Robust W-state preparation based on composite pulses implemented by the GRAPE algorithm

Experimental verification of composite inversion pulses obtained by series expansion of the offset angle

We report a demonstration of composite Raman pulses that achieve broadband population inversion and are used to increase the momentum splitting of an atom interferometer up to 18ℏk (corresponding to an increase in the inertial signal by a factor of nine). Composite Raman pulses suppress the effects of pulse length and detuning errors, providing higher transfer efficiency and velocity acceptance than single square pulses. We implement two composite pulse sequences, π/20°−π90°−π/20° and π/20°−π180°−3π/20°, and use the latter composite pulse to demonstrate large-area atom interferometry with stimulated Raman transitions. In addition to enabling larger momentum transfer and higher sensitivity, we argue that composite pulses can improve the robustness of atom interferometers operating in dynamic environments.

Composite pulse combinations for chirp excitation

BackgroundImproved motion-sensitized driven-equilibrium (iMSDE) preparations have been successfully used in carotid artery wall imaging to achieve blood suppression, but it causes notable signal loss, mostly due to inherent T2 decay, eddy current effects and B1+ inhomogeneity. In this study, we investigate the signal to noise ratio (SNR) and blood suppression performance of iMSDE using composite RF pulses and sinusoidal gradients. Optimized first moment (m1) values for iMSDE prepared T1- and T2- weighted (T1- and T2-w) imaging are presented.MethodsTwelve healthy volunteers and six patients with carotid artery disease underwent iMSDE and double inversion recovery (DIR) prepared T1- and T2-w fast spin echo (FSE) MRI of the carotid arteries. Modified iMSDE module using composite RF pulses and sinusoidal gradients were evaluated with a range of m1. SNR of adjacent muscle, vessel wall and the lumen were reported. The optimized iMSDE module was also tested in a 3D variable flip angle FSE (CUBE) acquisition.ResultsThe SNR of muscle was highest using sinusoidal gradients, and the relative improvement over the trapezoidal gradient increased with higher m1 (p<0.001). Optimal SNR was observed using an iMSDE preparation scheme containing two 180° composite pulses and standard 90° and -90° pulses (p=0.151). iMSDE produced better blood suppression relative to DIR preparations even with a small m1 of 487 mT*ms2/m (p<0.001). In T1-w iMSDE, there was a SNR decrease and an increased T2 weighting with increasing m1. In T2-w iMSDE, by matching the effective echo time (TE), the SNR was equivalent when m1 was <= 1518 mT*ms2/m, however, higher m1 values (2278 – 3108 mT*ms2/m) reduced the SNR. In the patient study, iMSDE improved blood suppression but reduced vessel wall CNR efficiency in both T1-w and T2-w imaging. iMSDE also effectively suppressed residual flow artifacts in the CUBE acquisition.ConclusionsiMSDE preparation achieved better blood suppression than DIR preparation with reduced vessel wall CNR efficiency in T1-w and T2-w images. The optimized m1s are 487 mT*ms2/m for T1-w imaging and 1518 mT*ms2/m for T2-w imaging. Composite 180° refocusing pulses and sinusoidal gradients improve SNR performance. iMSDE further improves the inherent blood suppression of CUBE.

Numerical design of composite radiofrequency pulses

The importance of the average Hamiltonian theory and its antecedent the Magnus expansion are discussed. The investigation of its convergence in different situations is very important. In this paper, we introduced a well-established approach to minimize the zeroth-order average Hamiltonian for modified composite pulse sequence in quadrupolar spectroscopy of spin-1. We designed two modified composite pulse sequences constructed by modifying the timing sequence in the original composite pulse sequences.17 We tested various configurations of times associated with the free evolution of the spin system in the modified composite pulses. We found that by decreasing the time delays between the pulses associated with the free evolution of spin system, the line shapes become increasingly better until we obtained the new modified composite pulses showing improvement of the signal compared to the original composite pulse sequences.17 This promising work is expected to play an important role not only for recording high resolution spectra of amino acids, pharmaceutical samples, and peptides but also for probing structural and dynamic information in biomolecules. The generality of the present theoretical scheme points to potential applications in solid-state NMR, to problems in chemical physics, quantum mechanics and theoretical developments, chemistry, and physical chemistry, and in interdisciplinary research areas whenever they include spin dynamics approach.

A new class of atomic interferences using ultra-narrow optical transitions are pushing quantum engineering control to a very high level of precision for a next generation of sensors and quantum gate operations. In such context, we propose a new quantum engineering approach to Ramsey-Bord\'e interferometry introducing multiple composite laser pulses with tailored pulse duration, Rabi field amplitude, frequency detuning and laser phase-step. We explore quantum metrology with hyper-Ramsey and hyper-Hahn-Ramsey clocks below the $10^-18$ level of fractional accuracy by a fine tuning control of light excitation parameters leading to spinor interferences protected against light-shift coupled to laser-probe field variation. We review cooperative composite pulse protocols to generate robust Ramsey-Bord\'e, Mach-Zehnder and double-loop atomic sensors shielded against measurement distortion related to Doppler-shifts and light-shifts coupled to pulse area errors. Fault-tolerant auto-balanced hyper-interferometers are introduced eliminating several technical laser pulse defects that can occur during the entire probing interrogation protocol. Quantum sensors with composite pulses and ultra-cold atomic sources should offer a new level of high accuracy in detection of acceleration and rotation inducing phase-shifts, a strong improvement in tests of fundamental physics with hyper-clocks while paving the way to a new conception of atomic interferometers tracking space-time gravitational waves with a very high sensitivity.

