Quantum Interference Effects Research Articles

Multi-particle quantum walks on 3D integrated photonic chip

Quantum walks provide a speed-up in computational power for various quantum algorithms and serve as inspiration for the construction of complex graph representations. Many pioneering works have been dedicated to expanding the experimental state space and the complexity of graphs. However, these experiments are mostly limited to small experimental scale, which do not reach a many-body level and fail to reflect the multi-particle quantum interference effects among non-adjacent modes. Here, we present a quantum walk with three photons on a two-dimensional triangular lattice, which is mapped to a 19 × 19 × 19 high-dimensional state space and constructs a complex graph with 6859 nodes and 45,486 edges. By utilizing the statistical signatures of the output combinations and incorporating machine learning techniques, we successfully validate the nonclassical properties of the experiment. Our implementation provides a paradigm for exponentially expanding the state space and graph complexity of quantum walks, paving the way for surmounting the classical regime in large-scale quantum simulations.

Spatial adiabatic passage of ultracold atoms in optical tweezers.

Coherent manipulation of matter waves, a distinctive hallmark of quantum mechanics, is fundamental to modern quantum technologies. Spatial adiabatic passage (SAP) is a prime example of this phenomenon, where a wave packet is transferred between two uncoupled localized modes by adjusting the tunneling coupling to an intermediate third mode in a counterintuitive sequence. Although this concept was introduced over two decades ago, its observation was previously limited to electromagnetic waves. In this study, we demonstrate this quantum interference effect using massive particles that tunnel between three micro-optical traps ("optical tweezers"). We begin by preparing ultracold fermionic atoms in low vibrational eigenstates of one trap, followed by manipulating the distance between the traps to execute the SAP protocol. We observe a smooth and high-efficiency transfer of atoms between the two outer traps, with a very low population remaining in the central trap. These findings open possibilities for advanced control schemes in optical tweezer array platforms.

Intermolecular Interactions and Quantum Interference Effects in Molecular Junctions

Intermolecular Interactions and Quantum Interference Effects in Molecular Junctions

Quantum Interference Effects on Josephson Current through Quadruple-Quantum-Dot Molecular Inserted between Superconductors.

We study theoretically the Josephson current through a junction composed of quadruple quantum dots (QDs), of which only one is coupled directly to the left and right superconductor leads (denoted by QD1). The other three QDs are side-coupled to QD1 and free from coupling to the leads. It is found that when the energy levels of all the four QDs are identical, the Josephson current varying with energy level of QD1 develops three peaks with two narrow and one wide, showing the typical Dicke lineshape. With increasing inter-dot coupling strength, the triple-peak configuration is well retained and accompanied by an obviously increased current amplitude. The critical current as a function of the energy level of QD1 shows a single resonance peak whose position and height depend on the energy levels of the side-coupled QDs and the inter-dot coupling strengths. We also find that the curve of the critical current versus energy levels of the side-coupled QDs shows a pair of Fano resonances and the same number Fano antiresonances (valleys). When the energy levels of the side-coupled QDs are different from each other, another Fano resonance and antiresonance are induced due to the quantum interference effect. The present results are compared with those in double and triple QDs systems, and may serve as unique means, such as the combination of quantum Dicke and Fano effects, to manipulate the Josehpson currents.

Bias switching in single-molecule junctions through destructive quantum interference

Highly nonlinear current-voltage (I-V) characteristics in single-molecule junctions based on destructive quantum interference (DQI) effects are key to realizing bias-controlled molecular switches. Using first-principles quantum transport calculations, we investigated the charge transport properties of 1,4-diphenyl-2,3-dioxa-7-tellurabicyclo(DPDT) coupled to gold electrodes via cyanide (-CN), isocyanide (-NC) and pyridyl (-PY) anchoring groups, respectively. We demonstrated that there are DQI effects between LUMO and LUMO+1 of the opposite phase in the three junctions. It was revealed that the p orbital of the tellurium atom can localize HOMO orbitals on central units of molecular systems, and weaken the amplitude of LUMO relative to LUMO+1. This eliminates the constructive quantum interference (CQI) between HOMO and LUMO, but enhances the DQI between LUMO and LUMO+1 near the Fermi energy level of gold electrodes (EF). As a result, the three molecular junctions dominated by two LUMOs exhibit extremely high nonlinear I-V characteristics, contributing to a current at a high bias (±0.8 V) >170 times larger than that at a low bias (±0.2 V). Our findings provide a potentially stable and low-loss bias switching in single-molecule junctions.

