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Measurement of the Casimir-Polder force through center-of-mass oscillations of a Bose-Einstein condensate

D. M. Harber, J. M. Obrecht, J. M. McGuirk, and E. A. Cornell

Phys. Rev. A 72, 033610 (2005) - Published 13 September, 2005

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We have performed a measurement of the Casimir-Polder force using a magnetically trapped ${}^{87}{Rb}$ Bose-Einstein condensate. By detecting perturbations of the frequency of center-of-mass oscillations of the condensate perpendicular to the surface, we are able to detect this force at a distance $\sim 5 μ m$ , significantly farther than has been previously achieved, and at a precision approaching that needed to detect the modification due to thermal radiation. Additionally, this technique provides a limit for the presence of non-Newtonian gravity forces in the $\sim 1 μ m$ range.

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Optical application and measurement of torque on microparticles of isotropic nonabsorbing material

Alexis I. Bishop, Timo A. Nieminen, Norman R. Heckenberg, and Halina Rubinsztein-Dunlop

Phys. Rev. A 68, 033802 (2003) - Published 10 September, 2003

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We show how it is possible to controllably rotate or align microscopic particles of isotropic nonabsorbing material in a ${TEM}_{00}$ Gaussian beam trap, with simultaneous measurement of the applied torque using purely optical means. This is a simple and general method of rotation, requiring only that the particle is elongated along one direction. Thus, this method can be used to rotate or align a wide range of naturally occurring particles. The ability to measure the applied torque enables the use of this method as a quantitative tool—the rotational equivalent of optical tweezers based force measurement. As well as being of particular value for the rotation of biological specimens, this method is also suitable for the development of optically driven micromachines.

FEATURED IN PHYSICSMILESTONE

Computable measure of entanglement

G. Vidal and R. F. Werner

Phys. Rev. A 65, 032314 (2002) - Published 22 February, 2002

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We present a measure of entanglement that can be computed effectively for any mixed state of an arbitrary bipartite system. We show that it does not increase under local manipulations of the system, and use it to obtain a bound on the teleportation capacity and on the distillable entanglement of mixed states.

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Dynamical diffraction of atomic matter waves by crystals of light

M. K. Oberthaler, R. Abfalterer, S. Bernet, C. Keller, J. Schmiedmayer, and A. Zeilinger

Phys. Rev. A 60, 456 (1999) - Published 1 July, 1999

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Atoms in light crystals formed by a standing light wave are a model system to study the propagation of matter waves in periodic potentials. The encountered phenomena can be described by dynamical diffraction theory which has been extensively studied for x-ray, electron, and neutron scattering from solid state crystals. In this paper we show that an atomic de Broglie wave traversing a standing light wave allows investigation of predictions of dynamical diffraction theory which were previously experimentally not accessible. We present standard diffraction efficiency characterizations for pure absorptive and pure refractive crystals. Additionally we were able to measure directly the total atomic wave field formed inside a refractive and an absorptive crystal and to confirm the predicted absolute position of the atomic wave field with respect to the lattice planes. By superposing two standing light waves of different frequency we tailored a new kind of crystal potential where Friedel’s law about usual diffraction symmetries is maximally violated.

FEATURED IN PHYSICSRAPID COMMUNICATIONMILESTONE

Scheme for reducing decoherence in quantum computer memory

Peter W. Shor

Phys. Rev. A 52, R2493(R) (1995) - Published 1 October, 1995

In the mid-1990s, theorists devised methods to preserve the integrity of quantum bits—techniques that may become the key to practical quantum computing on a large scale.

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Recently, it was realized that use of the properties of quantum mechanics might speed up certain computations dramatically. Interest has since been growing in the area of quantum computation. One of the main difficulties of quantum computation is that decoherence destroys the information in a superposition of states contained in a quantum computer, thus making long computations impossible. It is shown how to reduce the effects of decoherence for information stored in quantum memory, assuming that the decoherence process acts independently on each of the bits stored in memory. This involves the use of a quantum analog of errorcorrecting codes.

FEATURED IN PHYSICSMILESTONE

Theory of high-harmonic generation by low-frequency laser fields

M. Lewenstein, Ph. Balcou, M. Yu. Ivanov, Anne L’Huillier, and P. B. Corkum

Phys. Rev. A 49, 2117 (1994) - Published 1 March, 1994

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We present a simple, analytic, and fully quantum theory of high-harmonic generation by low-frequency laser fields. The theory recovers the classical interpretation of Kulander et al. in Proceedings of the SILAP III Works hop, edited by B. Piraux (Plenum, New York, 1993) and Corkum [Phys. Rev. Lett. 71, 1994 (1993)] and clearly explains why the single-atom harmonic-generation spectra fall off at an energy approximately equal to the ionization energy plus about three times the oscillation energy of a free electron in the field. The theory is valid for arbitrary atomic potentials and can be generalized to describe laser fields of arbitrary ellipticity and spectrum. We discuss the role of atomic dipole matrix elements, electron rescattering processes, and of depletion of the ground state. We present the exact quantum-mechanical formula for the harmonic cutoff that differs from the phenomenological law $I_{p}$ +3.17 $U_{p}$ , where $I_{p}$ is the atomic ionization potential and $U_{p}$ is the ponderomotive energy, due to the account for quantum tunneling and diffusion effects.

FEATURED IN PHYSICSMILESTONE

Orbital angular momentum of light and the transformation of Laguerre-Gaussian laser modes

L. Allen, M. W. Beijersbergen, R. J. C. Spreeuw, and J. P. Woerdman

Phys. Rev. A 45, 8185 (1992) - Published 1 June, 1992

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Laser light with a Laguerre-Gaussian amplitude distribution is found to have a well-defined orbital angular momentum. An astigmatic optical system may be used to transform a high-order Laguerre-Gaussian mode into a high-order Hermite-Gaussian mode reversibly. An experiment is proposed to measure the mechanical torque induced by the transfer of orbital angular momentum associated with such a transformation.

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Measurement of the Casimir-Polder force through center-of-mass oscillations of a Bose-Einstein condensate

Optical application and measurement of torque on microparticles of isotropic nonabsorbing material

Computable measure of entanglement

Dynamical diffraction of atomic matter waves by crystals of light

Scheme for reducing decoherence in quantum computer memory

Theory of high-harmonic generation by low-frequency laser fields

Orbital angular momentum of light and the transformation of Laguerre-Gaussian laser modes

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