En Route to the New Quan­tum World — Even one cen­tu­ry after its dis­cov­ery quan­tum physics still remains extreme­ly fas­ci­nat­ing. This is because the quan­tum world is so rad­i­cal­ly dif­fer­ent from the clas­si­cal world of our every­day expe­ri­ence. One of the most strik­ing and coun­ter­in­tu­itive prop­er­ties of quan­tum sys­tems is the pos­si­bil­i­ty to encode infor­ma­tion between the indi­vid­ual con­stituents, not in the con­stituents. Thanks to the many pos­si­ble con­cate­na­tions that are simul­ta­ne­ous­ly per­mit­ted between the con­stituents, quan­tum sys­tems can car­ry much more infor­ma­tion than clas­si­cal sys­tems. Only now one begins to under­stand the rev­o­lu­tion­ary pos­si­bil­i­ties which are opened up by such entan­gled sys­tems both for fun­da­men­tal inves­ti­ga­tions and nov­el appli­ca­tions.

Inves­ti­gat­ing the quan­tum world and mak­ing quan­tum effects avail­able for future appli­ca­tions in par­tic­u­lar in the pro­cess­ing of infor­ma­tion are main focal points of our research. The exper­i­ments essen­tial­ly fol­low two dif­fer­ent strate­gies: One is devot­ed to the devel­op­ment of inter­faces between the clas­si­cal world and the quan­tum world. ‘Work­hors­es’ are indi­vid­ual atoms and tai­lor-made pho­tons in opti­cal res­onators of the high­est qual­i­ty. Exam­ples of this research are the nov­el light sources devel­oped in our lab­o­ra­to­ry which at the push of a but­ton emit a bit stream of sin­gle pho­tons or even entan­gled pho­tons. We are also aim­ing to increase in a sys­tem­at­ic man­ner the size of our quan­tum sys­tems by adding one-at-a-time more and more atoms or pho­tons. In this way we want to find out if and how it is pos­si­ble to realise a dis­trib­uted quan­tum net­work or even a quan­tum inter­net, with sin­gle pho­tons exchang­ing infor­ma­tion between nodes.

This strat­e­gy of increas­ing the size of small sys­tems by step­wise adding addi­tion­al com­po­nents is com­ple­ment­ed by a sec­ond strat­e­gy which starts with a large sys­tem and which aims to improve the con­trol over the indi­vid­ual con­stituents. This work is large­ly per­formed with quan­tum gas­es at tem­per­a­tures close to absolute zero. Such gas­es dif­fer from clas­si­cal gas­es in that all atoms togeth­er form a gigan­tic mat­ter wave. They are ide­al­ly suit­ed to per­form quan­tum sim­u­la­tions and in this way explore open ques­tions of many-body physics. Com­pared to elec­trons in sol­id-state crys­tals, quan­tum gas­es have sev­er­al advan­tages, for exam­ple that the atoms and mol­e­cules we use are much eas­i­er to observe, that these move on length scales of microm­e­ters instead of nanome­ters, and that it is rel­a­tive­ly straight­for­ward to change the dimen­sion­al­i­ty of the sys­tem by freez­ing out the motion along cer­tain direc­tions. We also devel­op nov­el meth­ods to pro­duce and trap gaseous sam­ples of polar mol­e­cules like water at tem­per­a­tures below one Kelvin. With such gas­es we plan to inves­ti­gate nov­el class­es of chem­i­cal reac­tions at very low tem­per­a­tures, to name just one exam­ple.

Expe­ri­enc­ing the beau­ty and diver­si­ty of quan­tum physics in lab­o­ra­to­ry exper­i­ments and devel­op­ing the quan­tum tech­nol­o­gy of the future is a most reward­ing expe­ri­ence.


Ger­hard Rempe


ger­hard [.] rempe [@] mpq [.] mpg [.] de

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