Harold U. Baranger

Journal Article Journal of the Korean Physical Society · April 1, 2023 We study the properties of a quantum critical region of an XXZ model in two dimensions. The quantum critical point at zero temperature evolves as the temperature increases. Using the quantum Monte Carlo method with stochastic series expansions, we simulate ... Full text Cite

Conductance of a dissipative quantum dot: Nonequilibrium crossover near a non-Fermi-liquid quantum critical point

Journal Article Physical Review B · October 25, 2021 Featured Publication We find the nonlinear conductance of a dissipative resonant level in the nonequilibrium steady state near its quantum critical point. The system consists of a spin-polarized quantum dot connected to two resistive leads that provide ohmic dissipation. We fo ... Full text Open Access Link to item Cite

Driven-Dissipative Phase Transition in a Kerr Oscillator: From Semi-Classical PT Symmetry to Quantum Fluctuations.

Journal Article Physical Review A · March 24, 2021 Featured Publication We study a minimal model that has a driven-dissipative quantum phase transition, namely a Kerr non-linear oscillator subject to driving and dissipation. Using mean-field theory, exact diagonalization, and the Keldysh formalism, we analyze the critical phen ... Full text Open Access Link to item Cite

Nonequilibrium quantum critical steady state: Transport through a dissipative resonant level

Journal Article Physical Review Research · February 11, 2021 Featured Publication Full text Open Access Cite

Stabilization of a Majorana Zero Mode through Quantum Frustration.

Journal Article Physical Review B · July 1, 2020 Featured Publication We analyze a system in which a topological Majorana zero mode (MZM) combines with a MZM produced by quantum frustration. At the boundary between the topological and non-topological states, a MZM does not appear. The system that we study combines two parts, ... Full text Open Access Link to item Cite

Interference of Chiral Andreev Edge States

Journal Article Nature Physics · May 18, 2020 Featured Publication The search for topological excitations such as Majorana fermions has spurred interest in the boundaries between distinct quan- tum states. Here, we explore an interface between two prototypical phases of electrons with conceptually different ground states: ... Full text Open Access Link to item Cite

Heralded Bell State of Dissipative Qubits Using Classical Light in a Waveguide.

Journal Article Physical Review Letters · April 9, 2019 Featured Publication Maximally entangled two-qubit states (Bell states) are of central importance in quantum technologies. We show that heralded generation of a maximally entangled state of two intrinsically open qubits can be realized in a one-dimensional (1D) system through ... Full text Open Access Link to item Cite

Exciting a Bound State in the Continuum through Multiphoton Scattering Plus Delayed Quantum Feedback.

Journal Article Phys Rev Lett · February 22, 2019 Featured Publication Excitation of a bound state in the continuum (BIC) through scattering is problematic since it is by definition uncoupled. Here, we consider a type of dressed BIC and show that it can be excited in a nonlinear system through multiphoton scattering and delay ... Full text Open Access Link to item Cite

Particle Production in Ultrastrong-Coupling Waveguide QED

Journal Article Physical Review A · October 8, 2018 Understanding large-scale interacting quantum matter requires dealing with the huge number of quanta that are produced by scattering even a few particles against a complex quantum object. Prominent examples are found from high-energy cosmic ray showers, to ... Full text Open Access Link to item Cite

Non-Markovian Dynamics of a Qubit Due to Single-Photon Scattering in a Waveguide

Journal Article New Journal of Physics · April 16, 2018 We investigate the open dynamics of a qubit due to scattering of a single photon in an infinite or semi-infinite waveguide. Through an exact solution of the time-dependent multi-photon scattering problem, we find the qubitʼs dynamical map. Tools of open qu ... Full text Open Access Link to item Cite

Quantum interference and complex photon statistics in waveguide QED

Journal Article Physical Review A · February 7, 2018 Featured Publication We obtain photon statistics by using a quantum jump approach tailored to a system in which one or two qubits are coupled to a one-dimensional waveguide. Photons confined in the waveguide have strong interference effects, which are shown to play a vital rol ... Full text Open Access Link to item Cite

