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 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.
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.
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.
Although entanglement is necessary for observing nonlocality in a Bell experiment, there are entangled states that can never be used to demonstrate nonlocal correlations.In a seminal paper Buscemi [Phys.Rev. Lett.108, 200401 (2012)] extended the standard Bell experiment by allowing Alice and Bob to be asked quantum, instead of classical, questions.This gives rise to a broader notion of nonlocality, one which can be observed for every entangled state.In this work we study a resource theory of this type of nonlocality referred to as Buscemi nonlocality.We propose a geometric quantifier measuring the ability of a given state and local measurements to produce Buscemi nonlocal correlations and prove the following results.First, we show that any distributed measurement that can demonstrate Buscemi nonlocal correlations provides strictly better performance than any distributed measurement that does not use entanglement in the task of distributed state discrimination, and that this advantage is quantified by the geometric quantifier we propose, thus establishing its operational significance.Second, we prove a quantitative relationship between Buscemi nonlocality, the ability to perform nonclassical teleportation, and entanglement.In particular, we show that the maximal amount of Buscemi nonlocality that can be generated using a given state is precisely equal to its entanglement content.Using this relationship, we propose new discrimination tasks for which nonclassical teleportation and entanglement lead to an advantage over their classical counterparts.Third, we interpret Buscemi nonlocality from the perspective of information theory and show that it is related to a single-shot capacity of a quantum-to-classical bipartite channel.
Although entanglement is necessary for observing nonlocality in a Bell experiment, there are entangled states which can never be used to demonstrate nonlocal correlations. In a seminal paper [PRL 108, 200401 (2012)] F. extended the standard Bell experiment by allowing Alice and Bob to be asked quantum, instead of classical, questions. This gives rise to a broader notion of nonlocality, one which can be observed for every entangled state. In this work we introduce and study a resource theory of this type of nonlocality which we term Buscemi nonlocality. We propose a geometric quantifier measuring the ability of a given state and local measurements to produce nonlocal correlations and establish its operational significance. In particular, we show that any distributed measurement which can demonstrate nonlocal correlations provides strictly better performance than any distributed measurement which does not use entanglement in the task of distributed state discrimination. We also show that the maximal amount of nonlocality that can be generated using a given state is precisely equal to its entanglement content. Finally, we prove a quantitative relationship between: nonlocality, the ability to perform nonclassical teleportation, and entanglement. Using this relationship we propose new discrimination tasks for which nonclassical teleportation and entanglement lead to an advantage over their classical counterparts.
We consider a scenario where a party, say, Alice prepares a pure two-qubit (either maximally entangled or nonmaximally entangled) state and sends one half of this state to another distant party, say, Bob through a qubit (either unital or nonunital) channel. Finally, the shared state is used as a teleportation channel. In this scenario, we focus on characterizing the set of qubit channels with respect to the final state's efficacy as a resource of quantum teleportation (QT) in terms of maximal average fidelity and fidelity deviation (fluctuation in fidelity values over the input states). Importantly, we point out the existence of a subset of qubit channels for which the final state becomes useful for universal QT (having maximal average fidelity strictly greater than the classical bound and having zero fidelity deviation) when the initially prepared state is either useful for universal QT (i.e., for a maximally entangled state) or not useful for universal QT (i.e., for a subset of nonmaximally entangled pure states). Interestingly, in the latter case, we show that nonunital channels (dissipative interactions) are more effective than unital channels (nondissipative interactions) in producing useful states for universal QT from nonmaximally entangled pure states.
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.