Quantum Phenomena Research Articles

Tunable magnetoresistance driven by electronic structure in Kagome semimetal Co1−xFexSn

Topological quantum phenomena due to the presence of both Dirac fermions and flat bands in Kagome semimetal CoSn promise novel transport properties. In Kagome materials, the transport properties can be enhanced by moving the position of the flat band and Dirac fermions with doping. Here, we have investigated the magnetotransport and electronic properties by Fe doping in CoSn. A large positive magnetoresistance (MR) of ≈ 105% at 3 K and 8 T magnetic field has been observed in CoSn. Fe doping in Co1−xFexSn gives rise to negative MR with a large negative value for x = 0.2 (−8.4%) but decreases for x = 0.3 (−3.7%) and x = 0.4 (−2.7%). Tuning of MR from positive to negative values with Fe doping in CoSn is associated with the changes in energy position of the localized flat band and emergence of quasi-localized states near the Fermi level. The systematic variation of MR with increasing x depends both on the structural changes due to increase in the lattice parameters and on the near neighbor interactions of the Sn atoms with the Co atoms in the Kagome plane. The origin of quasi-localized states is associated with the electron hopping and the variation in the strength of localization with doping that leads to tunable MR properties in Co1−xFexSn.

High‐throughput Synthesis of Solution‐Processable van der Waals Heterostructures through Electrochemistry

AbstractTwo‐dimensional van der Waals heterostructures (2D vdWHs) have recently gained widespread attention because of their abundant and exotic properties, which open up many new possibilities for next‐generation nanoelectronics. However, practical applications remain challenging due to the lack of high‐throughput techniques for fabricating high‐quality vdWHs. Here, we demonstrate a general electrochemical strategy to prepare solution‐processable high‐quality vdWHs, in which electrostatic forces drive the stacking of electrochemically exfoliated individual assemblies with intact structures and clean interfaces into vdWHs with strong interlayer interactions. Thanks to the excellent combination of strong light absorption, interfacial charge transfer, and decent charge transport properties in individual layers, thin‐film photodetectors based on graphene/In2Se3 vdWHs exhibit great promise for near‐infrared (NIR) photodetection, owing to a high responsivity (267 mA W−1), fast rise (72 ms) and decay (426 ms) times under NIR illumination. This approach enables various hybrid systems, including graphene/In2Se3, graphene/MoS2 and graphene/MoSe2 vdWHs, providing a broad avenue for exploring emerging electronic, photonic, and exotic quantum phenomena.

A quantum computing implementation of nuclearelectronic orbital (NEO) theory: Toward an exact pre-Born-Oppenheimer formulation of molecular quantum systems.

Nuclear quantum phenomena beyond the Born-Oppenheimer approximation are known to play an important role in a growing number of chemical and biological processes. While there exists no unique consensus on a rigorous and efficient implementation of coupled electron-nuclear quantum dynamics, it is recognized that these problems scale exponentially with system size on classical processors and, therefore, may benefit from quantum computing implementations. Here, we introduce a methodology for the efficient quantum treatment of the electron-nuclear problem on near-term quantum computers, based upon the Nuclear-Electronic Orbital (NEO) approach. We generalize the electronic two-qubit tapering scheme to include nuclei by exploiting symmetries inherent in the NEO framework, thereby reducing the Hamiltonian dimension, number of qubits, gates, and measurements needed for calculations. We also develop parameter transfer and initialization techniques, which improve convergence behavior relative to conventional initialization. These techniques are applied to H2 and malonaldehyde for which results agree with NEO full configuration interaction and NEO complete active space configuration interaction benchmarks for ground state energy to within 10-6 hartree and entanglement entropy to within 10-4. These implementations therefore significantly reduce resource requirements for full quantum simulations of molecules on near-term quantum devices while maintaining high accuracy.