Waveguide QED: Power spectra and correlations of two photons scattered off multiple distant qubits and a mirror (vol 91, 053845, 2015)

Journal Article PHYSICAL REVIEW A · November 13, 2017 Full text Link to item Cite

Multiple emitters in a waveguide: Nonreciprocity and correlated photons at perfect elastic transmission

Journal Article Physical Review A · July 21, 2017 We investigate interference and correlation effects when several detuned emitters are placed along a one-dimensional photonic waveguide. Such a setup allows multiple interactions between the photons and the strongly coupled emitters, and underlies proposed ... Full text Open Access Cite

Rescuing a Quantum Phase Transition with Quantum Noise.

Journal Article Phys Rev Lett · February 3, 2017 We show that placing a quantum system in contact with an environment can enhance non-Fermi-liquid correlations, rather than destroy quantum effects, as is typical. The system consists of two quantum dots in series with two leads; the highly resistive leads ... Full text Open Access Link to item Cite

Photon correlations generated by inelastic scattering in a one-dimensional waveguide coupled to three-level systems

Journal Article PHYSICA E-LOW-DIMENSIONAL SYSTEMS & NANOSTRUCTURES · April 1, 2016 Full text Open Access Link to item Cite

Dynamics of a qubit in a high-impedance transmission line from a bath perspective

Journal Article Physical Review A · March 28, 2016 We investigate the quantum dynamics of a generic model of light-matter interaction in the context of high-impedance waveguides, focusing on the behavior of the photonic states generated in the waveguide. The model treated consists simply of a two-level sys ... Full text Open Access Cite

Detecting photon-photon interactions in a superconducting circuit

Journal Article Physical Review B - Condensed Matter and Materials Physics · October 6, 2015 A local interaction between photons can be engineered by coupling a nonlinear system to a transmission line. The required transmission line can be conveniently formed from a chain of Josephson junctions. The nonlinearity is generated by side-coupling this ... Full text Open Access Cite

Waveguide QED: Power spectra and correlations of two photons scattered off multiple distant qubits and a mirror

Journal Article Physical Review A - Atomic, Molecular, and Optical Physics · May 22, 2015 We study two-level systems (2LS) coupled at different points to a one-dimensional waveguide in which one end is open and the other is either open (infinite waveguide) or closed by a mirror (semi-infinite). Upon injection of two photons (corresponding to we ... Full text Open Access Cite

One-dimensional waveguide coupled to multiple qubits: Photon-photon correlations

Journal Article EPJ Quantum Technology · December 1, 2014 For a one-dimensional (1D) waveguide coupled to two or three qubits, we show that the photon-photon correlations have a wide variety of behavior, with structure that depends sensitively on the frequency and on the qubit-qubit separation L. We study the cor ... Full text Open Access Cite

Generalized multipolaron expansion for the spin-boson model: Environmental entanglement and the biased two-state system

Journal Article Physical Review B - Condensed Matter and Materials Physics · August 7, 2014 We develop a systematic variational coherent-state expansion for the many-body ground state of the spin-boson model, in which a quantum two-level system is coupled to a continuum of harmonic oscillators. Energetic constraints at the heart of this technique ... Full text Open Access Cite

Quantum critical region of a two-dimensional spin-half XXZ model

Conductance of a dissipative quantum dot: Nonequilibrium crossover near a non-Fermi-liquid quantum critical point

Driven-Dissipative Phase Transition in a Kerr Oscillator: From Semi-Classical PT Symmetry to Quantum Fluctuations.

Nonequilibrium quantum critical steady state: Transport through a dissipative resonant level

Journal Article Physical Review Research · February 11, 2021 Featured Publication Full text Open Access Cite

Stabilization of a Majorana Zero Mode through Quantum Frustration.

