Quantum-optics experiments in Olomouc

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

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

3. 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, 052321 (2004). • R. Filip et al, How quantum correlations enhance prediction of complementary measurements, Phys. Rev. Lett. 93, 180404 (2004).

4. Simple optical measurement of the overlap and fidelity of quantum states

5. Simple optical measurement of the overlap and fidelity of quantum states

6. Experimental testsof energy and time quantumcorrelationsin photon pairs

7. Experimental testsof energy and time quantumcorrelationsin photon pairs

8. 2nd 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. 4th order interference. Hong-Ou-Mandel interference dip

9. Programmable quantum-state discriminator

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

11. Programmablediscriminator ofunknownnon-orthogonalpolarizationstatesof photon • Phase-covariant quantum multimeter

12. Programmable discriminator Parameters of the polarization states: ellipticitytan  and orientation

13. Phase-covariant quantum multimeter

14. How quantum correlations enhance prediction of complementary measurements The measurement on the one of two correlated particlesgive us the power of prediction of the measurementresults on the other one. Of course, one can never predictexactly the results of two complementary measurementsat once. However, knowing what kind of measurement wewant to predict on signal particle, we can choose theoptimal measurement on the meter particle. But there isstill a fundamental limitation given by the sort andamount of correlations between the particles. Both ofthese kinds of constraints are quantitatively expressedby our inequality. The limitation stemming frommutual correlation of particles manifests itself by themaximal Bell factor appearing in the inequality. Wehave proved this inequality theoretically as well as testedit experimentally

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

17. p 0.82 Bmax=2.36 p 0.45 Bmax=1.32

18. Optical implementation of the encoding of two qubits into a single qutrit • A qutrit ina pure state is specified by four real numbers.The same number of parametersis 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

19. States of qubits: • State of qutrit: • Additional damping factor:

20. Observed fidelities of reconstructed qubit states forvarious input states.

22. 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.

23. Optical implementation of the optimal phase-covariant quantum cloning machine

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

27. Correction of noise and distorsions of quantum signals sent through imperfect

28. 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