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Journal of Instrumentation 15(3), P03021 (2020). doi:10.1088/1748-0221/15/03/P03021, Published by Inst. of Physics, London

We establish synthetic magnetic fields for nanomechanical transport by modulating optomechanical interactions. We show that the controlled breaking of time-reversal symmetry leads to chirality in the system’s eigenmodes, transport and thermodynamics.

The JEDI (Julich Electric Dipole Investigations) (http://collaborations.fz-juelich.de/ikp/jedi/) Collaboration aims to carry out a long term project for the measurement of the permanent electric dipole moments of charged particles in a storage ring. As a proof-of-concept, the COoler SYnchrotron (COSY) was equipped with a waveguide RF Wien filter designed to operate at some harmonics of the spin precession frequency ranging from 0.1 to 2 MHz. This device maintains the corresponding ratio between the RF electric and magnetic fields necessary not to induce any beam excitation and most importantly acts as a spin flipper. In the course of 2017, the waveguide RF Wien has been successfully commissioned and tested. The ability of the device to produce a Lorentz Force compensation and to rotate the particles’ polarization vector has been verified. Driven vertical spin oscillations and vertical polarization build-up has been observed. This short article briefly discusses the results of the Lorentz force measurements at 871 kHz.

It is difficult to burn a liquid fuel inside a fluidised bed. For the first time, liquid glycerol has been burned, when continuously injected into the bottom of an electrically heated bed of alumina particles (sieved to 355–425 µm), fluidised by air. The temperature in the bed was held at 700, 800 or 900 °C; usually (U/Umf) was 2.5. The bed's depth was varied, as also were (U/Umf) and the ratio of fuel to air supplied to the bed. Measurements were made of the concentrations of CH4, O2, CO and CO2, and also of the temperature, in the freeboard well above the bed. On entering the bed, the liquid glycerol rapidly formed bubbles of vapour, which quickly decomposed thermally, yielding mostly CO and H2. These gases then mixed with the other gases in the bed. It appears that the diffusive H2 mainly burns between the fluidised particles. With the bed at 700–900 °C, no CO was detected far downstream of the bed, provided the equivalence ratio, θ, was below 0.7, i.e., with more than 43% excess air. Under these fuel-lean conditions, all the carbon in the glycerol was oxidised to CO2. However, in a more fuel-rich situation, with θ > 0.7, CO was detected well above the bed, particularly with a deeper bed, at a lower temperature and operating more fuel-rich. Thus, with the bed at 900 °C, CO was mostly oxidised inside the bed, but occasionally some CO burned on top of the bed. When a fuel-rich bed was below ≈ 850 °C, not all the CO burned in the bed. Achieving complete combustion inside a fluidised bed is partly a problem of mixing the products of glycerol's thermal decomposition with the fluidising air, which on entry exists mainly in bubbles. Consequently, increasing (U/Umf) promoted both mixing and combustion in a bed. In addition, in-bed combustion requires the bed to be sufficiently deep, hotter than ≈ 850 °C and θ to be less than a critical value. The effects of other variables are discussed.

The Hamiltonian of a linearly driven two-level system, or qubit, in the standard rotating frame contains non-commuting terms that oscillate at twice the drive frequency, $\omega$, rendering the task of analytically finding the qubit's time evolution nontrivial. The application of the rotating wave approximation (RWA), which is suitable only for drives whose amplitude, or envelope, $H_1(t)$, is small compared to $\omega$ and varies slowly on the time scale of $1/\omega$, yields a simple Hamiltonian that can be integrated relatively easily. We present a series of corrections to the RWA Hamiltonian in $1/\omega$, resulting in an effective Hamiltonian whose time evolution is accurate also for time-dependent drive envelopes in the regime of strong driving, i.e., for $|H_1(t)| \lesssim \omega$. By extending the Magnus expansion with the use of a Taylor series we introduce a method that we call the Magnus-Taylor expansion, which we use to derive a recurrence relation for computing the effective Hamiltonian. We then employ the same method to derive kick operators, which complete our theory for non-smooth drives. The time evolution generated by our kick operators and effective Hamiltonian, both of which depend explicitly on the envelope and its time derivatives, agrees with the exact time evolution at periodic points in time. For the leading Hamiltonian correction we obtain a term proportional to the first derivative of the envelope, which competes with the Bloch-Siegert shift., Comment: 30 pages, 4 figures, changes made to improve clarity, references added, published version

