The group theoretical aspect of the description of passive lossless optical four-ports (beam splitters) is revisited. It is shown through an example, that this approach can be useful in understanding interferometric schemes where a low number of photons interfere. The formalism is extended to passive lossless optical six-ports, their SU(3)-theory is outlined.
We propose a setup for teleportation of continuous quantum variables which is optimized for teleportation of squeezed coherent states. Our scheme is a modified version of the original setup proposed by Braunstein and Kimble [Phys. Rev. Lett. 80, 869, 1998] and it involves an unbalanced beam splitter on the sender's side and a single mode squeezer on receiver's side. We show that the quality of the teleportation can be evaluated by means of a fidelity of entanglement swapping and we prove that our modified setup and the original Braunstein-Kimble setup are equivalent with respect to this fidelity measure.
We study teleportation of qubits with imperfect Bell analysis on the sender's side. For the chosen family of Alice's measurements we find Bob's operations maximizing the overall fidelity of the teleportation protocol. In certain cases the optimum maps turn out to be nonunitary operations. This means that decoherence can sometimes enhance the performance of quantum teleportation protocols.
Neutrons are proper tools for testing quantum mechanics because they are massive, they couple to electromagnetic fields due to their magnetic moment and they are subject to all basic interactions and they are sensitive to topological effects, as well. Related experiments will be discussed. Deterministic and stochastic partial absorption experiments can be described by Bell-type inequalities. Recent neutron interferometry experiments based on postselection methods renewed the discussion about quantum nonlocality and the quantum measuring process. It has been shown that interference phenomena can be revived even when the overall interference pattem has lost its contrast. This indicates a persisting coupling in phase space even in cases of spatially separated Schrödingercat-like situations. These states are extremely fragile and sensitive against any kind of fluctuations and other decoherence processes. More complete quantum experiments also show that a complete retrieval of quantum states behind an interaction volume becomes impossible in principle. First results of neutron quantum state reconstruction experiments will be presented.
Neutron interferometer experiments have served as elegant demonstrations of the foundations of quantum mechanics. We show here two interferometer-experiments: one is the demonstration of a geometric phase in a split-beam experiment and the other is the measurement of off-diagonal geometric phase acquired in an evolution of a 1/2-spin system. The former was accomplished with the use of a two-loop neutron interferometer, where a reference beam can be added to the beam from one interference ioop. The combination of phase shifters and partial absorbers permitted the compensation of the dynamical phase and measurement of the geometric phase. The latter is investigated by means of a polarized neutron interferometer. Final counts with and without the polarization analysis enabled us to observe both the off-diagonal and diagonal geometric phases in two detectors. All experimental results show complete agreement with theoretical treatments.
The time evolution of an unstable quantum system coupled with an external "measuring" apparatus is investigated. A quantum Zeno effect (hindered decay) or an inverse quantum Zeno effect (accelerated decay) may take place, depending on the features of the coupling and the response time of the apparatus. The transition between the two regimes is analyzed.
We analyze a double-slit experiment when the interfering particle is "mesoscopic" and one endeavors to obtain Weicher Weg information by shining light on it. We derive a compact expression for the visibility of the interference pattern: coherence depends on both the spatial and temporal features of the wave function during its travel to the screen. We set a bound on the temperature of the mesoscopic particle in order that its quantum mechanical coherence be maintained.
We analyze some interesting and peculiar phenomena that appear both in the well-known classical domain and in the quantum domain, related to the behavior of the visibility in interference experiments. One can show that, according to its usual definition, the visibility is not a monotonic function of appropriate quantities, such as the optical path difference. In the quantum domain, the visibility can be used to infer the quantum mechanical coherence properties of a quantum particle, like for example a neutron, interacting with a fluctuating environment. In some cases the wave function is more coherent even though it has interacted with a more disordered medium. We will refer to these results as anomalous, because they are against naive expectations.
The simultaneous inseparable reconstruction of quantum process and states is presented. The method is based on constrained extremization of the likelihood functional. This statistical approach is ingenuous in quantum mechanical frame and ensures physically correct results. Adopted scheme predicts the input density operators and the operator of quantum process all at once with help of noisy measured data only. Attention is paid to the comparison of posed method with sequential measurement of the states and the process. Method is illustrated by numerical simulations.
This paper proposes another application for the joint transform correlator. The principle of the correlator could be used for determination of a relative translation of two speckle patterns. An optical processor based on this architecture is designed. Such processor could be a part of an optical system for a noncontact measurement of object translations, rotations or normal vibrations. This paper is devoted to operation simulation of the optical processor. Firstly, the theoretical description of the processor is made. Then follows a depiction of the preparation of input data for the simulation analysis. The detailed results of the simulation can be found in the last part ofthe paper
This overview paper deals with the statistical properties of a speckle pattern. After the introduction, in which the speckle and its origin is shortly described, the first-order statistics of a polarized speckle pattern are derived. Further, a special case of the sum of a speckle pattern and a coherent background is briefly mentioned. The first-order statistics of this special case are presented, too.
We design a universal quantum homogenizer, which is a quantum machine that takes as an input a system qubit initially in the state ? and a set of N reservoir qubits initially prepared in the same state ?. In the homogenizer the system qubit sequentially interacts with the reservoir qubits via the partial swap transformation. The homogenizer realizes, in the limit sense, the transformation such that at the output each qubit is in an arbitratily small neighbourhood of the state ? irrespective of the initial states of the system and the reservoir qubits. This means that the system qubit undergoes an evolution that has a fixed point, which is the reservoir state ?. We also study approximate homogenization when the reservoir is composed of a finite set of identically prepared qubits. The homogenizer allows us to understand various aspects of the dynamics of open systems interacting with environments in non-equilibrium states. In particular, the reversibility vs or irreversibility of the dynamics of the open system is directly linked to specific (classical) information about the order in which the reservoir qubits interacted with the system qubit. This aspect of the homogenizer leads to a model of a quantum safe with a classical combination.We analyze in detail how entanglement between the reservoir and the system is created during the process of quantum homogenization. We show that the information about the initial state of the system qubit is stored in the entanglement between the homogenized qubits.
We consider the arrangement of two down-conversion crystals with parallel rather than usual serial alignment, which are so close together that a linear energy exchange, for example by means of evanescent waves, is possible. We examine conditions under which the signal beams are mutually coherent.
In this work, determination of the refractive index profile and the optical gap E02 of PbZr1-XTiO3 thin films is described. Measurements were performed with the J. A Woollam spectral ellipsometer working on rotate analyzer mode. The temperature dependence of optical constants was obtained with a specially designed heating device.
The article is dealing with the measurement of three-dimensional shapes of objects. Such measurement is called the topography. The one of moire methods — the projection moire topography —is used. For improvement of measurement quality some methods are introduced. At first it is the washing-up method which deletes the linear background. At second the fringe-shifting method is described used for increasing of data quantity. And finally the optical/digital fringe multiplication is mentioned as a method for increasing the accuracy ofmeasurement. The topography is illustrated on the example ofmeasurement ofpump blade including its theory, experimental set-up and results.
This paper describes a possibility of mathematical modeling of laser applications, especially laser cutting and drilling and its use in practice. In the first part of this contribution there is a very briefly description of contemporary use of high-power lasers in industry and also basic principles of interaction between laser beam and treated material. Next part of the paper deals with a mathematical modeling of temperature field. Two numerical methods are used for the calculation of the temperature field: the finite difference method and the finite element method. Two examples of results of these both methods are demonstrated and some problems occurring when creating the matheniatical models are described. In the conclusion we made a brief comparison between theoretical and experimental results.