically simulating H2 is likely limited only by qubit number, demonstrating the promise and scalability of the QCCD architecture as continued progress is made towards building larger machines.

Abstract: Superfluid helium-4 at millikelvin temperatures is an ideal acoustic medium, featuring ultralow dissipation and the unique possibility of tuning the mechanical frequency through pressurization. Combined with a cavity optomechanical readout to sensitively probe the motion, a superfluid resonant mass is a promising tabletop-scale platform to probe small mechanical signals and new physics, such as gravitational waves and dark matter. Previously, we demonstrated a prototype superfluid gravitational wave detector, setting the base for developing our Helium ultraLIght dark matter Optomechanical Sensor (HeLIOS). After reviewing superfluid optomechanical systems and motivating the detection of wavelike dark matter, I will present a recent characterization of our HeLIOS prototype. It promises unprecedented sensitivity and scalability to expand the search for dark matter, which nature is one of the biggest unsolved questions in modern science.

Abstract Forthcoming

Forthcoming