Experimental implementation of the optimal linear-optical controlled phase gate

We report on the first experimental realization of optimal linear-optical controlled phase gates for arbitrary phases. The realized scheme is entirely flexible in that the phase shift can be tuned to any given value. All such controlled phase gates are optimal in the sense that they operate at the maximum possible success probabilities that are achievable within the framework of any postselected linear-optical implementation. The quantum gate is implemented using bulk optical elements and polarization encoding of qubit states. We have experimentally explored the remarkable observation that the optimum success probability is not monotone in the phase.Comment: 4 pages, 5 figures, 1 tabl

Optical implementation of the encoding of two qubits to a single qutrit

We have devised an optical scheme for the recently proposed protocol for encoding two qubits into one qutrit. In this protocol, Alice encodes an arbitrary pure product state of two qubits into a state of one qutrit. Bob can then restore error-free any of the two encoded qubit states but not both of them simultaneously. We have successfully realized this scheme experimentally using spatial-mode encoding. Each qubit (qutrit) was represented by a single photon that could propagate through two (three) separate fibers. We theoretically propose two generalizations of the original protocol. We have found a probabilistic operation that enables to retrieve both qubits simultaneously with the average fidelity above 90% and we have proposed extension of the original encoding transformation to encode N qubits into one (N+1)-dimensional system.Comment: 6 pages, 3 figures, RevTeX

Experimental realization of linear-optical partial SWAP gates

We present a linear-optical implementation of a class of two-qubit partial SWAP gates for polarization states of photons. Different gate operations, including the SWAP and entangling square root of SWAP, can be obtained by changing a classical control parameter -- namely the path difference in the interferometer. Reconstruction of output states, full process tomography and evaluation of entanglement of formation prove very good performance of the gates.Comment: 4 pages, 4 figures, RevTeX

Creation of lateral structures in diblock copolymer thin films during vapor uptake and subsequent drying - effect of film thickness

We have studied the structure formation in compositionally nearly symmetric poly(4-octylstyrene-b-butylmethacrylate) diblock copolymer films during exposure to saturatedvapor of n-hexane (a poor solvent for both blocks) and subsequent drying using real-time,in situ grazing-incidence small-angle X-ray scattering (GISAXS). Previous bulk studiesrevealed a lamellar structure after thermo-annealing; and surface studies on hexane treatedsamples revealed a lateral surface structure (Cernoch et al., 2007) [14]. We focus hereon the effect of film thickness which is varied between 1.3 and 2.0 times the bulk lamellarthickness. We report on the lateral repeat distance as well as on the correlation length inthe film plane. Complex, non-monotonous behavior is observed for both parameters. Upondrying, the lateral structure created during vapor treatment is stable only for the thick film,not for the intermediate and the thin film. The kinetics depends strongly on the film thickness;especially for the thinnest film, it is very slow. For all film thicknesses, we attempt toidentify the most stable morphology, occurring when the inner film structure is close to theone in the bulk