Quantum statistical effect induced through conditioned postprocessing procedures with unitary t -designs

We propose a few-body quantum phenomenon, which manifests itself through stochastic state preparations and measurements followed by a conditioned post-processing procedure. We show two experimental protocols to implement these phenomena with existing quantum computers, and examine their feasibility by using simulations. Our simulation results suggest that the experimental demonstration is feasible if we repeat the state preparations and measurements about thirty thousand times to three-qubit systems.

Conference on “Emergent Phenomena in Quantum Materials (E-QMAT 2022)”

Department of Physics, Indian Institute of Technology, Roorkee, India October 12-14, 2022This conference was organized as part of celebrations to commemorate 175 years of Indian Institute of Technology Roorkee (erstwhile University of Roorkee), India. The conference covered various aspects of the recently observed emergent phenomena in the area of quantum materials. These materials pose the most exciting and challenging research problems in condensed matter physics. The scope of quantum materials is very broad. Focus of the conference was on the most recent challenges in research areas like quantum topology, quantum magnetism, low-dimensional electronic systems, multiferroic materials, superconductivity, quantum phenomena at the artificial interfaces and in the engineered materials etc. These materials show unusual novel properties with potential application for development of future electronic, spintronic and storage devices with better capabilities. This conference provided a common platform for the exchange of ideas and to identify cutting edge problems in the area.We had the honour and privilege of having Nobel laureate Professor Anthony J. Leggett giving a special evening lecture on quantum liquids in our conference. During the three days of the conference, we had many distinguished condensed matter physicists such as Prof. T. V. Ramakrishnan, Prof. Elbio Dagotto, Prof. D. D. Sarma, Prof. G. Baskaran, Prof. E. V. Sampathkumaran and Prof. R. Ramesh giving lectures on various emergent phenomena recently discovered in quantum materials. Many young researcher working in India and abroad also participated in the conference and exchanged their ideas with experts in the field. We also had poster sessions and oral presentations on all three days where many PhD students and postdocs participated. Some papers presented in the conference are being published after peer review process in this volume of J. Phys. : Conf. Series (IOP publishing).Finally, we would like to thank wholeheartedly the speakers, participants, peer reviewers, student volunteers, administration and staff members of our institute (IIT Roorkee) and acknowledge our sponsors namely, Indian Institute of Technology Roorkee, Science and Engineering Research Board (SERB), India, Board of Research in Nuclear Sciences (BRNS), India, Rohde & Schwarz India Pvt. Ltd, Thermo Fisher Scientific India Private Limited, Oxford Instruments India Private Limited and I. R. Technology Services Private Limited for their generous and continuous support to us to be able to make this event a success.Tulika Maitra and Vivek K MalikList of Committees of the conference is available in this pdf.

Scrutinizing the feasibility of macroscopic quantum coherence in the brain: a field-theoretical model of cortical dynamics

The neural activity patterns associated with advanced cognitive processes are characterized by a high degree of collective organization, which raises the question of whether macroscopic quantum phenomena play a significant role in cortical dynamics. In order to pursue this question and scrutinize the feasibility of macroscopic quantum coherence in the brain, a model is developed regarding the functioning of microcolumns, which are the basic functional units of the cortex. This model assumes that the operating principle of a microcolumn relies on the interaction of a pool of neurotransmitter (glutamate) molecules with the vacuum fluctuations of the electromagnetic field, termed zero-point field (ZPF). Quantitative calculations reveal that the coupling strength of the glutamate pool to the resonant ZPF modes lies in the critical regime in which the criterion for the initiation of a phase transition is fulfilled, driving the ensemble of initially independent molecules toward a coherent state and resulting in the formation of a coherence domain that extends across the full width of a microcolumn. The formation of a coherence domain turns out to be an energetically favored state shielded by a considerable energy gap that protects the collective state against thermal perturbations and entails decoherence being greatly slowed down. These findings suggest that under the special conditions encountered in cortical microcolumns the emergence of macroscopic quantum phenomena is feasible. This conclusion is further corroborated by the insight that the presence of a coherence domain gives rise to downstream effects which may be crucial for the cortical communication and the formation of large-scale activity patterns. Taken together, the presented model sheds new light on the fundamental mechanism underlying cortical dynamics and suggests that long-range synchronization in the brain results from a bottom-up orchestration process involving the ZPF.

