Quantum Phenomena Research Articles

Quantum life science: biological nano quantum sensors, quantum technology-based hyperpolarized MRI/NMR, quantum biology, and quantum biotechnology.

The emerging field of quantum life science combines principles from quantum physics and biology to study fundamental life processes at the molecular level. Quantum mechanics, which describes the properties of small particles, can help explain how quantum phenomena such as tunnelling, superposition, and entanglement may play a role in biological systems. However, capturing these effects in living systems is a formidable challenge, as it involves dealing with dissipation and decoherence caused by the surrounding environment. We overview the current status of the quantum life sciences from technologies and topics in quantum biology. Technologies such as biological nano quantum sensors, quantum technology-based hyperpolarized MRI/NMR, high-speed 2D electronic spectrometers, and computer simulations are being developed to address these challenges. These interdisciplinary fields have the potential to revolutionize our understanding of living organisms and lead to advancements in genetics, molecular biology, medicine, and bioengineering.

Fractional Spinon Quasiparticles in Open-Shell Triangulene Spin-1/2 Chains.

The emergence of spinon quasiparticles, which carry spin but lack charge, is a hallmark of collective quantum phenomena in low-dimensional quantum spin systems. While the existence of spinons has been demonstrated through scattering spectroscopy in ensemble samples, real-space imaging of these quasiparticles within individual spin chains has remained elusive. In this study, we construct individual Heisenberg antiferromagnetic spin-1/2 chains using open-shell [2]triangulene molecules as building blocks. Each [2]triangulene unit, owing to its sublattice imbalance, hosts a net spin-1/2 in accordance with Lieb's theorem, and these spins are antiferromagnetically coupled within covalent chains with a coupling strength of J = 45 meV. Through scanning tunneling microscopy and spectroscopy, we probe the spin states, excitation gaps, and their spatial excitation weights within covalent spin chains of varying lengths with atomic precision. Our investigation reveals that the excitation gap decreases as the chain length increases, extrapolating to zero for long chains, consistent with Haldane's gapless prediction. Moreover, inelastic tunneling spectroscopy reveals an m-shaped energy dispersion characteristic of confined spinon quasiparticles in a one-dimensional quantum box. These findings establish a promising strategy for exploring the unique properties of excitation quasiparticles and their broad implications for quantum information.

Mitigating errors in analog quantum simulation by Hamiltonian reshaping or Hamiltonian rescaling

Simulating quantum many-body systems is crucial for advancing physics but poses substantial challenges for classical computers. Quantum simulations overcome these limitations, with analog simulators offering unique advantages over digital methods, such as lower systematic errors and reduced circuit depth, making them efficient for studying complex quantum phenomena. However, unlike their digital counterparts, analog quantum simulations face significant limitations due to the absence of effective error mitigation techniques. This work introduces two novel error mitigation strategies—Hamiltonian reshaping and Hamiltonian rescaling—in analog quantum simulation for tasks like eigen-energy evaluation. Hamiltonian reshaping uses random unitary transformations to generate new Hamiltonians with identical eigenvalues but varied eigenstates, allowing error reduction through averaging. Hamiltonian rescaling mitigates errors by comparing eigenvalue estimates from energy-scaled Hamiltonians. Numerical calculations validate both methods, demonstrating their significant practical effectiveness in enhancing the accuracy and reliability of analog quantum simulators.

Photo-induced chirality in a nonchiral crystal.

Chirality, a pervasive form of symmetry, is intimately connected to the physical properties of solids, as well as the chemical and biological activity of molecular systems. However, inducing chirality in a nonchiral material is challenging because this requires that all mirrors and all roto-inversions be simultaneously broken. Here, we show that chirality of either handedness can be induced in the nonchiral piezoelectric material boron phosphate (BPO4) by irradiation with terahertz pulses. Resonant excitation of either one of two orthogonal, degenerate vibrational modes determines the sign of the induced chiral order parameter. The optical activity of the photo-induced phases is comparable to the static value of prototypical chiral α-quartz. Our findings offer new prospects for the control of out-of-equilibrium quantum phenomena in complex materials.

