# Blog - physics

## Conferenced out

### Sat Dec 9 09:19:15 EST 2006

For the last week I've been at the Australian Institute of Physics Congress here in Brisbane. It covered a wide range of topics with sessions running in parallel, so I didn't get to see everything (also it went from 8:30am until 8pm or later each day so I was a bit shattered by Thursday). Highlights:

• Physics and Education talks, especially the plenary talk by Eric Mazur on interactive teaching. The basic idea is to get the students to do prereading before the lecture, then discuss the reading in small groups and as a class during the lecture. This is a more interactive approach and lets peers discuss conceptual problems in a language that is natural for them, as opposed to the lecturer attempting to translate his mental picture back to the students' level. (...)

[me] [physics]

## Getting a Ti:sapphire laser to work

### Thu Oct 26 10:56:43 EST 2006

1) Get the laser to lase. Use a bandpass filter at the laser wavelength in front of a powermeter on the output to detect when you're getting close. Without this filter there is too much scattered light in the non-laser modes to tell whether you are going in the right direction. Ti:sapphire has a gain region covering hundreds of nanometres.

2) Align the crystal to be at Brewster's angle to the laser cavity mode to minimize losses. This is quite fiddly since there is no rotation stage to adjust the crystal angle, so it must be done freehand. Diagnostic is to operate the laser with low input power and rotate crystal, realign cavity end mirrors to close the cavity and translate the crystal until maximum power is reached for that angle. Repeat this for different crystal angles, find the angle that gives the maximum power. (...)

[physics]

## Today on the archive

### Thu Oct 12 08:29:44 EST 2006

• [quant-ph/0610065] -Title: Photon correlation vs interference of single-atom fluorescence in a half-cavity

• Authors: Francois Dubin, Daniel Rotter, Manas Mukherjee, Carlos Russo, Juergen Eschner, Rainer Blatt
• Abstract: Photon correlations are investigated for a single laser-excited ion trapped in front of a mirror. Varying the relative distance between the ion and the mirror, photon correlation statistics can be tuned smoothly from an antibunching minimum to a bunching-like maximum. Our analysis concerns the non-Markovian regime of the ion-mirror interaction and reveals the field establishment in a half-cavity interferometer.
• Title: Diffraction limited optics for single atom manipulation
• Authors: Y.R.P. Sortais, H. Marion, C. Tuchendler, A.M. Lance, M. Lamare, P. Fournet, C. Armellin, R. Mercier, G. Messin, A. Browaeys, P. (...)

[physics]

## Today on the archive

### Tue Oct 3 08:37:39 EST 2006

• [quant-ph/0609228]
• Title: Process tomography of ion trap quantum gates
• Authors: M. Riebe, K. Kim, P. Schindler, T. Monz, P. O. Schmidt, T. K. Koerber, W. Haensel, H. Haeffner, C. F. Roos, R. Blatt
• Abstract: A crucial building block for quantum information processing with trapped ions is a controlled-NOT quantum gate. In this paper, two different sequences of laser pulses implementing such a gate operation are analyzed using quantum process tomography. Fidelities of up to 92.6(6)% are achieved for single gate operations and up to 83.4(8)% for two concatenated gate operations. By process tomography we assess the performance of the gates for different experimental realizations and demonstrate the advantage of amplitude--shaped laser pulses over simple square pulses. We also investigate whether the performance of concatenated gates can be inferred from the analysis of the single gates. (...)

[physics]

## Today on the archive

### Tue Sep 26 08:40:06 EST 2006

• physics/0609191 [abs, ps, pdf, other] :
• Title: MontePython: Implementing Quantum Monte Carlo using Python
• Authors: J.K. Nilsen
• Abstract: We present a cross-language C++/Python program for simulations of quantum mechanical systems with the use of Quantum Monte Carlo (QMC) methods. We describe a system for which to apply QMC, the algorithms of variational Monte Carlo and diffusion Monte Carlo and we describe how to implement theses methods in pure C++ and C++/Python. Furthermore we check the efficiency of the implementations in serial and parallel cases to show that the overhead using Python can be negligible.

[physics]

## Today on the archive

### Fri Sep 22 08:32:59 EST 2006

• [physics/0609168]
• Title: The Application Hosting Environment: Lightweight Middleware for Grid-Based Computational Science
• Authors: P. V. Coveney, R. S. Saksena, S. J. Zasada, M. McKeown, S. Pickles
• Abstract: Grid computing is distributed computing performed transparently across multiple administrative domains. Grid middleware, which is meant to enable access to grid resources, is currently widely seen as being too heavyweight and, in consequence, unwieldy for general scientific use. Its heavyweight nature, especially on the client-side, has severely restricted the uptake of grid technology by computational scientists. In this paper, we describe the Application Hosting Environment (AHE) which we have developed to address some of these problems.