Measurement of the impact-parameter dependent azimuthal anisotropy in coherent ρ0 photoproduction in Pb–Pb collisions at [formula omitted] TeV

This Letter presents the first measurement of the impact-parameter dependent angular anisotropy in the decay of coherently photoproduced ρ0 mesons. The ρ0 mesons are reconstructed through their decay into pion pairs. The measured anisotropy corresponds to the amplitude of the cos⁡(2ϕ) modulation, where ϕ is the angle between the two vectors formed by the sum and the difference of the transverse momenta of the pions, respectively. The measurement was performed by the ALICE Collaboration at the LHC using data from ultraperipheral Pb–Pb collisions at a center-of-mass energy of sNN=5.02 TeV per nucleon pair. Different impact-parameter regions are selected by classifying the events in nuclear-breakup classes. The amplitude of the cos⁡(2ϕ) modulation is found to increase by about one order of magnitude from large to small impact parameters. Theoretical calculations describe the measured cos⁡(2ϕ) anisotropy and its impact-parameter dependence as the result of a quantum interference effect at the femtometer scale, arising from the ambiguity regarding which of the nuclei is the photon source in the interaction.

Quantum Interference at the Recombination Junction of Perovskite-Si Tandem Solar Cells Improves Efficiency.

We show quantum interference effects can enhance coherent electron transmission in perovskite tandem solar cells using ultrathin indium tin oxide (ITO) layers. We develop a model for the behavior of the power conversion efficiency based on a finite difference time domain solution of the time-dependent Schrödinger equation. The modeled potential includes an imaginary part to simulate probability loss by incoherent scattering. The results agree with observations of efficiency as a function of ITO thickness, suggesting an optimized design.

A generalized weighted evidence fusion algorithm based on quantum modeling

In the field of evidence theory, the Dempster-Shafer framework is widely used for combining evidence. However, it often produces counterintuitive results when dealing with highly conflicting evidence. To mitigate this issue, the weighted evidence fusion method has gained popularity. However, with the generalization of the mass function from the perspective of quantum theory, the weighting of conflicting evidence under quantum effects remains an open issue. To address this issue, a generalized weighted evidence fusion algorithm based on quantum modeling is proposed in this study. First, when quantum interference effects are considered, Dempster's rule is generalized into a generalized evidence combination rule based on quantum modeling. Second, a generalized quantum evidence distance is proposed to measure the similarity of quantum evidence in the presence of phase-term interference. Third, a global and nonlinear quantum evidence weighting operator is designed to reduce the impact of conflicting quantum evidence. Then, based on this operator and the similarities between pieces of quantum evidence, the weighted quantum evidence is fused to yield the final conclusion using the proposed generalized combination rule. Finally, the rationality, reliability, and accuracy of the proposed method are effectively proven through experiments using a few numerical examples and applications.

Endless Dirac nodal lines and high mobility in kagome semimetal Ni3In2Se2 : a theoretical and experimental study

Kagome-lattice crystal is crucial in quantum materials research, exhibiting unique transport properties due to its rich band structure and the presence of nodal lines and rings. Here, we investigate the electronic transport properties and perform first-principles calculations for Ni3In2Se2kagome topological semimetal. First-principles calculations of the band structure without the inclusion of spin-orbit coupling (SOC) shows that three bands are crossing the Fermi level (EF), indicating the semi-metallic nature. With SOC, the band structure reveals a gap opening of the order of 10 meV.Z2index calculations suggest the topologically nontrivial natures (ν0;ν1ν2ν3) = (1;111) both without and with SOC. Our detailed calculations also indicate six endless Dirac nodal lines and two nodal rings with aπ-Berry phase in the absence of SOC. The temperature-dependent resistivity is dominated by two scattering mechanisms:s-dinterband scattering occurs below 50 K, while electron-phonon (e-p) scattering is observed above 50 K. The magnetoresistance (MR) curve aligns with the theory of extended Kohler's rule, suggesting multiple scattering origins and temperature-dependent carrier densities. A maximum MR of 120% at 2 K and 9 T, with a maximum estimated mobility of approximately 3000 cm2V-1s-1are observed. Ni3In2Se2is an electron-hole compensated topological semimetal, as we have carrier density of electron (ne) and hole (nh) arene≈nh, estimated from Hall effect data fitted to a two-band model. Consequently, there is an increase in the mobility of electrons and holes, leading to a higher carrier mobility and a comparatively higher MR. The quantum interference effect leading to the two dimensional (2D) weak antilocalization effect (-σxx∝ln(B)) manifests as the diffusion of nodal line fermions in the 2D poloidal plane and the associated encircling Berry flux of nodal-line fermions.

