The sudden breaking of symmetry plays a fundamental role in physics, in particular for the description of phase transitions that change the whole state of a system. One example is the spontaneous alignment of the atomic magnets in a ferromagnetic material that is cooled down below the Curie-temperature. Being governed by such a “global order”, the system can be excited to a collective oscillation, in which all particles move in a coordinated way.
Figure: Illustration of the Higgs excitation in a two-dimensional system. The dynamics of the Higgs excitation (red sphere) is described by an oscillation in a ‘sombrero’-shaped potential.
Graphic: MPQ, Quantum Many-Body Division
If the collective behaviour follows the rules of relativity, a special kind of oscillation can develop, a so-call Higgs excitation (named after the British physicist Peter Higgs). Such an excitation plays a key role in the standard model of elementary particles, where it is called a Higgs-particle. Also, solid state-like systems can exhibit Higgs excitations, if the collective motion of the particles obeys rules that resemble those of the theory of relativity.
However, the detection of Higgs excitations is usually rather difficult, because the excitations typically decay in a short time. Moreover, they are expected to be especially short-lived in very flat, so-called low-dimensional systems and it has been a subject of theoretical debate whether they are observable at all in such geometries. Now, a team of physicists from the Quantum Many-Body Division of the Max-Planck-Institute of Quantum Optics (Garching near Munich) together with theory colleagues from Harvard University (Cambridge, USA) and the California Institute of Technology (Pasadena, USA) succeeded in experimentally identifying Higgs excitations in a two-dimensional system of ultracold atoms (Nature, 26 July, 2012). “We are excited to study phenomena close to absolute zero temperature that usually occur at the highest energies”, Prof. Immanuel Bloch, leader of the Division, explains.
The experiment starts with cooling rubidium atoms down to temperatures near absolute zero. Then the ultracold atoms are loaded into a two-dimensional optical lattice, a checkerboard-like pattern of dark and bright regions of light that is produced by interfering laser beams. Ultracold atoms in such lattices offer the opportunity to realize different states of matter.
For very intense optical lattices (which means a very high contrast between dark and bright areas), a highly ordered state develops, a so-called Mott insulator (named after the British physicist Sir Neville Mott). In this state, each lattice site is occupied with exactly one single atom, which is fixed to its place. If the lattice intensity is decreased more and more, a phase transition to a superfluid takes place. In a superfluid, all atoms are part of a single field, which extends over the whole lattice and describes the collective motion of the system as one extended quantum mechanical wave. The dynamics of this quantum field follows the laws of an “effective” relativistic field theory, in which the speed of light is replaced by the speed of sound. When the system is brought out of equilibrium, collective oscillations in the form of Higgs excitations can be generated.A fundamental challenge for the researchers has been to find out whether Higgs excitations can survive even in a two-dimensional system, and if so, how they can be detected. To answer these questions, the scientists set the system parameters such that the quantum gas is very close to the described transition from a superfluid to a Mott insulator. Then, for several milliseconds, the lattice intensity is gently modulated. This modulation is expected to create a few Higgs excitations, while minimally disturbing the system. “We shake the system only very gently to avoid undesired side effects. Otherwise, we could not isolate the signal of the Higgs excitations”, Manuel Endres, one of the senior researchers on the project, points out. “We are able to measure the temperature of the system with a precision of a billionth of a Kelvin using an extremely sensitive method developed in our group. With this method, we could detect small peaks in the temperature distribution at certain values of modulation frequencies.”
Dr. Olivia Meyer-Streng | Max-Planck-Institut
What happens when we heat the atomic lattice of a magnet all of a sudden?
18.07.2018 | Forschungsverbund Berlin
Subaru Telescope helps pinpoint origin of ultra-high energy neutrino
16.07.2018 | National Institutes of Natural Sciences
For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.
To rule out other origins with certainty, the team led by neutrino physicist Elisa Resconi from the Technical University of Munich and multi-wavelength...
For the first time a team of researchers have discovered two different phases of magnetic skyrmions in a single material. Physicists of the Technical Universities of Munich and Dresden and the University of Cologne can now better study and understand the properties of these magnetic structures, which are important for both basic research and applications.
Whirlpools are an everyday experience in a bath tub: When the water is drained a circular vortex is formed. Typically, such whirls are rather stable. Similar...
Physicists working with Roland Wester at the University of Innsbruck have investigated if and how chemical reactions can be influenced by targeted vibrational excitation of the reactants. They were able to demonstrate that excitation with a laser beam does not affect the efficiency of a chemical exchange reaction and that the excited molecular group acts only as a spectator in the reaction.
A frequently used reaction in organic chemistry is nucleophilic substitution. It plays, for example, an important role in in the synthesis of new chemical...
Optical spectroscopy allows investigating the energy structure and dynamic properties of complex quantum systems. Researchers from the University of Würzburg present two new approaches of coherent two-dimensional spectroscopy.
"Put an excitation into the system and observe how it evolves." According to physicist Professor Tobias Brixner, this is the credo of optical spectroscopy....
Ultra-short, high-intensity X-ray flashes open the door to the foundations of chemical reactions. Free-electron lasers generate these kinds of pulses, but there is a catch: the pulses vary in duration and energy. An international research team has now presented a solution: Using a ring of 16 detectors and a circularly polarized laser beam, they can determine both factors with attosecond accuracy.
Free-electron lasers (FELs) generate extremely short and intense X-ray flashes. Researchers can use these flashes to resolve structures with diameters on the...
13.07.2018 | Event News
12.07.2018 | Event News
03.07.2018 | Event News
18.07.2018 | Materials Sciences
18.07.2018 | Life Sciences
18.07.2018 | Health and Medicine