[physics]

## Today on the archive

### Thu Sep 21 08:49:37 EST 2006

• [physics/0609160]
• Title: Photonic mode density effects on single-molecule fluorescence blinking
• Authors: F. D. Stefani, K. Vasilev, N. Bocchio, F. Gaul, A. Pomozzi, M. Kreiter
• Abstract: We investigated the influence of the photonic mode density (PMD) on the triplet dynamics of individual chromophores on a dielectric interface by comparing their response in the presence and absence of a nearby gold film. Lifetimes of the excited singlet state were evaluated in ordet to measure directly the PMD at the molecules position. Triplet state lifetimes were simultaneously determined by statistical analysis of the detection time of the fluorescence photons. The observed singlet decay rates are in agreement with the predicted PMD for molecules with different orientations. The triplet decay rate is modified in a fashion correlated to the singlet decay rate. (...)

[physics]

## Today on the archive

### Wed Sep 20 08:25:59 EST 2006

• [cond-mat/0609378]
• Title: Single-molecule experiments in biological physics: methods and applications
• Authors: F. Ritort
• Abstract: I review single-molecule experiments (SME) in biological physics. Recent technological developments have provided the tools to design and build scientific instruments of high enough sensitivity and precision to manipulate and visualize individual molecules and measure microscopic forces. (Rest of abstract snipped)

[physics]

## Today on the archive

### Thu Sep 7 08:52:53 EST 2006

• [cond-mat/0609039]
• Title: New Trends in Density Matrix Renormalization
• Authors: Karen Hallberg
• Journal-ref: Advances in Physics 55 (5-6) (2006)
• Abstract: The Density Matrix Renormalization Group (DMRG) has become a powerful numerical method that can be applied to low-dimensional strongly correlated fermionic and bosonic systems. It allows for a very precise calculation of static, dynamic and thermodynamic properties. Its field of applicability has now extended beyond Condensed Matter, and it is now successfully used in Quantum Chemistry, Statistical Mechanics, Quantum Information Theory, Nuclear and High Energy Physics as well. In this article, we briefly review the main aspects of the method and present some of the most relevant applications so as to give an overview on the scope and possibilities of DMRG. (...)

[physics]

## Today on the archive

### Wed Sep 6 08:53:53 EST 2006

• [physics/0609028]
• Title: Large atom number Bose-Einstein condensate of sodium
• Authors: K.M.R. van der Stam, E.D. van Ooijen, R. Meppelink, J.M. Vogels, P. van der Straten
• Abstract: We describe the setup to create a large Bose-Einstein condensate containing more than 120x10^6 atoms. In the experiment a thermal beam is slowed by a Zeeman slower and captured in a dark-spot magneto-optical trap (MOT). A typical dark-spot MOT in our experiments contains 2.0x10^10 atoms with a temperature of 320 microK and a density of about 1.0x10^11 atoms/cm^3. The sample is spin polarized in a high magnetic field, before the atoms are loaded in the magnetic trap. Spin polarizing in a high magnetic field results in an increase in the transfer efficiency by a factor of 2 compared to experiments without spin polarizing. In the magnetic trap the cloud is cooled to degeneracy in 50 s by evaporative cooling. (...)

[physics]

## The last week on the archive

### Wed Aug 30 10:08:28 EST 2006

• [physics/0608223]
• Optical spectral pulse shaping by combining two oppositely chirped fiber Bragg grating
• Authors: Miguel A. Preciado, Victor Garcia-Munoz, Miguel A. Muriel
• Abstract: In this letter we present a new technique for pulse shaping. The desired pulse is shaped by two apodized chirped fiber Bragg gratings which dispersions are adjusted to be cancelled. This technique exploits the well-known property of linearly-chirped gratings, in which the apodization (amplitude) grating profile maps its spectral response. This technique presents inherent advantages of chirped fiber Bragg gratings and direct design in frequency domain.

