• Advanced Photonics
  • Vol. 3, Issue 6, 066002 (2021)
Alessia Suprano1、†, Danilo Zia1, Emanuele Polino1, Taira Giordani1, Luca Innocenti2、3、4, Alessandro Ferraro3, Mauro Paternostro3, Nicolò Spagnolo1, and Fabio Sciarrino1、*
Author Affiliations
  • 1Sapienza Università di Roma, Dipartimento di Fisica, Roma, Italy
  • 2Palacký University, Department of Optics, Olomouc, Czech Republic
  • 3Queen’s University Belfast, School of Mathematics and Physics, Centre for Theoretical Atomic, Molecular, and Optical Physics, Belfast, United Kingdom
  • 4Università degli Studi di Palermo, Dipartimento di Fisica e Chimica-Emilio Segrè, Palermo, Italy
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    Experimental engineering of high-dimensional quantum states is a crucial task for several quantum information protocols. However, a high degree of precision in the characterization of the noisy experimental apparatus is required to apply existing quantum-state engineering protocols. This is often lacking in practical scenarios, affecting the quality of the engineered states. We implement, experimentally, an automated adaptive optimization protocol to engineer photonic orbital angular momentum (OAM) states. The protocol, given a target output state, performs an online estimation of the quality of the currently produced states, relying on output measurement statistics, and determines how to tune the experimental parameters to optimize the state generation. To achieve this, the algorithm does not need to be imbued with a description of the generation apparatus itself. Rather, it operates in a fully black-box scenario, making the scheme applicable in a wide variety of circumstances. The handles controlled by the algorithm are the rotation angles of a series of waveplates and can be used to probabilistically generate arbitrary four-dimensional OAM states. We showcase our scheme on different target states both in classical and quantum regimes and prove its robustness to external perturbations on the control parameters. This approach represents a powerful tool for automated optimizations of noisy experimental tasks for quantum information protocols and technologies.

    Video Introduction to the Article

    1 Introduction

    Quantum-state engineering of high-dimensional states is a pivotal task in quantum information science.14 However, many existing protocols are platform-dependent and lack universality.510 Conversely, a scheme to engineer arbitrary quantum states, relying on quantum walk (QW) dynamics, was showcased in Ref. 11. QWs are a particularly simple class of quantum dynamics that can be considered to generalize classical random walks.12 QWs have been implemented in experimental platforms ranging from trapped ions13,14 and atoms15 to photonics circuits.1623 In particular, engineering of arbitrary qudit states has been experimentally demonstrated with QWs in orbital angular momentum (OAM) and polarization degrees of freedom of light.11,24,25