December 2024

Abstracts of the Quantum Center Lunch Seminar

Date: Thursday, December 5, 2024
Place: ETH Zurich, Hönggerberg, HPF G 6
Time: 12:00 - 13:30

Charge- and Spin-Dynamics and Destabilization of Shallow Nitrogen-Vacancy Centers under UV and Blue Light Illumination

Laura Völker - Spin Physics (Degen group), ETH Zurich

Blue and UV light-induced photoexcitation plays a pivotal role in biology, where it initiates electron transfer cascades and chemical transformation. Quantum sensing with near-surface nitrogen–vacancy (NV) centers in diamond could in principle allow to study photochemical processes at the single- to few molecule regime. However, experimental realisation requires detailed understanding of charge- and spin dynamics of shallow NV centers exposed to UV or blue light illumination. Here, we investigate the charge and spin dynamics of shallow NVs under 445 and 375 nm illumination. With blue excitation, we observe power-dependent charge-state preparation and modest spin initialization fidelity. Under UV excitation, charge-state preparation is power-independent, and no spin polarization is observed. Prolonged UV exposure does further induce aging of NV centers that manifests in reduced charge stability and spin contrast. We attribute this aging to modified local charge environments of near-surface NVs and identify distinct electronic traps only accessible at short wavelengths. Our findings allow to identify a parameter space that would enable sensing of photoexcitable species and further provide insight to degradation of NV electronic environments.

Quasiprobabilistic simulation of quantum computing with restricted quantum computers

Christophe Piveteau - Quantum Information Theory (Renner group), ETH Zurich

Quasiprobability simulation is a technique that allows a quantum computer to simulate the execution of operations which are not physically realizable on its hardware. The technique entails an additional sampling overhead which scales exponentially in the number of non-physical gates that are simulated. In recent years, quasiprobability simulation has found many applications such as classical simulation of near-Clifford quantum circuits and error mitigation. Another such application is circuit cutting, i.e. the task of simulating non-local quantum computation between two parties with only local operations. In this talk, I will give an overview of these applications as well as recent work on characterizing the optimal achievable sampling overhead for circuit cutting, which interestingly has connections with the resource theory of entanglement.