---
tags: bell inequality, device independent, self-testing, robust self-testing, 2018, PRL2018
---

# [WIP][Certifying the building blocks of quantum computers from Bell's theorem](https://arxiv.org/abs/1802.02170)
Pavel Sekatski, Jean-Daniel Bancal, Sebastian Wagner, Nicolas Sangouard

## Abstract
The power of quantum computers relies on the capability of their components to maintain faithfully and process accurately quantum information. Since this property eludes classical certification methods, **fundamentally new protocols are required to guarantee that elementary components are suitable for quantum computation.** These protocols must be device-independent, that is, they cannot rely on a particular physical description of the actual implementation if one is to qualify a block for all possible usages. Bell's theorem has been proposed to certify, in a device-independent way, blocks either producing or measuring quantum states. In this manuscript, we provide the missing piece: **a method based on Bell's theorem to certify coherent operations such as storage, processing and transfer of quantum information.** This completes the set of tools needed to certify all building blocks of a quantum computer. Our method is robust to experimental imperfections, and so can be readily used to certify that today's quantum devices are qualified for usage in future quantum computers.

## Backgrounds and Contributions

> it is crucial to proceed in a scalable way and certify that each new component is qualified for use in a quantum computer
> Such a certification must be device-independent

> Here, we fill this gap by showing how to certify a trace preserving quantum channel acting on one or several systems


著者らはこのうちのquantum process unitの部分をcertifyしようとしている。quantum sourceとquantum measurementは既にcertifyされている。

> Our goal is in sharp contrast with a line of research aiming to the certification of quantum computations
> Our work addresses elementary blocks of a quantum computer and certify that they are qualified for use in future larger quantum devices.

## Methods

Device independent とは:
> We say that the channel E is certified deviceindependently if the sole knowledge of the results given the measurement choices implies the existence of local isometries

この論文もやっぱり[Kaniewski, 2016](https://hackmd.io/7slMbxWmQn-fMsCFX6gQmw)を使っている。

## Open Problems

Discussionには:
> Discussions– We have introduced a framework for the device-independent certification of quantum channels. We applied our methods to two families of channels, namely single qubit identity channels and two qubit controlled unitary operations. They are of key importance for quantum computing and quantum networks and the robustness of our recipes insures that they can readily be used in present-day experiments.

とある。特にfuture workは書かれていない。

ありうるのは、
- たとえば、multi-qubit演算などについて、似たようなことを応用できれば、論文になる...? 必要性が少し薄い気もする。 (by BOBO)