Quantum Mechanical Interference Research Articles

Determining X-Ray Nonlinear Susceptibility of Diamond by the Optical Fano Effect

X-ray nonlinear optics, which has been considered as a scientific frontier to be explored with x-ray free-electron lasers, is accessible with existing synchrotron x-ray sources, revealing its unique features. We demonstrate that x-ray parametric down-conversion is observed indirectly through quantum mechanical interference known as the Fano effect. By introducing a novel concept of photonic discrete levels, we determine the second order nonlinear susceptibility of diamond, and find a strong resonance enhancement at the core absorption edge that presents firm experimental evidence to develop x-ray nonlinear optics.

Nearby resonances beyond the Breit–Wigner approximation

We consider a description of propagators for particle resonances which takes into account the quantum-mechanical interference due to the width of two or more nearby states that have common decay channels, by incorporating the effects arising from the imaginary parts of the one-loop self-energies. Depending on the couplings to the common decay channels, the interference effect, not taken into account in the usual Breit–Wigner approximation, can significantly modify the cross section or make the more long-lived resonance narrower. We give few examples of New Physics models for which the effect is sizable, namely a generic two and multiple Higgs model and neutral vector resonances in Higgsless models. Based on these results we suggest the implementation of a proper treatment of nearby resonances into Monte Carlo generators.

Chemical Bonding in the N2 Molecule and the Role of the Quantum Mechanical Interference Effect

The chemical bond in the N(2) molecule is analyzed from the perspective of the quantum mechanical interference effect by means of the recently developed generalized product function energy partitioning (GPF-EP) scheme. The analysis is carried out at the GVB-PP and SC levels, which constitute interpretable independent particle models, while ensuring the correct dissociation behavior for the molecule. The results suggest that some current ideas concerning the bond in the N(2) molecule should be revised. It is shown that, in the absence of the interference effect, there is no chemical bond in the N(2) molecule. The influence of the basis set on the energy partitioning is also evaluated. The interference contributions to the energy are substantially less sensitive to the choice of the basis set than the reference energy, making the investigation of the relative importance of inteference effects in larger systems feasible.

Use of the spatial phase of a focused laser beam to yield mechanistic information about photo-induced chemical reactions

Two-pathway quantum mechanical interference was used to control the photoionization and photodissociation of a number of polyatomic molecules. The phase lag between different pairs of products obtained from acetone and dimethyl sulfide was altered by translating the focus of the laser beam along an axis normal to the molecular beam axis. This effect was derived quantitatively from the spatial Gouy phase of the laser beam. Details of the chemical reaction mechanisms were deduced from the channel phase lags, obtained when the laser was focused on the axis of the molecular beam, and from the variation of the phase lag produced by axial translation of the laser focus.

General theory of excitation energy transfer in donor-mediator-acceptor systems

General theory of the excitation energy transfer (EET) in the case of donor-mediator-acceptor system was constructed by using generalized master equation (GME). In this theory, we consider the direct and indirect transitions in the EET consistently. Hence, our theory includes the quantum mechanical interference between the direct and indirect transitions automatically. Memory functions in the GME were expressed by the overlap integrals among the time-dependent emission spectrum of the donor, the absorption spectrum of the mediator, the time-dependent emission spectrum of the mediator, and the absorption spectrum of the acceptor. In the Markov limit of the memory functions, we obtained the rate of EET which consists of three terms due to the direct transition, the indirect transition, and the interference between them. We found that the interference works effectively in the limit of slow thermalization at the intermediate state. The formula of EET rate in this limit was expressed by the convolution of the EET interaction and optical spectra. The interference effect strongly depends on the width of the absorption spectrum of mediator molecule and the energy gap between the donor and the mediator molecules.

Energy partitioning for generalized product functions: The interference contribution to the energy of generalized valence bond and spin coupled wave functions

The main driving force for the formation of the covalent bond is the quantum-mechanical interference effect among one-electron states, as has been suggested in several works by the use of partition schemes to calculate the interference contributions to the energy. However, due to some difficulties associated with the original approaches, calculations were only carried out for a few, mostly diatomic molecules. In this work, we propose a general approach of partitioning based on generalized product functions with generalized valence bond at the perfect pairing approximation and spin-coupled groups, which should allow the investigation of a broader array of molecules, and hopefully, shed light on the nature of the chemical bond in molecules with unusual chemical features. Among other things, this approach lends itself naturally to the investigation of interference in individual bonds or groups of bonds in a molecule.

Quantum-mechanical description of in-medium fragmentation

We present a quantum-mechanical description of quark-hadron fragmentation in a nuclear environment. It employs the path-integral formulation of quantum mechanics, which takes care of all phases and interferences and contains all relevant time scales, such as production, coherence, and formation. The cross section includes the probability of prehadron (colorless dipole) production both inside and outside the medium. Moreover, it also includes inside-outside production, which is a typical quantum-mechanical interference effect (like twin-slit electron propagation). We observe a substantial suppression caused by the medium, even if the prehadron is produced outside the medium and no energy loss is involved. This important source of suppression is missed in the usual energy-loss scenario interpreting the effect of jet quenching observed in heavy ion collisions. This may be one reason for the too large gluon density reported by such analyses.

