Adiabatic Switching Research Articles

Accelerated molecular dynamics through stochastic iterations and collective variable based basin identification

We present a method called SISYPHUS (stochastic iterations to strengthen yield of path hopping over upper states) for extending accessible time scales in atomistic simulations. The method proceeds by separating phase space into basins and transition regions between the basins based on a general collective variable (CV) criterion. The transition regions are treated via traditional molecular dynamics (MD) while Monte Carlo (MC) methods are used to (i) estimate the expected time spent in each basin and (ii) thermalize the system between two MD episodes. In particular, an efficient adiabatic switching based scheme is used to estimate the time spent inside the basins. The method offers various advantages over existing approaches in terms of (i) providing an accurate real time scale, (ii) avoiding reliance on harmonic transition state theory, and (iii) avoiding the need to enumerate all possible transition events. Applications of SISYPHUS to low-temperature vacancy diffusion in bcc Ta and adatom island ripening in fcc Al are presented. A CV appropriate for such condensed phases, especially for transitions involving collective motions of several atoms, is also introduced.

The Ramped-step Voltage in Adiabatic Logic Circuits: Analysis of Parameters to Further Reduce Power Dissipation

Ramped-step voltage supplies are widely used in adiabatic switching. However, the set of analytical parameters available for understanding these voltage supplies is still limited. Our objective is to identify the parameters that have an effect on lowering power dissipation. Our results show that power dissipation can be significantly reduced using adiabatic logic, by increasing the charging and discharging times and by reducing the peak current flow through the transistors. The phenomenon of energy recovery is also demonstrated. A maximum of 40% reduction in the total power dissipation is shown from this analysis.

Manipulating spin hyper-polarization by means of adiabatic switching of a spin-locking RF-field

We propose a technique for transferring the multiplet spin polarization (CIDNP or PHIP, or one created by any other method), which is the mutual entanglement of spins, into net hyper-polarization with respect to the direction of a high magnetic field by slowly (adiabatically) switching-off a strong external RF-field with a specially selected frequency. The net hyper-polarized molecules can then be used in NMR spectroscopy or imaging for strong signal enhancement.

Adiabatic switching approach to multidimensional supersymmetric quantum mechanics for several excited states

We present a time-dependent method for determining several approximate excited-state energies and wave functions using a vectorial approach to multidimensional supersymmetric quantum mechanics. First, a vectorial approach is used to generate the tensor sector two Hamiltonian, which is isospectral with the original scalar sector one Hamiltonian above the ground state of the sector one Hamiltonian. We construct a time-dependent Hamiltonian interpolating between the scalar sector one Hamiltonian and the tensor sector two Hamiltonian. Then, we can adiabatically switch from the ground state of the sector one Hamiltonian to the ground state of the sector two Hamiltonian by solving the time-dependent Schrödinger equation. In addition, by employing an initial wave packet orthogonal to that leading to the ground state of sector two, we also obtain the first-excited state of sector two. Construction of the orthogonal sector one states is trivial due to the tensor nature of sector two. The ground and first-excited states of the sector two Hamiltonian can be used with the charge operator to obtain the first two excited state wave functions of the sector one Hamiltonian. Excellent computational results are obtained for two-dimensional nonseparable degenerate and nondegenerate systems.

Solution of the Dyson-Schwinger equation on a de Sitter background in the infrared limit

We propose an ansatz which solves the Dyson-Schwinger equation for the real scalar fields in Poincare patch of de Sitter space in the IR limit. The Dyson-Schwinger equation for this ansatz reduces to the kinetic equation, if one considers scalar fields from the principal series. Solving the latter equation we show that under the adiabatic switching on and then off the coupling constant the Bunch-Davies vacuum relaxes in the future infinity to the state with the flat Gibbons-Hawking density of out-Jost harmonics on top of the corresponding de Sitter invariant out-vacuum.

