Destructive Quantum Interference Research Articles

Two-Dimensional Weak Antilocalization Signatures Due to Quantum Coherent Transport in Nanocrystalline SnTe.

Nanostructured topological crystalline insulators (TCIs) in the presence of exotic surface states with spin momentum locking reported in individual nanostructures are predicted to hold a great promise for spintronics and quantum computing applications. However, practical application demands a strategy with large-scale production and integration for device applications. In this work, we demonstrate through prominent signatures of weak antilocalization (WAL), arising predominantly from destructive quantum interference on robust surface states, that a correlated TCI phase is possible in the nanobulk assembly of carefully nanostructured quasi-two-dimensional SnTe (edge-to-edge length ∼ 382 nm) synthesized by a simple, rapid, and scalable microwave-assisted solvothermal method. Hikami-Larkin-Nagaoka analysis (T-0.71), as well as the temperature dependence of resistivity, illustrates an interplay of both conductions from 2D channels and 3D EEI effects as the precursor for the observed WAL at low temperatures (2-6 K). Interestingly, the enhanced thermoelectric power of the sample of ∼45 μV/K, with a p-type carrier concentration of ∼1018/cm3 at 300 K, makes this SnTe nanocrystalline assembly more attractive as a multifunctional material for large-scale technological applications.

Light emission by free electrons in photonic time-crystals

Photonic time-crystals (PTCs) are spatially homogeneous media whose electromagnetic susceptibility varies periodically in time, causing temporal reflections and refractions for any wave propagating within the medium. The time-reflected and time-refracted waves interfere, giving rise to Floquet modes with momentum bands separated by momentum gaps (rather than energy bands and energy gaps, as in photonic crystals). Here, we present a study on the emission of radiation by free electrons in PTCs. We show that a free electron moving in a PTC spontaneously emits radiation, and when associated with momentum-gap modes, the electron emission process is exponentially amplified by the modulation of the refractive index. Moreover, under strong electron-photon coupling, the quantum formulation reveals that the spontaneous emission into the PTC bandgap experiences destructive quantum interference with the emission of the electron into the PTC band modes, leading to suppression of the interdependent emission. Free-electron physics in PTCs offers a platform for studying a plethora of exciting phenomena, such as radiating dipoles moving at relativistic speeds and highly efficient quantum interactions with free electrons.

Interaction-free bidirectional multi-channel all-optical switching in a multi-level coupling atom-cavity system.

We propose a scheme of interaction-free bidirectional multi-channel all-optical switching in a multi-level coupling system consisting of four-level atoms confined in a cavity and coupled by a free-space control laser. A signal laser field is coupled into the cavity and excites two separate transitions of atoms simultaneously under the collective strong coupling condition. The transmission and reflection of signal fields form bidirectional output channels. A free-space control laser induces destructive quantum interference in the multi-level excitation of an atom-cavity system, which can be used to switch on/off the output signal lights of transmission/reflection channels. There is no direct coupling of control light and signal light through the cavity-confined atoms because the output of signal light is nearly totally suppressed to the opposite direction when control light is present. The proposed all-optical switching scheme can be realized with high switching efficiency, broad bandwidth, and weak light intensity. It may be useful for future devices of optical routing, optical communications, and various quantum logic elements.

Multiple heteroatom substitution effect on destructive quantum interference in tripodal single-molecule junctions.

Quantum interference (QI) has been identified as a promising strategy for designing molecular-scale electronic devices. Heteroatom doping can effectively tailor the local structures and electronic states of intrinsic molecules, and endow them with modified electron transport properties. Herein, the impacts of multiple heteroatom substitution on destructive quantum interference (DQI) have been investigated based on tripodal meta-linked phenyl derivatives. Orbital views based on the Hückel method qualitatively predict the meta-anchored molecules with DQI features, while the introduction of nitrogen atoms can alleviate the suppression of DQI at the Fermi level (EF). This is generally consistent with the movement or even removal of the antiresonance dips in transmission spectra. The substituent on position 2 can raise the antiresonance energy, while the substituent on position 4 or 6 can lower the antiresonance energy. When more than one nitrogen atom is incorporated, the impact of the substitution on positions 4 and 6 can be superimposed and the substitution on positions 2 and 4 can be partly cancelled. The experimental single-molecule conductance for tripodal molecules follows the trend of 0N-3SMe < 1N-3SMe < 3N-3SMe < 2N-3SMe, in agreement with the theoretical prediction. Additionally, the regulation is the intrinsic property depending on the position and number of the nitrogen atoms in the backbone and is irrelevant to the number and type of the anchoring groups. Our findings provide qualitative guidance for tuning the electron transport based on DQI in heterocycle molecular devices.