We probe dephasing mechanisms within a quantum network node consisting of a single nitrogen-vacancy centre electron spin that is hyperfine coupled to surrounding $^{13} \text{C}$ nuclear-spin quantum memories. Previous studies have analysed memory dephasing caused by the stochastic electron-spin reset process, which is a component of optical internode entangling protocols. Here, we find, by using dynamical decoupling techniques and exploiting phase matching conditions in the electron-nuclear dynamics, that control infidelities and quasi-static noise are the major contributors to memory dephasing induced by the entangling sequence. These insights enable us to demonstrate a 19-fold improved memory performance which is still not limited by the electron reinitialization process. We further perform pump-probe studies to investigate the spin-flip channels during the optical electron spin reset. We find that spin-flips occur via decay from the meta-stable singlet states with a branching ratio of 8(1):1:1, in contrast with previous work. These results allow us to formulate straightforward improvements to diamond-based quantum networks and similar architectures., Comment: 11 pages, 6 figures

Physical review accelerators and beams 21(4), 042002 (2018). doi:10.1103/PhysRevAccelBeams.21.042002, Published by American Physical Society, College Park, MD

An implementation of the Polynomial Chaos Expansion is introduced here as a fast solver of the equations of beam and spin motion inside an RF Wien filter. The device shall be used to search for the deuteron electric dipole moment in the COSY storage ring. The new approach is based on the stochastic Galerkin method, and it is shown that this constitutes a new and very powerful alternative to the commonly used Monte-Carlo methods., 11 pages, 8 figures, 1 table

At Ka-band frequencies, small deviations in the antenna production process result in sub-optimal performance. Classically, Monte-Carlo methods are used to quantify the influence of those tolerances. In this application, Monte-Carlo simulations are not feasible due to the high computational effort and the high number of parameters to be considered. As an alternative, we use polynomial chaos expansion to create a surrogate model using very few full-wave simulations. This model predicts the influence of the production tolerances on the performance of the antenna. Measurements confirm the results of the polynomial chaos expansion method.

This letter reports the successful use of feedback from a spin polarization measurement to the revolution frequency of a 0.97 GeV/$c$ bunched and polarized deuteron beam in the Cooler Synchrotron (COSY) storage ring in order to control both the precession rate ($\approx 121$ kHz) and the phase of the horizontal polarization component. Real time synchronization with a radio frequency (rf) solenoid made possible the rotation of the polarization out of the horizontal plane, yielding a demonstration of the feedback method to manipulate the polarization. In particular, the rotation rate shows a sinusoidal function of the horizontal polarization phase (relative to the rf solenoid), which was controlled to within a one standard deviation range of $\sigma = 0.21$ rad. The minimum possible adjustment was 3.7 mHz out of a revolution frequency of 753 kHz, which changes the precession rate by 26 mrad/s. Such a capability meets a requirement for the use of storage rings to look for an intrinsic electric dipole moment of charged particles.

Membranes of suspended two-dimensional materials show a large variability in mechanical properties, in part due to static and dynamic wrinkles. As a consequence, experiments typically show a multitude of nanomechanical resonance peaks, which makes an unambiguous identification of the vibrational modes difficult. Here, we probe the motion of graphene nanodrum resonators with spatial resolution using a phase-sensitive interferometer. By simultaneously visualizing the local phase and amplitude of the driven motion, we show that unexplained spectral features represent split degenerate modes. When taking these into account, the resonance frequencies up to the eighth vibrational mode agree with theory. The corresponding displacement profiles however, are remarkably different from theory, as small imperfections increasingly deform the nodal lines for the higher modes. The Brownian motion, which is used to calibrate the local displacement, exhibits a similar mode pattern. The experiments clarify the complicated dynamic behaviour of suspended two-dimensional materials, which is crucial for reproducible fabrication and applications.

The conventional Wien filter is a device with orthogonal static magnetic and electric fields, often used for velocity separation of charged particles. Here we describe the electromagnetic design calculations for a novel waveguide RF Wien filter that will be employed to solely manipulate the spins of protons or deuterons at frequencies of about 0.1 to 2 MHz at the COoler SYnchrotron COSY at J\"ulich. The device will be used in a future experiment that aims at measuring the proton and deuteron electric dipole moments, which are expected to be very small. Their determination, however, would have a huge impact on our understanding of the universe., Comment: 10 pages, 10 figures, 4 tables

A new method to determine the spin tune is described and tested. In an ideal planar magnetic ring, the spin tune - defined as the number of spin precessions per turn - is given by $\nu_s = \gamma G$ (gamma is the Lorentz factor, $G$ the magnetic anomaly). For 970 MeV/c deuterons coherently precessing with a frequency of ~120 kHz in the Cooler Synchrotron COSY, the spin tune is deduced from the up-down asymmetry of deuteron carbon scattering. In a time interval of 2.6 s, the spin tune was determined with a precision of the order $10^{-8}$, and to $1 \cdot 10^{-10}$ for a continuous 100 s accelerator cycle. This renders the presented method a new precision tool for accelerator physics: controlling the spin motion of particles to high precision is mandatory, in particular, for the measurement of electric dipole moments of charged particles in a storage ring., Comment: 6 pages, 6 figures

The European physical journal / A 56(8), 211 (2020). doi:10.1140/epja/s10050-020-00215-8, Published by Springer, Berlin ; Heidelberg