Constructing networks of quantum channels for state preparation
 verfasst von
 Dmytro Bondarenko
 betreut von
 Tobias James Osborne
 Abstract
Entangled possibly mixed states are an essential resource for quantum computation, communication, metrology, and the simulation of manybody systems. It is important to develop and improve preparation protocols for such states. One possible way to prepare states of interest is to design an open system that evolves only towards the desired states. A Markovian evolution of a quantum system can be generally described by a Lindbladian. Tensor networks provide a framework to construct physically relevant entangled states. In particular, matrix product density operators (MPDOs) form an important variational class of states. MPDOs generalize matrix product states to mixed states, can represent thermal states of local onedimensional Hamiltonians at sufficiently large temperatures, describe systems that satisfy the area law of entanglement, and form the basis of powerful numerical methods. In this work we develop an algorithm that determines for a given linear subspace of MPDOs whether this subspace can be the stable space of some frustration free klocal Lindbladian and, if so, outputs an appropriate Lindbladian. We proceed by using machine learning with networks of quantum channels, also known as quantum neural networks (QNNs), to train denoising postprocessing devices for quantum sources. First, we show that QNNs can be trained on imperfect devices even when part of the training data is corrupted. Second, we show that QNNs can be trained to extrapolate quantum states to, e.g., lower temperatures. Third, we show how to denoise quantum states in an unsupervised manner. We develop a novel quantum autoencoder that successfully denoises GreenbergerHorneZeilinger, W, Dicke, and cluster states subject to spinflip, dephasing errors, and random unitary noise. Finally, we develop recurrent QNNs (RQNNs) for denoising that requires memory, such as combating drifts. RQNNs can be thought of as matrix product quantum channels with a quantum algorithm for training and are closely related to MPDOs. The proposed preparation and denoising protocols can be beneficial for various emergent quantum technologies and are within reach of presentday experiments.
 Organisationseinheit(en)

QUEST Leibniz Forschungsschule
 Typ
 Dissertation
 Anzahl der Seiten
 185
 Publikationsdatum
 2021
 Publikationsstatus
 Veröffentlicht
 Elektronische Version(en)

https://doi.org/10.15488/11050 (Zugang:
Offen)