Hydrogen-bond-induced quantum interference in single-molecule junctions of regioisomers.

Solvents can play a significant role in tuning the electrical conductance of single-molecule junctions. In this respect, protic solvents offer the potential to form hydrogen bonds with molecular backbones and induce electrostatic gating via their dipole moments. Here we demonstrate that the effect of hydrogen bond formation on conductance depends on whether transport through the junction is controlled by destructive quantum interference (DQI) or constructive quantum interference (CQI). Furthermore, we show that a protic solvent can be used to switch the conductance of single-molecule junctions between the two forms of quantum interference. To explore this possibility, two regioisomers (BIT-Zwitterion and BIT-Neutral) were synthesized and their single-molecule conductances in aprotic and protic solvents were investigated using a scanning-tunneling-microscope-based break junction technique, combined with density functional theory and quantum transport theory. We find that the protic solvent twists the geometry of BIT-Zwitterion by introducing intermolecular hydrogen bonds between the solvent and target molecule. Moreover, it increases the energy gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) of the molecule by imposing different electrostatic gating on the delocalized HOMO and localized LUMO, leading to a lower conductance compared to that in aprotic solvent. In contrast, the conductance of BIT-Neutral increases due to a transformation from DQI to CQI originating from a change from a planar to a folded conformation in the protic solvent. In addition, the stacking between the two folded moieties produces an extra through-space transport path, which further contributes to conductance. This study demonstrates that combinations of protic solvents and regioisomers present a versatile route to controlling quantum interference and therefore single-molecule conductance, by enabling control of hydrogen bond formation, electrostatic gating and through-space transport.

Antiresonance and negative differential conductance in parallel-coupled vibrating molecular dots coupled to Luttinger liquid leads

We theoretically study the interplays of electron–phonon interaction, inter-dot coupling tunneling and intralead electron interaction on transport properties of parallel-coupled double quantum dots connected to Luttinger liquid leads. The nonequilibrium Green’s function method is used. Numerical results show several intriguing physic phenomena. In the weak intralead electron interaction, there is a zero-bias antiresonance dip followed by phonon-assisted satellite peaks for strong electron–phonon interaction and inter-dot tunneling. With decreasing inter-dot tunneling, there is an evolution from satellite peaks to dips, which signifies the phase transition from phonon-assisted single-channel to two-channel Kondo physics. When the dot-lead coupling is asymmetric, in the case of moderately strong intralead interaction, strong electron–phonon coupling and weak inter-dot tunneling, there may appear the pronounced negative differential conductance and Fano resonance, while there does not when the coupling is symmetric. These results provide a convenient way to probe destructive quantum interference and extract information of the electron–phonon interaction strength, which is crucial for designing molecular switches and thermoelectric devices. • We study the transport properties of parallel coupled double quantum dots connected to Luttinger liquid leads. • We have theoretically studied a series of problems such as electron phonon interaction . • The method used is nonequilibrium Green’s function. • The phenomena of resonance and peak of satellite are found. • Negative differential conductance and Fano resonance are found.

Mechanical conductance tunability of a porphyrin-cyclophane single-molecule junction.

