Prospects for quantum process tomography at high energies

In quantum information theory, the evolution of an open quantum system -- a unitary evolution followed by a measurement -- is described by a quantum channel or, more generally, a quantum instrument. In this work, we formulate spin and flavour measurements in collider experiments as quantum instruments. We demonstrate that the Choi matrix, which completely determines input-output transitions, can be both theoretically computed from a given model and experimentally reconstructed from a set of final state measurements (quantum state tomography) using varied input states. The experimental reconstruction of the Choi matrix, known as quantum process tomography, offers a powerful new approach for probing potential extensions of the Standard Model, which predict different input-output transitions. In addition, the methodology constitutes a new foundational test of quantum mechanics itself. As an example, we outline the quantum process tomography approach applied to the e⁺ e⁻ → t t̄ process at a polarized lepton collider.