Defining quantum games

In this research article, we survey existing quantum physics-related games and, based on this survey, propose a definition for the concept of quantum games. We define a quantum game as any type of rule-based game that either employs the principles of quantum physics or references quantum phenomena or the theory of quantum physics through any of three proposed dimensions: the perceivable dimension of quantum physics, the dimension of quantum technologies, and the dimension of scientific purposes, such as citizen science or education. We also discuss the concept of quantum computer games, which are games on quantum computers, as well as definitions for the concept of science games. Various games explore quantum physics and quantum computing through digital, analogue, and hybrid means, with various incentives driving their development. As interest in games as educational tools for supporting quantum literacy grows, understanding the diverse landscape of quantum games becomes increasingly important. We propose that the three dimensions of quantum games identified in this article be used for designing, analysing, and defining the phenomenon of quantum games.

Extended quantum anomalous Hall states in graphene/hBN moiré superlattices.

Electrons in topological flat bands can form new topological states driven by correlation effects. The pentalayer rhombohedral graphene/hexagonal boron nitride (hBN) moiré superlattice was shown to host fractional quantum anomalous Hall effect (FQAHE) at approximately 400 mK (ref. 1), triggering discussions around the underlying mechanism and role of moiré effects2-6. In particular, new electron crystal states with non-trivial topology have been proposed3,4,7-15. Here we report electrical transport measurements in rhombohedral pentalayer and tetralayer graphene/hBN moiré superlattices at electronic temperatures down to below 40 mK. We observed two more fractional quantum anomalous Hall (FQAH) states and smaller Rxx values in pentalayer devices than those previously reported. In the new tetralayer device, we observed FQAHE at moiré filling factors v = 3/5 and 2/3. With a small current at the base temperature, we observed a new extended quantum anomalous Hall (EQAH) state and magnetic hysteresis, where Rxy = h/e2 and vanishing Rxx spans a wide range of v from 0.5 to 1.3. At increased temperature or current, EQAH states disappear and partially transition into the FQAH liquid16-18. Furthermore, we observed displacement field-induced quantum phase transitions from the EQAH states to the Fermi liquid, FQAH liquid and the likely composite Fermi liquid. Our observations established a new topological phase of electrons with quantized Hall resistance at zero magnetic field and enriched the emergent quantum phenomena in materials with topological flat bands.

Optical lattices with variable spacings generated by binary phase transmission gratings.

Optical accordion lattices are routinely used in quantum simulation and quantum computation experiments to tune optical lattice spacings. Here, we present a technique for creating tunable optical lattices using binary-phase transmission gratings. Lattices generated using this technique have high uniformity, contrast, lattice spacing tunability, and power efficiencies. These attributes are crucial for exploring collective quantum phenomena in highly ordered atomic arrays coupled to optical waveguides for quantum networking and quantum simulation. In this paper, we demonstrate adjustable-period lattices that are ideally suited for use with optical nanofibers.

Elf autoencoder for unsupervised exploration of flat-band materials using electronic band structure fingerprints

Two-dimensional materials with flat electronic bands are promising for realising exotic quantum phenomena such as unconventional superconductivity and nontrivial topology. However, exploring their vast chemical space is a significant challenge. Here we introduce elf, an unsupervised convolutional autoencoder that encodes electronic band structure images into fingerprint vectors, enabling the autonomous clustering of materials by electronic properties beyond traditional chemical paradigms. Unsupervised visualisation of the fingerprint space then uncovers hidden chemical trends and identifies promising candidates based on similarities to well-studied exemplars. This approach complements high-throughput ab initio methods by rapidly screening candidates and guiding further investigations into the mechanisms underlying flat-band physics. The elf autoencoder is a powerful tool for autonomous discovery of unexplored flat-band materials, enabling unbiased identification of compounds with desirable electronic properties across the 2D chemical space.

Rotation symmetry mismatch and interlayer hybridization in MoS2-black phosphorus van der Waals heterostructures

Interlayer coupling in 2D heterostructures can result in a reduction of the rotation symmetry and the generation of quantum phenomena. Although these effects have been demonstrated in transition metal dichalcogenides (TMDs) with mismatched interfaces, the role of band hybridization remains unclear. In addition, the creation of flat bands at the valence band maximum (VBM) of TMDs is still an open challenge. In this work, we investigate the electronic structure of monolayer MoS2-black phosphorus heterojunctions with a combined experimental and theoretical approach. The disruption of the rotational symmetry of the MoS2 bands, the creation of anisotropic minigaps and the appearance of flat bands at the Γ valley, accompanied by the switch of VBM from K to Γ, are clearly observed with micro-ARPES. Unfolded band structures obtained from first principles simulations precisely describe these multiple effects – all independent of the twist angle – and demonstrates that they arise from strong band hybridization between Mo dz2 and P px orbitals. The underlying physics revealed by our results paves the way for innovative electronics and optoelectronics based on TMDs superlattices, adding further flexibility to the approaches adopted in twisted hexagonal superlattices.

