Quantum-optics experiments in Olomouc Jan Soubusta, Martin Hendrych, Jan Peřina, Jr., Ondřej Haderka Radim Filip, Jaromír Fiurášek, Miloslav Dušek Antonín Černoch, Miroslav Gavenda, Eva Kachlíková, Lucie Bartůšková Palacký University & Institute of Physics of AS CR

Quantum identification system §M. Dušek et al, Phys. Rev. A 60, 149 (1999). 830 nm 100kHz Visibility >99.5% Losses < 4.5dB Rate: 4.3 kbits/s Error rate: 0.3% <1ph.pp 0.5 km QIS combines classical identification procedure and quantum key distribution. Dim laser pulses as a carrier of information.

Experiments with entangled photons produced by down- conversion in non-linear crystal pumped by Kr + laser §M. Hendrych et al, Simple optical measurement of the overlap and fidelity of quantum states, Phys. Lett. A 310, 95 (2003). §J. Soubusta et al, Experimental verification of energy correlations in entangled photon pairs, Phys. Lett. A 319, 251 (2003). §J. Soubusta et al, Experimental realization of a programmable quantum-state discriminator and a phase-covariant quantum multimeter, Phys. Rev. A 69, (2004). §R. Filip et al, How quantum correlations enhance prediction of complementary measurements, Phys. Rev. Lett. 93, (2004).

Simple optical measurement of the overlap and fidelity of quantum states

Experimental tests of energy and time quantum correlations in photon pairs

2 nd order interference. Reduction of the spectrum induces prolongation of the coherence length. Geometric filtering (FWHM=5.3 nm). Narrow band interference filter (FWHM of 1.8 nm). Fabry-Perot rezonator. 4 th order interference. Hong-Ou-Mandel interference dip

Programmable quantum-state discriminator

Phase-covariant quantum multimeter Quantum multimeters – measurement basis determined by a quantum state of a “program register” Phase-covariant multimeters – success probability independent of 

§Programmable discriminator of unknown non-orthogonal polarization states of photon §Phase-covariant quantum multimeter

Programmable discriminator Parameters of the polarization states: ellipticity tan  and orientation

Phase-covariant quantum multimeter

How quantum correlations enhance prediction of complementary measurements The measurement on the one of two correlated particles give us the power of prediction of the measurement results on the other one. Of course, one can never predict exactly the results of two complementary measurements at once. However, knowing what kind of measurement we want to predict on signal particle, we can choose the optimal measurement on the meter particle. But there is still a fundamental limitation given by the sort and amount of correlations between the particles. Both of these kinds of constraints are quantitatively expressed by our inequality. The limitation stemming from mutual correlation of particles manifests itself by the maximal Bell factor appearing in the inequality. We have proved this inequality theoretically as well as tested it experimentally

How quantum correlations enhance prediction of complementary measurements Polarization two-photon mixed states: Werner states with the mixing parameter p. Theoretical knowledge excess: Theoretical Bell factor:

 0.82 p  0.82 B max =2.36  0.45 p  0.45 B max =1.32

Optical implementation of the encoding of two qubits into a single qutrit A qutrit in a pure state is specified by four real numbers. The same number of parameters is necessary to specify two qubits in a pure product state. Encoding transformation: Any of the two encoded qubit states can be error-free restored but not both of them simultaneously. Decoding projectors: qubits qutrit

States of qubits: State of qutrit: Additional damping factor:

Observed fidelities of reconstructed qubit states forvarious input states.

Optical implementation of the optimal phase-covariant quantum cloning machine Exact copying of unknown quantum states is forbidden by the linearity of quantum mechanics. Approximate cloning machines are possible and many implementations for qubits, qudits and continuous variables were recently designed. If the qubit states lie exclusively on the equator of the Bloch sphere, then the optimal phase-covariant cloner exhibits better cloning fidelity than the universal cloning machine.

Optical implementation of the optimal phase-covariant quantum cloning machine

Another approach to optical implementation of phase-covariant clonning fiber Polarization-dependent loses

Correction of noise and distorsions of quantum signals sent through imperfect

Other cooperating groups Experimental multi-photon-resolving detector using a single avalanche photodiode Study of spatial correlations and photon statistics in twin beams generated by down conversion pumped by a pulsed laser The End