Conceptual molecular quantum phase transistor based on first-principles quantum transport calculations

A conceptual molecular phase-coherent transistor is proposed based on first-principles quantum transport calculations. The device is formed by two molecules connected via a one-dimensional wire and it is operated by gating the interconnect between the molecules and exploiting quantum-mechanical interference. The transistor thus works by controlling the electron phase instead of the position of the molecular energy levels, and it paves the way for phase-controllable electronic circuits.

Join the dots

A new variation on an old theme in atomic physics, a spectral distortion known as the Fano effect, has been revealed — not in an atom, but in an artificial nanostructure known as a quantum dot. The Fano effect is a spectral distortion arising from quantum-mechanical resonance or interference between two competing optical pathways. It is ubiquitous in optical spectroscopy of atoms, solids and semiconductor heterostructures. It indicates how discrete energy states, for example of an atom, are coupled to the continuum of states in its environment. The effect has been widely studied, but usually in a linear regime at low excitation power. A new study uses semiconductor quantum dots to explore the physics of the nonlinear Fano regime. Clear Fano resonances are observed, and they can be tuned by changing the device design or with applied voltages. In the nonlinear regime, visibility of Fano interferences increases dramatically, which could be used as a sensitive probe of the degree of coupling between discrete states and the continuum, which is relevant for example for qubits where coupling to the environment needs to be kept to a minimum.

Spin Injection Efficiency at the Source/Channel Interface of Spin Transistors

Almost all spintronic transistors (e.g., spin field-effect transistors, spin bipolar transistors, and spin-enhanced MOSFETs) require high efficiency of spin injection from a ferromagnetic contact into a semiconductor channel for proper operation. In this paper, we calculate the efficiency of spin injection from a realistic nonideal ferromagnetic contact into the semiconductor quantum wire channel of a spintronic transistor, taking into account the presence of an axial magnetic field (caused by either the ferromagnetic contact or external agents) and spin orbit interaction. In our calculations, the temperature is assumed to be low enough that phonon scattering is weak and transport is phase-coherent, although not ballistic because of elastic scattering caused by impurities and defects. We consider a single impurity in the channel and show that the conductance depends strongly on the exact location of this impurity because of quantum mechanical interference effects. This is a nuisance since it exacerbates device variability. The ldquosignrdquo of the impurity potential, i.e., whether it is attractive or repulsive, also influences the channel conductance. Surprisingly, at absolute zero temperature, the spin injection efficiency can reach 100% at certain gate biases, even though the ferromagnetic injector is nonideal. However, this efficiency drops rapidly with increasing temperature.

Stochastic Dipolar Recoupling in Nuclear Magnetic Resonance of Solids

I describe a nuclear magnetic resonance (NMR) technique, called stochastic dipolar recoupling (SDR), that permits continuous experimental control of the character of spin dynamics between coherent and incoherent limits in a system of magnetic dipole-coupled nuclei. In the fully incoherent limit of SDR, spin polarization transfers occur at distance-dependent rates without the quantum mechanical interferences among pairwise dipole-dipole couplings that often limit the feasibility or precision of structural studies of solids by NMR. In addition to facilitating structural studies, SDR represents a possible route to experimental studies of effects of decoherence on the dynamics of quantum many-body systems.

RESONANT RAYLEIGH SCATTERING OF LIGHT BY SEMICONDUCTOR MICROCAVITY

Experimental study of Resonant Rayleigh Scattering (RRS) of light by a semiconductor microcavity was carried out on a double cavity sample. The shifts of RRS lines spectral positions with sample rotation demonstrate clearly polariton dispersion. The shape of the lines depends strongly on the position of the excitation spot on the structure surface and temperature. The treatment of experimental data in terms of the Fano quantum mechanical interference between a discreet state and continuum gives a direct method to study polariton scattering probabilities.

Full counting statistics of transport through two-channel Coulomb blockade systems

A mesoscopic Coulomb blockade system with two identical transport channels is studied in terms of full counting statistics. It is found that the average current cannot distinguish the quantum constructive interference from the classical non-interference, but the shot noise and skewness are more sensitive to the nature of quantum mechanical interference and can fulfill that task. The interesting super-Poisson shot noise is found and is demonstrated as a consequence of constructive interference, which induces an effective system with fast-and-slow transport channels. Dephasing effects on the counting statistics are carried out to display the continuous transition from quantum interfering to non-interfering transports.

On the existence of supergravity duals to D1-D5 CFT states

We define a metric operator in the ½-BPS sector of the D1-D5 CFT, the eigenstates of which have a good semi-classical supergravity dual; the non-eigenstates cannot be mapped to semi-classical gravity duals. We also analyse how the data defining a CFT state manifests itself in the gravity side, and show that it is arranged into a set of multipoles. Interestingly, we find that quantum mechanical interference in the CFT can have observable manifestations in the semi-classical gravity dual. We also point out that the multipoles associated to the normal statistical ensemble fluctuate wildly, indicating that the mixed thermal state should not be associated to a semi-classical geometry.