Terahertz Metamaterials Inspired by Quantum Phenomena

Terahertz Metamaterials Inspired by Quantum Phenomena

Continuous-wave perovskite polariton lasers.

Solution-processed semiconductor lasers are next-generation light sources for large-scale, bio-compatible and integrated photonics. However, overcoming their performance-cost trade-off to rival III-V laser functionalities is a long-standing challenge. Here, we demonstrate room-temperature continuous-wave perovskite polariton lasers exhibiting remarkably low thresholds of ~0.4 W cm-2, enabled by a variable single-crystal perovskite microcavity. The threshold outperforms state-of-the-art III-V lasers by ~30 times under optical pumping, and is exceptional among solution-processed lasers. The ultralow-threshold lasing arises from steady-state exciton-polariton condensation, a macroscopic quantum phenomenon akin to Bose-Einstein condensation. The steady-state condensation is attained by fine-tuning the cavity photon-exciton energy separation near the degeneracy point for strong light-matter interactions. These mechanisms enabled the initial demonstration of an indirectly injected perovskite laser chip powered by a gallium nitride light-emitting diode. Our findings create exciting avenues toward on-chip integration of solution-processed lasers, opening opportunities for lasing with ultralow energy consumption and unprecedented performance.

Janus graphene nanoribbons with localized states on a single zigzag edge.

Topological design of π electrons in zigzag-edged graphene nanoribbons (ZGNRs) leads to a wealth of magnetic quantum phenomena and exotic quantum phases1-10. Symmetric ZGNRs typically show antiferromagnetically coupled spin-ordered edge states1,2. Eliminating cross-edge magnetic coupling in ZGNRs not only enables the realization of a class of ferromagnetic quantum spin chains11, enabling the exploration of quantum spin physics and entanglement of multiple qubits in the one-dimensional limit3,12, but also establishes a long-sought-after carbon-based ferromagnetic transport channel, pivotal for ultimate scaling of GNR-based quantum electronics1-3,9,13. Here we report a general approach for designing and fabricating such ferromagnetic GNRs in the form of Janus GNRs (JGNRs) with two distinct edge configurations. Guided by Lieb's theorem and topological classification theory14-16, we devised two JGNRs by asymmetrically introducing a topological defect array of benzene motifs to one zigzag edge, while keeping the opposing zigzag edge unchanged. This breaks the structural symmetry and creates a sublattice imbalance within each unit cell, initiating a spin-symmetry breaking. Three Z-shaped precursors are designed to fabricate one parent ZGNR and two JGNRs with an optimal lattice spacing of the defect array for a complete quench of the magnetic edge states at the 'defective' edge. Characterization by scanning probe microscopy and spectroscopy and first-principles density functional theory confirms the successful fabrication of JGNRs with a ferromagnetic ground-state localized along the pristine zigzag edge.

Vertical Quantum Confinement in Bulk MoS2.

We experimentally observe quantum confinement states in bulk MoS2 by using angle-resolved photoemission spectroscopy (ARPES). The band structure at the Γ̅ point reveals quantum well states (QWSs) linked to vertical quantum confinement of the electrons, confirmed by the absence of dispersion in kz and a strong intensity modulation with the photon energy. Notably, the binding energy dependence of the QWSs versus n does not follow the quadratic dependence of a two-dimensional electron gas. Instead, a linear behavior is observed that is consistent with a parabolic-like quantum well. This confinement arises from the mechanical exfoliation preparation method, which leads to the detachment of a multilayer stack from the underlying bulk. This is confirmed by density functional theory (DFT) calculations. The quantum confinement in bulk-like MoS2 not only offers the opportunity to explore intersubband transitions to exploit optical properties but also provides a means to study fundamental quantum phenomena in multilayer stacks of different thicknesses.

One-Dimensional Excitonic Insulator of M6Te6 (M = Mo, W) Atomic Wires.