[physics]

## Today on the archive

### Tue Aug 22 09:28:44 BST 2006

• [physics/0608202]
• Title: Long Term Operation and Performance of Cryogenic Sapphire Oscillators
• Authors: M.E. Tobar, E.N. Ivanov, C.R. Locke, P.L. Stanwix, J.G. Hartnett, A.N. Luiten, R.B. Warrington, P.T.H. Fisk, M.A. Lawn, M.J. Wouters, S. Bize, G. Santarelli, P. Wolf, A. Clairon, P. Guillemot
• Abstract: Cryogenic Sapphire Oscillators (CSO) developed at UWA have now been in operation around the world continuously for many years. Such oscillators, due to their excellent spectral purity are essential for interrogating atomic frequency standards at the limit of quantum projection noise; otherwise aliasing effects will dominate the frequency stability due to the periodic sampling between successive interrogations of the atomic transition. (...)

[physics]

## Today on the archive

### Mon Aug 21 08:48:23 BST 2006

• [physics/0608192]
• Title: Precision study of hyperfine structure in simple atoms
• Authors: S. Karshenboim, S. Eidelman, P. Fendel, V. G. Ivanov, N. Kolachevsky, V. Shelyuto, T. W. Haensch
• Abstract: We consider the most accurate tests of bound state QED theory of the hyperfine splitting in two-body atoms related to the HFS interval of the 1s state in muonium and positronium and the 2s state in hydrogen, deuterium and the helium-3 ion. We summarize their QED theory and pay special attention to involved effects of strong interactions and to recent optical measurements of the 2s HFS interval in hydrogen and deuterium. We present results for specific ratios of the 1s-2s frequencies in hydrogen and deuterium which happen to be among the most accurately measured and calculated quantities.

[physics]

## Today on the archive - teleportation

### Fri Aug 18 09:12:20 BST 2006

• [quant-ph/0608133]
• Title: High fidelity teleportation between light and atoms
• Authors: K. Hammerer, E.S. Polzik, J.I. Cirac
• Abstract: We show how high fidelity quantum teleportation of light to atoms can be achieved in the same setup as was used in the recent experiment [J. Sherson et.al., quant-ph/0605095, accepted by Nature], where such an inter-species quantum state transfer was demonstrated for the first time. Our improved protocol takes advantage of the rich multimode entangled structure of the state of atoms and scattered light and requires simple post-processing of homodyne detection signals and squeezed light in order to achieve fidelities up to 90% (85%) for teleportation of coherent (qubit) states under realistic experimental conditions. The remaining limitation is due to atomic decoherence and light losses.

[physics]

## Why Should I Care What Color the Bikeshed Is?

### Wed Aug 16 09:55:10 BST 2006

[Why Should I Care What Color the Bikeshed Is?] is a classic post describing the bikeshed principle to Open Source developers. The basic concept comes from the book "Parkinson's Law", the point being that people will spend a disproportionate amount of time dealing with small problems if those problems are within their skill set.

[code] [physics]

## Lensless focusing with subwavelength resolution

### Wed Aug 16 09:26:26 BST 2006

[Applied Physics 88 261107] discusses production of a focused spot below the Rayleigh limit by coherently combining several beams together to match the field emitted by a point source.

I remember seeing a seminar about this technique a couple of years ago, I think the lecturer was from a group in the Netherlands though (this group is from MIT). The seminar I remember used a quadrant waveplate to produce the desired optical field, this group uses 15 mirrors to produce the field. In principle this could be used with diffractive optics to allow focusing of X-rays etc, where the refractive index of traditional optical materials is not sufficiently different from vacuum to allow tradiotional optical elements. (...)

[physics]

## Today on the archive - photonic crystal fibres

### Tue Aug 15 08:41:53 BST 2006

• [physics/0608142]
• Title: Nonlinear photonic crystal fibres: pushing the zero-dispersion toward the visible
• Authors: Kunimasa Saitoh, Masanori Koshiba, Niels Asger Mortensen
• Abstract: The strong waveguide dispersion in photonic crystal fibres provides unique opportunities for nonlinear optics with a zero-dispersion wavelength $\lambda0$ far below the limit of ~1.3 micron set by the material dispersion of silica. By tuning the air-hole diameter d, the pitch Lambda, and the number of rings of air holes N, the strong waveguide dispersion can in principle be used to extend lambda0 well into the visible, albeit to some extend at the cost of multimode operation. We study in detail the interplay of the zero-dispersion wavelength, the cut-off wavelength lambda_c, and the leakage loss in the parameter space spanned by d, Lambda, and N. (...)

