93 research outputs found
Macroscopic magnetic guide for cold atoms
We demonstrate a macroscopic magnetic guide for cold atoms with suppressed
longitudinal field curvature which is highly desired for atom interferometry.
The guide is based on macroscopic copper tape coils in a copropagating currents
geometry, where the atoms are located between the coils few cm away from each
surface. The symmetric geometry provides a much lower magnetic field curvature
per fixed length that promises longer coherence time for atom interferometers.
A double-tape design of each coil allows a smooth translation of guided atoms
without addition of an external bias field. The guide is also immune from the
current and thermal noise by virtue of the turns averaging and a large working
distance, respectively. We present the experimental results of guide
application to atom interferometry
Demonstration of a moving guide based atom interferometer for rotation sensing
We demonstrate area-enclosing atom interferometry based on a moving guide.
Light pulses along the free propagation direction of a magnetic guide are
applied to split and recombine the confined atomic matter-wave, while the atoms
are translated back and forth along a second direction in 50 ms. The
interferometer is estimated to resolve ten times the earth rotation rate per
interferometry cycle. We demonstrate a ``folded figure 8'' interfering
configuration for creating a compact, large-area atom gyroscope with
multiple-turn interfering paths.Comment: Minor revisio
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Demonstration of a Multipulse Interferometer for Quantum Kicked-Rotor Studies
We implemented a multipulse interferometer scheme that allows us to study a quantum kicked rotor by observing dephasing of momentum coherence. Our study shows that momentum coherence can be nearly perfectly preserved under conditions where the mean energy as a function of the kick number is known to increase without bound. The accompanying width narrowing of these coherences may provide a new method for accurate measurement of the recoil frequency.Physic
Observation of coherence revival and fidelity saturation in a delta-kicked rotor potential
We experimentally investigate the effect of atomic -kicked rotor
potentials on the mutual coherence between wavepackets in an atom
interferometer. The differential action of the kicked rotor degrades the mutual
coherence, leading to a reduction of the interferometry fringe visibility;
however, when the repetition rate of the kicked rotor is at or near the quantum
resonance, we observe revival of matter-wave coherence as the number of kicks
increases, resulting in non-vanishing coherence in the large kick number limit.
This coherence saturation effect reflects a saturation of fidelity decay due to
momentum displacements in deep quantum regime. The saturation effect is
accompanied with an invariant distribution of matter-wave coherence under the
kicked rotor perturbations.Comment: 10 pages, 3 figures. Minor revision
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DNA Unzipping Phase Diagram Calculated Via Replica Theory
We show how single-molecule unzipping experiments can provide strong evidence that the zero-force melting transition of long molecules of natural dsDNA should be classified as a phase transition of the higher-order type (continuous). Toward this end, we study a statistical-mechanics model for the fluctuating structure of a long molecule of dsDNA, and compute the equilibrium phase diagram for the experiment in
which the molecule is unzipped under applied force. We consider a perfect-matching dsDNA model, in which the loops are volume-excluding chains with arbitrary loop exponent c. We include stacking interactions,
hydrogen bonds, and main-chain entropy. We include sequence heterogeneity at the level of random sequences; in particular, there is no correlation in the base-pairing (bp) energy from one sequence position to the next. We present heuristic arguments to demonstrate that the low-temperature macrostate does not exhibit degenerate
ergodicity breaking. We use this claim to understand the results of our replica-theoretic calculation of the equilibrium properties of the system. As a function of temperature, we obtain the minimal force at which the molecule separates completely. This critical-force curve is a line in the temperature-force phase diagram that marks the regions where the molecule exists primarily as a double helix versus the region where the molecule exists as two separate strands. We compare our random-sequence model to magnetic tweezer experiments performed on the 48 502 bp genome of bacteriophage λ. We find good agreement with the experimental data, which is restricted to temperatures between 24 and 50 °C. At higher temperatures, the critical-force curve of our random-sequence model is very different for that of the homogeneous-sequence version of our model. For both sequence models, the critical force falls to zero at the melting temperature T like . For the
homogeneous-sequence model, =1/2 almost exactly, while for the random-sequence model, 0.9. Importantly, the shape of the critical-force curve is connected, via our theory, to the manner in which the helix
fraction falls to zero at T. The helix fraction is the property that is used to classify the melting transition as a type of phase transition. In our calculation, the shape of the critical-force curve holds strong evidence that the zero-force melting transition of long natural dsDNA should be classified as a higher-order (continuous) phase
transition. Specifically, the order is 3rd or greater.Physic
Realization of Coherent Optically Dense Media via Buffer-Gas Cooling
We demonstrate that buffer-gas cooling combined with laser ablation can be
used to create coherent optical media with high optical depth and low Doppler
broadening that offers metastable states with low collisional and motional
decoherence. Demonstration of this generic technique opens pathways to coherent
optics with a large variety of atoms and molecules. We use helium buffer gas to
cool 87Rb atoms to below 7 K and slow atom diffusion to the walls.
Electromagnetically induced transparency (EIT) in this medium allows for 50%
transmission in a medium with initial OD >70 and for slow pulse propagation
with large delay-bandwidth products. In the high-OD regime, we observe
high-contrast spectrum oscillations due to efficient four-wave mixing.Comment: 4 pages, 4 figures. V2: modified title, abstract, introduction,
conclusion; added references; improved theoretical fit in figure 3(b);
shortened slow light theory description; clarified simplicity of apparatus.
Final version as published in Phys. Rev.
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The differential extension in dsDNA bound to Rad51 filaments may play important roles in homology recognition and strand exchange
RecA and Rad51 proteins play an important role in DNA repair and homologous recombination. For RecA, X-ray structure information and single molecule force experiments have indicated that the differential extension between the complementary strand and its Watson–Crick pairing partners promotes the rapid unbinding of non-homologous dsDNA and drives strand exchange forward for homologous dsDNA. In this work we find that both effects are also present in Rad51 protein. In particular, pulling on the opposite termini (3′ and 5′) of one of the two DNA strands in a dsDNA molecule allows dsDNA to extend along non-homologous Rad51-ssDNA filaments and remain stably bound in the extended state, but pulling on the 3′5′ ends of the complementary strand reduces the strand-exchange rate for homologous filaments. Thus, the results suggest that differential extension is also present in dsDNA bound to Rad51. The differential extension promotes rapid recognition by driving the swift unbinding of dsDNA from non-homologous Rad51-ssDNA filaments, while at the same time, reducing base pair tension due to the transfer of the Watson–Crick pairing of the complementary strand bases from the highly extended outgoing strand to the slightly less extended incoming strand, which drives strand exchange forward
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