Events on Friday, June 27th, 2025
- Fast, high fidelity, on demand qubit initialization out of a latched state using baseband pulses
- Time: 10:00 am - 12:00 pm
- Place: 5310 CH
- Speaker: Piotr Marciniec, Physics PhD Graduate Student
- Abstract: Latched schemes provide high-fidelity readout of quantum dot qubits by exploiting long-lived, nonequilibrium states with easily measured charge occupations. While long-lived latches simplify readout, fast re-initialization is also desirable and cannot be accomplished by relying on the natural decay process of the latched state. In this work, we demonstrate fast, high-fidelity reset of a latched quantum dot hybrid qubit that can be deployed on demand, using only baseband pulses. Our protocol circumnavigates the slow decay process of the latched state by pulsing to a region in gate-voltage space in which the latched state resets in a fast, two-step process. With this pulse, we achieve reset fidelities as high as 98% with reload times as short as 2μs. Our work provides a steppingstone to robust quantum error correction in quantum dot qubits, where the readout and initialization times should be comparable to gate times.
- Host: Mark Eriksson
- High-fidelity gates in a disordered Si/SiGe wiggle well with strong spin-orbit coupling
- Time: 1:00 pm - 3:00 pm
- Place: 5310 CH
- Speaker: Hudaiba Soomro, Physics PhD Graduate Student
- Abstract: Silicon-based single-electron spin qubits commonly use micromagnets to create an artificial spin orbit coupling (SOC) for Electric Dipole Spin Resonance (EDSR); however, this approach faces scalability challenges. Previously, it has been shown that the Wiggle Well may sufficiently enhance the otherwise weak SOC in the conduction band of Si, allowing for implementation of a strong EDSR protocol; previous calculations indicate that Rabi frequencies exceeding 500MHz/T may be possible [1]. However, SiGe random-alloy disorder causes spatial variations that have not been fully accounted for in these calculations. In this work, we show that alloy disorder gives rise to two main effects relevant for EDSR: the generation of a strong valley dipole (providing an additional EDSR mechanism), and randomization of valley parameters (providing a position-dependent Rabi frequency). We find that the valley-dipole contribution to the Rabi frequency is particularly pronounced in the low-valley-splitting regime. Additionally, we incorporate charge noise effects and compute the position-dependent T2,Rabi time, the dephasing rate, and the quality factor, finding quality factors of the order of 103 . Finally, we identify dephasing-protected ‘sweet spots’ where the qubit is resilient to charge noise.” [1] B. D. Woods, et al., Phys. Rev. B 107, 035418 (2023)
- Host: Mark Friesen