Wisconsin Quantum Institute |
Events During the Week of March 10th through March 17th, 2024
Monday, March 11th, 2024
- No events scheduled
Tuesday, March 12th, 2024
- Theory of g factors in semiconductors -- some history, and new insights
- Time: 3:30 pm - 5:00 pm
- Place: Discovery Building, DeLuca Forum
- Speaker: David DiVincenzo, Forschungszentrum Jülich GmbH
- Abstract:
The g factor of electrons and holes in crystals and heterostructures of silicon, germanium, galium arsenide, etc., is a key parameter in designing spin qubits. I will begin by discussing two different but interrelated definitions of the g factor. Authors have disagreed from the beginning about whether or not g is a symmetric second-rank tensor. I will discuss that g, which is specific to each eigenstate, whether extended or localized, is best discussed in terms of three singular values associated with eigendirections, with a separate discussion about its sign. Luttinger gave a correct formula for the g factors of band electrons, including the orbital contributions arising from the spin-orbit interaction. But it was not until fifty years later, with the advent of Berry-curvature concepts, that his formula could be given a clear physical interpretation. I will show results of a survey we have done of band g factors in silicon and germanium, emphasizing new topological aspects. It is interesting that even silicon, with its very weak spin-orbit interaction, can, because of a combination of topology and symmetry, exhibit g factors very far from 2.
This event starts at 3:30pm with refreshments, followed at 3:45pm by a short presentation by Merritt Losert (PhD student Mark Friesen group), titled "Valley Splitting and Spin Shuttling in Si/SiGe Heterostructures". The invited presentation starts at 4pm.
Join Zoom Meeting Meeting ID: 979 1417 7653 Passcode: 874970
- Host: Mark Friesen
Wednesday, March 13th, 2024
- Optical relaxation dynamics of nanocavity-coupled erbium ensembles
- Time: 1:00 pm - 2:00 pm
- Place: 2540 Engineering Hall
- Speaker: Dr. Alan Dibos, Argonne National Laboratory
- Abstract: Tailoring the interaction between optical emitters and their electromagnetic environment is of both fundamental scientific interest and practical relevance for applications such as quantum communication and quantum information processing. By tuning the photonic density of states, one can drastically modify the emission properties of these emitters, a phenomenon that underpins the thriving research area of cavity quantum electrodynamics. In this talk, we will first present our rare earth doped nanocavity platform that is being pursued for future quantum optical memory devices operating at cryogenic temperatures. Our spin qubit system consists of Er 3+ ions with a natural optical transition in the telecom (~1520 nm), but the long optical lifetime of these ions (order of milliseconds) necessitates the use of an optical cavity to greatly enhance the emission rate. More specifically, we grow thin film Er 3+ -doped titanium dioxide (TiO 2 ) atop silicon-on-insulator wafers and fabricate small mode volume photonic crystal cavities via etching through both the TiO 2 and Si device layers. We have thus far demonstrated that when the optical cavity is resonant with optical transition of the Er 3+ ions, the optical lifetime can show an enhancement (Purcell factor) up to several hundred [1]. However, in addition to quantum communication applications, we can use the long optical lifetimes of rare-earth ions for more fundamental optical decay modification experiments [2]. For our system, the ensemble of Er 3+ emitters that couples to the cavity exhibit a much broader inhomogeneous linewidth than the cavity. When the optical cavity is tuned through the Er 3+ inhomogeneous distribution, the resultant Purcell factor exhibits an anomalous slowing of the decay when the cavity is resonant with the center of the distribution. We will examine the experimental Purcell factor dependence on resonant laser pump power, as well as the spectral dependence of the PLE emission. We will discuss our attempts to capture qualitative aspects of this decay rate suppression using a semi-classical model of non-interacting emitters mediated by a common cavity. Finally, we will discuss a recent material synthesis development to make our Er 3+ :TiO 2 system potentially more scalable for foundry- level deployment [3].
[1] A. M. Dibos et al., “Purcell enhancement of erbium ions in TiO 2 on silicon nanocavities,” Nano Lett. 22,
6530 (2022).
[2] M. T. Solomon et al. “Anomalous Purcell decay of strongly driven inhomogeneous emitters coupled to
a cavity.” arXiv, DOI: 10.48550/arXiv.2309.16641 (2023).
[3] C. Ji et al. “Nanocavity-mediated Purcell enhancement of Er in TiO 2 thin films grown via atomic layer
deposition.” arXiv, DOI: 10.48550/arXiv.2309.13490 (2023). Accepted in ACS Nano.
- Host: Mikhail Kats
- Theoretical Chemistry Institute seminar and panel with Dr. Thi Ha Kyaw and Dr. Gaurav Saxena from LG Electronics.
- Time: 3:00 pm - 5:00 pm
- Place:
- Speaker: Dr. Thi Ha Kyaw and Dr. Gaurav Saxena, LG Electronics
- Abstract:
Talk 1: A critical limitation of quantum imaginary time evolution-like algorithms in noisy quantum hardware (Thi Ha Kyaw)
Abstract: The variational quantum imaginary time evolution algorithm is efficient in finding the ground state of a quantum Hamiltonian. This algorithm involves solving a system of linear equations in a classical computer and the solution is then used to propagate a quantum wavefunction. Here, we show that owing to the noisy nature of current quantum processors, such a quantum algorithm or the family of quantum algorithms that require classical computation of inverting a matrix with high condition number will require single- and two-qubit gates with very low error probability. Failure to meet such conditions will result in erroneous quantum data propagation even for a relatively small quantum circuit ansatz. Specifically, we find the upper bounds on how the quantum algorithmic error scales with the probability of errors in quantum hardware. Our work challenges the mainstream notion of hybrid quantum-classical quantum algorithms being able to perform under noisy environments while we show such algorithms require very low error quantum gates to get reliable results.
Talk 2: Improved error mitigation protocol by restricted evolution (Gaurav Saxena)
Abstract: To perform any meaningful computation using NISQ processors, error mitigation protocols need to be deployed in the quantum circuits. Here, we propose a constant runtime error mitigation protocol. Further, we propose a hybrid error mitigation protocol by combining our methods with the probabilistic error cancellation to improve the bias and the sampling overhead in estimating the expectation value of an observable. We showed that the sampling overhead and the bias of our protocol depend on a measure called generalized robustness and we also found bounds on this measure under general noise scenario.
- Host: Micheline Soley
Thursday, March 14th, 2024
- No events scheduled
Friday, March 15th, 2024
- No events scheduled