[physics]

## Today on the archive

### Fri Aug 11 12:09:17 BST 2006

• [quant-ph/0608089]
• Title: Efficient coherent internal state transfer in trapped ions using Stimulated Raman Adiabatic Passage
• Authors: Jens L. Sørensen, Ditte Møller, Theis Iversen, Jakob B. Thomsen, Frank Jensen, Peter Staanum, Dirk Voigt, Michael Drewsen
• Abstract: We demonstrate experimentally how the process of Stimulated Raman Adiabatic Passage (STIRAP) can be utilized for efficient coherent internal state transfer in single trapped and laser-cooled $^{40}$Ca$^+$ ions. The transfer from the D${3/2}$ to the D${5/2}$ state, is detected by a fluorescence measurement revealing the population not transfered to the D$_{5/2}$ state. A coherent population transfer efficiency at the level of 95 % in a setup allowing for the internal state detection of individual ions in a string has been obtained. (...)

[physics]

## Today on the archive

### Thu Aug 10 08:38:04 BST 2006

• [physics/0608100]
• Title: All-optical Control of the Propagation of Intense Laser Light in Condensed Media
• Authors: A. K. Dharmadhikari, K. Alti, J. A. Dharmadhikari, D. Mathur Comments: 4 figures. Submitted to PRL
• Abstract: We experimentally demonstrate optical control of filamentation that occurs during propagation of intense, ultrashort laser pulses through crystals like barium fluoride and sapphire. Control is exercised by rotating the plane of polarization of the incident laser radiation and is demonstrated by directly visualizing filamentation in the bulk via six-photon absorption-induced fluorescence and, concomitantly, by probing the spectral and spatial properties of white light that is generated.
• Comment: Filamentation occurs when an intense ultrashort pulse propagates through a medium, and results in localization of the optical energy into the region of the filament. (...)

[physics]

## Photoionization

### Mon Aug 7 08:46:30 BST 2006

• [quant-ph/0608043]
• Title: Efficient Photoionization-Loading of Trapped Cadmium Ions with Ultrafast Pulses
• Authors: L. Deslauriers, M. Acton, B. B. Blinov, K.-A. Brickman, P. C. Haljan, W. K. Hensinger, D. Hucul, S. Katnik, R. N. Kohn, Jr., P. J. Lee, M. J. Madsen, P. Maunz, S. Olmschenk, D. L. Moehring, D. Stick, J. Sterk, M. Yeo, K. C. Younge, C. Monroe
• Abstract: Atomic cadmium ions are loaded into radiofrequency ion traps by photoionization of atoms in a cadmium vapor with ultrafast laser pulses. The photoionization is driven through an intermediate atomic resonance with a frequency-quadrupled mode-locked Ti:Sapphire laser that produces pulses of either 100 fsec or 1 psec duration at a central wavelength of 229 nm. (...)

[cooling] [physics]

## Today on the archive

### Thu Aug 3 08:45:52 BST 2006

• [physics/0608015]
• Title: Relativistic ionization-rescattering with tailored laser pulses
• Authors: Michael Klaiber, Karen Z. Hatsagortsyan, Christoph H. Keitel
• Abstract: The interaction of relativistically strong tailored laser pulses with an atomic system is considered. Due to a special tailoring of the laser pulse, the suppression of the relativistic drift of the ionized electron and a dramatic enhancement of the rescattering probability is shown to be achievable. The high harmonic generation rate in the relativistic regime is calculated and shown to be increased by several orders of magnitude compared to the case of conventional laser pulses. The energies of the revisiting electron at the atomic core can approach the MeV domain, thus rendering hard x-ray harmonics and nuclear reactions with single atoms feasible. (...)

[physics]

## Today on the archive

### Tue Aug 1 09:26:12 BST 2006

• Title: Fast cooling of trapped ions using the dynamical Stark shift gate
• Authors: Authors: A. Retzker, M.B. Plenio
• Abstract: A laser cooling scheme for trapped ions is presented which is based on the fast dynamical Stark shift gate, described in [Jonathan etal, PRA 62, 042307]. Since this cooling method does not contain an off resonant carrier transition, low final temperatures are achieved even in traveling wave light field. The proposed method may operate in either pulsed or continuous mode and is also suitable for ion traps using microwave addressing in strong magnetic field gradients.

[physics]

## Nonlinear optics and phase sensitive detection

### Tue Aug 1 08:47:20 BST 2006

In less than a month I start work on a new project in Australia, working in [Dave Kielpinski's atomic cooling group] at Griffith University.
One aspect of the project is to use high repetition rate pulsed mode-locked lasers to cool atomic hydrogen. This relies on a couple of tricks, one being the phase coherence of the frequency comb (see [quant-ph/0306099]), and the other being the fact that nonlinear optics is a lot more efficient for pulsed lasers than for continuous wave lasers of the same average power. (This is for simple materials, periodically poled materials in a waveguide configuration can also give good conversion efficiency for CW lasers. However these materials are tailored for a specific frequency, may not be as flexible, require precise temperature stabilization, may not work at the wavelengths we want, are more expensive, less readily available, etc. (...)

