Advances in nanotechnology lay the ground for a thriving variety of novel devices suitable to explore new realms of quantum phenomena on the mesoscopic scale. Superconducting quantum bits, as an example, have reached very long coherence times by designs that avoid or weaken their coupling to undesired degrees of freedom. An important remaining problem are parasitic Two-level systems (TLS) which emerge from tunneling defects in the device material. These TLS act as a source of noise and decoherence which is detrimental to a large variety of microfabricated quantum devices. The flip side of this problem is that the strong coupling to even individual TLS makes superconducting qubits ideal tools for the study of material defects in the coherent regime.
Here, we show how a phase qubit is used to directly manipulate and readout the quantum states of individual TLS. We tune TLS properties by the applied mechanical strain and perform high-resolution defect spectroscopy by which we obtain a novel view onto the TLS distribution and their mutual interactions. Moreover, by analyzing their coherent dynamics, we utilize single defects as quantum spectrum analyzers in order to shed new light on their environment. I will present studies of TLS coherence in dependence of strain, temperature, and the density of in-situ generated quasi-particles. Moreover, I will briefly discuss our recently initiated project to create superconducting quantum interfaces for the study of TLS in arbitrary materials.
Glasses containing significant amounts of atoms carrying large nuclear electric quadrupole moments show very surprising effects both in the low frequency and the GHz regime.
The nucleus of Ho-165 carries a very large electric quadrupole moment and therefore appears to be a good candidate to investigate the influence of these quadrupole moments down to very low temperatures.The optical filter glass HY-1 containing several percent of holmium.
We measured by using an LC-resonator technique the dielectric permitting of this multicomponent glass at 30 MHz for temperatures between 7 mK and several Kelvin.
The real part of the permittivity – measured the relative change of the capacity – shows a slope ratio of -1 : 3. The dielectric loss is surprisingly high.
With the introduction of bulk metallic glasses a new material class has emerged which allows for the investigation of glassy properties at very low temperatures. Besides their disordered atomic structure metallic glasses are characterized by the presence of conduction electrons which can interact with tunneling systems.
We investigated the elastic properties of a superconducting bulk metallic glass between 10mK and 300K. In order to measure the entire temperature range, in particular the low temperature part, new experimental techniques were developed. Using an inductive readout scheme for a double paddle oscillator it was possible to determine the internal friction and the relative change of sound velocity of bulk metallic glasses with high precision. This allowed for a detailed comparison of the data with different models. The analysis focuses on the low temperature regime where the properties of glassy materials are governed by atomic tunneling systems as described by the tunneling model. The influence of conduction electrons in the normal conducting state and quasiparticles in the superconducting
state of the glass were accounted for in the theoretical description, resulting in a good agreement over a large temperature range between measured data and prediction of the tunneling model.
High purity germanium crystals operated at cryogenic temperatures (< 20mK) and low electric fi elds (< 1V/cm) are used in the direct dark matter search experiment EDELWEISS-III. The discrimination power of background events and dark matter candidates is strongly in influenced by
the charge collection efficiency in the germanium crystals. For the collection efficiency, surface and bulk trapping, intervalley scattering and the drift velocities of electrons and holes play the main role. As these properties determine the time dependence of the ionization signals, the rise time is a good parameter to study the quality of the detector performance.
In this talk I give an introduction to the EDELWEISS-III experiment and its background rejection methods. I explain how the charge migration can be simulated and compare the simulated time resolved ionization signals with results from measurements with a special EDELWEISS-type detector.
In addition, I show the setup for the time-resolved ionization signal read-out in the EDELWEISS-III experiment and first results from data taking in the underground laboratory of Modane.
The ALPS-II experiment, Any Light Particle Search II at DESY in Hamburg, will look for light (m < 10−4 eV) new fundamental bosons (e.g., axion-like particles, hidden photons and other WISPs) in the next years by the means of a light-shining-through the wall setup.
A few years ago, its predecessor had constrained the coupling to photons of axion-like particles (ALPS) to gaγ ≤ 7·10−8 GeV− 1, m ≤ 10−4 eV.
Several improvements are foreseen to reach much better sensitivities (gaγ ≤ 7 · 10 −11 GeV−1). One of the main modifications which have been done is the substitution of the CCD camera by two microcalorimetric W-TESs (Transition Edge Sensors with tungsten chips). These TESs, operated at 80 mK have already allowed single infrared photons detections as well as non-dispersive spectroscopy with very low background rates.
The detection efficiency for such TES is > 95 % and the dark count rate < 10-2 s-1 for 1064 nm photons. At this wavelength, the intrinsic dark count rate is of 10-4 s-1. The relative energy resolution for 1064 nm signals is < 8%. In order to bias accurately the device and for reading purposes, TESs are inductively coupled to a SQUID (Superconducting Quantum Interference Device).
In the near future, complete characterization, calibration and optimization (e.g., background suppression) need to be finalized. The latest progress in this task will be presented as well as next steps planned for future developments.
