In the last 30 days

• Open/close Quantum noise locking

  Kirk McKenzie et al  2005 J. Opt. B: Quantum Semiclass. Opt. 7 S421 Tag this article

  Article References Full text PDF (352 KB)

  Quantum optical states which have no coherent amplitude, such as squeezed vacuum states, cannot rely on standard readout techniques to generate error signals for control of the quadrature phase. Here we investigate the use of asymmetry in the quadrature variances to obtain a phase-sensitive readout and to lock the phase of a squeezed vacuum state, a technique which we call noise locking (NL). We carry out a theoretical derivation of the NL error signal and the associated stability of the squeezed and anti-squeezed lock points. Experimental data for the NL technique both in the presence and absence of coherent fields are shown, including a comparison with coherent locking techniques. Finally, we use NL to enable a stable readout of the squeezed vacuum state on a homodyne detector.

• Open/close Mott–Hubbard transition of cold atoms in optical lattices

  Wilhelm Zwerger  2003 J. Opt. B: Quantum Semiclass. Opt. 5 S9 Tag this article

  Article References Full text PDF (200 KB)

  We discuss the superfluid (SF) to Mott-insulator transition of cold atoms in optical lattices recently observed by Greiner et al (2002 Nature 415 39). The fundamental properties of both phases and their experimental signatures are discussed carefully, including the limitations of the standard Gutzwiller approximation. It is shown that in a one-dimensional dilute Bose-gas with a strong transverse confinement (Tonks-gas), even an arbitrary weak optical lattice is able to induce a Mott-like state with crystalline order, provided the dimensionless interaction parameter is larger than a critical value of order one. The SF–insulator transition of the Bose–Hubbard model in this case continuously evolves into a transition of the commensurate–incommensurate type with decreasing strength of the external optical lattice.

• Open/close Time-of-flight measurement of the temperature of cold atoms for short trap-probe beam distances

  Tomasz M Brzozowski et al  2002 J. Opt. B: Quantum Semiclass. Opt. 4 62 Tag this article

  Article References Full text PDF (243 KB)

  We analyse the time-of-flight method of measuring the temperature of cold trapped atoms in the specific case of short distances of the probe beam from the trap centre and finite atomic cloud size. We theoretically examine the influence of the probe beam shape and its distance from the initial position of the cloud on the temperature evaluation. These results are then verified with a three-dimensional Monte Carlo simulation and applied to our experimental data to show that the proposed procedure allows accurate and reliable determination of the temperature.

• Open/close Nonclassical high resolution optical effects produced by evanescent waves

  Y Ben-Aryeh  2003 J. Opt. B: Quantum Semiclass. Opt. 5 S553 Tag this article

  Article References Full text PDF (94 KB)

  Certain principles for obtaining super-resolution in near field optics are discussed. A simple mechanism which leads to subwavelength super-resolving power produced by evanescent waves is described. A comparison is made between near field super-resolution optical effects and similar effects which are obtained by nonclassical electromagnetic states. Possible connections between the near field high resolution optical processes and the high resolution effects produced by the nonclassical entangled states are discussed.

• Open/close Optical angular-momentum flux*

  Stephen M Barnett  2002 J. Opt. B: Quantum Semiclass. Opt. 4 S7 Tag this article

  Article References Full text PDF (129 KB)

  We introduce the angular-momentum flux as the natural description of the angular momentum carried by light. We present four main results: (i) angular-momentum flux is the flow of angular momentum across a surface and, in conjunction with the more familiar angular-momentum density, expresses the conservation of angular momentum. (ii) The angular-momentum flux for a light beam about its axis (or propagation direction) can be separated into spin and orbital parts. This separation is gauge invariant and does not rely on the paraxial approximation. (iii) Angular-momentum flux can describe the propagation of angular momentum in other geometries, but the identification of spin and orbital parts is then more problematic. We calculate the flux for a component of angular momentum that is perpendicular to the axis of a light beam and for the field associated with an electric dipole. (iv) The theory can be extended to quantum electrodynamics.

• Open/close Quantum imaging

  L A Lugiato et al  2002 J. Opt. B: Quantum Semiclass. Opt. 4 S176 Tag this article

  Article References Full text PDF (593 KB)

  We provide a brief overview of the newly born field of quantum imaging, and discuss some concepts that lie at the root of this field.

• Open/close Spatiotemporal optical solitons

  Boris A Malomed et al  2005 J. Opt. B: Quantum Semiclass. Opt. 7 R53 Tag this article

  Article References Full text PDF (923 KB)

  In the course of the past several years, a new level of understanding has been achieved about conditions for the existence, stability, and generation of spatiotemporal optical solitons, which are nondiffracting and nondispersing wavepackets propagating in nonlinear optical media. Experimentally, effectively two-dimensional (2D) spatiotemporal solitons that overcome diffraction in one transverse spatial dimension have been created in quadratic nonlinear media. With regard to the theory, fundamentally new features of light pulses that self-trap in one or two transverse spatial dimensions and do not spread out in time, when propagating in various optical media, were thoroughly investigated in models with various nonlinearities. Stable vorticity-carrying spatiotemporal solitons have been predicted too, in media with competing nonlinearities (quadratic–cubic or cubic–quintic). This article offers an up-to-date survey of experimental and theoretical results in this field. Both achievements and outstanding difficulties are reviewed, and open problems are highlighted. Also briefly described are recent predictions for stable 2D and 3D solitons in Bose–Einstein condensates supported by full or low-dimensional optical lattices.

• Open/close Non-classical interference between independent sources

  J G Rarity et al  2005 J. Opt. B: Quantum Semiclass. Opt. 7 S171 Tag this article

  Article References Full text PDF (165 KB)

  When a one-photon state is mixed with a (separate) weak coherent state at a beamsplitter the probability for seeing one photon in each beamsplitter output approaches zero due to destructive interference. We demonstrate this non-classical interference effect using pulse-gated single photons and weak mode-locked laser pulses.

• Open/close Nonexponential decay at late times and a different Zeno paradox

  Jay Lawrence  2002 J. Opt. B: Quantum Semiclass. Opt. 4 S446 Tag this article

  Article References Full text PDF (150 KB)

  The decay profile of a metastable quantum state decaying in isolation is predicted to depart from exponential behaviour after many lifetimes, and in typical cases to adopt algebraic behaviour as the late-time limit. The effect of environmental interactions, including measurement, is quite different from that of the familiar Zeno (and anti-Zeno) effects that have been observed at very early times. Instead of arresting the decay (or hastening it), the late-time interactions tend to enforce the exponential decay law, without substantially changing the decay constant intrinsic to the isolated system. The experimental challenge is to prevent these interactions and observe the crossover to the nonexponential regime.

• Open/close Elliptical orbits in the Bloch sphere

  A Mandilara et al  2005 J. Opt. B: Quantum Semiclass. Opt. 7 S277 Tag this article

  Article References Full text PDF (194 KB)

  As is well known, when an SU(2) operation acts on a two-level system, its Bloch vector rotates without change of magnitude. Considering a system composed of two two-level systems, it is proven that for a class of nonlocal interactions of the two subsystems including (with ) and the Heisenberg interaction, the geometric description of the motion is particularly simple: each of the two Bloch vectors follows an elliptical orbit within the Bloch sphere. The utility of this result is demonstrated in two applications, the first of which bears on quantum control via quantum interfaces. By employing nonunitary control operations, we extend the idea of controllability to a set of points which are not necessarily connected by unitary transformations. The second application shows how the orbit of the coherence vector can be used to assess the entangling power of Heisenberg exchange interaction.