[physics]

## Ultrafast lasers and nuclear fusion

### Tue Jul 25 21:44:39 BST 2006

Things that we can do now that we could not five years ago: create attosecond pulses of coherent X-rays. We can do this by hitting a gas with a very short (femtoseconds long), very intense laser (terrawatt peak power) pulses. The underlying physics is multiphoton acceleration of the electrons in the atoms of the gas - the laser is intense enough that the potential seen by the electron changes on the timescale of the electron's vibration in the atom, so resonant forcing occurs.

How does this relate to fusion? One approach to fusion is to hit the fusion pellet fast enough and with enough energy that [inertial confinement] occurs. This means that the energy has no time to be distributed over the entire pellet, but instead is concentrated in the area where the laser pulse hits. This region turns into a plasma and the back reaction compresses and heats the pellet enough that fusion occurs. (...)

[ideas] [physics]

## Multiple optical traps using a mesh diffraction element

### Tue Jul 18 08:51:15 BST 2006

• physics/0607149
• Title: Multiple optical traps from a single laser beam using a mechanical element
• Authors: J.A. Dharmadhikari, A.K. Dharmadhikari, D. Mathur
• Abstract: The use of a wire mesh facilitates creation of multiple optical traps for manipulation of small micron or sub-micron particles. Such an array of optical traps can be easily controlled. The trap that is formed in this manner is a continuous trap; it obviates the need to time share a laser beam among a set of positions, as is presently done in conventional multiple traps.
• Comments: The aim of the paper is to construct an optical tweezer arrangement having multiple trapping regions. The standard optical tweezer setup produces a single trapping region by focussing a laser through a microscope objective. (...)

[cooling] [physics]

## Decoherence of motional states

### Mon Jul 17 14:06:11 BST 2006

I am working on a paper at the moment describing the Schroedinger cat experiments that we performed with a single ion coupled to its motional state. In the referee comments there were a number of questions about the theoretical derivations. The majority I could answer as they related to the details of our particular experiment and analysis, however for the more fundamental ones I needed to ask one of my coauthors and he referred to the paper [Phys. Rev. A. 62 053807] by Turchette et al. This seems to be a useful for a lot of the theoretical results in the area of coupling between an ion and a bath of harmonic oscillators, as well as describing some very nice experiments.

• Coupling of a charged harmonic oscillator with the surrounding electric field, E from the environment is of the form

V = -q x.E

where q is the charge on the particle and x is the position. (...)

[cooling] [physics] [qo]

## Cooling with ultrafast lasers

### Tue May 30 10:32:46 BST 2006

• Title: Broadband laser cooling of trapped atoms with ultrafast pulses
• Authors: B.B. Blinov, R.N. Kohn Jr., M.J. Madsen, P. Maunz, D.L. Moehring, C. Monroe
• Abstract: We demonstrate broadband laser cooling of atomic ions in an rf trap using ultrafast pulses from a modelocked laser. The temperature of a single ion is measured by observing the size of a time-averaged image of the ion in the known harmonic trap potential. While the lowest observed temperature was only about 1 K, this method efficiently cools very hot atoms and can sufficiently localize trapped atoms to produce near diffraction-limited atomic images.

[cooling] [physics]

## Entangled light from a single cold atom

### Tue May 30 09:02:02 BST 2006

[quant-ph/0605231] [abs, ps, pdf, other] :

• Title: A single cold atom as efficient stationary source of EPR-entangled light
• Authors: David Vitali, Giovanna Morigi, Jürgen Eschner
• Abstract: The Stokes and anti-Stokes components of the spectrum of resonance fluorescence of a single trapped atom, which originate from the mechanical coupling between the scattered photons and the quantized motion of the atomic center of mass, exhibit quantum correlations which are of two-mode-squeezing type. We study and demonstrate the build-up of such correlations in a specific setup, which is experimentally accessible, and where the atom acts as efficient and continuous source of EPR-entangled, two-mode squeezed light.

