arXiv subjects
Publications and source records attributed to S. Kulik.
We report a design and implementation of a resource-efficient spatial demultiplexer which produces 4 indistinguishable photons with efficiency of 39.7% per channel. Our scheme is based on a free-space storage/delay line which accumulates 4 photons and releases them by a controlled polarization rotation using a single Pockels cell.
The novel experimental realization of three-level optical quantum systems is presented. We use the polarization state of biphotons to generate a specific sequence of states that are used in the extended version of BB84 protocol. We experimentally verify the orthogonality of the basis states and demonstrate the ability to easily switch between them. The tomography procedure is employed to reconstruct the density matrices of generated states.
Our last experimental results on the realization of a measurement-conditional unitary operation at single photon level are presented. This gate operates by rotating by $90^o$ the polarization of a photon produced by means of Type-II Parametric Down Conversion conditional to a polarization measurement on the correlated photon. We then propose a new scheme for measuring the quantum efficiency of a single photon detection apparatus by using this set-up. We present experimental results obtained with this scheme compared with {\it traditional} biphoton calibration. Our results show the interesting potentiality of the suggested scheme.
A conditioned unitary transformation ($90^o$ polarization rotation) is performed at single-photon level. The transformation is realized by rotating polarization for one of the photons of a polarization-entangled biphoton state (signal photon) by means of a Pockel's cell triggered by the detection of the other (idler) photon after polarization selection. As a result, polarization degree for the signal beam changes from zero to the value given by the idler detector quantum efficiency. This result is relevant to practical realization of various quantum information schemes and can be used for developing a new method of absolute quantum efficiency calibration.