Power Efficient VLSI Inverter Design using Adiabatic Logic and Estimation of Power dissipation using VLSI-EDA Tool

Power dissipation becoming a limiting factor in VLSI circuits and systems. Due to relatively high complexity of VLSI systems used in various applications, the power dissipation in CMOS inverter, arises from it’s switching activity, which is mainly influenced by the supply voltage and effective capacitance.[1,2,3] To optimize power dissipation, the researches show various techniques like appropriate coding, appropriate design architectures, appropriate manipulation algorithms. In this paper we have applied adiabatic logic design approach to design COMS inverter. Adiabatic switching techniques based on energy recovery principle are one of the innovative solutions at a circuit and logic level achieve reduction in power [12] Various adiabatic logic based inverters are shown. Mainly our aim is to design and simulate PFAL inverters. Finally we have calculated dissipated power of static CMOS inverter and compare it with that of PFAL based inverter. [4, 6]

On some aspects of the definition of scattering states in quantum field theory

Abstract The problem of extending quantum-mechanical formal scattering theory to a more general class of models that also includes quantum field theories is discussed, with the aim of clarifying certain aspects of the definition of scattering states. As the strong limit is not suitable for the definition of scattering states in quantum field theory, some other limiting procedure is needed. Two possibilities are considered, the abelian limit and adiabatic switching. Formulas for the scattering states based on both methods are discussed, and it is found that generally there are significant differences between the two approaches. As an illustration of the applications and the features of these formulas, S-matrix elements and energy corrections in two quantum field theoretical models are calculated using (generalized) old-fashioned perturbation theory. The two methods are found to give equivalent results.

First‐principles calculations of spontaneous polarization for TTF‐QBrCl3

AbstractWe have evaluated spontaneous polarization for TTF‐QBrCl3, whose crystal structure is similar to that of TTF‐CA, by first‐principles calculations. The obtained results are compared with those for closely related materials TTF‐CA and TTF‐BA and found to have some similarities to those for TTF‐CA. No magnetic state is found and polarization grows non‐linearly with the adiabatic switching parameter λ when the system varies from the virtual paraelectric state to the actual ferroelectric state. The evaluated spontaneous polarization values are in the same range as the experimental ones.

LSI implementation of a low-power 4×4-bit array two-phase clocked adiabatic static CMOS logic multiplier

As the density and operating speed of complementary metal oxide semiconductor (CMOS) circuits increases, dynamic power dissipation has become a critical concern in the design and development—of personal information systems and large computers. The reduction of supply voltage, node capacitance, and switching activity are common approaches used in conventional CMOS. In adiabatic switching circuits, the current flow through transistors can be significantly reduced by ensuring uniform charge transfer over the entire available time. This paper presents the simulation of this current in two-phase clocked adiabatic static CMOS logic (2PASCL) and conventional CMOS. From the SPICE simulations, at transition frequencies from 1 to 12MHz, a 4×4-bit array 2PASCL multiplier shows a maximum reduction in power dissipation of 77% relative to that of a static CMOS. The measurement results of a 4×4-bit array 2PASCL multiplier demonstrate a 57% reduction compared to a 4×4-bit array two-phase clocked adiabatic dynamic CMOS logic (2PADCL). These results indicate that 2PASCL technology can be advantageous when applied to low-power digital devices operated at low frequencies, such as radio-frequency identification (RFID) tags, smart cards, and sensors.

Exploring sequential quantum adiabatic switching across supersymmetric partners for finding the eigenstates of a system

AbstractWe demonstrate that one can exhaustively determine the n‐bound eigenstates of a Hamiltonian H by constructing a sequence of supersymmetric (SUSY) partner Hamiltonians and invoking a time‐dependent quantum adiabatic switching algorithm for passage from the ground state of one to the other. The ground states of the initial pair H(0) and H(1) are constructed by solving the Riccati equation for the superpotential ϕ(0) for H(0) and adiabatically switching from the ground state Ψ of H(0) to the ground state Ψ of H(1). The charge operator Q is then used to recover the first excited state Ψ of H(0). The procedure is repeated for the ground states of SUSY pairs H(n + 1) and H(n + 2), and appropriate charge operators lead to the excited states Ψ of H(0) with $n = 0,1,2, \cdots.$, thereby exhausting the full eigenspectrum of H(0). The workability of the proposed method is shown with several well‐known examples. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2011