Normal-mode splitting in an optomechanical system enhanced by an optical parametric amplifier and coherent feedback

Normal-mode splitting (NMS) is an evident signature of strong coupling interactions for observing quantum phenomena, such as optomechanical squeezing and entanglement. In the previous literature, optical parametric amplifier (OPA) and coherent feedback are independently proposed to enhance the NMS. Here, we combine OPA and coherent feedback into a single optomechanical system to enhance the NMS. Controllable parameters, such as input optical power, OPA gain and phase, coherent feedback strength, are varied to observe NMS variations. In particular, we consider positive and negative feedback in terms of the amplitude reflectivity of the beam splitter for coherent feedback. The NMS appears mostly with the positive coherent feedback rather than the negative. Furthermore, the largest mode separation occurs at an OPA phase of approximately rather than zero because the effective cavity detuning changes the effective intracavity round-trip phase, and therefore changes the OPA amplification/deamplification condition. The results indicate that the interplay between OPA and coherent feedback can enhance the NMS with more controllable parameter freedoms. This scheme provides a promising way to increase the optomechanical coupling strength, thereby having potential applications in the ground state cooling of a mechanical oscillator, the preparation of optomechanical quantum states, and the sensitive detection of a weak force.

Entanglement entropy as an order parameter for strongly coupled nodal line semimetals

Topological semimetals are a class of many-body systems exhibiting novel macroscopic quantum phenomena at the interplay between high energy and condensed matter physics. They display a topological quantum phase transition (TQPT) which evades the standard Landau paradigm. In the case of Weyl semimetals, the anomalous Hall effect is a good non-local order parameter for the TQPT, as it is proportional to the separation between the Weyl nodes in momentum space. On the contrary, for nodal line semimetals (NLSM), the quest for an order parameter is still open. By taking advantage of a recently proposed holographic model for strongly-coupled NLSM, we explicitly show that entanglement entropy (EE) provides an optimal probe for nodal topology. We propose a generalized c-function, constructed from the EE, as an order parameter for the TQPT. Moreover, we find that the derivative of the renormalized EE with respect to the external coupling driving the TQPT diverges at the critical point, signaling the rise of non-local quantum correlations. Finally, we show that these quantum information quantities are able to characterize not only the critical point but also features of the quantum critical region at finite temperature.

Correlated Quantum Phenomena of Spin–Orbit Coupled Perovskite Oxide Heterostructures: Cases of SrRuO3 and SrIrO3 Based Artificial Superlattices

AbstractUnexpected, yet useful functionalities emerge when two or more materials merge coherently. Artificial oxide superlattices realize atomic and crystal structures that are not available in nature, thus providing controllable correlated quantum phenomena. This review focuses on 4d and 5d perovskite oxide superlattices, in which the spin–orbit coupling plays a significant role compared with conventional 3d oxide superlattices. Modulations in crystal structures with octahedral distortion, phonon engineering, electronic structures, spin orderings, and dimensionality control are discussed for 4d oxide superlattices. Atomic and magnetic structures, Jeff = 1/2 pseudospin and charge fluctuations, and the integration of topology and correlation are discussed for 5d oxide superlattices. This review provides insights into how correlated quantum phenomena arise from the deliberate design of superlattice structures that give birth to novel functionalities.

