Eberhard Widman, In-beam hyperfine spectroscopy of (anti)hydrogen


On Wednesday 22nd of February, we had the pleasure of to host Professor Eberhard Widman as one of our weekly invited speakers for AMOPP seminars.  His research in the ASACUSA (Atomic Spectroscopy And Collisions Using Slow Antiprotons) collaboration is heavily related to the kind of antimatter experiments that we do at UCL, except they deal with anti-hydrogen atoms which they produce using positrons and anti-protons from the Antiproton Decelerator (AD) at CERN. The main focus of his talk was the prospect of making measurements of the hyperfine structure of anti-hydrogen.

He kindly agreed to provide a copy of his slides, which you can download  here.


In-beam hyperfine spectroscopy of (anti)hydrogen

Prof. Dr. Eberhard Widmann, Director, Stefan Meyer Institute for Subatomic Physics, Austrian Academy of Sciences Boltzmanngasse 3, A-1090 Wien

The ground-state hyperfine structure (GS-HFS) of hydrogen is known from the hydrogen maser to relative precision of 10–12. It is of great interest to measure the same quantity for its antimatter counterpart, antihydrogen, to test the fundamental CPT symmetry, which states that all particles and antiparticles have exactly equal or exactly opposite properties. Since CPT is strictly conserved in the Standard Model of particle physics, a violation, if found, would point directly to theories behind this framework. The application of the maser technique requires the confinement of the atoms in a matter box for 1000 seconds and is currently not applicable to antihydrogen. Therefore, the ASACUSA collaboration at the Antiproton Decelerator of CERN has built a Rabi-type beam spectroscopy setup for a measurement of GS-HFS.

With the initial aim of characterizing the setup devised to measure the GS-HFS and to evaluate its potential, a beam of cold, polarized, monoatomic hydrogen was built and used together with the microwave cavity and sextupole magnet designed for the antihydrogen experiment. The (F,M)=(1,0) to (0,0) transition was measured to a precision of several ppb [1], more than a factor 10 better than in the previous measurement using a hydrogen beam. This result shows that the apparatus developed is capable of making a precise measurement of the GS-HFS of antihydrogen provided a beam of similar characteristics (velocity, polarization, quantum state) becomes available.

In a recent publication on the non-minimal Standard Model Extension (SME), describing possible violations of Lorentz and CPT invariance, Kostelecky and Vargas [2] conclude that the in-beam hyperfine measurements of hydrogen alone can be used to constrain certain coefficients of their model, which have never been measured before. The status and prospects of in-beam measurements of hydrogen and antihydrogen will be presented.

[1] M. Diermaier et al., arxiv : 1610.06392

[2] V.A. Kostelecky and A.J. Vargas, Physical Review D 92, 056002 (2015).

Sougato Bose, Probing macroscopic quantum superpositions and the quantum nature of gravity through levitated objects

20170215_160711We often have internal speakers giving talks at the Atomic, Molecular Optical and Positron Physics (AMOPP) group about their cutting-edge research. Last wednesday (15th February 2017) Professor Sugato Bose presented some of his latest results and calculations based on experiments being performed by  Professor Peter Barker’s group on macroscopic quantum behaviour.

The talk had the broad interest of the department as you can see from the fully-occupied lecture hall above,  and Professor Sugato agreed to provide a copy of his slides, which you can download here, so you may too get an insight into this topic.



Probing macroscopic quantum superpositions and the quantum nature of gravity through levitated objects

Prof. Sougato Bose, Dept of Physics & Astronomy University College London

We will discuss theoretical proposals of how quantum superpositions of distinct centre of mass states of a nano-crystal may be created and probed purely by measuring a spin embedded in the object. The idea is to use a levitated diamond with an NV centre spin. Next we will also describe how to reach conditions whereby two such masses interacting purely through gravitational interaction can become entangled. Witnessing such an entanglement experimentally is equivalent to establishing the quantum nature of the gravitational field. Time permitting, we will discuss how the violation of macro-realism can be verified for a levitated nano-object in a loop-hole free manner simply by coarse grained position measurements.

Charles W. Clark, Twisting the neutron wavefunction

charles_clarkLast Wednesday (February 8th 2016) we were lucky enough to have Charles W. Clark from the Joint Quantum Institute at NIST as an invited speaker to give a talk about “Twisting the neutron wavefunction”. The talk focused on the importance of fundamental wave theory and how the wave-particle duality of neutrons studied with interferometers (particularly on a Mach-Zehnder configuration) can provide great insight about basic optical principles being applied to matter waves, such as the addition of angular momentum to neutron wavefunctions.

The abstract for his talk can be found below, and he kindly agreed to provide a copy of his presentation slides which you can download here.

We will be updating our blog with subsequent talks from visiting speakers that may visit UCL, so stay tuned!


Twisting the neutron wavefunction

Charles W. Clark, Joint Quantum Institute, University of Maryland , USA

Wave motions in nature were known to the ancients, and their mathematical expression in physics today is essentially the same as that first provided by d’Alembert and Euler in the mid-18th century. Yet it was only in the early 1990s that physicists managed to control a basic property of light waves: their capability of swirling around their own axis of propagation. During the past decade such techniques of control have also been developed for quantum particles: atoms, electrons and neutrons. I will present a simple description of these phenomena, emphasizing the most basic aspects of wave and quantum particle motion. Neutron interferometry offers a poignant perspective on wave- particle duality: at the time one neutron is detected, the next neutron has not yet even been born. Here, indeed, each neutron “then only interferes with itself.” Yet, using macroscopically-machined objects, we are able to twist neutron deBroglie waves with sub-nanometer wavelengths.