# Communicating without shared reference frames

## TL;DR

This paper extends quantum communication protocols to scenarios where communicating parties lack a shared reference frame, analyzing how reference frame changes affect information transfer and recovery.

## Contribution

It generalizes a quantum communication protocol to noncompact Lie groups, detailing how reference frame uncertainties impact state recovery.

## Key findings

- The protocol's effectiveness depends on the reference token properties.
- Fidelity quantifies the success of state recovery.
- Analysis applied to translation group reference frames.

## Abstract

We generalize a quantum communication protocol introduced by Bartlett et al. [New. J. Phys. 11, 063013 (2009)] in which two parties communicating do not share a classical reference frame, to the case where changes of their reference frames form a one-dimensional noncompact Lie group. Alice sends to Bob the state $\rho_R \otimes \rho_S$, where $\rho_S$ is the state of the system Alice wishes to communicate and $\rho_R$ is the state of an ancillary system serving as a token of her reference frame. Because Bob is ignorant of the relationship between his reference frame and Alice's, he will describe the state $\rho_R \otimes \rho_S$ as an average over all possible reference frames. Bob measures the reference token and applies a correction to the system Alice wished to communicate conditioned on the outcome of the measurement. The recovered state $\rho_S'$ is decohered with respect to $\rho_S$, the amount of decoherence depending on the properties of the reference token $\rho_R$. We present an example of this protocol when Alice and Bob do not share a reference frame associated with the one-dimensional translation group and use the fidelity between $\rho_S$ and $\rho_S'$ to quantify the success of the recovery operation.