"BEST" homonuclear adiabatic decoupling for 13C- and 15N-double-labeled proteins.

The cyclic irradiation sidebands appearing in homonuclear adiabatic decoupling are calculated in detail, which reveals the origin of the antisymmetric sidebands. The sidebands can be inverted by inserting an initial decoupling with a different period, but the same f1rms as the main decoupling that is required for Bloch-Siegert shift compensation. The sidebands can be eliminated in a broad decoupling range by adding spectra of opposite sidebands. Based on this scheme, an offset-independent double-adiabatic decoupling, named Bloch-Siegert Shift Eliminated and Cyclic Sideband Trimmed Double-Adiabatic Decoupling, or "BEST" decoupling for short, is constructed, which not only compensates the Bloch-Siegert shift as shown earlier by Zhang and Gorenstein (1998) but also eliminates residual sidebands effectively.     

Topological dynamical decoupling

Science China Physics, Mechanics & Astronomy - Active galactic nuclei (AGNs) have been attracting research attention due to their special observable properties. Specifically, a majority of AGNs...     

Adiabatic decoupling sidebands

An analytical solution is given for amplitudes and phases of adiabatic decoupling sidebands as a function of spin inversion time tau. Since all the adiabatic decoupling phases theta(t, tau) refocus at two periods (2T) of the decoupling pulse, the sidebands are located at n/2T rather than at n/T as observed in other decoupling schemes. The real (R(n)(tau)) and imaginary (I(n)(tau)) amplitudes of the sidebands have symmetry R(n)(tau) = R(-n)(tau) and I(n)(tau) = -I(-n)(tau), forming a mirror image between the counterparts of the sidebands. When frequency sweep changes direction all I(n)(tau) are inverted while all R(n)(tau) remain unchanged, leading to pure absorption sidebands with two accumulations as demonstrated by Kupce and Freeman, and to an exchange of sidebands between counterparts. The sum of the real parts for sidebands n = 1 and 2 is almost a constant near on-resonance decoupling, and it increases substantially for large decoupling offsets. The phase defocusing can be minimized for all decoupling offsets by inserting an initial decoupling period with T(ini) = T/2, eliminating all sidebands located at n/2T (n = +/-1, +/-3, +/-5, ...).     

Topological dynamical decoupling

We show that topological equivalence classes of circles in a two-dimensional square lattice can be used to design dynamical decoupling procedures to protect qubits attached on the edges of the lattice. Based on the circles of the topologically trivial class in the original and the dual lattices, we devise a procedure which removes all kinds of local Hamiltonians from the dynamics of the qubits while keeping information stored in the homological degrees of freedom unchanged. If only the linearly independent interaction and nearest-neighbor two-qubit interactions are concerned, a much simpler procedure which involves the four equivalence classes of circles can be designed. This procedure is compatible with Eulerian and concatenated dynamical decouplings,which make it possible to implement the procedure with bounded-strength controls and for a long time period. As an application,it is shown that our method can be directly generalized to finite square lattices to suppress uncorrectable errors in surface codes.     

The adiabatic approximation

In large amplitude nuclear deformation the role of level crossings or pseudo-crossings of intrinsic levels is an outstanding problem. A model consisting of a harmonic oscillator as a collective part and a spin whose orientation energy depends on the collective coordinate is studied in order to clarify this problem. Especially the timeindependent stationary state problem is discussed. Various perturbational expansions are presented and conditions for their convergence are given. The adiabatic approximation leading to a renormalization of the collective mass due to the level crossing is valid for vibrations with energies small compared to intrinsic energy differences.     

Test of a method for sampling the internal degrees of freedom of a flexible solute molecule based on adiabatic decoupling and temperature or force scaling

Simulation of the folding equilibrium of a polypeptide in solution is a computational challenge. Standard molecular dynamics (MD) simulations of such systems cover hundreds of nanoseconds, which is barely sufficient to obtain converged ensemble averages for properties that depend both on folded and unfolded peptide conformations. If one is not interested in dynamical properties of the solute, techniques to enhance the conformational sampling can be used to obtain the equilibrium properties more efficiently. Here the effect on particular equilibrium properties at 298?K of adiabatically decoupling the motion a β-hepta-peptide from the motion of the solvent and subsequently up-scaling its temperature or down-scaling the forces acting on it is investigated. The ensemble averages and rate of convergence are compared to those for standard MD simulations at two different temperatures and a simulation in which the temperature of the solute is increased to 340?K while keeping the solvent at 298?K. Adiabatic decoupling with a solute mass scaling factor s _m ?=?100 and a temperature scaling factor of s _T ?=?1.1 seems to slightly increase the convergence of several properties such as enthalpy of folding, NMR NOE atom–atom distances and ³J-couplings compared to a standard MD simulation at 298?K. Convergence is still slower than that observed at 340?K. The system with a temperature of 340?K for the solute and 298?K for the solvent without scaling of the mass converges fastest. Using a force scaling factor s _V ?=?0.909 perturbs the system too much and leads to a destabilization of the folded structure. The sampling efficiency and possible distortive effects on the configurational distribution of the solute degrees of freedom due to adiabatic decoupling and temperature or force scaling are also analysed for a simpler model, a dichloroethane molecule in water. It appears that an up-scaling of the mass of the solute reduces the sampling more than the subsequent up-scaling of the temperature or down-scaling of the force enhances it. This means that adiabatic decoupling the solute degrees of freedom from the solvent ones followed by an up-scaling of temperature of down-scaling of the forces does not lead to significantly enhanced sampling of the folding equilibrium.     

