Prospects for quantum process tomography at high energies

Abstract 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 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msup> <mml:mi>e</mml:mi> <mml:mo>+</mml:mo> </mml:msup> <mml:msup> <mml:mi>e</mml:mi> <mml:mo>−</mml:mo> </mml:msup> <mml:mo accent="false" stretchy="false">→</mml:mo> <mml:mi>t</mml:mi> <mml:mrow> <mml:mover> <mml:mi>t</mml:mi> <mml:mo stretchy="false">¯</mml:mo> </mml:mover> </mml:mrow> </mml:mrow> </mml:math> process at a polarised lepton collider.