Square-root measurements and degradation of the resource state in port-based teleportation scheme

Abstract

Port-based teleportation (PBT) is a protocol of quantum teleportation in which a receiver does not have to apply correction to the transmitted state. In this protocol two spatially separated parties can teleport an unknown quantum state only by exploiting joint measurements on number of shared $d-$dimensional maximally entangled states (resource state) together with a state to be teleported and one way classical communication. In this paper we analyse for the first time the recycling protocol for the deterministic PBT beyond the qubit case. In the recycling protocol the main idea is to re-use the remaining resource state after one or many rounds of PBT for further processes of teleportation. The key property is to learn how much the underlying resource state degrades after every round of the teleportation process. We measure this by evaluating quantum fidelity between respective resource states. To do so we first present analysis of the square-root measurements used by the sender in PBT by exploiting the symmetries of the system. In particular, we show how to effectively evaluate their square-roots and composition. These findings allow us to present the explicit formula for the recycling fidelity involving only group-theoretic parameters describing irreducible representations in the Schur-Weyl duality. For the first time, we also analyse the degradation of the resource state for the optimal PBT scheme and show its degradation for all $d\geq 2$. In the both versions, the qubit case is discussed separately resulting in compact expression for fidelity, depending only on the number of shared entangled pairs.

Continuous variable port-based teleportation

“…This is maximised by setting P(r α ) to a delta function centred on 0. Thus, we recover equation (20).…”

“…For more details about how channel simulation can be used to bound the distinguishability of two channels, see [21]. Using equation (20) and bounding the trace norm between the resource states ϕ x± using the fidelity and the Fuchs-van de Graaf inequality, we get the plot in figure 4, which bounds the diamond norm between the channels in terms of δ. The extension to multiple channel uses is simple.…”

“…Ishizaka and Hiroshima introduced a new type of teleportation protocol, called port-based teleportation (PBT) [13,14], later studied and improved in a number of works [15][16][17][18][19][20]. In PBT, the sender and receiver share several entangled states (called ports), rather than one, and these collectively form the shared resource state.…”