Ready to Leap (by Co-Design)? Join Order Optimisation on Quantum Hardware

The prospect of achieving computational speedups by exploiting quantum phenomena makes the use of quantum processing units (QPUs) attractive for many algorithmic database problems. Query optimisation, which concerns problems that typically need to explore large search spaces, seems like an ideal match for quantum algorithms. We present the first quantum implementation of join ordering, one of the most investigated and fundamental query optimisation problems, based on a reformulation to quadratic binary unconstrained optimisation problems. We empirically characterise our method on two state-of-the-art approaches (gate-based quantum computing and quantum annealing), and identify speed-ups compared to the best know classical join ordering approaches for input sizes conforming to current quantum annealers. Yet, we also confirm that limits of early-stage technology are quickly reached. Current QPUs are classified as noisy, intermediate scale quantum computers (NISQ), and are restricted by a variety of limitations that reduce their capabilities as compared to ideal future QPUs, which prevents us from scaling up problem dimensions and reaching practical utility. To overcome these challenges, our formulation accounts for specific QPU properties and limitations, and allows us to trade between achievable solution quality and problem size. In contrast to all prior work on quantum computing for query optimisation and database-related challenges, we go beyond currently available QPUs, and explicitly target the scalability limitations: Using insights gained from numerical simulations and our experimental analysis, we identify key criteria for co-designing QPUs to improve their usefulness for join ordering, and show how even relatively minor physical architectural improvements can result in substantial enhancements. Finally, we outline a path towards practical utility of custom-designed QPUs.

Manipulating charge density wave state in kagome compound RbV3Sb5

Owing to the unique electronic structure, kagome materials AV3Sb5 (A = K, Rb, Cs) provide a fertile platform of quantum phenomena such as the strongly correlated state and topological Dirac band. It is well known that RbV3Sb5 exhibits a 2 × 2 unconventional charge density wave (CDW) state at low temperature, and the mechanism is controversial. Here, by using scanning tunneling microscopy/spectroscopy (STM/STS), we successfully manipulated the CDW state in the Sb plane of RbV3Sb5, and realized a new modulation together with the ubiquitous 2 × 2 period in the CDW state of RbV3Sb5. This work provides a new understanding of the collective quantum ground states in the kagome materials.

Single crystal growth and electronic structure of Rh-doped Sr3Ir2O7

Ruddlesden-Popper iridate Sr3Ir2O7 is a spin–orbit coupled Mott insulator. Hole doped Sr3Ir2O7 provides an ideal platform to study the exotic quantum phenomena that occur near the metal–insulator transition (MIT) region. Rh substitution of Ir is an effective method to induce hole doping into Sr3Ir2O7. However, the highest doping level reported in Sr3(Ir1−x Rh x )2O7 single crystals was only around 3%, which is far from the MIT region. In this paper, we report the successful growth of single crystals of Sr3(Ir1−x Rh x )2O7 with a doping level of ~ 9%. The samples have been fully characterized, demonstrating the high quality of the single crystals. Transport measurements have been carried out, confirming the tendency of MIT in these samples. The electronic structure has also been examined by angle-resolved photoemission spectroscopy (ARPES) measurements. Our results establish a platform to investigate the heavily hole doped Sr3Ir2O7 compound, which also provide new insights into the MIT with hole doping in this material system.

On the statistical background of quantum mechanics: generalities and a concrete example

We revisit our description of randomness in quantum processes that began in collaboration of Jean Ginibre. The calculations were performed on a worked example: the fluorescence of a single two-level atom pumped by a resonant laser field. This pump laser is described classically (by a function, not an operator). Our aim is first to built a Kolmogorov-type equation (K-equation) for the atomic state, so that the two parameters θ, φ that define this density matrix are random functions of time, therefore the atomic density matrix is a random density matrix. Such an approach, initiated for gas kinetics, was not yet applied to quantum phenomena, whereas it is especially tailored to very quick events well separated (in time) like the quantum jumps observed in spontaneous emission of photons by an atom. Here, we try to clarify the basis of our statistical approach leading to the K-equation below, and we present the main results deduced from it. We explain finally that our approach can be interpreted in terms of Everett’s theory of many-worlds, because at every emission a new history begins for the atom, with two nonoverlapping wave functions.