Classical approach in atomic physics

The application of a classical approach to various quantum problems - the secular perturbation approach to quantization of a hydrogen atom in external fields and a helium atom, the adiabatic switching method for calculation of a semiclassical spectrum of hydrogen atom in crossed electric and magnetic fields, a spontaneous decay of excited states of a hydrogen atom, Gutzwiller's approach to Stark problem, long-lived excited states of a helium atom recently discovered with the help of Poincar$\acute{\mathrm{e}}$ section, inelastic transitions in slow and fast electron-atom and ion-atom collisions - is reviewed. Further, a classical representation in quantum theory is discussed. In this representation the quantum states are treating as an ensemble of classical states. This approach opens the way to an accurate description of the initial and final states in classical trajectory Monte Carlo (CTMC) method and a purely classical explanation of tunneling phenomenon. The general aspects of the structure of the semiclassical series such as renormgroup symmetry, criterion of accuracy and so on are reviewed as well. In conclusion, the relation between quantum theory, classical physics and measurement is discussed.

Adiabatic switching for power dissipation reduction in complementary metal-oxide semiconductor (CMOS) gates of portable battery-powered devices

Electrical power dissipation in portable battery-powered devices has become worrisome to both consumers and producers of these devices. The need for this work is to investigate the practical low-power circuit solution for electrical power dissipation reduction in portable battery-powered devices. Experiments are performed on electrical power dissipation in Adiabatic switching and that of Complementary Metal-Oxide Semiconductor (CMOS) switching gates. The experiments are performed with the use of an electronic software simulator TINA TI MT to simulate Adiabatic and CMOS switching circuits. The results obtain from simulated circuits are analyzed. The difference between electrical power dissipation in Adiabatic switching and CMOS switching reveals that Adiabatic switching reduces electrical power dissipation in portable battery-powered devices. This reduction in electrical power dissipation of battery-powered devices lowers the average electrical power consumption and lowers heat generation.

Towards a nonequilibrium Green’s function description of nuclear reactions: One-dimensional mean-field dynamics

Nonequilibrium Green’s function methods allow for an intrinsically consistent description of the evolution of quantal many-body body systems, with inclusion of different types of correlations. In this paper, we focus on the practical developments needed to build a Green’s function methodology for nuclear reactions. We start out by considering symmetric collisions of slabs in one dimension within the mean-field approximation. We concentrate on two issues of importance for actual reaction simulations. First, the preparation of the initial state within the same methodology as for the reaction dynamics is demonstrated by an adiabatic switching on of the mean-field interaction, which leads to the mean-field ground state. Second, the importance of the Green’s function matrix-elements far away from the spatial diagonal is analyzed by a suitable suppression process that does not significantly affect the evolution of the elements close to the diagonal. The relative lack of importance of the far-away elements is tied to system expansion. We also examine the evolution of the Wigner function and verify quantitatively that erasing of the off-diagonal elements corresponds to averaging out of the momentum–space details in the Wigner function.

Crossover from adiabatic to sudden interaction quenches in the Hubbard model: prethermalization and non-equilibrium dynamics

The recent experimental implementation of condensed matter models in optical lattices has motivated research on their non-equilibrium behavior. Predictions about the dynamics of superconductors following a sudden quench of the pairing interaction have been made based on the effective Bardeen–Cooper–Schrieffer (BCS) Hamiltonian; however, their experimental verification requires the preparation of a suitable excited state of the Hubbard model along a twofold constraint: (i) a sufficiently non-adiabatic ramping scheme is essential to excite the non-equilibrium dynamics and (ii) overheating beyond the critical temperature of superconductivity must be avoided. For commonly discussed interaction ramps, there is no clear separation of the corresponding energy scales. Here we show that the matching of both conditions is simplified by the intrinsic relaxation behavior of ultracold fermionic systems: for the particular example of a linear ramp we examine the transient regime of prethermalization (Moeckel and Kehrein 2008 Phys. Rev. Lett.100 175702) under the crossover from sudden to adiabatic switching using Keldysh perturbation theory. A real-time analysis of the momentum distribution exhibits a temporal separation of an early energy relaxation and its later thermalization by scattering events. For long but finite ramping times this separation can be large. In the prethermalization regime, the momentum distribution resembles a zero-temperature Fermi liquid as the energy inserted by the ramp remains located in high-energy modes. Thus ultracold fermions prove to be robust to heating, which simplifies the observation of non-equilibrium BCS dynamics in optical lattices.

