Unambiguous arbitrary high-dimensional Bell states analyzer via indefinite causal order

TL;DR

This paper introduces a method for fully and deterministically distinguishing high-dimensional Bell states using indefinite causal order, enabling nondestructive quantum state analysis for quantum communication.

Contribution

It presents a novel high-dimensional Bell-state analyzer leveraging indefinite causal order, which is deterministic, nondestructive, and applicable to arbitrary dimensions.

Findings

Complete discrimination of high-dimensional Bell states achieved.

Indefinite causal order used as a resource without being consumed.

Nondestructive analysis possible through iterative process.

Abstract

High-dimensional quantum systems greatly outperform their two-dimensional counterparts in channel capacity, quantum complexity and efficiency, quantum communication security, etc. Bell-state analyzer (BSA) is a crucial prerequisite for a number of quantum communication protocols. We propose an approach for completely and deterministically distinguishing a set of arbitrary $d$-dimensional ($d \geq 3$) Bell states via indefinite causal order (ICO). In previous schemes, bit and phase information are discriminated in succession. Exploiting the gravitational ICO as the sole resource, we propose some high-dimensional BSA schemes. Independent of the dimensions, a set of generalized Bell states are completely and deterministically discriminated by adjusting the form of the embedded local single-qudit gates within ICO switch and measuring each qudit in the $\{|0\rangle, |1\rangle, \cdots, |d-1\rangle\}$ basis. Notably, in our high-dimensional BSA process, the indefinite causal structure is not consumed. Hence a completely nondestructive high-dimensional BSA can be achieved by iterating the indefinite causal structure process for two rounds.