A quan­tum
inter­net may very well be the first quan­tum infor­ma­tion tech­nol­o­gy to
become real­i­ty. Researchers at QuTech in Delft, The Nether­lands, today
pub­lished a com­pre­hen­sive guide towards this goal in Sci­ence.
It describes six phas­es, start­ing with sim­ple net­works of qubits that
could already enable secure quan­tum com­mu­ni­ca­tions – a phase that could
be real­i­ty in the near future. The devel­op­ment ends with net­works of
ful­ly quan­tum-con­nect­ed quan­tum com­put­ers. In each phase, new
appli­ca­tions become avail­able such as extreme­ly accu­rate clock
syn­chro­niza­tion or inte­grat­ing dif­fer­ent tele­scopes on Earth in one
vir­tu­al ‘superte­le­scope’. This work cre­ates a com­mon lan­guage that
unites the high­ly inter­dis­ci­pli­nary field of quan­tum net­work­ing towards
achiev­ing the dream of a world-wide quan­tum inter­net.

A
quan­tum inter­net will rev­o­lu­tion­ize com­mu­ni­ca­tion tech­nol­o­gy by
exploit­ing phe­nom­e­na from quan­tum physics, such as entan­gle­ment.
Researchers are work­ing on tech­nol­o­gy that enables the trans­mis­sion of
quan­tum bits between any two points on earth. Such quan­tum bits can be
‘0’ and ‘1’ at the same time, and can be ‘entan­gled’: their fates are
merged in such a way that an oper­a­tion on one of the qubits instant­ly
affects the state of the oth­er.

This brings two fea­tures which
are prov­ably out of reach for the Inter­net that we know today. The first
is that entan­gle­ment allows improved coor­di­na­tion between dis­tant
sites. This makes it extreme­ly suit­able for tasks such as clock
syn­chro­niza­tion or the link­ing of dis­tant tele­scopes to obtain bet­ter
images. The sec­ond is that entan­gle­ment is inher­ent­ly secure. If two
quan­tum bits are max­i­mal­ly entan­gled, then noth­ing else in the uni­verse
can have any share in that entan­gle­ment. This fea­ture makes entan­gle­ment
unique­ly suit­able for appli­ca­tions that require secu­ri­ty and pri­va­cy.

Many
oth­er appli­ca­tions of a quan­tum inter­net are already known, and more
are like­ly to be dis­cov­ered as the first net­works come online.
Researchers at QuTech, a col­lab­o­ra­tion between Delft Uni­ver­si­ty of
Tech­nol­o­gy and the Nether­lands organ­i­sa­tion for applied sci­en­tif­ic
research TNO have now set forth stages of quan­tum inter­net devel­op­ment
dis­tin­guished by tech­no­log­i­cal capa­bil­i­ties and cor­re­spond­ing
appli­ca­tions. 

The low­est stage of a true quan­tum net­work – a
pre­pare and mea­sure net­work – allows the end-to-end deliv­ery of quan­tum
bits between any two net­work nodes, one quan­tum bit at a time. This is
already suf­fi­cient to sup­port many cryp­to­graph­ic appli­ca­tions of a
quan­tum net­work. The high­est stage is the long-term goal of con­nect­ing
large quan­tum com­put­ers on which arbi­trary quan­tum appli­ca­tions can be
exe­cut­ed. 

In
addi­tion to pro­vid­ing a guide to fur­ther devel­op­ment, the work sets
chal­lenges both to engi­neer­ing efforts and to the devel­op­ment of
appli­ca­tions. “On the one hand, we would like to build ever more
advanced stages of such at net­work”, says Stephanie Wehn­er, lead author
of the work, “On the oth­er hand, quan­tum soft­ware devel­op­ers are
chal­lenged to reduce the require­ments of appli­ca­tion pro­to­cols so they
can be real­ized already with the more mod­est tech­no­log­i­cal capa­bil­i­ties
of a low­er stage.” Co-author Ronald Han­son adds: “This work estab­lish a
much-need­ed com­mon lan­guage between the high­ly inter­dis­ci­pli­nary field
of quan­tum net­work­ing span­ning physics, com­put­er sci­ence and
engi­neer­ing.”

The first true quan­tum net­works, allow­ing the
end-to-end trans­mis­sion of quan­tum bits, are expect­ed to be real­ized in
the com­ing years, herald­ing the dawn of a large-scale quan­tum inter­net.