Interference of Chiral Andreev Edge States

Heralded Bell State of Dissipative Qubits Using Classical Light in a Waveguide.

Exciting a Bound State in the Continuum through Multiphoton Scattering Plus Delayed Quantum Feedback.

Particle Production in Ultrastrong-Coupling Waveguide QED

Non-Markovian Dynamics of a Qubit Due to Single-Photon Scattering in a Waveguide

Quantum interference and complex photon statistics in waveguide QED

Waveguide QED: Power spectra and correlations of two photons scattered off multiple distant qubits and a mirror (vol 91, 053845, 2015)

Journal Article PHYSICAL REVIEW A · November 13, 2017 Full text Link to item Cite

Multiple emitters in a waveguide: Nonreciprocity and correlated photons at perfect elastic transmission

Rescuing a Quantum Phase Transition with Quantum Noise.

Photon correlations generated by inelastic scattering in a one-dimensional waveguide coupled to three-level systems

Journal Article PHYSICA E-LOW-DIMENSIONAL SYSTEMS & NANOSTRUCTURES · April 1, 2016 Full text Open Access Link to item Cite

Dynamics of a qubit in a high-impedance transmission line from a bath perspective

Detecting photon-photon interactions in a superconducting circuit

Waveguide QED: Power spectra and correlations of two photons scattered off multiple distant qubits and a mirror

One-dimensional waveguide coupled to multiple qubits: Photon-photon correlations

Generalized multipolaron expansion for the spin-boson model: Environmental entanglement and the biased two-state system

Transport signatures of Majorana quantum criticality realized by dissipative resonant tunneling

Journal Article Physical Review B - Condensed Matter and Materials Physics · June 27, 2014 We consider theoretically the transport properties of a spinless resonant electronic level coupled to strongly dissipative leads, in the regime of circuit impedance near the resistance quantum. Using the Luttinger liquid analogy, one obtains an effective H ... Full text Open Access Cite

Stabilizing spin coherence through environmental entanglement in strongly dissipative quantum systems

Journal Article Physical Review B - Condensed Matter and Materials Physics · March 18, 2014 The key feature of a quantum spin coupled to a harmonic bath - a model dissipative quantum system - is competition between oscillator potential energy and spin tunneling rate. We show that these opposing tendencies cause environmental entanglement through ... Full text Open Access Cite

Tunable quantum phase transitions in a resonant level coupled to two dissipative baths

Journal Article Physical Review B - Condensed Matter and Materials Physics · February 18, 2014 We study tunneling through a resonant level connected to two dissipative bosonic baths: one is the resistive environment of the source and drain leads, while the second comes from coupling to potential fluctuations on a resistive gate. We show that several ... Full text Open Access Cite

Waveguide-QED-based photonic quantum computation.

Journal Article Phys Rev Lett · August 30, 2013 We propose a new scheme for quantum computation using flying qubits--propagating photons in a one-dimensional waveguide interacting with matter qubits. Photon-photon interactions are mediated by the coupling to a four-level system, based on which photon-ph ... Full text Open Access Link to item Cite

Floquet majorana fermions for topological qubits in superconducting devices and cold-atom systems

Journal Article Physical Review Letters · July 22, 2013 We develop an approach to realizing a topological phase transition and non-Abelian braiding statistics with dynamically induced Floquet Majorana fermions (FMFs). When the periodic driving potential does not break fermion parity conservation, FMFs can encod ... Full text Open Access Cite

Zigzag phase transition in quantum wires

Journal Article Physical Review Letters · June 11, 2013 We study the quantum phase transition of interacting electrons in quantum wires from a one-dimensional (1D) linear configuration to a quasi-1D zigzag arrangement using quantum Monte Carlo methods. As the density increases from its lowest values, first, the ... Full text Open Access Cite

Persistent quantum beats and long-distance entanglement from waveguide-mediated interactions.