Coherent Dynamics in Solutions of Colloidal Plexcitonic Nanohybrids at Room Temperature

AbstractThe increasing ability to prepare systems with nanoscale resolution and address their optical properties with ultrashort time precision is revealing quantum phenomena with tremendous potential in quantum nanotechnologies. Colloidal plexcitonic materials promise to play a pivotal role in this scenario. Plexcitons are hybrid states originating from the mixing of the plasmon resonances of metal nanostructures with molecular excitons. They allow nanoscale confinement of electromagnetic fields and the establishment of strong couplings between light and matter, potentially giving rise to controllable and tunable coherent phenomena. However, the characterization of the ultrafast coherent and incoherent dynamics of colloidal plexciton nanohybrids remains highly unexplored. Here, two dimensional electronic spectroscopy (2DES) is employed to study the quantum coherent interactions active after the photoexcitation of these systems. By comparing the response of the nanohybrids with the one of the uncoupled systems, the nonlinear photophysical processes at the base of the coherent dynamics are identified, allowing a step forward toward the effective understanding and exploitation of these nanomaterials.

Observation of Fermi arcs and Weyl nodes in a noncentrosymmetric magnetic Weyl semimetal

Weyl semimetal (WSM), a novel state of quantum matter, hosts Weyl fermions as emergent quasiparticles resulting from the breaking of either inversion or time-reversal symmetry. Magnetic WSMs that arise from broken time-reversal symmetry provide an exceptional platform to understand the interplay between magnetic order and Weyl physics, but only a few WSMs have been realized. Here, we identify CeAlSi as a new noncentrosymmetric magnetic WSM via angle-resolved photoemission spectroscopy (ARPES) and first-principles, density-functional theory based calculations. Our surface-sensitive vacuum ultraviolet ARPES data confirm the presence of surface Fermi arcs as the conclusive evidence for the existence of the Weyl semimetallic state in CeAlSi. We also observe bulk Weyl cones at the Fermi arc terminations in CeAlSi using bulk-sensitive soft-x-ray ARPES measurements. These results implicate CeAlSi as a unique platform for investigating exotic quantum phenomena resulting from the interaction of topology and magnetism.

Dimensionality-driven metal to Mott insulator transition in two-dimensional 1T-TaSe2

Abstract Two-dimensional materials represent a major frontier for research into exotic many-body quantum phenomena. In the extreme two-dimensional limit, electron-electron interaction often dominates over other electronic energy scales, leading to strongly correlated effects such as quantum spin liquid and unconventional superconductivity. The dominance is conventionally attributed to the lack of electron screening in the third dimension. Here, we discover an intriguing metal to Mott insulator transition in 1T-TaSe2 that defies conventional wisdom. Specifically, we find that dimensionality crossover, instead of reduced screening, drives the transition in atomically thin 1T-TaSe2. A dispersive band crossing the Fermi level is found to be responsible for the bulk metallicity in the material. Reducing the dimensionality, however, effectively quenches the kinetic energy of these initially itinerant electrons, and drives the material into a Mott insulating state. The dimensionality-driven metal to Mott insulator transition resolves the long-standing dichotomy between metallic bulk and insulating surface of 1T-TaSe2. Our work further reveals a new pathway for modulating two-dimensional materials that enables exploring strongly correlated systems across uncharted parameter space.

