Lorenzo Piroli

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Quantum-state preparation and measurement protocols are well established branches of quantum information and computation theory, with immediate implications for quantum simulation. While several existing algorithms rely on the assumption of disposing of a perfect quantum computer, current noisy intermediate-scale quantum (NISQ) devices are limited in the number of qubits and the coherence time. Therefore, simulating many-body physics poses the challenge of devising preparation and measurement schemes characterised by short "running time". In this talk, I will present recent ideas to address this challenge. In the first part of the talk, I will discuss how traditional quantum-state preparation algorithms, based on unitary quantum circuits, can be improved making use of additional ancillas, measurements, and feedforward operations. Notably, I will show examples where topologically ordered and long-range entangled states can be prepared in a time independent of the system size. In the second part of the talk, I will focus on measurement protocols to estimate quantum entanglement of many-body states. While this is a notoriously difficult task, typically requiring a number of measurements or classical postprocessing resources growing exponentially in the system size, I will show that efficient estimation strategies exist under some physically motivated assumptions on the state to be measured. Specifically, under the conditions that all the spatial correlation lengths are finite, I will show that the entanglement can be detected and measured from polynomially-many local measurements. I will argue that some of the ideas and methods discussed could be of practical interest for implementation in today’s quantum platforms.

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University of Bologna
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Contact: Xhek Turkeshi