Journal Article Physical review letters · March 2013 We study photon-photon correlations and entanglement generation in a one-dimensional waveguide coupled to two qubits with an arbitrary spatial separation. To treat the combination of nonlinear elements and 1D continuum, we develop a novel Green function me ... Full text Open Access Cite

Decoy-state quantum key distribution with nonclassical light generated in a one-dimensional waveguide.

Journal Article Optics letters · March 2013 We investigate a decoy-state quantum key distribution (QKD) scheme with a sub-Poissonian single-photon source, which is generated on demand by scattering a coherent state off a two-level system in a one-dimensional waveguide. We show that, compared to cohe ... Full text Open Access Cite

Unveiling environmental entanglement in strongly dissipative qubits

Journal Article arXiv · January 30, 2013 The coupling of a qubit to a macroscopic reservoir plays a fundamental role in understanding the complex transition from the quantum to the classical world. Considering a harmonic environment, we use both intuitive arguments and numerical many-body quantum ... Open Access Link to item Cite

Observation of majorana quantum critical behaviour in a resonant level coupled to a dissipative environment

Journal Article Nature Physics · January 1, 2013 A quantum phase transition is an abrupt change between two distinct ground states of a many-body system, driven by an external parameter. In the vicinity of the quantum critical point (QCP) where the transition occurs, a new phase may emerge that is determ ... Full text Open Access Cite

Fermi-liquid regime of the mesoscopic Kondo problem

Journal Article Eur. Phys. J. B · October 16, 2012 We consider the low temperature regime of the mesoscopic Kondo problem, and in particular the relevance of a Fermi-liquid description of this regime. Using two complementary approaches -- a mean field slave fermion approximation on the one hand and a Fermi ... Open Access Link to item Cite

Quantum phase transition in a resonant level coupled to interacting leads.

Journal Article Nature · August 2012 A Luttinger liquid is an interacting one-dimensional electronic system, quite distinct from the 'conventional' Fermi liquids formed by interacting electrons in two and three dimensions. Some of the most striking properties of Luttinger liquids are revealed ... Full text Open Access Cite

Mesoscopic Anderson box: Connecting weak to strong coupling

Journal Article Physical Review B - Condensed Matter and Materials Physics · April 27, 2012 We study the Anderson impurity problem in a mesoscopic setting, namely the "Anderson box," in which the impurity is coupled to finite reservoir having a discrete spectrum and large sample-to-sample mesoscopic fluctuations. Note that both the weakly coupled ... Full text Open Access Cite

Strongly correlated photons generated by coupling a three- or four-level system to a waveguide

Journal Article Physical Review A - Atomic, Molecular, and Optical Physics · April 19, 2012 We study the generation of strongly correlated photons by coupling an atom to photonic quantum fields in a one-dimensional waveguide. Specifically, we consider a three-level or four-level system for the atom. Photon-photon bound states emerge as a manifest ... Full text Open Access Cite

Hamiltonian methods in quantum error correction and fault tolerance

Chapter · January 1, 2012 Introduction The existence of efficient quantum error correction (QEC), combined with the concept of the accuracy threshold [G98, KLZ98a], inspired confidence that reliable quantum computation is achievable in principle. However, a key point to understand ... Full text Cite

From weak- to strong-coupling mesoscopic Fermi liquids

Journal Article EPL · January 1, 2012 We study mesoscopic fluctuations in a system in which there is a continuous connection between two distinct Fermi liquids, asking whether the mesoscopic variation in the two limits is correlated. The particular system studied is an Anderson impurity couple ... Full text Open Access Cite

Cavity-free photon blockade induced by many-body bound States

Journal Article Physical Review Letters · November 21, 2011 The manipulation of individual, mobile quanta is a key goal of quantum communication; to achieve this, nonlinear phenomena in open systems can play a critical role. We show theoretically that a variety of strong quantum nonlinear phenomena occur in a compl ... Full text Open Access Cite

