J. Klepp

Experimental Test of Quantum Contextuality in Neutron Interferometry

We performed an experimental test of the Kochen-Specker theorem based on an inequality derived from the Peres-Mermin proof, using spin-path (momentum) entanglement in a single neutron system. Following the strategy proposed by Cabello et al. [Phys. Rev. Lett. 100, 130404 (2008)10.1103/PhysRevLett.100.130404], a Bell-like state was generated, and three expectation values were determined. The observed violation 2.291 +/- 0.008 not less, dbl equals1 clearly shows that quantum mechanical predictions cannot be reproduced by noncontextual hidden-variable theories.

Experimental demonstration of the stability of Berry's phase for a spin-1/2 particle.

The geometric phase has been proposed as a candidate for noise resilient coherent manipulation of fragile quantum systems. Since it is determined only by the path of the quantum state, the presence of noise fluctuations affects the geometric phase in a different way than the dynamical phase. We have experimentally tested the robustness of Berrys geometric phase for spin-1/2 particles in a cyclically varying magnetic field. Using trapped polarized ultracold neutrons, it is demonstrated that the geometric phase contributions to dephasing due to adiabatic field fluctuations vanish for long evolution times.

Neutron optical beam splitter from holographically structured nanoparticle-polymer composites.

We report a breakthrough in the search for versatile diffractive elements for cold neutrons. Nanoparticles are spatially arranged by holographical means in a photopolymer. These grating structures show remarkably efficient diffraction of cold neutrons up to about 50% for effective thicknesses of only 200   μm. They open up a profound perspective for next generation neutron-optical devices with the capability to tune or modulate the neutron diffraction efficiency.

Photopolymerizable nanocomposite photonic materials and their holographic applications in light and neutron optics

We present an overview of recent investigations of photopolymerizable nanocomposite photonic materials in which, thanks to their high degree of material selectivity, recorded volume gratings possess high refractive index modulation amplitude and high mechanical/thermal stability at the same time, providing versatile applications in light and neutron optics. We discuss the mechanism of grating formation in holographically exposed nanocomposite materials, based on a model of the photopolymerization-driven mutual diffusion of monomer and nanoparticles. Experimental inspection of the recorded grating’s morphology by various physicochemical and optical methods is described. We then outline the holographic recording properties of volume gratings recorded in photopolymerizable nanocomposite materials consisting of inorganic/organic nanoparticles and monomers having various photopolymerization mechanisms. Finally, we show two examples of our holographic applications, holographic digital data storage and slow-neutron beam control.

Mirrors for slow neutrons from holographic nanoparticle-polymer free-standing film-gratings

We report on successful tests of holographically arranged grating-structures in nanoparticle-polymer composites in the form of 100 microns thin free-standing films, i.e. without sample containers or covers that could cause unwanted absorption/incoherent scattering of very-cold neutrons. Despite their large diameter of 2 cm, the flexible materials are of high optical quality and yield mirror-like reflectivity of about 90% for neutrons of 4.1 nm wavelength.

Noncyclic Pancharatnam phase for mixed state SU(2) evolution in neutron polarimetry

Abstract We have measured the Pancharatnam relative phase for spin- 1 / 2 states. In a neutron polarimetry experiment the minima and maxima of intensity modulations, giving the Pancharatnam phase, were determined. We also considered general SU ( 2 ) evolution for mixed states. The results are in good agreement with theory.

Nanoparticle polymer composite volume gratings incorporating chain transfer agents for holography and slow-neutron optics

We demonstrate twofold enhancement of the saturated refractive index modulation (Δn(sat)) recorded in a photopolymerizable nanoparticle-acrylate polymer composite film by incorporating thiols acting as chain transfer agents. The chain transfer reaction of thiols with (meth)acrylate monomer reduces the polymer crosslinking density and facilitates the mutual diffusion of nanoparticles and monomer during holographic exposure. These modifications provide increased density modulations of nanoparticles and the formed polymer, resulting in the enhancement of Δn(sat) as high as 1.6×10(-2) at a wavelength of 532 nm. The incorporation of thiols also leads to shrinkage suppression and to improvement of the gratings spatial frequency response. Such simultaneous improvement is very useful for holographic applications in light and neutron optics.

Fundamental phenomena of quantum mechanics explored with neutron interferometers

Ongoing fascination with quantum mechanics keeps driving the development of the wide field of quantum-optics, including its neutron-optics branch. Application of neutron-optical methods and, especially, neutron interferometry and polarimetry has a long-standing tradition for experimental investigations of fundamental quantum phenomena. We give an overview of related experimental efforts made in recent years.

Coherent energy manipulation in single-neutron interferometry

We have observed the stationary interference oscillations of a triple-entangled neutron state in an interferometric experiment. Time-dependent interaction with two radio-frequency (rf) fields enables coherent manipulation of an energy degree of freedom in a single neutron. The system is characterized by a multiply entangled state governed by a Jaynes-Cummings Hamiltonian. The experimental results confirm coherence of the manipulation as well as the validity of the description.

Three-port beam splitter for slow neutrons using holographic nanoparticle-polymer composite diffraction gratings

Diffraction of slow neutrons by nanoparticle-polymer composite gratings has been observed. By carefully choosing grating parameters such as grating thickness and spacing, a three-port beam splitter operation for slow neutrons—splitting the incident neutron intensity equally into the ±1st and the 0th diffraction orders—has been realized. As a possible application, a Zernike three-path interferometer is briefly discussed.