Two Phase Clocked Adiabatic Static CMOS Logic and its Logic Family

This paper proposes a two-phase clocked adiabatic static CMOS logic (2PASCL) circuit that utilizes the principles of adiabatic switching and energy recovery. The low-power 2PASCL circuit uses two complementary split-level sinusoidal power supply clocks whose height is equal to V dd . It can be directly derived from static CMOS circuits. By removing the diode from the charging path, higher output amplitude is achieved and the power consumption of the diode is eliminated. 2PASCL has switching activity that is lower than dynamic logic. We also design and simulate NOT, NAND, NOR, and XOR logic gates on the basis of the 2PASCL topology. From the simulation results, we find that 2PASCL 4-inverter chain logic can save up to 79% of dissipated energy as compared to that with a static CMOS logic at transition frequencies of 1 to 100 ㎒. The results indicate that 2PASCL technology can be advantageously applied to low power digital devices operated at low frequencies, such as radio-frequency identifications (RFIDs), smart cards, and sensors.

Formation of the extreme Kuiper-belt binary 2001 QW322 through adiabatic switching of orbital elements

Binaries in the Kuiper-belt are unlike all other known binaries in the Solar System. Both their physical and orbital properties are highly unusual and, because these objects are thought to be relics dating back to the earliest days of the Solar System, understanding how they formed may provide valuable insight into the conditions which then prevailed. A number of different mechanisms for the formation of Kuiper-belt binaries (KBBs) have been proposed including; two-body collisions inside the Hill sphere of a larger body; strong dynamical friction; exchange reactions; and chaos assisted capture. So far, no clear consensus has emerged as to which of these mechanisms (if any) can best explain the observed population of KBBs. Indeed, the recent characterization of the mutual orbit of the symmetric (i.e., roughly equal mass) KBB 2001 QW322 has only served to complicate the picture because its orbit does not seem readily explicable by any of the available models. The binary 2001 QW322 stands out even among the already unusual population of KBBs for the following reasons: its mutual orbit is extremely large (≈105 km or about 30% of the Hill sphere radius), retrograde, it is inclined ≈120° from the ecliptic and has very low eccentricity, i.e., e ≤ 0.4 (and possibly e ≤ 0.05). Here we propose a hybrid formation mechanism for this object which combines aspects of several of the mechanisms already proposed. Initially two objects are temporarily trapped in a long-living chaotic orbit that lies close to a retrograde periodic orbit in the three-dimensional Hill problem. This is followed by capture through gravitational scattering with a small intruder object. Finally, weak dynamical friction gradually switches the original orbit “adiabatically” into a large, almost circular, retrograde orbit similar to that actually observed.

Tunneling in 2-D quantum dots via quantum adiabatic switching route

We explore the phenomenon of tunneling in single carrier 2-D quantum dot by quantum adiabatic switching route. The confinement in the y-direction is kept harmonic which ensures that tunneling is allowed only along the x-direction. The harmonic confinement potential is kept fixed and a constant external magnetic field is applied along the z-direction. The growth of probability density in the classically forbidden zones and tunneling current are monitored critically which reveals how tunneling significantly depends on the barrier parameters. The efficacy of the switching function in enforcing adiabaticity of the evolution is demonstrated. The effective mass, barrier width, and height emerge as important control parameters.