Effect of A-site disorder and reduced grain size on low temperature resistivity minima and magnetoresistance behaviour in Nd0.7-xGdxSr0.3MnO3 (0 ≤ x ≤ 0.3)

ABSTRACT The present work provides a detailed investigation of the electronic- and magneto-transport properties of bulk and nanostructured Nd0.7-xGdxSr0.3MnO3 (x = 0, 0.1, 0.2 and 0.3) polycrystalline manganites. We have specially addressed the issue of the observed minimum in the temperature dependent resistivity of these manganites in the low temperature regime (<50 K). It is observed that increase of A-site disorder due to progressive substitution of Gd and decrease of grain size enhances the observed resistivity minima. Different theoretical models have been employed to analyze the resistivity data in the low temperature regime. It has been established that the quantum interference effect due to electron–electron interaction, most likely, is the dominant factor of the observed resistivity minimum and upturn in resistivity in the lower temperature regime. The effect of phase separation is also found to play a key role in the electronic-transport of the materials. Further the magnetoresistance is found to increase with the increase of Gd concentration as well as with the decrease of grain size in the low temperature regime. The origin of magnetoresistance has been critically analyzed.

Electron Transport through Linear-, Broken-, and Cross-Conjugated Polycyclic Compounds.

Quantum interference (QI) effects offer unique opportunities to modulate charge transport through single molecules. In recent years, several transmission selection rules have been developed to determine constructive and destructive QIs in an intuitive and simple manner, although some of these rules fail for cross-conjugated systems. In this work, we evaluate the performance of distinct transmission rules on a broad series of anthracene and fluorene derivatives with distinctive structural features including linear-, broken-, and cross-conjugation, heteroatoms, and five-membered rings as such species affords a predictive challenge for the qualitative selection rules for QI effects. The electron transport properties and local transmission plots are first evaluated by combining DFT and the nonequilibrium Green function method allowing for an equal-footing comparison of the conductance of the different polycyclic compounds. Our findings are in line with experimental observations on the influence of the type of conjugation and the connectivity to the metallic electrodes on the transport properties. Thus, cross-conjugated systems exhibit reduced conductance values as compared to the linear-conjugated ones, although the transmission is enhanced in the meta-connected junctions. Remarkably, our study reveals that aromatic cores exhibit generally larger zero-bias conductance for a given connectivity, in contrast to the negative aromaticity-conductance relationship found in literature.

Josephson Diode Effect in Parallel-Coupled Double-Quantum Dots Connected to Unalike Majorana Nanowires.

We study theoretically the Josephson diode effect (JDE) when realized in a system composed of parallel-coupled double-quantum dots (DQDs) sandwiched between two semiconductor nanowires deposited on an s-wave superconductor surface. Due to the combined effects of proximity-induced superconductivity, strong Rashba spin-orbit interaction, and the Zeeman splitting inside the nanowires, a pair of Majorana bound states (MBSs) may possibly emerge at opposite ends of each nanowire. Different phase factors arising from the superconductor substrate can be generated in the coupling amplitudes between the DQDs and MBSs prepared at the left and right nanowires, and this will result in the Josephson current. We find that the critical Josephson currents in positive and negative directions are different from each other in amplitude within an oscillation period with respect to the magnetic flux penetrating through the system, a phenomenon known as the JDE. It arises from the quantum interference effect in this double-path device, and it can hardly occur in the system of one QD coupled to MBSs. Our results also show that the diode efficiency can reach up to 50%, but this depends on the overlap amplitude between the MBSs, as well as the energy levels of the DQDs adjustable by gate voltages. The present model is realizable within current nanofabrication technologies and may find practical use in the interdisciplinary field of Majorana and Josephson physics.

Nonlinear optical signatures of topological Dirac fermion.

