Coherent interaction-free detection of microwave pulses with a superconducting circuit

We show that it is possible to ascertain the presence of a microwave pulse resonant with the second transition of a superconducting transmon circuit, while at the same time avoiding to excite the device onto the third level. In contrast to standard interaction-free measurement setups, where the dynamics involves a series of projection operations, our protocol employs a fully coherent evolution, which results, surprisingly, in a higher efficiency. Experimentally, this is done by using a series of Ramsey microwave pulses coupled into the first transition and monitoring the ground-state population.Comment: 19 pages, 17 figures. Comments are welcome

Theory of coherent interaction-free detection of pulses

Quantum physics allows an object to be detected even in the absence of photon absorption, by the use of so-called interaction-free measurements. We provide a formulation of this protocol using a three-level system, where the object to be detected is a pulse coupled resonantly into the second transition. In the original formulation of interaction-free measurements, the absorption is associated with a projection operator onto the third state. We perform an in-depth analytical and numerical analysis of the coherent protocol, where coherent interaction between the object and the detector replaces the projective operators, resulting in higher detection efficiencies. We provide approximate asymptotic analytical results to support this finding. We find that our protocol reaches the Heisenberg limit when evaluating the Fisher information at small strengths of the pulses we aim to detect -- in contrast to the projective protocol that can only reach the standard quantum limit. We also demonstrate that the coherent protocol remains remarkably robust under errors such as pulse rotation phases and strengths, the effect of relaxation rates and detunings, as well as different thermalized initial states.Comment: 17 pages, 13 figure

Coherent interaction-free detection of noise

Noise is an important concept and its measurement and characterization has been a flourishing area of research in contemporary mesoscopic physics. Here we propose interaction-free measurements as a noise-detection technique, exploring two conceptually different schemes: the coherent and the projective realizations. These detectors consist of a qutrit whose second transition is coupled to a resonant oscillatory field that may have noise in amplitude or phase. For comparison, we consider a more standard detector previously discussed in this context - a qubit coupled in a similar way to the noise source. We find that the qutrit scheme offers clear advantages, allowing precise detection and characterization of the noise, while the qubit does not. Finally, we study the signature of noise correlations in the detector's signal.Comment: 10 pages, 5 figure

A Novel RPI Set Computation Method for Discrete-time LPV Systems with Bounded Uncertainties

Set invariance plays a fundamental role in the analysis and design of linear systems. This paper proposes a novel method for constructing robust positively invariant (RPI) sets for discrete-time linear parameter varying (LPV) systems. Starting from the stability assumption in the absence of disturbances, we aim to construct the RPI sets for parametric uncertain system. The existence condition of a common quadratic Lyapunov function for all vertices of the polytopic system is relaxed in the present study. Thus the proposed method enlarges the application field of RPI sets to LPV systems. A family of approximations of minimal robust positively invariant(mRPI) sets are obtained by using a shrinking procedure. Finally, the effect of scheduling variables on the size of the mRPI set is analyzed to obtain more accurate set characterization of the uncertain LPV system. A numerical example is used to illustrate the effectiveness of the proposed method

Freezing Kinetics in Overcompressed Water

We report high pressure dynamic compression experiments of liquid water along a quasi-adiabatic path leading to the formation of ice VII. We observe dynamic features resembling Van der Waals loops and find that liquid water is compacted to a metastable state close to the ice density before the onset of crystallization. By analyzing the characteristic kinetic time scale involved we estimate the nucleation barrier and conclude that liquid water has been compressed to a high pressure state close to its thermodynamic stability limit

The FENE dumbbell polymer model: existence and uniqueness of solutions for the momentum balance equation

We consider the FENE dumbbell polymer model which is the coupling of the incompressible Navier-Stokes equations with the corresponding Fokker-Planck-Smoluchowski di ffusion equation. We show global well-posedness in the case of a 2D bounded domain. We assume in the general case that the initial velocity is sufficiently small and the initial probability density is sufficiently close to the equilibrium solution; moreover an additional condition on the coeffcients is imposed. In the corotational case, we only assume that the initial probability density is sufficiently close to the equilibrium solution

Multimaterial Piezoelectric Fibres

Fibre materials span a broad range of applications ranging from simple textile yarns to complex modern fibre-optic communication systems. Throughout their history, a key premise has remained essentially unchanged: fibres are static devices, incapable of controllably changing their properties over a wide range of frequencies. A number of approaches to realizing time-dependent variations in fibres have emerged, including refractive index modulation1, 2, 3, 4, nonlinear optical mechanisms in silica glass fibres5, 6, 7, 8 and electroactively modulated polymer fibres9. These approaches have been limited primarily because of the inert nature of traditional glassy fibre materials. Here we report the composition of a phase internal to a composite fibre structure that is simultaneously crystalline and non-centrosymmetric. A ferroelectric polymer layer of 30 μm thickness is spatially confined and electrically contacted by internal viscous electrodes and encapsulated in an insulating polymer cladding hundreds of micrometres in diameter. The structure is thermally drawn in its entirety from a macroscopic preform, yielding tens of metres of piezoelectric fibre. The fibres show a piezoelectric response and acoustic transduction from kilohertz to megahertz frequencies. A single-fibre electrically driven device containing a high-quality-factor Fabry–Perot optical resonator and a piezoelectric transducer is fabricated and measured.National Science Foundation (U.S.) (Materials Research Science and Engineering Centers Program, award number DMR-0819762)United States. Defense Advanced Research Projects Agency (Griggs)United States. Army Research Office (Institute for Soldier Nanotechnologies, contract no. W911NF-07-D-0004