Analog Schwarzschild black holes of Bose-Einstein condensates in a cavity: Quasinormal modes and quasibound states

Analog models of black holes have unequivocally proven to be extremely beneficial in providing critical information regarding black hole spectroscopy, superradiance, quantum phenomena and most importantly Hawking radiation and black hole evaporation; topics that have either recently begun to bloom through gravitational wave observations or have not yet been investigated in astrophysical setups. Black hole analog experiments have made astonishing steps toward the aforementioned directions and are paramount in understanding the quantum nature of the gravitational field. Recently, a tabletop analog Schwarzschild black hole has been proposed by placing Bose-Einstein condensates of photons inside a mirror's cavity, leading to a sink with a radial vortex that represents a velocity singularity. Here, we provide an extensive spectral analysis of both the tabletop acoustic black hole and its higher-dimensional gravitational analog. We find that quasinormal modes and quasibound states share qualitative similarities in both systems and show that the eikonal quasinormal modes of the analog acoustic black hole have a photon-sphere-like interpretation, which points to the existence of a phonon sphere in the analog black hole. Our results, complemented with the recently calculated graybody factors and Hawking radiation of the acoustic analog, can provide a theoretical test bed for future tabletop experiments with condensates of light in a mirror's cavity and provide significant insights regarding classical and quantum phenomena in higher-dimensional black holes.

Exploring the relationship between students’ conceptual understanding and model thinking in quantum optics

Learning quantum physics is essential for understanding the physical world. However, learning about quantum phenomena and principles poses a challenge as many of the phenomena that are observed at the quantum level cannot be directly observed or intuitively understood in terms of classical physics or thinking. Models play an important role in learning quantum physics by providing conceptual frameworks and visual representations that allow reasoning about and predicting the behavior of quantum systems. Therefore, understanding models is an essential part of learning quantum physics. In this article, we report the results of an exploratory survey study (N = 116) investigating the relationship between secondary school students’ conceptual understanding and model thinking in quantum optics with a particular focus on photons. The findings suggest a strong positive correlation between students’ functional understanding of the photon model and their conceptual understanding of quantum optics. This study contributes to our understanding of how students learn and make sense of quantum concepts through the use of models and may inform the development of instructional strategies for quantum physics education and outreach.

13C Radiofrequency Amplification by Stimulated Emission of Radiation Threshold Sensing of Chemical Reactions.

Conventional nuclear magnetic resonance (NMR) enables detection of chemicals and their transformations by exciting nuclear spin ensembles with a radio-frequency pulse followed by detection of the precessing spins at their characteristic frequencies. The detected frequencies report on chemical reactions in real time and the signal amplitudes scale with concentrations of products and reactants. Here, we employ Radiofrequency Amplification by Stimulated Emission of Radiation (RASER), a quantum phenomenon producing coherent emission of 13C signals, to detect chemical transformations. The 13C signals are emitted by the negatively hyperpolarized biomolecules without external radio frequency pulses and without any background signal from other, nonhyperpolarized spins in the ensemble. Here, we studied the hydrolysis of hyperpolarized ethyl-[1-13C]acetate to hyperpolarized [1-13C]acetate, which was analyzed as a model system by conventional NMR and 13C RASER. The chemical transformation of 13C RASER-active species leads to complete and abrupt disappearance of reactant signals and delayed, abrupt reappearance of a frequency-shifted RASER signal without destroying 13C polarization. The experimentally observed "quantum" RASER threshold is supported by simulations.

Giant nonlocal edge conduction in the axion insulator state of MnBi2Te4

The recently discovered antiferromagnetic (AFM) topological insulator (TI) MnBi2Te4 represents a versatile material platform for exploring exotic topological quantum phenomena in nanoscale devices. It has been proposed that even-septuple-layer (even-SL) MnBi2Te4 can host helical hinge currents with unique nonlocal behavior, but experimental confirmation is still lacking. In this work, we report transport studies of exfoliated MnBi2Te4 flakes with varied thicknesses down to the few-nanometer regime. We observe giant nonlocal transport signals in even-SL devices when the system is in the axion insulator state but vanishingly small nonlocal signal in the odd-SL devices at the same magnetic field range. In conjunction with theoretical calculations, we demonstrate that the nonlocal transport is via the helical edge currents mainly distributed at the hinges between the side and top/bottom surfaces. The helical edge currents in the axion insulator state may find unique applications in topological quantum devices.