Coulomb attraction with weak screening can trigger spontaneous exciton formation and condensation, resulting in a strongly correlated many-body ground state, namely, the excitonic insulator. One-dimensional (1D) materials natively have ineffective dielectric screening. For the first time, we demonstrate the excitonic instability of single atomic wires of transition metal telluride M6Te6 (M = Mo, W), a family of 1D van der Waals (vdW) materials accessible in the laboratory. The many-body GW and Bethe-Salpeter equation scheme shows giant exciton binding energies up to 1.6 eV for these narrow-gap semiconductors, much exceeding their single-particle band gaps and implying a robust thermal-equilibrium exciton Bose-Einstein condensation with high critical temperatures. The excitonic instability of these single atomic wires is attributed to their small dielectric constant, same parity and ultraflat dispersion for the band edge states. Our work shed light in exploiting the strong excitonic effects in 1D vdW materials to realize macroscopic quantum phenomena.

Tunable Casimir Equilibria in a Dual-Liquid System

The Casimir effect, a macroscopic manifestation of quantum phenomena, arises from zero-point energy and thermal fluctuations. When two objects are brought into close proximity, the Casimir effect manifests as a repulsive force, while at greater separations, it transitions to an attractive force. There exists a specific distance at which the Casimir force vanishes, referred to as the stable Casimir equilibrium. Stable Casimir equilibria arise from the curve minima of the Casimir energy, which can create spatial trapping. The manipulation of stable Casimir equilibria offers promising applications in areas such as tunable optical resonators and self-assembly. This paper presents a scheme for achieving tunable Casimir equilibria in a dual-liquid system. The system comprises a multilayered stratified structure with a gold substrate. Above the gold substrate, a stratified liquid system is formed due to the immiscibility between organic solutions and water. The lower-density solution is on top, while the higher-density one lies beneath. Our results suggest that a stable Casimir equilibrium for a suspended gold nanoplate can be realized, when the suspended gold nanoplate is immersed in organic solutions of toluene or benzene. Moreover, the height of the suspended gold nanoplate, determined by the stable Casimir equilibrium, can be precisely tuned by varying the thickness of the water layer. The effects of finite temperature and ionic concentration on the Casimir equilibria are also analyzed in this work. The results suggest that the separation heights of Casimir equilibria decrease with increasing the temperature. Interestingly, the ionic concentration in water significantly affects the Casimir pressure when the Debye screening length is comparable or smaller than the separation, allowing for a wide range of modulations on Casimir equilibria. This work opens a new avenue for tuning Casimir equilibria, with significant applications for "quantum trapping" of micro-nano particles.

The Structure of Space and Problems of Our Time

Since antiquity the image of space as emptiness has been opposed to the image of material space filled with some essence. For a long time this role was played by the theories of ether. During the twentieth century, a model of space filled with metrics, i.e., information, was formed in physics. Since the middle of the last century, the social and psychological sciences have rapidly developed models which treat space as a structured continuum. Many phenomena of quantum and relativistic theory look quite adequate in the sphere of humanities, particularly in the history and theory of architecture. It is shown how the model of structured space can be used to understand architectural and urban planning problems of our time.

Correlated Dirac Fermions in Twisted Bilayers of MoS2.

Artificial honeycomb lattices are essential for understanding exotic quantum phenomena arising from the interplay between Dirac physics and electron correlation. This work shows that the top two moiré valence bands in rhombohedral-stacked twisted MoS2 bilayers (tb-MoS2) form a honeycomb lattice with massless Dirac fermions. The hopping and Coulomb interaction parameters are explicitly determined based on large-scale ab initio calculations. The system exhibits significant nonlocal Coulomb repulsion and can be described by the extended Hubbard model. At half-filling, strong Coulomb repulsion in free-standing tb-MoS2 drives the system away from the semimetal phase, resulting in strongly correlated Dirac fermions. By varying the twist angle and dielectric environment, the Hamiltonian parameters can be tuned in a wide range, enabling transitions between distinct quantum phases. The high tunability makes tb-MoS2 a promising simulator for exploring many-body effects of Dirac fermions.