The possibility to study quantum interference phenomena at ambient conditions is an appealing feature of molecular electronics. By connecting two porphyrins in a cofacial cyclophane, we create an attractive platform for mechanically controlling electric transport through the intramolecular extent of π-orbital overlap of the porphyrins facing each other and through the angle of xanthene bridges with regard to the porphyrin planes. We analyze theoretically the evolution of molecular configurations in the pulling process and the corresponding changes in electric conduction by combining density functional theory (DFT) with Landauer scattering theory of phase-coherent elastic transport. Predicted conductances during the stretching process show order of magnitude variations caused by two robust destructive quantum interference features that span through the whole electronic gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO). Mechanically-controlled break junction (MCBJ) experiments at room temperature verify the mechanosensitive response of the molecular junctions. During the continuous stretching of the molecule, they show conductance variations of up to 1.5 orders of magnitude over single breaking events. Uncommon triple- and quadruple-frequency responses are observed in periodic electrode modulation experiments with amplitudes of up to 10 Å. This further confirms the theoretically predicted double transmission dips caused by the spatial and energetic rearrangement of molecular orbitals, with contributions from both through-space and through-bond transport.

Molecular quantum interference effects on thermopower in hybrid 2-dimensional monolayers.

Quantum interference effects in single-molecule devices can significantly enhance the thermoelectric properties of these devices. However, single-molecule systems have limited utility for power conversion. In this work, we study the effects of destructive quantum interference in molecular junctions on the thermoelectric properties of hybrid, 2-dimensional molecule-nanoparticle monolayers. We study two isomers of benzenedithiol molecules, with either a para or meta configuration for the thiol groups, as molecular interlinkers between gold nanoparticles in the structure. The asymmetrical structure in the meta configuration significantly improves the Seebeck coefficient and power factor over the para configuration. These results suggest that thermoelectric performance of engineered, nanostructured material can be enhanced by harnessing quantum interference effects in the substituent components.

Quantum interference dependence on molecular configurations for cross-conjugated systems in single-molecule junctions

Interactions between electrodes and pendant groups in cross-conjugated systems destroy destructive quantum interference resulting in an increase of G and a decrease of S.

One-sided destructive quantum interference from an exceptional-point-based metasurface

We propose the concept of one-sided quantum interference based on non-Hermitian metasurfaces.By designing bianisotropic metasurfaces with a non-Hermitian exceptional point, we show that quantum interference can exist only on only one side but not another. This is the quantum inheritance of unidirectional zero reflection in classical optics.The one-side interference can be further manipulated with tailor-made metasurface. With two photons simultaneously entering the metasurface from different sides, the probability for only outputting one photon on the side with reflection can be modified to zero as a one-sided destructive quantum interference while the output on another side is free of interference. We design the required bianisotropic metasurface and numerically demonstrate the proposed effect. The non-Hermitian bianisotropic metasurfaces provide more degrees of freedom in tuning two-photon quantum interference, in parallel to the celebrated Hong-Ou-Mandel effect.

Substituent-mediated quantum interference toward a giant single-molecule conductance variation

Quantum interference (QI) in single molecular junctions shows a promising perspective for realizing conceptual nanoelectronics. However, controlling and modulating the QI remains a big challenge. Herein, two-type substituents at different positions of meta-linked benzene, namely electron-donating methoxy (–OMe) and electron-withdrawing nitryl (–NO2), are designed and synthesized to investigate the substituent effects on QI. The calculated transmission coefficients T(E) indicates that –OMe and –NO2 could remove the antiresonance and destructive quantum interference (DQI)-induced transmission dips at position 2. –OMe could raise the antiresonance energy at position 4 while –NO2 groups removes the DQI features. For substituents at position 5, both of them are nonactive for tuning QI. The conductance measurements by scanning tunneling microscopy break junction show a good agreement with the theoretical prediction. More than two order of magnitude single-molecule conductance on/off ratio could be achieved at the different positions of –NO2 substituent groups at room temperature. The present work proves chemical substituents can be used for tuning QI features in single molecular junctions, which provides a feasible way toward realization of high-performance molecular devices.