[physics] [qo]

## EIT and Raman processes

### Mon May 29 10:18:43 BST 2006

• Title: Competition between Electromagnetically Induced Transparency and Raman Processes
• Authors: G. S. Agarwal, T. N. Dey, Daniel J. Gauthier
• Abstract: We present a theoretical formulation of competition among electromagnetically induced transparency (EIT) and Raman processes. The latter become important when the medium can no longer be considered to be dilute. Unlike the standard formulation of EIT, we consider all fields applied and generated as interacting with both the transitions of the $\Lambda$ scheme. We solve Maxwell equations for the net generated field using a fast-Fourier-transform technique and obtain predictions for the probe, control and Raman fields. We show how the intensity of the probe field is depleted at higher atomic number densities due to the build up of multiple Raman fields.

[physics]

## Two-level systems and modelocked lasers

### Fri May 26 09:25:21 BST 2006

Read up on papers about driving two level systems with strong phase modulated fields eg PM CW laser or modelocked pulsed laser

• Phys. Rev. A 31, 3175-3182 (1985)
• Title: Absorption and fluorescence in frequency-modulated fields under conditions of strong modulation and saturation
• Authors: N. Nayak and G. S. Agarwal
• Phys. Rev. A 50, R4465-R4467 (1994)
• Title: Realization of trapping in a two-level system with frequency-modulated fields
• Authors: Girish S. Agarwal and W. Harshawardhan

[physics] [qo]

## Strontium ion clock

### Wed May 24 08:34:24 BST 2006

• Title: An accurate optical lattice clock with 87Sr atoms
• Authors: Rodolphe Le Targat (SYRTE), Xavier Baillard (SYRTE), Mathilde Fouché (SYRTE), Anders Brusch (SYRTE), Olivier Tcherbakoff (SYRTE), Giovanni D. Rovera (SYRTE), Pierre Lemonde (SYRTE)
• Abstract: We report a frequency measurement of the 1S0-3P0 transition of 87Sr atoms in an optical lattice clock. The frequency is determined to be 429 228 004 229 879 (5) Hz with a fractional uncertainty that is comparable to state-of-the-art optical clocks with neutral atoms in free fall. Two previous measurements of this transition were found to disagree by about 2x10^{-13}, i.e. almost four times the combined error bar, instilling doubt on the potential of optical lattice clocks to perform at a high accuracy level. In perfect agreement with one of these two values, our measurement essentially dissipates this doubt.

[physics]

## Ion trap papers

### Mon May 22 09:05:45 BST 2006

• [quant-ph/0605170]
• Title: A microfabricated surface-electrode ion trap in silicon
• Authors: J. Britton, D. Leibfried, J. Beall, R. B. Blakestad, J. J. Bollinger, J. Chiaverini, R. J. Epstein, J. D. Jost, D. Kielpinski, C. Langer, R. Ozeri, R. Reichle, S. Seidelin, N. Shiga, J. H. Wesenberg, D. J. Wineland
• Abstract: The prospect of building a quantum information processor underlies many recent advances ion trap fabrication techniques. Potentially, a quantum computer could be constructed from a large array of interconnected ion traps. We report on a micrometer-scale ion trap, fabricated from bulk silicon using micro-electromechanical systems (MEMS) techniques. The trap geometry is relatively simple in that the electrodes lie in a single plane beneath the ions. In such a trap we confine laser-cooled 24Mg+ ions approximately 40 microns above the surface. (...)

[physics]

### Thu May 18 09:34:48 BST 2006

• Phys. Rev. Lett. 96, 183601 (2006)
• Title: Multicolored Coherent Population Trapping in a \Lambda System Using Phase Modulated Fields
• Author: Harshawardhan Wanare
• Abstract: We demonstrate the simultaneous occurrence of coherent population trapping at a series of frequencies separated by modulation frequency of phase-modulated fields. The two arms of the \Lambda system are coupled to two phase-modulated fields and the response of the atomic system to such fields is calculated nonperturbatively. A judicious choice of modulation characteristics allows one to selectively switch on or off the occurrence of coherent population trapping at specific frequencies. A new technique is developed to compute two-dimensional tridiagonal matrix equations. This generalized technique provides the vital methodology needed to calculate the response of such systems in the strong modulation regime and for arbitrary field strengths.

