Experimental temporal quantum steering

We have studied both theoretically and experimentally a quantum phenomenon of temporal steering of a quantum state. This phenomenon is a temporal analog of a spatial quantum steering known earlier and it has direct impact to the area of security of quantum communications. We performed experimental tests, based on the violation of temporal steering inequalities, of the security of two quantum key distribution protocols. Thus, these results can lead to applications for secure quantum communications and quantum engineering.

Here we use abbreviations: BS for beam splitter, PBS for polarising BS, NDF for neutral density filter of tunable transmittance τ, BDn for beam dividers, PCn for the polarisation controllers compensating polarisation rotation in the fibers, Qn for quarter-wave plates, Hn for half-wave plates, SPCM for single-photon counting module, SM for the 15 m long single-mode optical fiber which forms a delay line of t = 80 ns (this is larger than the 50 ns long dead time of the SPCM). Alice prepares the initial state by rotating a H-polarised photon with QA and HA plates. Bob performs state analysis by setting his measurement basis with HB and QB, and detecting the incoming photon in one of the orthogonal polarisation states.

¹Faculty of Physics, Adam Mickiewicz University, PL-61-614 Poznań, Poland
²RCPTM, Joint Laboratory of Optics of Palacký University and Institute of Physics of the Czech Academy of Sciences, 17. listopadu 12, 772 07 Olomouc, Czech Republic
³Institute of Physics of the Czech Academy of Sciences, Joint Laboratory of Optics of Palacký University and Institute of Physics of the Czech Academy of Sciences, 17. listopadu 50A, 77207 Olomouc, Czech Republic
⁴CEMS, RIKEN, 351-0198 Wako-shi, Japan
⁵Department of Physics, The University of Michigan, Ann Arbor, MI 48109-1040, USA