Thermo-optically induced transparency on a photonic chip

Controlling the optical response of a medium through suitably tuned coherent electromagnetic fields is highly relevant in a number of potential applications, from all-optical modulators to optical storage devices. In particular, electromagnetically induced transparency (EIT) is an established phenomenon in which destructive quantum interference creates a transparency window over a narrow spectral range around an absorption line, which, in turn, allows to slow and ultimately stop light due to the anomalous refractive index dispersion. Here we report on the observation of a new form of both induced transparency and amplification of a weak probe beam in a strongly driven silicon photonic crystal resonator at room temperature. The effect is based on the oscillating temperature field induced in a nonlinear optical cavity, and it reproduces many of the key features of EIT while being independent of either atomic or mechanical resonances. Such thermo-optically induced transparency will allow a versatile implementation of EIT-analogs in an integrated photonic platform, at almost arbitrary wavelength of interest, room temperature and in a practical, low cost, and scalable system.

Minimal model for Hilbert space fragmentation with local constraints

Motivated by previous works on a Floquet version of the PXP model [Mukherjee {\it et al.} Phys. Rev. B 102, 075123 (2020), Mukherjee {\it et al.} Phys. Rev. B 101, 245107 (2020)], we study a one-dimensional spin-$1/2$ lattice model with three-spin interactions in the same constrained Hilbert space (where all configurations with two adjacent $S^z=\uparrow$ spins are excluded). We show that this model possesses an extensive fragmentation of the Hilbert space which leads to a breakdown of thermalization upon unitary evolution starting from a large class of simple initial states. Despite the non-integrable nature of the Hamiltonian, many of its high-energy eigenstates admit a quasiparticle description. A class of these, which we dub as "bubble eigenstates", have integer eigenvalues (including mid-spectrum zero modes) and strictly localized quasiparticles while another class contains mobile quasiparticles leading to a dispersion in momentum space. Other anomalous eigenstates that arise due to a {\it secondary} fragmentation mechanism, including those that lead to flat bands in momentum space due to destructive quantum interference, are also discussed. The consequences of adding a (non-commuting) staggered magnetic field and a PXP term respectively to this model, where the former preserves the Hilbert space fragmentation while the latter destroys it, are discussed. A Floquet version with time-dependent staggered field also evades thermalization with additional features like freezing of exponentially many states at special drive frequencies. Finally, we map the model to a $U(1)$ lattice gauge theory coupled to dynamical fermions and discuss the interpretation of some of these anomalous states in this language. A class of gauge-invariant states show reduced mobility of the elementary charged excitations with only certain charge-neutral objects being mobile suggesting a connection to fractons.

Thermoelectric Performance Enhanced by Destructive Quantum Interference in Nanoporous Carbon Nanotube Based Junctions

Aided by density functional theory with nonequilibrium Green's functions simulations, the thermoelectric (TE) properties of nanoporous carbon nanotube junctions formed by covalently binding carbon nanotubes via benzene bridges with either meta‐ or para‐connections are investigated. The results show that the TE performances of meta‐connected nanoporous carbon nanotube junctions are significantly improved due to the influence of destructive quantum interference (DQI) effect. Moreover, the TE properties of meta‐connected carbon nanotube junctions can be further improved by substitution of nitrogen atom and gate voltage. The reason is that the quantum interference patterns can be transformed from DQI to constructive quantum interference (or Fano resonance). The theoretical analysis shows that the TE figure of merit (ZT) for meta‐connected carbon nanotube junctions at room temperature is close to 0.5 near the Fermi level, ≈20 times higher than that of the perfect carbon nanotube junction. These results reveal that quantum interference effect can indeed be used to enhance the TE performance of molecular junctions.

Promotion and suppression of single-molecule conductance by quantum interference in macrocyclic circuits

Promotion and suppression of single-molecule conductance by quantum interference in macrocyclic circuits

Heteroatom Effects on Quantum Interference in Molecular Junctions: Modulating Antiresonances by Molecular Design.

