Compare Papers

Paper 1

Randomized benchmarking for qudit Clifford gates

Mahnaz Jafarzadeh, Ya-Dong Wu, Yuval R. Sanders, Barry C. Sanders

Year

2019

Journal

arXiv preprint

DOI

arXiv:1911.08162

arXiv

1911.08162

We introduce unitary-gate randomized benchmarking (URB) for qudit gates by extending single-and multi-qubit URB to single- and multi-qudit gates. Specifically, we develop a qudit URB procedure that exploits unitary 2-designs. Furthermore, we show that our URB procedure is not simply extracted from the multi-qubit case by equating qudit URB to URB of the symmetric multi-qubit subspace. Our qudit URB is elucidated by using pseudocode, which facilitates incorporating into benchmarking applications.

Open paper

Paper 2

Single photon emitters in hBN: Limitations of atomic resolution imaging and potential sources of error.

Lamprecht D, Chokappa S, Freilinger AM, Mayer BM, Melchior M, Dzíbelová J, Lorber D, Tizei LHG, Kociak M, Mangler C, Filipovic L, Kotakoski J

Year

2026

Journal

Ultramicroscopy

DOI

10.1016/j.ultramic.2026.114318

arXiv

-

There is a growing interest in identifying the origin of single-photon emission in hexagonal boron nitride (hBN), with proposed candidates including boron and nitrogen vacancies as well as carbon substitutional dopants. Because photon emission intensity often increases with sample thickness, hBN flakes used in these studies commonly exceed 30 atomic layers. To identify potential emitters at the atomic scale, annular dark-field scanning transmission electron microscopy (ADF-STEM) is frequently employed. However, due to the intrinsic AA' stacking of hBN with vertically alternating boron and nitrogen atoms, this approach is complicated even in few-layer systems. Here, we demonstrate using STEM image simulations and experiments that, even under idealized conditions, the intensity differences between boron- and nitrogen-dominated columns and carbon substitutions become indistinguishable at thicknesses beyond 17 atomic layers (ca. 6 nm). While vacancy-type defects can remain detectable at somewhat larger thicknesses, also their detection becomes unreliable at thicknesses typically used in photonic studies. We further show that common residual aberrations, particularly threefold astigmatism, can lead to artificial contrast differences between columns, which may result in misidentification of atomic defects. We systematically study the effects of non-radially symmetric aberrations on multilayer hBN and demonstrate that even small residual threefold astigmatism can significantly distort the STEM contrast, leading to misleading interpretations.

Open paper