Fault-tolerant quantum dynamical decoupling

Dynamical decoupling pulse sequences have been used to extend coherence times in quantum systems ever since the discovery of the spin-echo effect. Here we introduce a method of recursively concatenated dynamical decoupling pulses, designed to overcome both decoherence and operational errors. This is important for coherent control of quantum systems such as quantum computers. For bounded-strength, non-Markovian environments, such as for the spin-bath that arises in electron- and nuclear-spin based solid-state quantum computer proposals, we show that it is strictly advantageous to use concatenated pulses, as opposed to standard periodic dynamical decoupling pulse sequences. Namely, the concatenated scheme is both fault tolerant and superpolynomially more efficient, at equal cost. We derive a condition on the pulse noise level below which concatenation is guaranteed to reduce decoherence.     

Combined Role of Synchronized Amplitude Modulation and Synchronized Phase Modulator for Soliton-Soliton Interaction

In this paper, the interaction between two solitons has been studied by the perturbation approach in the presence of synchronized amplitude modulation and synchronized phase modulation. The results show : the combined role of synchronized amplitude modulation and synchronized phase modulation can suppress effectively the interaction.     

Isolated and adiabatic susceptibilities

It is shown from quantum statistical calculations that the possible difference between isolated and adiabatic susceptibilities is due to a partial energy being conserved in a slowly increasing field. This energy is constructed using the unitary space of linear operators. The consequences for thermodynamics are discussed, and the isolated susceptibility is found to be exactly equal to the total adiabatic susceptibility as obtained from generalized thermodynamics (Fick and Schwegler) with two different temperatures.     

Realistic heavy-ion adiabatic potentials

The K-matrix model of Cusson, Trivedi, Meldner and Weiss has been used to compute static adiabatic heavy-ion cluster potentials in a constrained self-consistent Brueckner-Hartree-Fock scheme. Heavy-ion potentials are found which can simultaneously reproduce the experimentally deduced heavy-ion potentials in the asymptotic region and the total energy versus quadrupole moment in the fused, compound nucleus region. Potentials for α-α, α-¹²C, α-¹⁶O, ¹²C-¹²C, ¹⁶O-¹⁶O are shown and compared with other work. The total energy of ¹²C and ²⁴Mg versus deformation is also given.     

Wireless adiabatic power transfer

We propose a technique for efficient mid-range wireless power transfer between two coils, by adapting the process of adiabatic passage for a coherently driven two-state quantum system to the realm of wireless energy transfer. The proposed technique is shown to be robust to noise, resonant constraints, and other interferences that exist in the neighborhood of the coils.     

Synchronized whistlers recorded at Varanasi

Some interesting events of synchronized whistlers recorded at low latitude station Varanasi during magnetic storm period of the year 1977 are presented. The dynamic spectrum analysis shows that the component whistlers are Eckersley whistlers having dispersion 10 s^1/2 and 30 s^1/2. An attempt has been made to explain the dynamic spectra using lightning discharge generated from magnetospheric sources     

The decoupling problem at RHIC

We investigate whether it is possible to dynamically generate from classical transport theory the observed surprising R_out ≈ R_side in Au+Au at \(\sqrt s = 130A\) GeV at RHIC [1,2]. We obtained covariant solutions to the Boltzmann transport equation via the MPC technique [3], for a wide range of partonic initial conditions and opacities. We demonstrate that there exist transport solutions that yield a freezeout distribution with R _out < R _side for K _⊥ ? 1.5 GeV. These solutions correspond to continuous evaporation-like freezeout, where the emission duration is comparable to the source size. Naively this would mean R _out > R _side. Nevertheless, our sources exhibit R _out < R _side because they are narrower in the‘out’ than in the‘side’ direction and, in addition, a positive x _out-t correlation develops reducing R _out further.     

Carbon-proton dipolar decoupling in REDOR

Dipolar decoupling of protons with radiofrequency field amplitudes comparable to those used for the rare-spin refocusing and dephasing pi pulses results in accurate, high-sensitivity determinations of internuclear distances in rotational-echo double-resonance experiments and simulations performed on (13)C and (15)N-labeled l-alanine. Copyright 2000 Academic Press.     

Self-consistent Pomeron dynamics without decoupling

More conservative conditions on the independently uniform convergence of multi-Regge asymptotic expansions lead to a consistent Pomeron pole dynamics, without requiring the coupling Λ (0,0,0) of three such poles to vanish. The onset of large mass diffractive processes at high energies in an asymptotically constant renormalization. of the pole residue. This threshold mechanism may be responsible for the rise in σ_total and σ_el at ISR and for building the forward quasi-elastic peak in the leading proton x-distribution.     

Heteronuclear decoupling by optimal tracking

The problem to design efficient heteronuclear decoupling sequences is studied using optimal control methods. A generalized version of the gradient ascent engineering (GRAPE) algorithm is presented that makes it possible to design complex non-periodic decoupling sequences which are characterized by tens of thousands of pulse sequence parameters. In contrast to conventional approaches based on average Hamiltonian theory, the concept of optimal tracking is used: a pulse sequence is designed that steers the evolution of an ensemble of spin systems such that at a series of time points, a specified trajectory of the density operator is tracked as closely as possible. The approach is demonstrated for the case of low-power heteronuclear decoupling in the liquid state for in vivo applications. Compared to conventional sequences, significant gains in decoupling efficiency and robustness with respect to offset and inhomogeneity of the radio-frequency field were found in simulations and experiments.