Controlling charge transport through molecular wires by utilizing quantum interference (QI) is a growing topic in single-molecular electronics. In this article, scanning tunneling microscopy-break junction techniques and density functional theory calculations are employed to investigate the single-molecule conductance properties of four molecules that have been specifically designed to test extended curly arrow rules (ECARs) for predicting QI in molecular junctions. Specifically, for two new isomeric 1-phenylpyrrole derivatives, the conductance pathway between the gold electrodes must pass through a nitrogen atom: this novel feature is designed to maximize the influence of the heteroatom on conductance properties and has not been the subject of prior investigations of QI. It is shown, experimentally and computationally, that the presence of a nitrogen atom in the conductance pathway increases the effect of changing the position of the anchoring group on the phenyl ring from para to meta, in comparison with biphenyl analogues. This effect is explained in terms of destructive QI (DQI) for the meta-connected pyrrole and shifted DQI for the para-connected isomer. These results demonstrate modulation of antiresonances by molecular design and verify the validity of ECARs as a simple “pen-and-paper” method for predicting QI behavior. The principles offer new fundamental insights into structure–property relationships in molecular junctions and can now be exploited in a range of different heterocycles for molecular electronic applications, such as switches based on external gating, or in thermoelectric devices.

Interference Controls Conductance in Phthalocyanine Molecular Junctions

We report an experimental and theoretical study of the single-molecule conductance of two separate families of regioisomeric phthalocyanine derivatives in which the binding groups are connected at opposite or at contiguous positions about the phthalocyanine moiety. We observe that compounds with the longest distance between the anchoring groups yield molecular junctions with a higher conductance compared to those with a shorter distance. We performed both density functional theory (DFT) and tight binding calculations to understand how interference effects explain the experimental results including the role of constructive and destructive quantum interference in five phthalocyanine derivatives.

Quantum interference enhanced thermopower in single-molecule thiophene junctions

Quantum interference (QI) effects, which offer unique opportunities to widely manipulate the charge transport properties in the molecular junctions, will have the potential for achieving high thermopower. Here we developed a scanning tunneling microscope break junction technique to investigate the thermopower through single-molecule thiophene junctions. We observed that the thermopower of 2,4-TP-SAc with destructive quantum interference (DQI) was nearly twice of 2,5-TP-SAc without DQI, while the conductance of the 2,4-TP-SAc was two orders of magnitude lower than that of 2,5-TP-SAc. Furthermore, we found the thermopower was almost the same by altering the anchoring group or thiophene core in the control experiments, suggesting that the QI effect is responsible for the increase of thermopower. The density functional theory (DFT) calculations are in quantitative agreement with the experimental data. Our results reveal that QI effects can provide a promising platform to enhance the thermopower of molecular junctions.

Reversible Switching between Destructive and Constructive Quantum Interference Using Atomically Precise Chemical Gating of Single-Molecule Junctions.

Quantum interference (QI) plays an imperative role in the operation of molecular devices within the phase-coherent length, and it is vital to harness the patterns of QI, i.e., constructive and destructive interference. However, the size of the single-molecule device is too small compared to most gate electrodes. Those gates act like a backgate to affect the molecular component uniformly. Switching the patterns of QI in the same molecular skeleton remains challenging. Here, we develop the atomically precise gating strategy that manipulates the frontier orbitals of molecular components, achieving the complete switching of QI patterns between destructive to constructive QI and leading to a significant conductance modulation at room temperature. The chemical gating effect is exerted locally on the pyridine nitrogen through the selective interaction to cationic reagents, with which we can also control the switching reversibility as desired. We demonstrate the unique effect of atomically precise gating to modulate the quantum interference at the single-molecule scale, opening an avenue to develop new-conceptual electronic devices.

Nonreciprocal unconventional photon blockade with spinning atom-cavity

In this work, we propose to manipulate the statistical properties of the photons transport nonreciprocally via rotating nonlinear devices consisting of an atom coupled to a spinning cavity. This nonreciprocal effect allows the flow of light from one side but blocks it from the other with the same driving strength. We show that the nonreciprocal unconventional photon blockade can happen when the cavity is driven by the laser field. Under the weak driving condition, we discuss the physical origins of the nonreciprocal unconventional photon blockade, which originates from the destructive quantum interference between different paths from the ground state to the two-photon state by driving the device from the left side, while the quantum interference paths are broken when the device is driven from the right side, which leads to the occurring of the photon bunching. The optimal conditions for strong photon antibunching are analytically derived, which are in good agreement with those obtained by numerical simulations. Our proposal has potential applications for the on-chip nonreciprocal single-photon devices and provides an effective way for potential applications in solid state quantum computation and quantum information process.