[physics]

### Tue May 16 08:34:51 BST 2006

• Title: The Modern FPGA as Discriminator, TDC and ADC
• Authors: Gary S. Varner
• Abstract: Recent generations of Field Programmable Gate Arrays (FPGAs) have become indispensible tools for complex state machine control and signal processing, and now routinely incorporate CPU cores to allow execution of user software code. At the same time, their exceptional performance permits low-power implementation of functionality previously the exclusive domain of dedicated analog electronics. Specific examples presented here use FPGAs as discriminator, time-to-digital (TDC) and analog-to-digital converter (ADC). All three cases are examples of instrumentation for current or future astroparticle experiments.
• Title: General recursive solution for one dimensional quantum potentials
• Authors: Sérgio L. Morelhão, André V. (...)

[physics]

## Kindergarten quantum mechanics

### Fri May 12 14:37:22 BST 2006

Bob Coecke - researcher in comlab working on the formalism of quantum computing

[physics]

### Fri May 12 08:49:53 BST 2006

• Title: Perturbation theory via Feynman diagrams in classical mechanics
• Authors: R. Penco, D. Mauro
• Abstract: In this paper we show how Feynman diagrams, which are used as a tool to implement perturbation theory in quantum field theory, can be very useful also in classical mechanics, provided we introduce also at the classical level concepts like path integrals and generating functionals.
• Title: Deterministic single photons via conditional quantum evolution
• Authors: D. N. Matsukevich, T. Chaneliere, S. D. Jenkins, S.-Y. Lan, T. A. B. Kennedy, A. Kuzmich
• Abstract: A source of deterministic single photons is proposed and demonstrated by the application of a measurement-based feedback protocol to a heralded single photon source consisting of an ensemble of cold rubidium atoms. (...)

[physics]

### Mon May 8 09:32:37 BST 2006

• [physics/0605047]
• Title: Nano-fluidic dye laser
• Authors: Morten Gersborg-Hansen, Anders Kristensen
• Abstract: This letter describes the design and operation of a single mode polymer-based nano-fluidic dye laser. The device relies on light-confinement in a nano-structured polymer film where an array of nano-fluidic channels is filled by capillary action with a liquid dye solution which has a refractive index lower than that of the polymer. In combination with a third order distributed feed-back (DFB) grating, formed by the array of nano-fluidic channels, this yields a low threshold for lasing. The laser is straight-forward to integrate on Lab-on-a-Chip micro-systems, e.g. for novel sensor concepts, where coherent, tunable light in the visible range is desired.

[physics]

### Mon May 8 09:12:44 BST 2006

• [physics/0605046]
• Title: Interference-filter-stabilized external-cavity diode lasers
• Authors: X. Baillard, A. Gauguet, S. Bize, P. Lemonde, Ph. Laurent, A. Clairon, P. Rosenbusch
• Abstract: We have developed external-cavity diode lasers, where the wavelength selection is assured by a low loss interference filter instead of the common diffraction grating. The filter allows a linear cavity design reducing the sensitivity of the wavelength and the external cavity feedback against misalignment. By separating the feedback and wavelength selection functions, both can be optimized independently leading to an increased tunability of the laser. The design is employed for the generation of laser light at 698, 780 and 852 nm. Its characteristics make it a well suited candidate for space-born lasers.

[physics]

## Physics of terrorism

### Fri May 5 08:37:52 BST 2006

• [physics/0605035]
• Title: Universal patterns underlying ongoing wars and terrorism
• Authors: Neil F. Johnson, Mike Spagat, Jorge A. Restrepo, Oscar Becerra, Juan Camilo Bohorquez, Nicolas Suarez, Elvira Maria Restrepo, Roberto Zarama
• Abstract: We report a remarkable universality in the patterns of violence arising in three high-profile ongoing wars, and in global terrorism. Our results suggest that these quite different conflict arenas currently feature a common type of enemy, i.e. the various insurgent forces are beginning to operate in a similar way regardless of their underlying ideologies, motivations and the terrain in which they operate. We provide a microscopic theory to explain our main observations. This theory treats the insurgent force as a generic, self-organizing system which is dynamically evolving through the continual coalescence and fragmentation of its constituent groups.

[physics]

## Quantum lithography with classical light

### Thu May 4 09:18:48 BST 2006

• Phys. Rev. Lett. 96, 163603 (2006)
• Title: Quantum Lithography with Classical Light
• Authors: P. R. Hemmer, A. Muthukrishnan, M. O. Scully, and M. S. Zubairy
• Abstract: We show how to achieve subwavelength diffraction and imaging with classical light, previously thought to require quantum fields. By correlating wave vector and frequency in a narrow band, multiphoton detection process that uses Doppleron-type resonances, we show how to achieve arbitrary focal and image plane patterning with classical laser light at submultiples of the Rayleigh limit, with high efficiency, visibility, and spatial coherence. A frequency-selective measurement process thus allows one to simulate, semiclassically, the path-number correlations that distinguish a quantum entangled field. (...)

