1,133 research outputs found
Using Abrupt Changes in Magnetic Susceptibility within Type-II Superconductors to Explore Global Decoherence Phenomena
A phenomenon of a periodic staircase of macroscopic jumps in the admitted
magnetic field has been observed, as the magnitude of an externally applied
magnetic field is smoothly increased or decreased upon a superconducting (SC)
loop of type II niobium-titanium wire which is coated with a
non-superconducting layer of copper. Large temperature spikes were observed to
occur simultaneously with the jumps, suggesting brief transitions to the normal
state, caused by en masse motions of Abrikosov vortices. An experiment that
exploits this phenomenon to explore the global decoherence of a large
superconducting system will be discussed, and preliminary data will be
presented. Though further experimentation is required to determine the actual
decoherence rate across the superconducting system, multiple classical
processes are ruled out, suggesting that jumps in magnetic flux are fully
quantum mechanical processes which may correspond to large group velocities
within the global Cooper pair wavefunction.Comment: 13 pages, 4 figures, part of proceedings for FQMT 2011 conference in
Prague, Czech Republi
Weak-wave advancement in nearly collinear four-wave mixing
We identify a new four-wave mixing process in which two nearly collinear pump
beams produce phase-dependent gain into a weak bisector signal beam in a
self-defocusing Kerr medium. Phase matching is achieved by weak-wave
advancement caused by cross-phase modulation between the pump and signal beams.
We relate this process to the inverse of spatial modulational instability and
suggest a time-domain analog.Comment: 7 pages, 3 figure
Can a charged ring levitate a neutral, polarizable object? Can Earnshaw's Theorem be extended to such objects?
Stable electrostatic levitation and trapping of a neutral, polarizable object
by a charged ring is shown to be theoretically impossible. Earnshaw's Theorem
precludes the existence of such a stable, neutral particle trap.Comment: 11 pages, 1 figur
Microwave measurements of the photonic bandgap in a two-dimensional photonic crystal slab
We have measured the photonic bandgap in the transmission of microwaves
through a two-dimensional photonic crystal slab. The structure was constructed
by cementing acrylic rods in a hexagonal closed-packed array to form
rectangular stacks. We find a bandgap centered at approximately 11 GHz, whose
depth, width and center frequency vary with the number of layers in the slab,
angle of incidence and microwave polarization.Comment: 8 pages, 3 figures, submitted to Journal of Applied Physic
Photonic crystal polarizers and polarizing beam splitters
We have experimentally demonstrated polarizers and polarizing beam splitters
based on microwave-scale two-dimensional photonic crystals. Using polarized
microwaves within certain frequency bands, we have observed a squared-sinusoid
(Malus) transmission law when using the photonic crystal as a polarizer. The
photonic crystal also functions as a polarizing beamsplitter; in this
configuration it can be engineered to split incident polarizations in either
order, making it more versatile than conventional, Brewster-angle
beamsplitters.Comment: 7 pages, 3 figures, published Journal Applied Physics 93, 9429 (2003
The limits of the rotating wave approximation in the electromagnetic field propagation in a cavity
We consider three two-level atoms inside a one-dimensional cavity,
interacting with the electromagnetic field in the rotating wave approximation
(RWA), commonly used in the atom-radiation interaction. One of the three atoms
is initially excited, and the other two are in their ground state. We
numerically calculate the propagation of the field spontaneously emitted by the
excited atom and scattered by the second atom, as well as the excitation
probability of the second and third atom. The results obtained are analyzed
from the point of view of relativistic causality in the atom-field interaction.
We show that, when the RWA is used, relativistic causality is obtained only if
the integrations over the field frequencies are extended to ; on the
contrary, noncausal tails remain even if the number of field modes is
increased. This clearly shows the limit of the RWA in dealing with subtle
problems such as relativistic causality in the atom-field interaction.Comment: 13 pages, 6 figure
Field-induced thermal metal-to-insulator transition in underdoped LSCO
The transport of heat and charge in cuprates was measured in undoped and
heavily-underdoped single crystal La_{2-x}Sr_xCuO_{4+delta} (LSCO). In
underdoped LSCO, the thermal conductivity is found to decrease with increasing
magnetic field in the T --> 0 limit, in striking contrast to the increase
observed in all superconductors, including cuprates at higher doping. The
suppression of superconductivity with magnetic field shows that a novel thermal
metal-to-insulator transition occurs upon going from the superconducting state
to the field-induced normal state.Comment: 2 pages, 2 figures, submitted to M2S-Rio 2003 Proceeding
The Electron Spectral Function in Two-Dimensional Fractionalized Phases
We study the electron spectral function of various zero-temperature
spin-charge separated phases in two dimensions. In these phases, the electron
is not a fundamental excitation of the system, but rather ``decays'' into a
spin-1/2 chargeless fermion (the spinon) and a spinless charge e boson (the
chargon). Using low-energy effective theories for the spinons (d-wave pairing
plus possible N\'{e}el order), and the chargons (condensed or quantum
disordered bosons), we explore three phases of possible relevance to the
cuprate superconductors: 1) AF*, a fractionalized antiferromagnet where the
spinons are paired into a state with long-ranged N\'{e}el order and the
chargons are 1/2-filled and (Mott) insulating, 2) the nodal liquid, a
fractionalized insulator where the spinons are d-wave paired and the chargons
are uncondensed, and 3) the d-wave superconductor, where the chargons are
condensed and the spinons retain a d-wave gap. Working within the gauge
theory of such fractionalized phases, our results should be valid at scales
below the vison gap. However, on a phenomenological level, our results should
apply to any spin-charge separated system where the excitations have these
low-energy effective forms. Comparison with ARPES data in the undoped,
pseudogapped, and superconducting regions is made.Comment: 10 page
Fast light, slow light, and phase singularities: a connection to generalized weak values
We demonstrate that Aharonov-Albert-Vaidman (AAV) weak values have a direct
relationship with the response function of a system, and have a much wider
range of applicability in both the classical and quantum domains than
previously thought. Using this idea, we have built an optical system, based on
a birefringent photonic crystal, with an infinite number of weak values. In
this system, the propagation speed of a polarized light pulse displays both
superluminal and slow light behavior with a sharp transition between the two
regimes. We show that this system's response possesses two-dimensional,
vortex-antivortex phase singularities. Important consequences for optical
signal processing are discussed.Comment: 9 pages, 4 figures, accepted in Physical Review Letters (2003
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