221 research outputs found
Quantum simulation of the Klein paradox with trapped ions
We report on quantum simulations of relativistic scattering dynamics using
trapped ions. The simulated state of a scattering particle is encoded in both
the electronic and vibrational state of an ion, representing the discrete and
continuous components of relativistic wave functions. Multiple laser fields and
an auxiliary ion simulate the dynamics generated by the Dirac equation in the
presence of a scattering potential. Measurement and reconstruction of the
particle wave packet enables a frame-by-frame visualization of the scattering
processes. By precisely engineering a range of external potentials we are able
to simulate text book relativistic scattering experiments and study Klein
tunneling in an analogue quantum simulator. We describe extensions to solve
problems that are beyond current classical computing capabilities.Comment: 3 figures, accepted for publication in PR
Demonstration and characterization of α-human atrial natriuretic factor in human plasma
AbstractThis paper describes a highly specific and sensitive radioimmunoassay for α-human atrial natriuretic factor (α-hANF), the C-terminal 28-amino-acid residue portion of human prepro-ANF in human plasma. A novel extraction and prepurification procedure allowed for detection of levels of immunoreactive-α-hANF as low as 0.5 fmolml. In normotensive subjects, levels in the range 1–23 fmolml (mean = 8.9 fmolml) were found. Combined gel permeation and HPLC analysis demonstrated that this ir-α-hANF was comprised virtually exclusively of authentic 28-residue β-hANF. No evidence for occurrence of larger precursor forms in human plasma was acquired. A heterogenous group of hypertensive patients displayed considerably higher levels (mean = 62.2 fmolml), of interest in view of the hypotensive properties of ANF.Atrial natriuretic factorHuman plasmaExtractionChromatographie characterizationHypertensio
Deterministic entanglement of ions in thermal states of motion
We give a detailed description of the implementation of a Molmer-Sorensen
gate entangling two Ca+ ions using a bichromatic laser beam near-resonant with
a quadrupole transition. By amplitude pulse shaping and compensation of
AC-Stark shifts we achieve a fast gate operation without compromising the error
rate. Subjecting different input states to concatenations of up to 21
individual gate operations reveals Bell state fidelities above 0.80. In
principle, the entangling gate does not require ground state cooling of the
ions as long as the Lamb-Dicke criterion is fulfilled. We present the first
experimental evidence for this claim and create Bell states with a fidelity of
0.974(1) for ions in a thermal state of motion with a mean phonon number of
=20(2) in the mode coupling to the ions' internal states.Comment: 18 pages, 9 figures (author name spelling corrected
A novel mixed and energy‐momentum consistent framework for coupled nonlinear thermo‐electro‐elastodynamics
A novel mixed framework and energy-momentum consistent integration scheme in the field of coupled nonlinear thermo-electro-elastodynamics is proposed. The mixed environment is primarily based on a framework for elastodynamics in the case of polyconvex strain energy functions. For this elastodynamic framework, the properties of the so-called tensor cross product are exploited to derive a mixed formulation via a Hu-Washizu type extension of the strain energy function. Afterwards, a general path to incorporate nonpotential problems for mixed formulations is demonstrated. To this end, the strong form of the mixed framework is derived and supplemented with the energy balance as well as Maxwell\u27s equations neglecting magnetic and time dependent effects. By additionally choosing an appropriate energy function, this procedure leads to a fully coupled thermo-electro-elastodynamic formulation which benefits from the properties of the underlying mixed framework. In addition, the proposed mixed framework facilitates the design of a new energy-momentum consistent time integration scheme by employing discrete derivatives in the sense of Gonzalez. A one-step integration scheme of second-order accuracy is obtained which is shown to be stable even for large time steps. Eventually, the performance of the novel formulation is demonstrated in several numerical examples
Compatibility and noncontextuality for sequential measurements
A basic assumption behind the inequalities used for testing noncontextual
hidden variable models is that the observables measured on the same individual
system are perfectly compatible. However, compatibility is not perfect in
actual experiments using sequential measurements. We discuss the resulting
"compatibility loophole" and present several methods to rule out certain hidden
variable models which obey a kind of extended noncontextuality. Finally, we
present a detailed analysis of experimental imperfections in a recent trapped
ion experiment and apply our analysis to that case.Comment: 15 pages, 2 figures, v2: problem with latex solve
Random Time-Dependent Quantum Walks
We consider the discrete time unitary dynamics given by a quantum walk on the
lattice performed by a quantum particle with internal degree of freedom,
called coin state, according to the following iterated rule: a unitary update
of the coin state takes place, followed by a shift on the lattice, conditioned
on the coin state of the particle. We study the large time behavior of the
quantum mechanical probability distribution of the position observable in
when the sequence of unitary updates is given by an i.i.d. sequence of
random matrices. When averaged over the randomness, this distribution is shown
to display a drift proportional to the time and its centered counterpart is
shown to display a diffusive behavior with a diffusion matrix we compute. A
moderate deviation principle is also proven to hold for the averaged
distribution and the limit of the suitably rescaled corresponding
characteristic function is shown to satisfy a diffusion equation. A
generalization to unitary updates distributed according to a Markov process is
also provided. An example of i.i.d. random updates for which the analysis of
the distribution can be performed without averaging is worked out. The
distribution also displays a deterministic drift proportional to time and its
centered counterpart gives rise to a random diffusion matrix whose law we
compute. A large deviation principle is shown to hold for this example. We
finally show that, in general, the expectation of the random diffusion matrix
equals the diffusion matrix of the averaged distribution.Comment: Typos and minor errors corrected. To appear In Communications in
Mathematical Physic
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