[physics]

## Quantum optics with ultrafast lasers

### Thu May 4 08:49:28 BST 2006

• [physics/0605034]
• Title: Kilohertz-resolution spectroscopy of cold atoms with an optical frequency comb
• Authors: T. M. Fortier, Y. Le Coq, J. E. Stalnaker, D. Ortega, S. A. Diddams, C. W. Oates, L. Hollberg
• Abstract: We have performed sub-Doppler spectroscopy on the narrow intercombination line of cold calcium atoms using the amplified output of a femtosecond laser frequency comb. Injection locking of a 657-nm diode laser with a femtosecond comb allows for two regimes of amplification, one in which many lines of the comb are amplified, and one where a single line is predominantly amplified. The output of the laser in both regimes was used to perform kilohertz-level spectroscopy. This experiment demonstrates the potential for high-resolution absolute-frequency spectroscopy over the entire spectrum of the frequency comb output using a single high-finesse optical reference cavity.

[physics] [qo]

## Feedback and quantum systems

### Wed May 3 08:57:19 BST 2006

• [quant-ph/0605015]
• Title: Applications of Feedback Control in Quantum Systems
• Authors: Kurt Jacobs
• Abstract: We give an introduction to feedback control in quantum systems, as well as an overview of the variety of applications which have been explored to date. This introductory review is aimed primarily at control theorists unfamiliar with quantum mechanics, but should also be useful to quantum physicists interested in applications of feedback control. We explain how feedback in quantum systems differs from that in traditional classical systems, and how in certain cases the results from modern optimal control theory can be applied directly to quantum systems. In addition to noise reduction and stabilization, an important application of feedback in quantum systems is adaptive measurement, and we discuss the various applications of adaptive measurements. (...)

[physics] [qo]

## Spectroscopy with frequency comb

### Fri Apr 28 09:36:00 BST 2006

• Phys. Rev. Lett. 96, 153001 (2006)
• Title: High Resolution Atomic Coherent Control via Spectral Phase Manipulation of an Optical Frequency Comb Authors: Matthew C. Stowe, Flavio C. Cruz, Adela Marian, and Jun Ye
• Abstract: We demonstrate high resolution coherent control of cold atomic rubidium utilizing spectral phase manipulation of a femtosecond optical frequency comb. Transient coherent accumulation is directly manifested by the enhancement of signal amplitude and spectral resolution via the pulse number. The combination of frequency comb technology and spectral phase manipulation enables coherent control techniques to enter a new regime with natural linewidth resolution.
• Comments: Uses phase stabilized optical frequency comb to perform coherent manipulation of Rb atoms. (...)

[physics] [qo]

## Quantum optics in Mathematica

### Thu Apr 20 15:45:20 BST 2006

Quantum optics in Mathematica

• http://library.wolfram.com/infocenter/MathSource/4898/
• Author: César Augusto Guerra Gutiérrez
• Quantum Algebra - QAfiles.zip and QAtutorial.nb

[physics] [qo]

### Thu Apr 20 09:04:14 BST 2006

• Phys. Rev. Lett. 96, 140403 (2006)
• Title: Achieving Peak Brightness in an Atom Laser
• Authors: N. P. Robins, C. Figl, S. A. Haine, A. K. Morrison, M. Jeppesen, J. J. Hope, and J. D. Close (Australian National University)
• Abstract: In this Letter we present experimental results and a simple analytic theory on the first continuous (long pulse) Raman atom laser. We analyze the flux and brightness of a generic two state atom laser with an analytic model that shows excellent agreement with our experiments. We show that, for the same source size, the brightness achievable with a Raman atom laser is at least 3 orders of magnitude greater than achievable in any other demonstrated continuously outcoupled atom laser.
• Comment: Most atom lasers use an RF transition to couple between the magnetic trapped and untrapped (output) states. (...)

[physics]

## Finding scientific gems with Google

### Wed Apr 19 08:35:55 BST 2006

• [physics/0604130]
• Title: Finding Scientific Gems with Google
• Authors: P. Chen, H. Xie, S. Maslov, S. Redner
• Comment: The Google PageRank algorithm is used to judge the importance of papers in PRL, and compared to the raw number of citations. The algorithm gives more weight to papers that are cited by important papers, or those that have few references (the assumption is that each reference is then more important)
• Idea: Modify my RefParse program to use the PageRank algorithm

[physics]

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