Detecting a Majorana-fermion zero mode using a quantum dot

Journal Article Physical Review B - Condensed Matter and Materials Physics · November 16, 2011 We propose an experimental setup for detecting a Majorana zero mode consisting of a spinless quantum dot coupled to the end of a p-wave superconducting nanowire. The Majorana bound state at the end of the wire strongly influences the conductance through th ... Full text Open Access Cite

Kondo effect and mesoscopic fluctuations

Journal Article Pramana - Journal of Physics · November 1, 2011 Two important themes in nanoscale physics in the last two decades are correlations between electrons and mesoscopic fluctuations. Here we review our recent work on the intersection of these two themes. The setting is the Kondo effect, a paradigmatic exampl ... Full text Open Access Cite

Waveguide QED: Many-body bound-state effects in coherent and Fock-state scattering from a two-level system

Journal Article Physical Review A - Atomic, Molecular, and Optical Physics · December 14, 2010 Strong coupling between a two-level system (TLS) and bosonic modes produces dramatic quantum optics effects. We consider a one-dimensional continuum of bosons coupled to a single localized TLS, a system which may be realized in a variety of plasmonic, phot ... Full text Open Access Cite

Two-stage Kondo effect and Kondo-box level spectroscopy in a carbon nanotube

Journal Article Physical Review B - Condensed Matter and Materials Physics · October 18, 2010 The concept of the "Kondo box" describes a single spin, antiferromagnetically coupled to a quantum dot with a finite level spacing. Here, a Kondo box is formed in a carbon nanotube interacting with a localized electron. We investigate the spins of its firs ... Full text Open Access Cite

Bound on quantum computation time: Quantum error correction in a critical environment

Journal Article Physical Review A - Atomic, Molecular, and Optical Physics · August 31, 2010 We obtain an upper bound on the time available for quantum computation for a given quantum computer and decohering environment with quantum error correction implemented. First, we derive an explicit quantum evolution operator for the logical qubits and sho ... Full text Open Access Cite

Time-Dependent Transport Through Molecular Junctions

Journal Article J. Chem. Phys. · June 2010 Open Access Link to item Cite

Graphene rings in magnetic fields: Aharonov-Bohm effect and valley splitting

Journal Article Semiconductor Science and Technology · February 23, 2010 We study the conductance of mesoscopic graphene rings in the presence of a perpendicular magnetic field by means of numerical calculations based on a tight-binding model. First, we consider the magnetoconductance of such rings and observe the Aharonov-Bohm ... Full text Cite

Conductance of quantum impurity models from quantum Monte Carlo

Journal Article Physical Review B · 2010 Open Access Link to item Cite

Quantum Phase Transition and Dynamically Enhanced Symmetry in Quadruple Quantum Dot System

Journal Article Physical Review Letters · 2010 Link to item Cite

Localization in an inhomogeneous quantum wire

Journal Article Physical Review B - Condensed Matter and Materials Physics · November 2, 2009 We study interaction-induced localization of electrons in an inhomogeneous quasi-one-dimensional system-a wire with two regions, one at low density and the other high. Quantum Monte Carlo techniques are used to treat the strong Coulomb interactions in the ... Full text Cite

Interfaces within graphene nanoribbons

Journal Article New Journal of Physics · September 30, 2009 We study the conductance through two types of graphene nanostructures: nanoribbon junctions in which the width changes from wide to narrow, and curved nanoribbons. In the wide-narrow structures, substantial reflection occurs from the wide-narrow interface, ... Full text Cite

Thermopower of molecular junctions: an ab initio study.

Journal Article Nano letters · March 2009 Molecular nanojunctions may support efficient thermoelectric conversion through enhanced thermopower. Recently, this quantity has been measured for several conjugated molecular nanojunctions with gold electrodes. Considering the wide variety of possible me ... Full text Cite

Symmetry classes in graphene quantum dots: universal spectral statistics, weak localization, and conductance fluctuations.