Dirac fermion in topological materials exhibits intriguing nonlinear optical responses. However, their direct correlation with the linearly dispersed band remains elusive experimentally. Here, we take topological semimetal ZrSiS as a paradigm, unveiling three unique nonlinear optical signatures of Dirac fermion. These signatures include strong quadrupolar response, quantum interference effect, and exponential divergent four-wave mixing (FWM), all of which are described by the prominent third-order nonlinear optical susceptibility. Resonantly enhanced by linear bands, quadrupolar second harmonic generation in centrosymmetric bulk overwhelms the electric-dipole contribution at the surface with inherent inversion symmetry breaking. Furthermore, owing to the interference between multiple resonant transition pathways within linear bands, difference-frequency FWM is several orders of magnitude stronger than sum-frequency FWM and third harmonic generation. The difference-frequency FWM further displays an inverse-square divergence toward degenerate excitation, whose scaling law perfectly matches with the long-sought behavior of Dirac fermion. These signatures lay the solid foundation toward the practical applications of topological materials in nonlinear optoelectronics and photonics.

Accuracy of the scalar magnetometer aboard ESA's JUICE mission

Abstract. This paper discusses the accuracy of the scalar Coupled Dark State Magnetometer on board the Jupiter Icy Moons Explorer (JUICE) mission of the European Space Agency (ESA). The scalar magnetometer, referred to as MAGSCA, is part of the J-MAG instrument. MAGSCA is an optical omnidirectional scalar magnetometer based on coherent population trapping, a quantum interference effect, within the hyperfine manifold of the 87Rb D1 line. The measurement principle is only based on natural constants; therefore, it is in principle drift-free, and no calibration is required. However, the technical realisation can influence the measurement accuracy. The most dominating effects are heading characteristics, which are deviations of the magnetic field strength measurements from the ambient magnetic field strength. These deviations are a function of the angle between the sensor axis and the magnetic field vector and are an intrinsic physical property of the measurement principle of the magnetometer. The verification of the accuracy of the instrument is required to ensure its compliance with the performance requirement of 0.2 nT (1σ) with a data rate of 1 Hz. The verification is carried out with four dedicated sensor orientations in a Merritt coil system, which is located in the geomagnetic Conrad Observatory (COBS). The coil system is used to compensate the Earth's magnetic field and to apply appropriate test fields to the sensor. This paper presents a novel method to separate the heading characteristics of the instrument from residual (offset) fields within the coil system by fitting a mathematical model to the measured data and by the successful verification of the MAGSCA performance requirement.

Thermopower and resistivity of the topological insulator Bi2Te3 in the amorphous and crystalline phase

We have, in-situ, prepared and measured the temperature dependence of thermopower S(T) and resistance R(T) of Bi2Te3 topological insulator (TI) thin films in the amorphous and crystalline phase. Samples were prepared by sequential flash-evaporation at liquid 4He temperature. The S(T) in the amorphous phase is negative and much larger compared to other known amorphous materials, while in the crystalline phase it is also negative and behaves linearly with the temperature. The resistivity ρ(T) in the amorphous phase shows a semiconducting like behavior that changes to a linear metallic behavior after crystallization. S(T) an ρ(T) results in the crystalline phase are in good agreement with results obtained both in bulk and thin films reported in the literature. Linear behavior of the ρ(T) for T > 15 K indicates the typical metallic contribution from the surface states as observed in other TI novel materials. The low temperature conductivity T < 10 K exhibits logarithmic temperature dependent positive slope κ ≈ 0.21, indicating the dominance of electron-electron interaction (EEI) over the quantum interference effect, with a clear two dimensional nature of the contribution. Raman spectroscopy showed that the sample has crystallized in the trigonal R3―m space group. Energy-dispersive x-ray spectroscopy reveales high homogeneity in the concentration and no magnetic impurities introduced during preparation or growth.

Coexistence of antiferromagnetism and glassy magnetic state and signature of quantum interference effects in the frustrated ternary silicides HoScSi and ErScSi

Coexistence of antiferromagnetism and glassy magnetic state and signature of quantum interference effects in the frustrated ternary silicides HoScSi and ErScSi

Long-range superconducting proximity effect in YBa2Cu3O7/La0.7Ca0.3MnO3 weak-link arrays

The interplay between ferromagnetism and superconductivity has attracted substantial interest due to its potential for exotic quantum phenomena and advanced electronic devices. Although ferromagnetism and superconductivity are antagonistic phenomena, ferromagnets (F) can host spin-triplet superconductivity induced via proximity with superconductors (S). To date, most of the experimental effort has been focused on single S/F/S junctions. Here, we have found the fingerprints of long-range superconducting proximity effect in micrometric weak-link arrays, formed by embedding YBa2Cu3O7 superconducting islands in a half-metallic ferromagnet La0.7Ca0.3MnO3 film. These arrays show magnetoresistance oscillations that appear at temperatures below the critical temperature of YBa2Cu3O7 for currents below a threshold, indicating their superconducting origin. This realization paves the way for device architectures displaying macroscopic quantum interference effects, which are of interest for field sensing applications, among others.

