Experimental Study of Nonclassical Teleportation Beyond Average Fidelity
Gonzalo Carvacho, Francesco Andreoli, Luca Santodonato, Marco Bentivegna, Vincenzo D’Ambrosio, Paul Skrzypczyk, Ivan Šupić, Daniel Cavalcanti, Fabio Sciarrino
Quantum teleportation establishes a correspondence between an entangled state shared by two separate parties that can communicate classically and the presence of a quantum channel connecting the two parties. The standard benchmark for quantum teleportation, based on the average fidelity between the input and output states, indicates that some entangled states do not lead to channels which can be certified to be quantum. It was recently shown that if one considers a finer-grained witness, then all entangled states can be certified to produce a nonclassical teleportation channel. Here we experimentally demonstrate a complete characterization of a new family of such witnesses, of the type proposed in Phys. Rev. Lett. 119, 110501 (2017)PRLTAO0031-900710.1103/PhysRevLett.119.110501 under different conditions of noise. We report nonclassical teleportation using quantum states that cannot achieve average fidelity of teleportation above the classical limit. We further use the violation of these witnesses to estimate the negativity of the shared state. Our results have fundamental implications in quantum information protocols and may also lead to new applications and quality certification of quantum technologies.
Quantum teleportation establishes a correspondence between an entangled state shared by two separate parties that can communicate classically and the presence of a quantum channel connecting the two parties. The standard benchmark for quantum teleportation, based on the average fidelity between the input and output states, indicates that some entangled states do not lead to channels which can be certified to be quantum. It was recently shown that if one considers a finer-grained witness, then all entangled states can be certified to produce a nonclassical teleportation channel. Here we experimentally demonstrate a complete characterization of a new family of such witnesses, of the type proposed in Phys. Rev. Lett. 119, 110501 (2017)PRLTAO0031-900710.1103/PhysRevLett.119.110501 under different conditions of noise. We report nonclassical teleportation using quantum states that cannot achieve average fidelity of teleportation above the classical limit. We further use the violation of these witnesses to estimate the negativity of the shared state. Our results have fundamental implications in quantum information protocols and may also lead to new applications and quality certification of quantum technologies.
Quantum teleportation, the process by which Alice can transfer an unknown quantum state to Bob by using preshared entanglement and classical communication, is one of the cornerstones of quantum information. The standard benchmark for certifying quantum teleportation consists in surpassing the maximum average fidelity between the teleported and the target states that can be achieved classically. According to this figure of merit, not all entangled states are useful for teleportation. Here we propose a new benchmark that uses the full information available in a teleportation experiment and prove that all entangled states can implement a quantum channel which cannot be reproduced classically. We introduce the idea of nonclassical teleportation witness to certify if a teleportation experiment is genuinely quantum and discuss how to quantify this phenomenon. Our work provides new techniques for studying teleportation that can be immediately applied to certify the quality of quantum technologies.
How to properly certify the quantum function of a quantum process (device) is one of the key problems in quantum information science, particularly, for a function beyond its classical counterpart. To properly verify quantum teleportation is a critical task because of its fundamental roles in quantum communication and quantum computation. Here, we experimentally certified nonclassical quantum teleportation with one setting by the random teleportation robustness introduced by [Phys. Rev. Lett. 119, 110501 (2017)]. Our results show that the random teleportation robustness is experimentally convenient and powerful for verifying nonclassical teleportation and entanglement.
The standard benchmark for teleportation is the average fidelity of teleportation and according to this benchmark not all states are useful for teleportation.It was recently shown, however, that all entangled states lead to nonclassical teleportation, with there being no classical scheme able to reproduce the states teleported to Bob.Here we study the operational significance of this result.On the one hand, we demonstrate that every state is useful for teleportation if a generalization of the average fidelity of teleportation is considered which concerns teleporting quantum correlations.On the other hand, we show the strength of a particular entangled state and entangled measurement for teleportation-as quantified by the robustness of teleportation-precisely characterizes their ability to offer an advantage in the task of subchannel discrimination with side information.This connection allows us to prove that every entangled state outperforms all separable states when acting as a quantum memory in this discrimination task.Finally, within the context of a resource theory of teleportation, we show that the two operational tasks considered provide complete sets of monotones for two partial orders based on the notion of teleportation simulation, one classical and one quantum.
The conventional certification method for quantum teleportation protocols relies on surpassing the highest achievable classical average fidelity between target and teleported states. Our paper highlights the limitations of this approach: inconsistent conclusions can be obtained when considering different distance measures in the quantum state space, leading to contradictory interpretations. In particular, this behavior is manifested when modeling a very common noisy experimental scenario, in which the resource state takes the form of a Werner state generated by the influence of a depolarizing channel acting on the Bell state resource. Two additional noise models, based on amplitude-damping channels, are also analyzed. Our paper, therefore, stresses the necessity of new certification methods for quantum teleportation.
Quantum teleportation, a cornerstone of quantum information science, allows for the transfer of an unknown quantum state from a sender (Alice) to a receiver (Bob) using a shared entangled resource and classical communication. A fundamental challenge arises when the state to be teleported is unclonable, as dictated by the no-cloning theorem, precluding direct comparison between the initial and teleported states for certification. This paper proposes a robust Bell-certification scheme for validating the successful teleportation of such unclonable quantum states. We move beyond conventional fidelity benchmarks, which prove insufficient for unknown states, by focusing on the integrity of the Bell state entanglement and the correctness of the Bell measurement performed by Alice. Our methodology leverages the inherent properties of maximally entangled Bell states as the resource, combined with a verifiable Bell measurement analysis and a rigorous assessment of the classical communication channel. We detail how the quality of the shared entangled pair, potentially characterized by entanglement witnesses or purity measures, directly contributes to the certification of the teleportation process. Furthermore, we analyze the scheme's resilience to common noise models, such as depolarizing channels affecting the resource state, demonstrating how fluctuations in resource entanglement propagate to the certification confidence. The proposed Bell-certification provides a crucial framework for ensuring the reliability of quantum teleportation protocols in practical applications where direct state verification is impossible or impractical, paving the way for more secure and verifiable quantum communication and computation architectures.
Abstract The superposition principle provides us the opportunity to unfold many surprising facts. One such fact leads to the generation of entanglement which may allow one to teleport an unknown quantum state from one location to another. We try to understand the role of superposition in the process of quantum teleportation, as a question of potentially fundamental importance. We consider, within the scenario of quantum teleportation, a set-up where the sender and the receiver are in a superposed situation of using a maximally entangled state and not using any entangled state in the teleportation protocol, controlled by a qubit. We address two distinct protocols: in the first case, the sender and the receiver do nothing when they do not have the authority to use entanglement, while in the second case, they still use classical communication even if they do not use entanglement. After accomplishing the protocols, we operate a Hadamard gate on the control qubit, measure the control qubit’s state, and consider the outcome corresponding to a particular state of the control. We compare the protocol’s fidelity with the maximum fidelity achievable through classical resources only. In particular, we provide conditions to achieve nonclassical fidelity in teleportation, in the presence of the control qubit. To explore if there is any quantum advantage (advantage of superposition present in the control qubit), we compare the fidelities of the control qubit-based protocols with the fidelity achieved in a situation where the two parties are in a classical mixture of using and not using the maximally entangled state. We observe that there exists a wide range of parameters defining the initial state of the control qubit for which our protocols provide quantum advantage. To analyse the role of superposition quantitatively, we discuss whether the amount of quantum advantage can be expressed in terms of quantum coherence present in the state of the control qubit.