Journal Article Physical review letters · February 2009 We study the symmetry classes of graphene quantum dots, both open and closed, through the conductance and energy level statistics. For abrupt termination of the lattice, these properties are well described by the standard orthogonal and unitary ensembles. ... Full text Cite

Ground state and excitations of quantum dots with magnetic impurities

Journal Article Phys. Rev. B · 2009 We consider an “impurity” with a spin degree of freedom coupled to a finite reservoir of non-interacting electrons, a system which may be realized by either a true impurity in a metallic nano-particle or a small quantum dot coupled to a large one. We show ... Link to item Cite

Thermopower of Molecular Junctions

Journal Article Nano Lett. · January 2009 Link to item Cite

Quantum-interference-controlled molecular electronics.

Journal Article Nano letters · October 2008 Quantum interference in coherent transport through single molecular rings may provide a mechanism to control the current in molecular electronics. We investigate its applicability, using a single-particle Green function method combined with ab initio elect ... Full text Cite

Hamiltonian formulation of quantum error correction and correlated noise: Effects of syndrome extraction in the long-time limit

Journal Article Physical Review A - Atomic, Molecular, and Optical Physics · July 9, 2008 We analyze the long-time behavior of a quantum computer running a quantum error correction (QEC) code in the presence of a correlated environment. Starting from a Hamiltonian formulation of realistic noise models, and assuming that QEC is indeed possible, ... Full text Cite

Interaction-induced strong localization in quantum dots

Journal Article Physical Review B - Condensed Matter and Materials Physics · January 2, 2008 We argue that Coulomb blockade phenomena are a useful probe of the crossover to strong correlation in quantum dots. Through calculations at low density using variational and diffusion quantum Monte Carlo (up to rs ∼55), we find that the addition energy sho ... Full text Cite

Fermi edge singularities in the mesoscopic regime: Photoabsorption spectra

Journal Article Physical Review B - Condensed Matter and Materials Physics · December 18, 2007 We study Fermi edge singularities in photoabsorption spectra of generic mesoscopic systems such as quantum dots or nanoparticles. We predict deviations from macroscopic-metallic behavior and propose experimental setups for the observation of these effects. ... Full text Cite

Improving intrinsic decoherence in multiple-quantum-dot charge qubits

Journal Article Physical Review B - Condensed Matter and Materials Physics · December 12, 2007 We discuss decoherence in charge qubits formed by multiple lateral quantum dots in the framework of the spin-boson model and the Born-Markov approximation. We consider the intrinsic decoherence caused by the coupling to bulk phonon modes. Two distinct quan ... Full text Cite

Level spacings in random matrix theory and Coulomb blockade peaks in quantum dots

Journal Article Physical Review B - Condensed Matter and Materials Physics · November 30, 2007 We obtain analytic formulas for the spacing between conductance peaks in the Coulomb blockade regime based on the universal Hamiltonian model of quantum dots. Random matrix theory results are developed in order to treat correlations between two and three c ... Full text Cite

Electron transport through single conjugated organic molecules: basis set effects in ab initio calculations.

Journal Article The Journal of chemical physics · October 2007 We investigate electron transport through single conjugated molecules--including benzenedithiol, oligophenylene ethynylenes of different lengths, and a ferrocene-containing molecule sandwiched between two gold electrodes with different contact structures-- ... Full text Cite

Contact transparency of nanotube-molecule-nanotube junctions.

Journal Article Physical review letters · October 2007 The transparency of contacts between conjugated molecules and metallic single-walled carbon nanotubes is investigated using a single-particle Green's function method which combines a Landauer approach with ab initio density functional theory. We find that ... Full text Cite

Cobaltocene as a spin filter.

