Quan­tum Mem­o­ries are devices that can store the quan­tum state of a pho­ton, with­out destroy­ing the volatile quan­tum infor­ma­tion.

Quan­tum Mem­o­ries will be key com­po­nents in future quan­tum net­works, such as Quan­tum Repeaters which can pro­vide a solu­tion for long-dis­tance quan­tum com­mu­ni­ca­tion beyond the lim­it of 200 km using today’s tech­nol­o­gy. In addi­tion to future appli­ca­tions, Quan­tum Mem­o­ries are fas­ci­nat­ing because they pro­vide a way to study how quan­tum effects such as entan­gle­ment can be trans­ferred between phys­i­cal sys­tems of wide­ly dif­fer­ent nature, eg. between light and mat­ter sys­tems.

In our research we study light-mat­ter inter­ac­tions between pho­tons, in the vis­i­ble and telecom­mu­ni­ca­tions wave­length, with rare-earth-met­al ions doped into opti­cal crys­tals. These are high­ly inter­est­ing Quan­tum Mem­o­ry mate­ri­als since they have excel­lent coher­ence prop­er­ties when cooled to below 4 Kelvin. This is cru­cial in order to avoid destroy­ing the quan­tum inter­ac­tion through local inter­ac­tions such as with phonons. Using ideas devel­oped in our research we have achieved sev­er­al mile­stones, for exam­ple the first stor­age of a pseu­do sin­gle pho­tons, stor­age of mul­ti­ple pho­ton­ic qubits in a sin­gle neodymi­um-doped crys­tal, and more recent­ly stor­age of a vis­i­ble pho­ton entan­gled with a tele­com pho­ton.


Mikael Afzelius

Group leader

mikael [.] afzelius [@] unige [.] ch

per­son­al page and pub­li­ca­tions