The Nikhef ATLAS group, in partnership with the University of Amsterdam, is offering two PhD positions focused on Higgs boson physics and advanced data analysis techniques, including machine learning, within the context of the ATLAS experiment at CERN. Nikhef is the national institute for subatomic physics in the Netherlands, renowned for its collaborative and international research environment, and is a founding member of the ATLAS collaboration. The group is deeply involved in both detector construction and physics data analysis, with a strong emphasis on Higgs boson and top quark physics, as well as searches for new physics signatures. The first PhD position centers on the search for the extremely rare process of ttHH production in LHC Run-3 data, utilizing all tt final states and boosted final states. The analysis will leverage advanced machine learning techniques, particularly attention-based transformer models, to classify events directly from low-level data and perform tasks such as Higgs boson mass regression. This work will synergize with other boosted analyses in two-Higgs channels. The second PhD position focuses on reconstructing the two-Higgs decay channel into a pair of photons and a pair of b-quarks (HH → bbγγ), which currently provides the tightest constraints on diHiggs production. The role also involves the combined interpretation of all reconstructed diHiggs channels, contributing to the ultimate statement on diHiggs production from LHC Run-3 data. This research will help constrain the trilinear and quartic Higgs couplings, offering unprecedented precision in understanding the Higgs potential. Both positions are part of a larger NWO-funded physics program, 'The potential of the Higgs boson,' which will include seven PhD and two postdoc positions in the Nikhef ATLAS group between 2025 and 2030, all focused on the Higgs boson potential. The program is complemented by nine Nikhef staff scientists who provide supervision, networking, and specialized training in data analysis and Higgs boson physics. Candidates will be employed by the University of Amsterdam and primarily based at Nikhef in Amsterdam, with opportunities for extended stays at CERN. The positions offer a four-year contract (initially 18 months, extendable upon satisfactory evaluation), a competitive salary, holiday and year-end allowances, and potential tax benefits for non-Dutch applicants. Applicants should have an (almost) completed Master's degree in high-energy physics or a closely related field, strong data analysis and software skills (Python, C++, ROOT), and some research experience in experimental particle physics. Experience with machine learning is desirable but not required. The application process requires submission of a detailed CV, motivation letter, publication list, and references via the Nikhef online form by 16 November 2025. Interviews are expected to take place in December 2025.