Journal Article The Journal of chemical physics · October 2007 In the context of investigating organic molecules for molecular electronics, doping molecular wires with transition metal atoms provides additional means of controlling their transport behavior. The incorporation of transition metal atoms may generate spin ... Full text Cite

Incipient Wigner localization in circular quantum dots

Journal Article Physical Review B - Condensed Matter and Materials Physics · August 28, 2007 We study the development of electron-electron correlations in circular quantum dots as the density is decreased. We consider a wide range of both electron number, N≤20, and electron gas parameter, rs 18, using the diffusion quantum Monte Carlo technique. F ... Full text Cite

Role of the exchange-correlation potential in ab initio electron transport calculations.

Journal Article The Journal of chemical physics · May 2007 The effect of the exchange-correlation potential in ab initio electron transport calculations is investigated by constructing optimized effective potentials using different energy functionals or the electron density from second-order perturbation theory. T ... Full text Cite

Resilient quantum computation in correlated environments: a quantum phase transition perspective.

Journal Article Physical review letters · January 2007 We analyze the problem of a quantum computer in a correlated environment protected from decoherence by quantum error correction using a perturbative renormalization group approach. The scaling equation obtained reflects the competition between the dimensio ... Full text Cite

Disorder-Induced Superfluidity in Hardcore Bosons in Two Dimensions

Journal Article Phys. Rev. B · 2007 Link to item Cite

Hamiltonian Formulation of Quantum Error Correction and Correlated Noise

Journal Article CoRR · 2007 Cite

Development of ab initio calculation for electron transport and the effects of lead and contact structures in molecular electronics

Journal Article Journal of Computational and Theoretical Nanoscience · December 29, 2006 A fully self-consistent method combining density functional theory (DFT) and nonequilibrium Green function approach for calculating electron transport through molecular devices is reviewed. It uses periodic boundary conditions for DFT and treats the leads ... Full text Cite

Decoherence by correlated noise and quantum error correction.

Journal Article Physical review letters · July 2006 We study the decoherence of a quantum computer in an environment which is inherently correlated in time and space. We first derive the nonunitary time evolution of the computer and environment in the presence of a stabilizer error correction code, providin ... Full text Cite

Correlation-induced inhomogeneity in circular quantum dots

Journal Article Nature Physics · May 17, 2006 Full text Cite

Negative differential resistance and hysteresis through an organometallic molecule from molecular-level crossing.

Journal Article Journal of the American Chemical Society · May 2006 Analogous to a quantum double-dot system, diblock structured molecules could also show negative differential resistance (NDR). Using combined density functional theory and nonequilibrium Green function technique, we show that molecular-level crossing in a ... Full text Cite

Nanotube-metal junctions: 2- and 3-terminal electrical transport.

Journal Article The Journal of chemical physics · May 2006 We address the quality of electrical contact between carbon nanotubes and metallic electrodes by performing first-principles calculations for the electron transmission through ideal 2- and 3-terminal junctions, thus revealing the physical limit of tube-met ... Full text Cite

Organometallic molecular rectification.

Journal Article The Journal of chemical physics · January 2006 We study the rectification of current through a single molecule with an intrinsic spatial asymmetry. The molecule contains a cobaltocene moiety in order to take advantage of its relatively localized and high-energy d states. A rectifier with large voltage ... Full text Cite

Quantum Phase Transitions of Hard-Core Bosons in Background Potentials

Journal Article Phys. Rev. Lett. · 2006 Link to item Cite

Spectroscopy of the Kondo Problem in a Box

Journal Article Phys.Rev.Lett. · 2006 Motivated by experiments on double quantum dots, we study the problem of a single magnetic impurity confined in a finite metallic host. We prove an exact theorem for the ground state spin, and use analytic and numerical arguments to map out the spin struct ... Link to item Cite

Phonon decoherence in quantum dot qubits

Journal Article Proceedings of SPIE - The International Society for Optical Engineering · November 15, 2005 The spin of an electron confined into a lateral semiconductor quantum dot has been proposed as a possible physical realization of a qubit. While the spin has the advantage of large decoherence times, operations with more than one qubit will necessarily inv ... Full text Cite

