Polarization-sensitive quantum-optical coherence tomography

We set forth a polarization-sensitive quantum-optical coherence tomography (PS-QOCT) technique that provides axial optical sectioning with polarization-sensitive capabilities. The technique provides a means for determining information about the optical path length between isotropic reflecting surfaces, the relative magnitude of the reflectance from each interface, the birefringence of the interstitial material, and the orientation of the optical axis of the sample. PS-QOCT is immune to sample dispersion and therefore permits measurements to be made at depths greater than those accessible via ordinary optical coherence tomography. We also provide a general Jones matrix theory for analyzing PS-QOCT systems and outline an experimental procedure for carrying out such measurements.Comment: 15 pages, 5 figures, to appear in Physical Review

Non-classical Photon Statistics For Two-mode Optical Fields

The non-classical property of subpoissonian photon statistics is extended from one to two-mode electromagnetic fields, incorporating the physically motivated property of invariance under passive unitary transformations. Applications to squeezed coherent states, squeezed thermal states, and superposition of coherent states are given. Dependences of extent of non-classical behaviour on the independent squeezing parameters are graphically displayed.Comment: 15 pages, RevTex, 5 figures, available by sending email to [email protected]

Characterisations of Classical and Non-classical states of Quantised Radiation

A new operator based condition for distinguishing classical from non-classical states of quantised radiation is developed. It exploits the fact that the normal ordering rule of correspondence to go from classical to quantum dynamical variables does not in general maintain positivity. It is shown that the approach naturally leads to distinguishing several layers of increasing nonclassicality, with more layers as the number of modes increases. A generalisation of the notion of subpoissonian statistics for two-mode radiation fields is achieved by analysing completely all correlations and fluctuations in quadratic combinations of mode annihilation and creation operators conserving the total photon number. This generalisation is nontrivial and intrinsically two-mode as it goes beyond all possible single mode projections of the two-mode field. The nonclassicality of pair coherent states, squeezed vacuum and squeezed thermal states is analysed and contrasted with one another, comparing the generalised subpoissonian statistics with extant signatures of nonclassical behaviour.Comment: 16 pages, Revtex, One postscript Figure compressed and uuencoded Replaced, minor changes in eq 4.30 and 4.32. no effect on the result

Geometric approach to nonlinear coherent states using the Higgs model for harmonic oscillator

In this paper, we investigate the relation between the curvature of the physical space and the deformation function of the deformed oscillator algebra using non-linear coherent states approach. For this purpose, we study two-dimensional harmonic oscillators on the flat surface and on a sphere by applying the Higgs modell. With the use of their algebras, we show that the two-dimensional oscillator algebra on a surface can be considered as a deformed one-dimensional oscillator algebra where the effect of the curvature of the surface is appeared as a deformation function. We also show that the curvature of the physical space plays the role of deformation parameter. Then we construct the associated coherent states on the flat surface and on a sphere and compare their quantum statistical properties, including quadrature squeezing and antibunching effect.Comment: 12 pages, 7 figs. To be appeared in J. Phys.

Gaussian Wigner distributions and hierarchies of nonclassical states in quantum optics-The single mode case

A recently introduced hierarchy of states of a single mode quantised radiation field is examined for the case of centered Guassian Wigner distributions. It is found that the onset of squeezing among such states signals the transition to the strongly nonclassical regime. Interesting consequences for the photon number distribution, and explicit representations for them, are presented.Comment: 11 Pages Revtex one eps figure. Replaced with minor changes in ref

From quantum cellular automata to quantum lattice gases

A natural architecture for nanoscale quantum computation is that of a quantum cellular automaton. Motivated by this observation, in this paper we begin an investigation of exactly unitary cellular automata. After proving that there can be no nontrivial, homogeneous, local, unitary, scalar cellular automaton in one dimension, we weaken the homogeneity condition and show that there are nontrivial, exactly unitary, partitioning cellular automata. We find a one parameter family of evolution rules which are best interpreted as those for a one particle quantum automaton. This model is naturally reformulated as a two component cellular automaton which we demonstrate to limit to the Dirac equation. We describe two generalizations of this automaton, the second of which, to multiple interacting particles, is the correct definition of a quantum lattice gas.Comment: 22 pages, plain TeX, 9 PostScript figures included with epsf.tex (ignore the under/overfull \vbox error messages); minor typographical corrections and journal reference adde

Quantum Langevin equations for semiconductor light-emitting devices and the photon statistics at a low-injection level

From the microscopic quantum Langevin equations (QLEs) we derive the effective semiconductor QLEs and the associated noise correlations which are valid at a low-injection level and in real devices. Applying the semiconductor QLEs to semiconductor light-emitting devices (LEDs), we obtain a new formula for the Fano factor of photons which gives the photon-number statistics as a function of the pump statistics and several parameters of LEDs. Key ingredients are non-radiative processes, carrier-number dependence of the radiative and non-radiative lifetimes, and multimodeness of LEDs. The formula is applicable to the actual cases where the quantum efficiency $\eta$ differs from the differential quantum efficiency $\eta_{d}$, whereas previous theories implicitly assumed $\eta = \eta_{d}$. It is also applicable to the cases when photons in each mode of the cavity are emitted and/or detected inhomogeneously. When $\eta_{d} < \eta$ at a running point, in particular, our formula predicts that even a Poissonian pump can produce sub-Poissonian light. This mechanism for generation of sub-Poissonian light is completely different from those of previous theories, which assumed sub-Poissonian statistics for the current injected into the active layers of LEDs. Our results agree with recent experiments. We also discuss frequency dependence of the photon statistics.Comment: 10 pages, 8 figure

Conditional Quantum Dynamics and Logic Gates

Quantum logic gates provide fundamental examples of conditional quantum dynamics. They could form the building blocks of general quantum information processing systems which have recently been shown to have many interesting non--classical properties. We describe a simple quantum logic gate, the quantum controlled--NOT, and analyse some of its applications. We discuss two possible physical realisations of the gate; one based on Ramsey atomic interferometry and the other on the selective driving of optical resonances of two subsystems undergoing a dipole--dipole interaction.Comment: 5 pages, RevTeX, two figures in a uuencoded, compressed fil

Amplification by stochastic interference

A new method is introduced to obtain a strong signal by the interference of weak signals in noisy channels. The method is based on the interference of 1/f noise from parallel channels. One realization of stochastic interference is the auditory nervous system. Stochastic interference may have broad potential applications in the information transmission by parallel noisy channels

Two Mode Quantum Systems: Invariant Classification of Squeezing Transformations and Squeezed States

A general analysis of squeezing transformations for two mode systems is given based on the four dimensional real symplectic group Sp(4,\Re)\/. Within the framework of the unitary metaplectic representation of this group, a distinction between compact photon number conserving and noncompact photon number nonconserving squeezing transformations is made. We exploit the Sp(4,\Re)-SO(3,2)\/ local isomorphism and the U(2)\/ invariant squeezing criterion to divide the set of all squeezing transformations into a two parameter family of distinct equivalence classes with representative elements chosen for each class. Familiar two mode squeezing transformations in the literature are recognized in our framework and seen to form a set of measure zero. Examples of squeezed coherent and thermal states are worked out. The need to extend the heterodyne detection scheme to encompass all of U(2)\/ is emphasized, and known experimental situations where all U(2)\/ elements can be reproduced are briefly described.Comment: Revtex 37 pages, Latex figures include