CQT: Concepts of Quantum Transport

Luis E. F. Foa Torres, Stephan Roche, Jean‐Christophe Charlier

Luis E. F. Foa Torres, Stephan Roche, Jean‐Christophe Charlier

S. Archana, Aditi Das, Venkat Abhignan +1 more

In distributed quantum computing, quantum networks provide a potential infrastructure for long-range quantum information processing. Controlled quantum teleportation (CQT) is a key practically relevant protocol that can connect two parties on a network and enables a third party, the controller to allow or abort the secure teleportation of an arbitrary single-qubit state between the two parties. We investigate the robustness of a three-qubit GHZ resource under bit-flip, phase-flip, depolarizing, and amplitude-damping noise. Using the Kraus-operator formalism, we characterize the noisy resource through multipartite quantum discord, genuine multipartite concurrence (GMC), localizable entanglement (LE), and CQT fidelity. We also outline a proof-of-concept photonic implementation for preparing the three-qubit GHZ resource and realizing the CQT protocol, which could enable experimental investigation of the effects of noise. Our results show that bit-flip and amplitude-damping noise generally preserve useful mutipartite quantum correlations over broader noise parameter ranges. Interestingly, multipartite discord exhibits freezing under bit-flip noise over a finite parameter regime. Moreover, discord can persist beyond the sudden death of genuine multipartite entanglement, revealing the distinct robustness of nonclassical correlations. We further demonstrate that CQT fidelity which characterizes the performance of CQT can exceed the classical threshold even after GMC vanishes, while LE more closely reflects the operational usefulness of the noisy resource. These findings highlight the complementary roles of quantum correlations and entanglement in assessing the resilience of GHZ-based protocols.

Frieder Kleefeld

(Anti)causal boundary conditions being imposed on the (seemingly) Hermitian Quantum Theory (HQT) as described in standard textbooks lead to an (Anti)Causal Quantum Theory ((A)CQT) with an indefinite metric. Therefore, an (anti)causal neutral scalar field is not Hermitian, as one (anti)causal neutral scalar field consists of a non-Hermitian linear combination of two (Hermitian) acausal fields. Fundamental symmetries in (A)CQT are addressed. The quantum theoretical (transition) probability and antiparticle concepts are revised. Imaginary parts of cross sections and refraction indices are related.

Meryem El Kirdi, Hanane El Hadfi, L.B. Drissi +2 more

Bennett and his team pioneered the quantum teleportation protocol, a breakthrough where Alice transmits quantum information to Bob through a pre-shared entangled quantum channel. Remarkably, this transmission occurs without physically moving the information, relying on a combination of classical communication and quantum entanglement. This protocol not only demonstrates the essence of quantum entanglement but also underscores its potential in the realm of information transfer. The success of quantum teleportation experiments extends across various physical systems, with a particular emphasis on achieving effectiveness over long distances. Looking forward, future developments in this field may lead to multi-party protocols, thereby advancing both quantum communication and computing capabilities. A crucial component in quantum teleportation networks is controlled quantum teleportation (CQT), holding significant promise for the emerging concept of the quantum internet. In the preceding chapter, our exploration centered on the practical application of quantum teleportation protocols, with a specific focus on two key approaches: standard quantum teleportation and CQT. Our examination delved into the fundamental principles of quantum teleportation, encompassing critical concepts such as quantum entanglement, non-cloning, superposition, and the importance of measurements like fidelity. Throughout the chapter, we dedicated special attention to both the theoretical and experimental aspects of quantum teleportation, considering the intricacies of systems with continuous variables (CVs) as well as those with discrete variables (DVs).

Alex Kamenev