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Identifier

000465254

Title

Extraction and stabilization of quantum many-body states

Alternative Title

Απόσπαση και σταθεροποίηση κβαντικών καταστάσεων πολλών σωματιδίων

Author

Φραντζεσκάκης, Ραφαήλ Ι

Thesis advisor

Γεωργακίλας, Αλέξανδρος
Economou, Sophia

Reviewer

Κομίνης, Ιωάννης
Τσιρώνης, Γεώργιος
Νιάρχος, Βασίλειος
Petrosyan, David
Νικολόπουλος, Γεώργιος

Abstract

“Graph” states are highly entangled quantum states that are crucial resources in measurement - based quantum computing and quantum communications. Despite the importance of photonic graph and cluster states for quantum technologies, their generation presents considerable difficulties and it is a matter of current research. In this dissertation, we propose two entanglement concentration protocols where we extract graph states from noisy graph states called weighted graph states. In the first protocol, we initialize an 1D weighted graph state and by measuring the even number of qubits we are able to extract GHZ states. We also study how single-qubit errors affect the protocol and if the extraction is sufficient in the presence of this type of error. In the second protocol, we generalize our first result and show that we can extract more general states. In particular, we apply an edge extraction for every edge of the graph state by replacing it with a weighted graph state and measuring three qubits for each edge. We comment on the success probability of the protocol and we explore possible adaptive measurements in order to boost the success rate. In the second part of the thesis, we study non-equilibrium quantum systems. Specifically, we define what a discrete-time-crystal phase is and how to identify one. We study a central spin system that arises naturally in the different physical platforms and the possibility of observing a time crystal phase in the presence of Heisenberg interactions. We show that a large Zeeman splitting mismatch between the central spin and the satellite spins can be beneficial to stabilize computational basis quantum states and observe a time crystal. In the other method, we apply spinlocking pulses to the central spin to decouple the system dynamically from the in-plane interactions and be able to generate a time crystal phase.

Language

English

Subject

Discrete time crystals

Entanglement concentration

Graph states

Γράφοι

Διακριτοί χρονοκρύσταλλοι

Συγκέντρωση σύμπλεξης

Issue date

2024-06-10

Collection