Events at Physics
Events on Friday, February 4th, 2022
- Theory Seminar (High Energy/Cosmology)
- Maximizing Direct Detection with HYPER Dark Matter
- Time: 1:00 pm
- Place: Chamberlin 5280
- Speaker: Robert Mcgehee, University of Michigan
- Abstract: In this talk, we estimate the maximum direct detection cross section for sub-GeV dark matter scattering off nucleons. For dark matter masses in the range of 10 keV − 100 MeV, cross sections greater than 10^(−36) - 10^(−30) cm^2 seem implausible. We introduce a dark matter candidate which realizes this maximum cross section: HighlY interactive ParticlE Relics (HYPERs). After HYPERs freeze-in, a dark sector phase transition decreases the mass of the mediator which connects HYPERs to the visible sector. This increases the HYPER’s direct detection cross section, but in such a way as to leave the HYPER’s abundance unaffected and avoid conflict with measurements of Big Bang Nucleosynthesis and the Cosmic Microwave Background. HYPERs present a benchmark for direct detection experiments in a parameter space with few known dark matter models.
- Host: George Wojcik
- Physics Department Colloquium
- Quantum computing with neutral Yb atoms
- Time: 3:30 pm
- Place: 2241 Chamberlin Hall
- Speaker: Jeff Thompson, Princeton
- Abstract: Quantum computing with neutral atoms has progressed rapidly in recent years, combining large system sizes, flexible and dynamic connectivity, and quickly improving gate fidelities. The pioneering work in this field has been implemented using alkali atoms, primarily rubidium and cesium. However, divalent, alkaline-earth-like atoms such as ytterbium offer significant technical advantages. In this talk, I will present our progress on quantum computing using 171-Yb atoms, including high-fidelity imaging, nuclear spin qubits with extremely long coherence times, and two-qubit gates on nuclear spins using Rydberg states [1,2]. I will also discuss several unexpected benefits of alkaline-earth-atoms: an extremely robust and power-efficient local gate addressing scheme , and a novel approach to quantum error correction called “erasure conversion”, which has the potential to implement the surface code with a threshold exceeding 4%, using the unique level structure of 171-Yb to convert spontaneous emission events into erasure errors . Time permitting, I will also discuss a new project to implement very high fidelity quantum computing and simulation using circular Rydberg states with 100-second lifetimes .  S. Saskin et al, Phys. Rev. Lett. 122, 143002 (2019).  A. P. Burgers et al, arXiv:2110.06902 (2021).  S. Ma, A. P. Burgers, et al, arXiv: 2112.06799 (2021).  Y. Wu, et al: arXiv:2201.03540 (2022).  S. R. Cohen et al, PRX Quantum 2, 030322 (2021).
- Host: Shimon Kolkowitz