On the brueckner and goldstone forms of the linked-cluster theorem

Connections between the Brueckner and Goldstone forms of the linked-cluster theorem are clarified in an elementary fashion employing a finite many-body system of electrons interacting via two-body forces as an illustrative example. It is shown that the order-by-order cancellations of Brueckner unlinked terms in the many-body wave function and energy occur in the Goldstone development upon the additions of the different time orderings of Feynman-Goldstone diagrams having disconnected vacuum parts. The factoring of the vacuum amplitude from the wave function, upon which customary presentations of the theorem focus attention, is seen to be irrelevant to the cancellations of Brueckner unlinked terms, and has to do, rather, with the presence of secular and normalization terms in the time-dependent perturbation functions for an adiabatically switched static perturbation. Similarly, the equivalence of the vacuum amplitude with the exponential of all connected vacuum diagrams, originally demonstrated by Feynman in the case of hole theory, is seen to be irrelevant to the cancellations of Brueckner unlinked terms in the energy, which occur in the Goldstone development upon the summations over all time orderings of disconnected vacuum diagrams. The distinction between Brueckner unlinked terms on the one hand, and secular and normalization terms on the other, is confused in customary presentations of the linked-cluster theorem by the use of exponential switching, following Gell-Mann and Low, and is clarified in the present development by considering the Friedrichs limit of ideal adiabatic switching.

Quantum path-integral study of the phase diagram and isotope effects of neon

The phase diagram of natural neon has been calculated for temperatures in the range of 17-50 K and pressures between 10(-2) and 2 x 10(3) bar. The phase coexistence between solid, liquid, and gas phases has been determined by the calculation of the separate free energy of each phase as a function of temperature. Thus, for a given pressure, the coexistence temperature was obtained by the condition of equal free energy of coexisting phases. The free energy was calculated by using nonequilibrium techniques such as adiabatic switching and reversible scaling. The phase diagram obtained by classical Monte Carlo simulations has been compared to that obtained by quantum path-integral simulations. Quantum effects related to the finite mass of neon cause that coexistence lines are shifted toward lower temperatures when compared to the classical limit. The shift found in the triple point amounts to 1.5 K, i.e., about 6% of the triple-point temperature. The triple-point isotope effect has been determined for (20)Ne, (21)Ne, (22)Ne, and natural neon. The simulation data show satisfactory agreement to previous experimental results, which report a shift of about 0.15 K between triple-point temperatures of (20)Ne and (22)Ne. The vapor pressure isotope effect has been calculated for both solid and liquid phases at triple-point conditions. The quantum simulations predict that this isotope effect is larger in the solid than in the liquid phase, and the calculated values show nearly quantitative agreement to available experimental data.

Adiabatic pipelining: a key to ternary computing with quantum dots

The quantum-dot cellular automaton (QCA), a processing platform based on interactingquantum dots, was introduced by Lent in the mid-1990s. What followed was anexhilarating period with the development of the line, the functionally complete set oflogic functions, as well as more complex processing structures, however all in therealm of binary logic. Regardless of these achievements, it has to be acknowledgedthat the use of binary logic is in computing systems mainly the end result of thetechnological limitations, which the designers had to cope with in the early days of theirdesign. The first advancement of QCAs to multi-valued (ternary) processing wasperformed by Lebar Bajec et al, with the argument that processing platforms of thefuture should not disregard the clear advantages of multi-valued logic. Some ofthe elementary ternary QCAs, necessary for the construction of more complexprocessing entities, however, lead to a remarkable increase in size when comparedto their binary counterparts. This somewhat negates the advantages gained byentering the ternary computing domain. As it turned out, even the binary QCAhad its initial hiccups, which have been solved by the introduction of adiabaticswitching and the application of adiabatic pipeline approaches. We present here astudy that introduces adiabatic switching into the ternary QCA and employs theadiabatic pipeline approach to successfully solve the issues of elementary ternaryQCAs. What is more, the ternary QCAs presented here are sizewise comparableto binary QCAs. This in our view might serve towards their faster adoption.