Perturbative reheating and thermalization of pure Yang-Mills plasma

We investigate the thermalization of high-energy particles injected from the perturbative decay of inflaton during the pre-thermal phase of reheating in detail. In general, thermalization takes a relatively long time in a low-temperature plasma; therefore, the instantaneous thermalization approximation is not justified, even for the reheating of the Standard Model (SM) sector. We consider a pure Yang-Mills (YM) theory as an approximation of the SM sector or a possible dark sector, considering the Landau-Pomeranchuk-Migdal effect, a quantum interference effect in a finite temperature plasma. We perform the first numerical calculation to solve the time evolution of the system, including the redshift due to the expansion of the Universe, and show the details of the temperature evolution near the maximum and the behavior of the quasi-attractors at later times. The maximal temperature Tmax and time scale tmax are determined quantitatively, such as Tmax ≃ 0.05 × ΓIMPI2/mI32/5mI\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ {\\left({\\Gamma}_I{M}_{\ extrm{PI}}^2/{m}_I^3\\right)}^{2/5}{m}_I $$\\end{document} and tmax ≃ 2 × 103 × ΓIMPI2/mI3−3/5mI−1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ {\\left({\\Gamma}_I{M}_{\ extrm{PI}}^2/{m}_I^3\\right)}^{-3/5}{m}_I^{-1} $$\\end{document} in the SM-like system, where mI and ΓI are the mass and decay rate of inflaton. We also provide a similar formula for pure SU(N) and SO(N) YM theories for general values of N and coupling constant α, including Tmax ∝ α4/5 and tmax ∝ N−2α−16/5 behaviors and their numerical coefficients. The thermalization occurs in a finite time scale, resulting in a lower maximal temperature of the Universe after inflation than that under the instantaneous thermalization approximation.

Amplification and excitation of surface plasmon polaritons via four-wave mixing process

We suggest a scheme for the excitation and amplification of surface plasmon polaritons (SPPs) along the interface between metal and semiconductor quantum well (SQW), employing a four-wave mixing (FWM) process. The SQW consists of four-level asymmetric double quantum wells that exhibit quantum interference effects, which leads to the coupler-free excitation of SPPs. In our proposed system, the inherent losses of SPPs are compensated by introducing gain through the FWM process, resulting in a significant enhancement in the propagation length and penetration depth of SPPs. We further analyze the effect of gain on the long-range and short-range SPPs and observe that the propagation distance and lifetime of both types of SPPs are increased.

Effects of Connectivity Isomerization on Electron Transport Through Thiophene Heterocyclic Molecular Junction.

Connectivity isomerization of the same aromatic molecular core with different substitution positions profoundly affects electron transport pathways and single-molecule conductance. Herein, we designed and synthesized all connectivity isomers of a thiophene (TP) aromatic ring substituted by two dihydrobenzo[b]thiophene (BT) groups with ethynyl spacers (m,n-TP-BT, (m,n = 2,3; 2,4; 2,5; 3,4)), to systematically probe how connectivity contributes to single-molecule conductance. Single-molecule conductance measurements using a scanning tunneling microscopy break junction (STM-BJ) technique show ∼12-fold change in conductance values, which follow an order of 10-4.83 G0 (2,4-TP-BT) < 10-4.78 G0 (3,4-TP-BT) < 10-4.06 G0 (2,3-TP-BT) < 10-3.75 G0 (2,5-TP-BT). Electronic structure analysis and theoretical simulations show that the connectivity isomerization significantly changes electron delocalization and HOMO-LUMO energy gaps. Moreover, the connectivity-dependent molecular structures lead to different quantum interference (QI) effects in electron transport, e.g., a strong destructive QI near E = EF leads the smallest conductance value for 2,4-TP-BT. This work proves a clear relationship between the connectivity isomerization and single-molecule conductance of thiophene heterocyclic molecular junctions for the future design of molecular devices.