Quantum-interference effects in the o 1Πu(v=1)∼b 1Πu(v=9) Rydberg–valence complex of molecular nitrogen

Two distinct high-resolution experimental techniques, 1 UV laser-based ionization spectroscopy and synchrotron-based XUV photoabsorption spectroscopy, have been used to study the o Rydberg–valence complex of 14N2, providing new and detailed information on the perturbed rotational structures, oscillator strengths, and predissociation linewidths. Ionization spectra probing the b state of 14N2, which crosses o1Πu(v=1) between J = 24 and J = 25, and the o1Πu(v=1), b,1Πu(v=9), and b states of 14N15N, have also been recorded. In the case of 14N2, rotational and deperturbation analyses correct previous misassignments for the low-J levels of o(v=1) and b(v=9). In addition, a two-level quantum-mechanical interference effect has been found between the o–X(1, 0) and b–X(9, 0) transition amplitudes which is totally destructive for the lower-energy levels just above the level crossing, making it impossible to observe transitions to b(v=9,J=6). A similar interference effect is found to affect the o(v=1) and b(v=9) predissociation linewidths, but, in this case, a small non-interfering component of the b(v=9) linewidth is indicated, attributed to an additional spin–orbit predissociation by the repulsive state.

The K239 2Σg+3 state: Observation and analysis

The K239 2Σg+3 state has been observed by perturbation-facilitated infrared-infrared double resonance spectroscopy and two-photon excitation. Resolved fluorescence spectra into the aΣu+3 state have been recorded. The observed vibrational levels have been assigned as the v=23–25, 27, 28, 31–33, 38–45, 47, and 53 levels by comparing the observed and calculated spectra of the 2Σg+3→aΣu+3 transitions. Molecular constants have been obtained using a global fitting procedure with a comprehensive set of experimental data. Fine and hyperfine splittings have been resolved in the excitation spectra. Perturbations between the 2Σg+3 and 2Πg3 states were observed. The hyperfine patterns of the 2Σg+3 levels are strongly affected by the perturbation. The perturbation-free and weakly perturbed levels follow the case bβS coupling scheme, while the perturbed levels follow case bβJ coupling. A Fermi contact constant, bF=65±10MHz, has been obtained. Intensity anomalies of rotational lines appeared both in the 2Σg+3∼2Πg3←bΠu3 excitation spectra and in the 2Σg+3∼2Πg3→aΣu+3 resolved fluorescence spectra. These intensity anomalies can be explained in terms of a quantum-mechanical interference effect.

Large orbital magnetic moments in carbon nanotubes generated by resonant transport

The nonequilibrium Green's function method is used to study the ballistic transport in metallic carbon nanotubes when a current is injected from the electrodes with finite bias voltages. We reveal, both analytically and numerically, that large loop currents circulating around the tube are induced, which come from a quantum mechanical interference and are much larger than the current along the tube axis when the injected electron is resonant with a time-reversed pair of degenerate states, which are, in fact, inherent in the zigzag and chiral nanotubes. This results in large orbital magnetic moments, making the nanotube a molecular solenoid.

LARGE MAGNETIC MOMENTS GENERATED FROM LOOP CURRENTS IN CARBON NANOTUBE ATTACHED TO ELECTRODES — A THEORETICAL PICTURE

Inspired by a recent experiment which has detected a large orbital magnetic moment when electrodes are attached to a carbon nanotube, we study the ballistic transport in metallic carbon nanotubes when a current is injected from electrodes with finite bias voltages with nonequilibrium Green's function method. We reveal, both analytically and numerically, that large loop currents circulating around the tube are induced, which come from a quantum mechanical interference, when the injected electron is resonant with a time-reversed pair of degenerate states inherent in the zigzag and chiral nanotubes. This results in large orbital magnetic moments, making the nanotube a molecular solenoid. The current distribution for various types of tube and the magnetic moment as a function of the bias are displayed.

Observation of transverse interference fringes on an atom laser beam

Using the unique detection properties offered by metastable helium atoms we have produced high resolution images of the transverse spatial profiles of an atom laser beam. We observe fringes on the beam, resulting from quantum mechanical interference between atoms that start from rest at different transverse locations within the outcoupling surface and end up at a later time with different velocities at the same transverse position. Numerical simulations in the low output-coupling limit give good quantitative agreement with our experimental data.

Role of the Gouy Phase in the Coherent Phase Control of the Photoionization and Photodissociation of Vinyl Chloride

We demonstrate theoretically and experimentally that the Gouy phase of a focused laser beam may be used to control the photoinduced reactions of a polyatomic molecule. Quantum mechanical interference between one- and three-photon excitation of vinyl chloride produces a small phase lag between the dissociation and ionization channels on the axis of the molecular beam. Away from the axis, the Gouy phase introduces a much larger phase lag that agrees quantitatively with theory without any adjustable parameters.