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Events on Thursday, September 14th, 2023

R. G. Herb Condensed Matter Seminar
Strained Si/SiGe quantum wells with oscillating Ge concentration: valley and spin-orbit physics
Time: 10:00 am - 6:00 pm
Place: 5310 Chamberlin
Speaker: Benjamin Woods, UW-Madison
Abstract: Electron spin qubits in Si/SiGe quantum dots hold promise for quantum computation due to their scalability and long coherence times. However, challenges persist, notably small and variable valley splitting introduces low-energy states near the qubit subspace, causing decoherence and read-out difficulties. In addition, reliance on magnetic field gradients from micromagnets in leading Si/SiGe qubit designs poses scalability issues. I will outline our solution to both problems, which utilizes Si/SiGe heterostructures featuring long-wavelength λ ≈ 1.7 nm Ge concentration oscillations and shear strain. For such a structure, we show that the spin-orbit coupling is dramatically enhanced compared to conventional Si/SiGe quantum wells without Ge concentration oscillations. This enhancement permits rapid spin manipulation via electric dipole spin resonance without the need for micromagnets. Furthermore, we show that the necessary level of shear strain for valley splitting enhancement aligns with existing fabrication techniques. Finally, I will touch on promising future directions. This includes the exploration of electric dipole spin resonance under the influence of valley disorder and the potential for significant g-factor renormalization in multi-electron quantum dots.
Host: Robert McDermott
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NPAC (Nuclear/Particle/Astro/Cosmo) Forum
Neutrinos, Quantum Gravity and the Big Questions - New Ideas for New Data
Time: 2:30 pm - 3:30 pm
Place: CH5310/
Speaker: Heinrich Päs, TU Dortmund University
Abstract: Neutrinos are perfect probes of quantum gravity. The particles’ weak interactions allow to preserve quantum coherence for very long timespans, and neutrino telescopes have started to collect data of neutrinos at extreme energies that have travelled extra-galactic distances. Moreover, the expected breaking of global symmetries such as lepton number in quantum gravity may induce neutrino Majorana masses. The talk discusses how new ideas about quantum gravity could imply exotic properties or phenomena in the neutrino sector, such as altered dispersion relations, quantum-gravitational decoherence, or UV/IR mixing that may be linked to the big open questions of particle physics and cosmology like the nature of dark matter or the electroweak hierarchy problem.
Host: Sanjib Kumar Agarwalla
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