We introduce ultrabroad-band composite pulses (CPs), which maximize (at the expense of a finite error tolerance $\ensuremath{\epsilon}$) the pulse area range wherein the population inversion remains above $1\ensuremath{-}\ensuremath{\epsilon}$. We present such CPs for error thresholds $\ensuremath{\epsilon}=0.01$, 0.001, and 0.0001 in two versions: CPs with different pulse areas of the constituent pulses, used as control parameters, and with equal pulse areas. The former CPs naturally outperform the CPs of identical pulses, which in turn outperform conventional broad-band CPs obtained by annulling the population inversion derivatives at a single point. Moreover, we derive double-compensation CPs, which correct errors in both the pulse area and the detuning. They outperform the corresponding conventional CPs as well. By using the same error-tolerance approach, we construct ultranarrow-band CPs, which squeeze the population inversion in as narrow a range as possible while keeping the excitation outside this range below the error threshold $\ensuremath{\epsilon}$.

Composite pulses for RF phase encoded MRI: A simulation study

A new NMR technique for determining long-range 1H-19F distances in solids is demonstrated. Using a modified rotational-echo double resonance (REDOR) sequence involving 1H homonuclear decoupling and composite 19F pulses, we show that it is possible to determine 1H-19F distances to approximately 8 A. The detrimental effect of the large 19F chemical shift to REDOR dephasing is partially compensated for by the composite pulse, 90 degrees 225 degrees 315 degrees . The 1HNLeu-19FPhe distance in the peptide f-MLF-OH was found to be 7.7 A. This was used to refine the Phe side chain conformation. The 1H-19F REDOR technique should be useful for restraining the three-dimensional structure of proteins.

Broadband, Narrowband, and Passband Composite Pulses for Use in Advanced NMR Experiments

We developed a three-dimensional, gradient-recalled-echo imaging technique that incorporates a short-duration spatial-spectral excitation pulse from the family of binomial pulses. Binomial pulses of different orders were tested on phantoms and on normal volunteers to find the composite pulse that produced in the shortest duration the most reliable fat suppression. Composite pulses employing unipolar slice-selective gradients with explicit rewinder gradients between each radio-frequency (RF) pulse were compared with composite RF pulses employing alternating-polarity, slice-select gradients. The advantage of the sequences using the unipolar gradients is improved fat suppression. Images of the knees of volunteers produced with the composite RF pulse have contrast between fat and articular cartilage equivalent to that on images created by the gradient-recalled-echo imaging technique employing a conventional chemsat pulse. The optimum RF pulse consisted of three amplitude- and phase-modulated pulses combined with unipolar slice-select gradients.

Broadband Echo Sequence Using a π Composite Pulse for the Pure NQR of a Spin I = [formula omitted] Powder Sample

We present two methods for efficient detection of chiral molecules based on sequences of single pulses and Raman pulse pairs. The chiral molecules are modelled by a closed-loop three-state system with different signs in one of the couplings for the two enantiomers. One method uses a sequence of three interaction steps: a single pulse, a Raman pulse, and another single pulse. The other method uses a sequence of only two interaction steps: a Raman pulse, and a single pulse. The second method is simpler and faster but requires a more sophisticated Raman pulse than the first one. Both techniques allow for straightforward generalizations by replacing the single and Raman pulses with composite pulse sequences. The latter achieve very high signal contrast and far greater robustness to experimental errors than by using single pulses. We demonstrate that both constant-rotation (i.e., with phase compensation) and variable-rotation (i.e., with phase distortion) composite pulses can be used, the former being more accurate and the latter being simpler and faster.

Improved myocardium-blood contrast by myocardial suppression resulting from T1 rho-weighting in contrast-enhanced, gradient-echo, bright-blood cine images, acquired at 1.5T, is shown. In the standard images, blood has twice the intensity of muscle. In similar T1 rho-weighted images, it has 3-4 times the intensity of muscle. A composite spin-lock pulse before each observation pulse provides T1 rho-weighting. A typical pulse was: 90y-135x-360x-135x-90(-y) with element durations: 0.84, 1.26, 8.12, 1.26, and 0.84 ms. The tolerance of this composite pulse to shimmering and frequency errors allows spin locking with comparatively weak RF and therefore low specific absorption rate (SAR). Initial clinical evaluation on patients with poor ventricular function demonstrates both a qualitative and quantitative improvement in delineation of myocardial borders.