Dephasing-assisted Gain and Loss in Mesoscopic Quantum Systems

Motivated by recent experiments, we analyse the phonon-assisted steady-state gain of a microwave field driving a double quantum-dot in a resonator. We apply the results of our companion paper, which derives the complete set of fourth-order Lindblad dissipators using Keldysh methods, to show that resonator gain and loss are substantially affected by dephasing-assisted dissipative processes in the quantum-dot system. These additional processes, which go beyond recently proposed polaronic theories, are in good quantitative agreement with experimental observationsComment: 5 pages, 3 Figures, published together with arXiv:1608.0416

Towards understanding two-level-systems in amorphous solids -- Insights from quantum circuits

Amorphous solids show surprisingly universal behaviour at low temperatures. The prevailing wisdom is that this can be explained by the existence of two-state defects within the material. The so-called standard tunneling model has become the established framework to explain these results, yet it still leaves the central question essentially unanswered -- what are these two-level defects? This question has recently taken on a new urgency with the rise of superconducting circuits in quantum computing, circuit quantum electrodynamics, magnetometry, electrometry and metrology. Superconducting circuits made from aluminium or niobium are fundamentally limited by losses due to two-level defects within the amorphous oxide layers encasing them. On the other hand, these circuits also provide a novel and effective method for studying the very defects which limit their operation. We can now go beyond ensemble measurements and probe individual defects -- observing the quantum nature of their dynamics and studying their formation, their behaviour as a function of applied field, strain, temperature and other properties. This article reviews the plethora of recent experimental results in this area and discusses the various theoretical models which have been used to describe the observations. In doing so, it summarises the current approaches to solving this fundamentally important problem in solid-state physics.Comment: 34 pages, 7 figures, 1 tabl

Site formation and faunal remains of the Middle Pleistocene site Bilzingsleben

Bilzingsleben is internationally known as a palaeontological, palaeoanthropological and archaeological reference site of a Middle Pleistocene Interglacial (Holstein). From 1969 until 2003 Dietrich Mania excavated almost 1800 m2 and retrieved several tons of faunal material which he interpreted as remains of human hunting. In order to confirm this interpretation, three areas were excavated between 2004 and 2007. The aim of the present study is to add to an understanding of the site formation processes by an analysis of the stratigraphy and taphonomy of the faunal remains of these recent excavations. In addition, the already published results of the faunal investigations of the former excavations were assembled and are presented. The stratigraphic relationships of the former excavation were confirmed. In addition, the relative abundance of the different species is very similar for the former and recent excavations, with the predominance of rhinoceros and red deer, followed by beaver and bear with significantly fewer remains, while bovid, horse and elephant remains are very rare. Also very rare are bird and fish remains, while mid-sized mammals are absent. The frequencies of the skeletal elements demonstrate, at least for the two dominant species, that all elements were present and became incorporated into the find bearing layer. Traces on the surfaces of the bones that, according to their morphology and position on the bones, must be identified as human-made cut-marks, are very rare. Taken together this indicates that the faunal remains have to be considered as natural components of the Interglacial palaeo-landscape. However, incorporated in the find-bearing layer are also local stones including flint, as well as pre-Pleistocene ostracods and fish remains. This means that parts of still older sediments were also reworked. The non-selective recovery and three-dimensional recording of all faunal remains during the recent excavations revealed a vertical distribution of over 1 m in depth, independent of animal species and size. Furthermore, in areas where the find-bearing layer is inclined the obliquely embedded elements show a preferred orientation towards the slope of the layer. This all points towards an embedding of the faunal remains under the influence of fluvial, terrestrial and limnic processes

Strategy-proofness and responsiveness imply minimal participation

We study a model in which agents with single-peaked preferences can participate in a costly voting procedure to determine the value of a one-dimensional variable. We show that, for all positive participation cost and all profiles of individual preferences, there exists a (generically) unique equilibrium with (at most) one single participant whenever the voting mechanism is strategy-proof, anonymous, and responsive in the sense that the outcome reacts to a unanimous move of the votes of all agents in the same direction

Strategy-proofness implies minimal participation under single-peakedness

We study a model in which agents with single-peaked preferences can participate in a costly voting procedure to determine the value of a one-dimensional variable. We show that, for all positive participation costs and all profiles of individual preferences, there exists a unique equilibrium outcome with one single participant whenever the voting rule is strategy-proof, anonymous, and responsive in the sense that the outcome reacts to a unanimous move of the votes of all agents in the same direction; moreover, the single participant is always one of the ‘extremist’ voters, i.e. either one with the lowest or one with the highest peak. While this uncovers a strong tension between strategy-proofness and participation for all deterministic voting rules on the single-peaked domain (just as in the case of an unrestricted domain), there are simple probabilistic and strategy-proof voting rules that induce full participation in equilibrium

Breaking time-reversal symmetry with a superconducting flux capacitor

We present the design of a passive, on-chip microwave circulator based on a ring of superconducting tunnel junctions. We investigate two distinct physical realisations, based on either Josephson junctions (JJ) or quantum phase slip elements (QPS), with microwave ports coupled either capacitively (JJ) or inductively (QPS) to the ring structure. A constant bias applied to the center of the ring provides the symmetry breaking (effective) magnetic field, and no microwave or rf bias is required. We find that this design offers high isolation even when taking into account fabrication imperfections and environmentally induced bias perturbations and find a bandwidth in excess of 500 MHz for realistic device parameters.Comment: 10 pages, 11 figures, including supplementary material - published as "Passive on-chip, superconducting circulator using rings of tunnel junctions

Oscillating Modes of Driven Colloids in Overdamped Systems

Microscopic particles suspended in liquids are the prime example of an overdamped system because viscous forces dominate over inertial effects. Apart from their use as model systems, they receive considerable attention as sensitive probes from which forces on molecular scales can be inferred. The interpretation of such experiments rests on the assumption, that, even if the particles are driven, the liquid remains in equilibrium, and all modes are overdamped. Here, we experimentally demonstrate that this is no longer valid when a particle is forced through a viscoelastic fluid. Even at small driving velocities where Stokes law remains valid, we observe particle oscillations with periods up to several tens of seconds. We attribute these to non-equilibrium fluctuations of the fluid, which are excited by the particle's motion. The observed oscillatory dynamics is in quantitative agreement with an overdamped Langevin equation with negative friction-memory term and which is equivalent to the motion of a stochastically driven underdamped oscillator. This fundamentally new oscillatory mode will largely expand the variety of model systems but has also considerable implications on how molecular forces are determined by colloidal probe particles under natural viscoelastic conditions.Comment: Accepted with Nat. Comm. (originally submitted version, complying with Nature policies). 10 pages, 8 figure