4,672 research outputs found
A Quantum Rosetta Stone for Interferometry
Heisenberg-limited measurement protocols can be used to gain an increase in
measurement precision over classical protocols. Such measurements can be
implemented using, e.g., optical Mach-Zehnder interferometers and Ramsey
spectroscopes. We address the formal equivalence between the Mach-Zehnder
interferometer, the Ramsey spectroscope, and the discrete Fourier transform.
Based on this equivalence we introduce the ``quantum Rosetta stone'', and we
describe a projective-measurement scheme for generating the desired
correlations between the interferometric input states in order to achieve
Heisenberg-limited sensitivity. The Rosetta stone then tells us the same method
should work in atom spectroscopy.Comment: 8 pages, 4 figure
Optical Communication Noise Rejection Using Correlated Photons
This paper describes a completely new way to perform noise rejection using a
two-photon sensitive detector and taking advantage of the properties of
correlated photons to improve an optical communications link in the presence of
uncorrelated noise. In particular, a detailed analysis is made of the case
where a classical link would be saturated by an intense background, such as
when a satellite is in front of the sun,and identifies a regime where the
quantum correlating system has superior performance.Comment: 12 pages, 1 figure, 1 tabl
The creation of large photon-number path entanglement conditioned on photodetection
Large photon-number path entanglement is an important resource for enhanced
precision measurements and quantum imaging. We present a general constructive
protocol to create any large photon number path-entangled state based on the
conditional detection of single photons. The influence of imperfect detectors
is considered and an asymptotic scaling law is derived.Comment: 6 pages, 4 figure
Triangle Diagram with Off-Shell Coulomb T-Matrix for (In-)Elastic Atomic and Nuclear Three-Body Processes
The driving terms in three-body theories of elastic and inelastic scattering
of a charged particle off a bound state of two other charged particles contain
the fully off-shell two-body Coulomb T-matrix describing the intermediate-state
Coulomb scattering of the projectile with each of the charged target particles.
Up to now the latter is usually replaced by the Coulomb potential, either when
using the multiple-scattering approach or when solving three-body integral
equations. General properties of the exact and the approximate on-shell driving
terms are discussed, and the accuracy of this approximation is investigated
numerically, both for atomic and nuclear processes including bound-state
excitation, for energies below and above the corresponding three-body
dissociation threshold, over the whole range of scattering angles.Comment: 22 pages, 11 figures, figures can be obtained upon request from the
Authors, revte
Continuous-Variable Quantum Key Distribution using Thermal States
We consider the security of continuous-variable quantum key distribution
using thermal (or noisy) Gaussian resource states. Specifically, we analyze
this against collective Gaussian attacks using direct and reverse
reconciliation where both protocols use either homodyne or heterodyne
detection. We show that in the case of direct reconciliation with heterodyne
detection, an improved robustness to channel noise is achieved when large
amounts of preparation noise is added, as compared to the case when no
preparation noise is added. We also consider the theoretical limit of infinite
preparation noise and show a secure key can still be achieved in this limit
provided the channel noise is less than the preparation noise. Finally, we
consider the security of quantum key distribution at various electromagnetic
wavelengths and derive an upper bound related to an entanglement-breaking
eavesdropping attack and discuss the feasibility of microwave quantum key
distribution.Comment: 12 pages, 11 figures. Updated from published version with some minor
correction
Die wese van godsdienssin - ’n empiriese studie
In this article the following issues concerning the essence of religiosity are considered: faith, trust, decision making, knowledge of principles, commitment, direction, hope, peace, meaning and security. The respondents used in this study were politicians, businessmen and teacher educators from all sectors and regions of South Africa. Higher order factor analysis and item analysis were used to evaluate the validity and reliability of the questionnaire. Subsequently differential differences were investigated by applying Hotelling's T-square test followed by the Student t-test as well as Multivariate Analysis of Variance (ANOVA) and Scheffe. Significant differences in the degree of religiosity were found between language and religious groups, as well as between respondents with different educational qualifications and between those living in urban and rural areas. Ministers of religion should note that it is essential to guide believers to a greater commitment and to the religious seeking of meaning and peace. The correct knowledge of and insight into the essence of religiosity will lead to attaining this goal
From Linear Optical Quantum Computing to Heisenberg-Limited Interferometry
The working principles of linear optical quantum computing are based on
photodetection, namely, projective measurements. The use of photodetection can
provide efficient nonlinear interactions between photons at the single-photon
level, which is technically problematic otherwise. We report an application of
such a technique to prepare quantum correlations as an important resource for
Heisenberg-limited optical interferometry, where the sensitivity of phase
measurements can be improved beyond the usual shot-noise limit. Furthermore,
using such nonlinearities, optical quantum nondemolition measurements can now
be carried out at the single-photon level.Comment: 10 pages, 5 figures; Submitted to a Special Issue of J. Opt. B on
"Fluctuations and Noise in Photonics and Quantum Optics" (Herman Haus
Memorial Issue); v2: minor change
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
Practical quantum repeaters with linear optics and double-photon guns
We show how to create practical, efficient, quantum repeaters, employing
double-photon guns, for long-distance optical quantum communication. The guns
create polarization-entangled photon pairs on demand. One such source might be
a semiconducter quantum dot, which has the distinct advantage over parametric
down-conversion that the probability of creating a photon pair is close to one,
while the probability of creating multiple pairs vanishes. The swapping and
purifying components are implemented by polarizing beam splitters and
probabilistic optical CNOT gates.Comment: 4 pages, 4 figures ReVTe
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