Editing Quantum key distribution (section)

=== Device-independent quantum key distribution ===
In traditional QKD, the quantum devices used must be perfectly calibrated, trustworthy, and working exactly as they are expected to.<ref name=":1">{{Cite journal |last1=Nadlinger |first1=D. P. |last2=Drmota |first2=P. |last3=Nichol |first3=B. C. |last4=Araneda |first4=G. |last5=Main |first5=D. |last6=Srinivas |first6=R. |last7=Lucas |first7=D. M. |last8=Ballance |first8=C. J. |last9=Ivanov |first9=K. |last10=Tan |first10=E. Y.-Z. |last11=Sekatski |first11=P. |last12=Urbanke |first12=R. L. |last13=Renner |first13=R. |last14=Sangouard |first14=N. |last15=Bancal |first15=J.-D. |date=July 2022 |title=Experimental quantum key distribution certified by Bell's theorem |url=https://www.nature.com/articles/s41586-022-04941-5 |journal=Nature |language=en |volume=607 |issue=7920 |pages=682–686 |doi=10.1038/s41586-022-04941-5 |pmid=35896644 |issn=1476-4687|arxiv=2109.14600 |bibcode=2022Natur.607..682N |s2cid=251131731 }}</ref> Deviations from expected measurements can be extremely hard to detect, which leaves the entire system vulnerable. A new protocol called device independent QKD (DIQKD) or measurement [[device-independent quantum key distribution|device independent QKD]] (MDIQKD) allows for the use of uncharacterized or untrusted devices, and for deviations from expected measurements to be included in the overall system.<ref name=":1" /><ref name=":2">{{Cite journal |last1=Zhang |first1=Wei |last2=van Leent |first2=Tim |last3=Redeker |first3=Kai |last4=Garthoff |first4=Robert |last5=Schwonnek |first5=René |last6=Fertig |first6=Florian |last7=Eppelt |first7=Sebastian |last8=Rosenfeld |first8=Wenjamin |last9=Scarani |first9=Valerio |last10=Lim |first10=Charles C.-W. |last11=Weinfurter |first11=Harald |date=July 2022 |title=A device-independent quantum key distribution system for distant users |journal=Nature |language=en |volume=607 |issue=7920 |pages=687–691 |doi=10.1038/s41586-022-04891-y |pmid=35896650 |pmc=9329124 |arxiv=2110.00575 |bibcode=2022Natur.607..687Z |issn=1476-4687|doi-access=free }}</ref> These deviations will cause the protocol to abort when detected, rather than resulting in incorrect data.<ref name=":1" />

DIQKD was first proposed by Mayers and Yao,<ref>{{Cite arXiv|last1=Mayers |first1=Dominic |last2=Yao |first2=Andrew |date=1998-09-14 |title=Quantum Cryptography with Imperfect Apparatus  |eprint=quant-ph/9809039  }}</ref> building off of the BB84 protocol. They presented that in DIQKD, the quantum device, which they refer to as the photon source, be manufactured to come with tests that can be run by Alice and Bob to "self-check" if their device is working properly. Such a test would only need to consider the classical inputs and outputs in order to determine how much information is at risk of being intercepted by Eve. A self checking, or "ideal" source would not have to be characterized,<ref name=":2" /><ref>{{Cite journal |last1=Schwonnek |first1=René |last2=Goh |first2=Koon Tong |last3=Primaatmaja |first3=Ignatius W. |last4=Tan |first4=Ernest Y.-Z. |last5=Wolf |first5=Ramona |last6=Scarani |first6=Valerio |last7=Lim |first7=Charles C.-W. |date=2021-05-17 |title=Device-independent quantum key distribution with random key basis |journal=Nature Communications |language=en |volume=12 |issue=1 |pages=2880 |doi=10.1038/s41467-021-23147-3 |pmid=34001885 |pmc=8128898 |arxiv=2005.02691 |bibcode=2021NatCo..12.2880S |issn=2041-1723|doi-access=free }}</ref> and would therefore not be susceptible to implementation flaws.<ref name=":2" />

Recent research has proposed using a Bell test to check that a device is working properly.<ref name=":1" /> Bell's theorem ensures that a device can create two outcomes that are exclusively correlated, meaning that Eve could not intercept the results, without making any assumptions about said device. This requires highly entangled states, and a low quantum bit error rate.<ref name=":2" /> DIQKD presents difficulties in creating qubits that are in such high quality entangled states, which makes it a challenge to realize experimentally.<ref name=":1" />