Coulomb blockade peak spacings: Interplay of spin and dot-lead coupling

Journal Article Physical Review B - Condensed Matter and Materials Physics · October 15, 2005 For Coulomb blockade peaks in the linear conductance of a quantum dot, we study the correction to the spacing between the peaks due to dot-lead coupling. This coupling can affect measurements in which Coulomb blockade phenomena are used as a tool to probe ... Full text Cite

Anisotropy in ferromagnetic nanoparticles: Level-to-level fluctuations of a collective effect

Journal Article Europhysics Letters · October 1, 2005 We calculate the mesoscopic fluctuations of the magnetic anisotropy of ferromagnetic nanoparticles; that is, the effect of single-particle interference on the direction of the collective magnetic moment. A microscopic spin-orbit Hamiltonian considered as a ... Full text Cite

Organometallic spintronics: dicobaltocene switch.

Journal Article Nano letters · October 2005 A single-molecule spintronic switch and spin valve using two cobaltocene moieties is proposed. Spin-dependent transport through a lead-molecule-lead junction has been calculated using first-principles density functional and nonequilibrium Green function me ... Full text Cite

Models of electrodes and contacts in molecular electronics.

Journal Article The Journal of chemical physics · September 2005 Bridging the difference in atomic structure between experiments and theoretical calculations and exploring quantum confinement effects in thin electrodes (leads) are both important issues in molecular electronics. To address these issues, we report here, b ... Full text Cite

Fermi edge singularities in the mesoscopic regime: Anderson orthogonality catastrophe

Journal Article Physical Review B - Condensed Matter and Materials Physics · July 15, 2005 For generic mesoscopic systems, such as quantum dots or nanoparticles, we study the Anderson orthogonality catastrophe (AOC) and Fermi-edge singularities in photoabsorption spectra in a series of two papers. In the present paper we focus on AOC for a finit ... Full text Cite

Statistics of wave functions in disordered systems with applications to Coulomb blockade peak spacing

Journal Article Physical Review B - Condensed Matter and Materials Physics · July 15, 2005 Despite considerable work on the energy-level and wave function statistics of disordered quantum systems, numerical studies of those statistics relevant for electron-electron interactions in mesoscopic systems have been lacking. We plug this gap by using a ... Full text Cite

Near-perfect conduction through a ferrocene-based molecular wire

Journal Article Physical Review B - Condensed Matter and Materials Physics · June 15, 2005 Here we describe the design, single-molecule transport measurements, and theoretical modeling of a ferrocene-based organometallic molecular wire, whose bias-dependent conductance shows a clear Lorentzian form with magnitude exceeding 70% of the conductance ... Full text Cite

Interaction effects in the mesoscopic regime: A quantum Monte Carlo study of irregular quantum dots

Journal Article Physical Review B - Condensed Matter and Materials Physics · June 15, 2005 We address the issue of accurately treating interaction effects in the mesoscopic regime by investigating the ground-state properties of isolated irregular quantum dots. Quantum Monte Carlo techniques are used to calculate the distributions of ground-state ... Full text Cite

Contact atomic structure and electron transport through molecules.

Journal Article The Journal of chemical physics · February 2005 Using benzene sandwiched between two Au leads as a model system, we investigate from first principles the change in molecular conductance caused by different atomic structures around the metal-molecule contact. Our motivation is the variable situations tha ... Full text Cite

Phonon decoherence of a double quantum dot charge qubit

Journal Article Physical Review B - Condensed Matter and Materials Physics · January 1, 2005 We study decoherence of a quantum dot charge qubit due to coupling to piezoelectric acoustic phonons in the Born-Markov approximation. After including appropriate form factors, we find that phonon decoherence rates are one to two orders of magnitude weaker ... Full text Cite