Quantum dot photonic crystal lasers

Coupled cavity designs on two-dimensional square lattice photonic crystal slabs were used to demonstrate optically pumped indium arsenide quantum dot photonic crystal lasers at room temperature. Threshold pump powers of 120 and 370 μW were observed for coupled cavities including two and four defect cavities defined in optimised photonic crystals

Dephasing of a superconducting flux qubit

In order to gain a better understanding of the origin of decoherence in superconducting flux qubits, we have measured the magnetic field dependence of the characteristic energy relaxation time ($T_1$) and echo phase relaxation time ($T_2^{\rm echo}$) near the optimal operating point of a flux qubit. We have measured $T_2^{\rm echo}$ by means of the phase cycling method. At the optimal point, we found the relation $T_2^{\rm echo}\approx 2T_1$. This means that the echo decay time is {\it limited by the energy relaxation} ($T_1$ process). Moving away from the optimal point, we observe a {\it linear} increase of the phase relaxation rate ($1/T_{2}^{\rm echo}$) with the applied external magnetic flux. This behavior can be well explained by the influence of magnetic flux noise with a $1/f$ spectrum on the qubit

The OTIS Reference Manual

This document describes the port definitions, electrical specifications, modes of operation and programming sequences of the OTIS TDC. The chip is developed for the Outer Tracker of the LHCb experiment. OTIS1.0 is the first full-scale prototype of this 32 channel TDC and has been submitted in April 2002 in a standard 0.25µm CMOS process. Within the clock driven architecture of the chip a DLL provides the reference for the drift time measurement. The drift time data of every channel is stored in the pipeline memory until a trigger decision arrives. A control unit provides memory and trigger management and handles data transmission to the subsequent DAQ stage. The latest chip version is OTIS1.3

Dephasing of a superconducting flux qubit

In order to gain a better understanding of the origin of decoherence in superconducting flux qubits, we have measured the magnetic field dependence of the characteristic energy relaxation time ($T_1$) and echo phase relaxation time ($T_2^{\rm echo}$) near the optimal operating point of a flux qubit. We have measured $T_2^{\rm echo}$ by means of the phase cycling method. At the optimal point, we found the relation $T_2^{\rm echo}\approx 2T_1$. This means that the echo decay time is {\it limited by the energy relaxation} ($T_1$ process). Moving away from the optimal point, we observe a {\it linear} increase of the phase relaxation rate ($1/T_{2}^{\rm echo}$) with the applied external magnetic flux. This behavior can be well explained by the influence of magnetic flux noise with a $1/f$ spectrum on the qubit

Non-Fermi liquid states in the pressurized CeCu2(Si1−xGex)2CeCu_2(Si_{1-x}Ge_x)_2 system: two critical points

In the archetypal strongly correlated electron superconductor CeCu$_2$Si$_2$ and its Ge-substituted alloys CeCu$_2$(Si$_{1-x}$Ge$_{x}$)$_2$ two quantum phase transitions -- one magnetic and one of so far unknown origin -- can be crossed as a function of pressure \cite{Yuan 2003a}. We examine the associated anomalous normal state by detailed measurements of the low temperature resistivity ($\rho$) power law exponent $\alpha$. At the lower critical point (at $p_{c1}$, $1\leq\alpha\leq 1.5$) $\alpha$ depends strongly on Ge concentration $x$ and thereby on disorder level, consistent with a Hlubina-Rice-Rosch scenario of critical scattering off antiferromagnetic fluctuations. By contrast, $\alpha$ is independent of $x$ at the upper quantum phase transition (at $p_{c2}$, $\alpha\simeq 1$), suggesting critical scattering from local or Q=0 modes, in agreement with a density/valence fluctuation approach.Comment: 4 pages, including 4 figures. New results added. Significant changes on the text and Fig.

High spontaneous emission coupling factor in photonic crystal nanolasers

We have demonstrated high spontaneous emission coupling factor ~ 0.1 from photonic crystal nanolasers with quantum dots. This high coupling resulted from narrow homogenous broadening of the quantum dots and the small number of resonances

Scanning a photonic crystal slab nanocavity by condensation of xenon

Allowing xenon or nitrogen gas to condense onto a photonic crystal slab nanocavity maintained at 10–20 K results in shifts of the nanocavity mode wavelength by as much as 5 nm (~=4 meV). This occurs in spite of the fact that the mode defect is achieved by omitting three holes to form the spacer. This technique should be useful in changing the detuning between a single quantum dot transition and the nanocavity mode for cavity quantum electrodynamics experiments, such as mapping out a strong coupling anticrossing curve. Compared with temperature scanning, it has a much larger scan range and avoids phonon broadening

Neuromorphic Twins for Networked Control and Decision-Making

We consider the problem of remotely tracking the state of and unstable linear time-invariant plant by means of data transmitted through a noisy communication channel from an algorithmic point of view. Assuming the dynamics of the plant are known, does there exist an algorithm that accepts a description of the channel's characteristics as input, and returns 'Yes' if the transmission capabilities permit the remote tracking of the plant's state, 'No' otherwise? Does there exist an algorithm that, in case of a positive answer, computes a suitable encoder/decoder-pair for the channel? Questions of this kind are becoming increasingly important with regards to future communication technologies that aim to solve control engineering tasks in a distributed manner. In particular, they play an essential role in digital twinning, an emerging information processing approach originally considered in the context of Industry 4.0. Yet, the abovementioned questions have been answered in the negative with respect to algorithms that can be implemented on idealized digital hardware, i.e., Turing machines. In this article, we investigate the remote state estimation problem in view of the Blum-Shub-Smale computability framework. In the broadest sense, the latter can be interpreted as a model for idealized analog computation. Especially in the context of neuromorphic computing, analog hardware has experienced a revival in the past view years. Hence, the contribution of this work may serve as a motivation for a theory of neuromorphic twins as a counterpart to digital twins for analog hardware