2,719 research outputs found
Conditional linear-optical measurement schemes generate effective photon nonlinearities
We provide a general approach for the analysis of optical state evolution
under conditional measurement schemes, and identify the necessary and
sufficient conditions for such schemes to simulate unitary evolution on the
freely propagating modes. If such unitary evolution holds, an effective photon
nonlinearity can be identified. Our analysis extends to conditional measurement
schemes more general than those based solely on linear optics.Comment: 16 pages, 2 figure
Nanocalorimetric Evidence for Nematic Superconductivity in the Doped Topological Insulator SrBiSe
Spontaneous rotational-symmetry breaking in the superconducting state of
doped has attracted significant attention as an
indicator for topological superconductivity. In this paper, high-resolution
calorimetry of the single-crystal
provides unequivocal evidence of a two-fold rotational symmetry in the
superconducting gap by a \emph{bulk thermodynamic} probe, a fingerprint of
nematic superconductivity. The extremely small specific heat anomaly resolved
with our high-sensitivity technique is consistent with the material's low
carrier concentration proving bulk superconductivity. The large basal-plane
anisotropy of is attributed to a nematic phase of a two-component
topological gap structure and caused by a
symmetry-breaking energy term .
A quantitative analysis of our data excludes more conventional sources of this
two-fold anisotropy and provides the first estimate for the symmetry-breaking
strength , a value that points to an onset transition of
the second order parameter component below 2K
The apparent roughness of a sand surface blown by wind from an analytical model of saltation
We present an analytical model of aeolian sand transport. The model
quantifies the momentum transfer from the wind to the transported sand by
providing expressions for the thickness of the saltation layer and the apparent
surface roughness. These expressions are derived from basic physical principles
and a small number of assumptions. The model further predicts the sand
transport rate (mass flux) and the impact threshold (the smallest value of the
wind shear velocity at which saltation can be sustained). We show that, in
contrast to previous studies, the present model's predictions are in very good
agreement with a range of experiments, as well as with numerical simulations of
aeolian saltation. Because of its physical basis, we anticipate that our model
will find application in studies of aeolian sand transport on both Earth and
Mars
Effective field theory of 3He
3He and the triton are studied as three-body bound states in the effective
field theory without pions. We study 3He using the set of integral equations
developed by Kok et al. which includes the full off-shell T-matrix for the
Coulomb interaction between the protons. To leading order, the theory contains:
two-body contact interactions whose renormalized strengths are set by the NN
scattering lengths, the Coulomb potential, and a three-body contact
interaction. We solve the three coupled integral equations with a sharp
momentum cutoff, Lambda, and find that a three-body interaction is required in
3He at leading order, as in the triton. It also exhibits the same limit-cycle
behavior as a function of Lambda, showing that the Efimov effect remains in the
presence of the Coulomb interaction. We also obtain the difference between the
strengths of the three-body forces in 3He and the triton.Comment: 18 pages, 6 figures; further discussion and references adde
Efficient optical quantum information processing
Quantum information offers the promise of being able to perform certain
communication and computation tasks that cannot be done with conventional
information technology (IT). Optical Quantum Information Processing (QIP) holds
particular appeal, since it offers the prospect of communicating and computing
with the same type of qubit. Linear optical techniques have been shown to be
scalable, but the corresponding quantum computing circuits need many auxiliary
resources. Here we present an alternative approach to optical QIP, based on the
use of weak cross-Kerr nonlinearities and homodyne measurements. We show how
this approach provides the fundamental building blocks for highly efficient
non-absorbing single photon number resolving detectors, two qubit parity
detectors, Bell state measurements and finally near deterministic control-not
(CNOT) gates. These are essential QIP devicesComment: Accepted to the Journal of optics B special issue on optical quantum
computation; References update
Overcoming phonon-induced dephasing for indistinguishable photon sources
Reliable single photon sources constitute the basis of schemes for quantum
communication and measurement based quantum computing. Solid state single
photon sources based on quantum dots are convenient and versatile but the
electronic transitions that generate the photons are subject to interactions
with lattice vibrations. Using a microscopic model of electron-phonon
interactions and a quantum master equation, we here examine phonon-induced
decoherence and assess its impact on the rate of production, and
indistinguishability, of single photons emitted from an optically driven
quantum dot system. We find that, above a certain threshold of desired
indistinguishability, it is possible to mitigate the deleterious effects of
phonons by exploiting a three-level Raman process for photon production
Influence of the bias voltage on the structure and the tribological performance of nanoscale multilayer C/Cr PVD coatings
Nanoscale multilayer C/Cr coatings have been deposited by utilising the combined steered cathodic arc/unbalanced magnetron sputtering technique. The coating microstructure and tribological performance have been investigated as a function of the bias voltage, ranging from U-b=-65 to -350 V. The XRD results revealed that C/Cr coatings are amorphous at low U-b, but became more crystalline when the Ub increased to -350 V. High-resolution XTEM analysis indicated coating densification and smoothening as well as formation of novel amorphous nanostructure, in which carbon-rich clusters are surrounded by a Cr-rich matrix, leading to the formation of self-organised multilayer structure as the bias voltage was increased from -65 to -350 V. An increase of the bias voltage from -65 to -350 V resulted in an increase in the hardness from 8 to 25 CiPa and Young's modulus, E from 186 to 319 GPa. A pin-on-disc test showed that the friction coefficient was reduced from 0.22 to 0.16 when the bias voltage was increased from -65 to -95 V However, a further increase in the bias voltage to -350 V led to an increase in the friction coefficient to 0.31. The lowest wear coefficient K(c)similar to6.25 x 10(-17) m(3) N-1 m(-1) was achieved at U-b = - 120 V. Standard HSS drills, 8 mm in diameter, coated with C/Cr have been tested using solution annealed AISI 304 stainless steel as the work piece material. An improvement of the lifetime by a factor of similar to9 has been achieved as compared to the uncoated tools. In this test, the C/Cr coating outperformed a number of commercially available PVD coatings, such as TiCN, TiAlCrN and showed similar performance to TiAlCrYN. (C) 2004 Elsevier B.V. All rights reserved
Weak nonlinearities: A new route to optical quantum computation
Quantum information processing (QIP) offers the promise of being able to do
things that we cannot do with conventional technology. Here we present a new
route for distributed optical QIP, based on generalized quantum non-demolition
measurements, providing a unified approach for quantum communication and
computing. Interactions between photons are generated using weak
non-linearities and intense laser fields--the use of such fields provides for
robust distribution of quantum information. Our approach requires only a
practical set of resources, and it uses these very efficiently. Thus it
promises to be extremely useful for the first quantum technologies, based on
scarce resources. Furthermore, in the longer term this approach provides both
options and scalability for efficient many-qubit QIP.Comment: 7 Pages, 4 Figure
Universal continuous-variable quantum computation: Requirement of optical nonlinearity for photon counting
Although universal continuous-variable quantum computation cannot be achieved
via linear optics (including squeezing), homodyne detection and feed-forward,
inclusion of ideal photon counting measurements overcomes this obstacle. These
measurements are sometimes described by arrays of beam splitters to distribute
the photons across several modes. We show that such a scheme cannot be used to
implement ideal photon counting and that such measurements necessarily involve
nonlinear evolution. However, this requirement of nonlinearity can be moved
"off-line," thereby permitting universal continuous-variable quantum
computation with linear optics.Comment: 6 pages, no figures, replaced with published versio
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