A. Lupascu's research works | University of Waterloo, Waterloo (UWaterloo) and other places

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FIG. 2. (a) An SEM image showing the qubit, coupler, and bias lines....

FIG. 3. (a) The transmission |S 21 | as a function of I and I β in the...

FIG. 4. (a)-(c) Transmission |S 21 | as a function of f and ω p at f β...

FIG. 9. The matrix elements of γ 5 and the ratio of transverse and...

FIG. 10. Schematic of the qubit embedded in a TL, where one side of the...

Tunable coupler for mediating interactions between a two-level system and a waveguide from a decoupled state to the ultrastrong coupling regime

Article

Full-text available

Sep 2023

Two-level systems (TLSs) coupled to waveguides are a fundamental paradigm for light-matter interactions and quantum networks. We introduce and experimentally demonstrate a method to tune the interaction between a TLS, implemented as a flux qubit, and a transmission line waveguide from a decoupled state to a coupling strength that is a significant f...

Decoherence of a tunable capacitively shunted flux qubit

Preprint

Jul 2023

We present a detailed study of the coherence of a tunable capacitively-shunted flux qubit, designed for coherent quantum annealing applications. The measured relaxation at the qubit symmetry point is mainly due to intrinsic flux noise in the main qubit loop for qubit frequencies below $\sim3~\text{GHz}$. At higher frequencies, thermal noise in the...

Optimizing for periodicity: a model-independent approach to flux crosstalk calibration for superconducting circuits

Preprint

Full-text available

Nov 2022

Flux tunability is an important engineering resource for superconducting circuits. Large-scale quantum computers based on flux-tunable superconducting circuits face the problem of flux crosstalk, which needs to be accurately calibrated to realize high-fidelity quantum operations. Typical calibration methods either assume that circuit elements can b...

Aluminum air bridges for superconducting quantum devices realized using a single-step electron-beam lithography process

Article

Aug 2022

In superconducting quantum devices, air bridges enable increased circuit complexity and density, and mitigate the risk of microwave loss arising from mode mixing. We implement aluminum air bridges using a simple process based on single-step electron-beam gradient exposure. The resulting bridges have sizes ranging from 20 µm to 100 µm, with a yield...

Tunable Coupler for Mediating Interactions between a Two-Level System and a Waveguide from a Decoupled State to the Ultra-Strong Coupling Regime

Preprint

Full-text available

Aug 2022

Two-level systems (TLS) coupled to waveguides are a fundamental paradigm for light-matter interactions and quantum networks. We introduce and experimentally demonstrate a method to tune the interaction between a TLS, implemented as a flux qubit, and a transmission line waveguide from a decoupled state to a coupling strength that is a significant fr...

Aluminum air bridges for superconducting quantum devices realized using a single step electron-beam lithography process

Preprint

Jun 2022

In superconducting quantum devices, air bridges enable increased circuit complexity and density as well as mitigate the risk of microwave loss arising from mode mixing. We implement aluminum air bridges using a simple process based on single-step electron-beam gradient exposure. The resulting bridges have sizes ranging from $20~\mu m$ to $100~\mu m...

FIG. 4. (a) The error of the Clifford gate vs the sum of the errors of...

Characterization of control in a superconducting qutrit using randomized benchmarking

Article

Full-text available

Oct 2021

We characterize control of a qutrit implemented in the lowest three energy levels of a capacitively shunted flux-biased superconducting circuit. Randomized benchmarking over the qutrit Clifford group yields an average fidelity of 98.89±0.05%. For a selected subset of the Clifford group, we perform quantum process tomography and observe the behavior...