Phases Unlocked: The Crucial Role of Qubit Phases in Quantum Computing

Quantum computing applies quantum physics ideas to problems that traditional computers cannot address. The qubit, or quantum equivalent of the classical bit, is fundamental to this paradigm shift. Unlike its classical equivalent, a qubit can exist in a superposition of states, representing both 0 and 1. This superposition is defined not only by magnitudes, but also by important phase variables. These phases have a significant impact on qubit behavior and quantum computation outputs. This work conducts a thorough investigation of qubit phases, exploring their tremendous impact on the efficacy and capabilities of quantum algorithms. We investigate how constructive and destructive interference caused by phase interactions provides the foundation of quantum algorithms. Furthermore, we look into the intricate role of phases in establishing and managing entanglement, a unique quantum phenomenon that allows tremendous interactions between qubits. Our investigation includes the effects of numerous quantum operations on qubit phases. We present a thorough mathematical framework for describing how typical quantum gates, such as Hadamard, Pauli, and phase-shift gates, change the phase and thus the overall state of a qubit. We show these concepts through actual implementations of the Qiskit library. Finally, we discuss the intrinsic difficulty of managing and monitoring qubit phases, particularly the negative impacts of decoherence, which disrupts the delicate phase relationships. We describe tactics for mitigating these obstacles and investigate techniques for extracting phase information indirectly, such as quantum state tomography and interferometry. This comprehensive study seeks to provide a better understanding of the critical role phases play in quantum computing, paving the way for advances in algorithm design, quantum control, and the development of fault-tolerant quantum computers.

Electrically Pumped h-BN Single-Photon Emission in van der Waals Heterostructure.

Atomic defects in solids offer a versatile basis to study and realize quantum phenomena and information science in various integrated systems. All-electrical pumping of single defects to create quantum light emission has been realized in several platforms including color centers in diamond and silicon carbide, which could lead to the circuit network of electrically triggered single-photon sources. However, a wide conduction channel which reduces the carrier injection per defect site has been a major obstacle. Here, we realize a device concept to construct electrically pumped single-photon emission using a van der Waals stacked structure with atomic plane precision. Defect-induced tunneling currents across graphene and NbSe2 electrodes sandwiching an atomically thin h-BN layer allow robust and persistent generation of nonclassical light from h-BN. The collected emission photon energies range between 1.4 and 2.9 eV, revealing the electrical excitation of a variety of atomic defects. By analyzing the dipole axis of observed emitters, we further confirm that emitters are crystallographic defect structures of h-BN crystal. Our work facilitates implementing efficient and miniaturized single-photon devices in van der Waals platforms toward applications in quantum optoelectronics.

On understanding of quantum entanglement: contemporary holistic approach

Idea of quantum entanglement is discussed in the context of debate about the Einstein-Podolsky-Rosen thought experiment and some theoretical studies of quantum systems. It is noted that Schrödinger invented this idea in 1935 in order to fix some features of the quantum-mechanical description of two systems with temporary interaction. However, he did not grasp essence of these features really. In view of the concepts of mixture and statistical operator proposed by von Neumann and adopted by Schrödinger in 1936, it is argued that the idea of entanglement and related terminology are not necessary in quantum mechanics. One can use this idea and terms "entanglement" etc. as "visual" surrogates for the "mixture – statistical operator" pair. Deeper comparative analysis of several theoretical works by Schrödinger, von Neumann, and Landau showed that the modeling of non-trivial complex quantum systems as quasi-classical aggregates has been gradually overcome. Instead, wholeness of such quantum systems was actually recognized step by step. Thus, wholeness is immanent not only to quantum phenomena, as Niels Bohr had argued, but also to the quantum systems themselves, objectively. The pair "mixture – statistical operator" and especially the pair "mixed state – density matrix" similar to it appear to be adequate tools to comprehend and describe wholeness of diverse quantum reality. It is insisted, it is advisable to understand the surrogate idea of entanglement and relevant terminology in the same sense. In mature quantum paradigm, they are possible but not necessary theoretical tools to grasp wholeness of reality. Respectively, acceptable understanding of quantum entanglement must be based on recognition of quantum wholeness. Philosophically speaking, the idea of entanglement is understandable and conditionally acceptable in the view of contemporary rational holism, or holistic rationality. The clarified understanding of quantum entanglement, as well as Bohr's substantiation of wholeness of quantum phenomena, demonstrates irreducibility of the Universe to any quasi-classical aggregate. Moreover, all this supports the view of the Universe as real wholeness, which rational holism intends to grasp. It is concluded, further development and regular implementation of rational holism have the undoubted potential for revolutionary replacement of the hitherto widespread worldview in the spirit of Democritus and pure analytical methodology of knowledge.