Macroscopic Quantum Research Articles

Distant entanglement via photon hopping in a coupled cavity magnomechanical system

We theoretically propose a scheme to generate distant bipartite entanglement between various subsystems in coupled magnomechanical systems where both the microwave cavities are coupled through single photon hopping coupling strength Γ. Each cavity contains a magnon mode and phonon mode and this gives six excitation modes in our model Hamiltonian which are cavity-1 photons, cavity-2 photons, magnon and phonon in cavity-1, and magnon and phonon in cavity-2. We found that significant bipartite entanglement exists between indirectly coupled subsystems in coupled microwave cavities for an appropriate set of parameters regime. Moreover, we also obtain suitable cavity and magnon detuning parameters for a significant distant bipartite entanglement in different bipartitions. In addition, it can be seen that a single photon hopping parameter significantly affects both the degree as well as the transfer of quantum entanglement between various bipartitions. Hence, our present study related to coupled microwave cavity magnomechanical configuration will open new perspectives in coherent control of various quantum correlations including quantum state transfer among macroscopic quantum systems.

A Macroscopic Quantum Three-Box Paradox: Finding Consistency with Weak Macroscopic Realism.

The quantum three-box paradox considers a ball prepared in a superposition of being in any one of three boxes. Bob makes measurements by opening either box 1 or box 2. After performing some unitary operations (shuffling), Alice can infer with certainty that the ball was detected by Bob, regardless of which box he opened, if she detects the ball after opening box 3. The paradox is that the ball would have been found with certainty by Bob in either box if that box had been opened. Resolutions of the paradox include that Bob's measurement cannot be made non-invasively or else that realism cannot be assumed at the quantum level. Here, we strengthen the case for the former argument by constructing macroscopic versions of the paradox. Macroscopic realism implies that the ball is in one of the boxes prior to Bob or Alice opening any boxes. We demonstrate the consistency of the paradox with macroscopic realism, if carefully defined (as weak macroscopic realism, wMR) to apply to the system at the times prior to Alice or Bob opening any boxes but after the unitary operations associated with preparation or shuffling. By solving for the dynamics of the unitary operations and comparing with mixed states, we demonstrate agreement between the predictions of wMR and quantum mechanics: the paradox only manifests if Alice's shuffling combines both local operations (on box 3) and nonlocal operations, on the other boxes. Following previous work, the macroscopic paradox is shown to correspond to a violation of a Leggett-Garg inequality, which implies failure of non-invasive measurability if wMR holds.

High sensitivity of semimetal photodetection via Bose–Einstein condensation

AbstractThe discovery of semiconductor has witnessed remarkable strides toward high performance of photodetectors attributed to its excellent carrier properties. However, semimetal, owning to the high carrier concentration and low carrier mobility compared to those of semiconductor, is generally considered unsuitable for photodetection. Herein, we demonstrate an outstanding photodetection in a layered semimetal titanium diselenide (TiSe2) in Bose–Einstein condensation (BEC) state. High sensitivity of semimetal photodetector is realized in the range of visible, infrared and terahertz bands. The noise equivalent power (NEP) has threefold improvement at the visible and infrared wavebands, and significant decrease by one order of magnitude in the terahertz frequencies via BEC phenomenon, attributed to the electrical parameter variation after condensation. The best NEP value in the terahertz frequency is comparable to that of commercial Si photodetector. Our results show another recipe to fabricate high performance of photodetection via semimetal except for semiconductor and pave the way to exploit macroscopic quantum phenomena for optoelectronics.image

Entanglement and Symmetry Structure of N(= 3) Quantum Oscillators with Disparate Coupling Strengths in a Common Quantum Field Bath

In this paper, we study the entanglement structure of a system of N quantum oscillators with distinctive coupling strengths, all linearly coupled to a common massless scalar quantum field. This study is helpful in characterizing the notion of an entanglement domain and its symmetry features, which is useful for understanding the interplay between different levels of structure in many-body quantum systems. The effect of the quantum field on the system is derived via the influence functional and the correlation functions are obtained from the solutions of the evolutionary operator of the reduced density matrix. They are then used to construct the covariance matrix, which forms the basis for our analysis of the structure of quantum entanglement in this open system. To make the physical features explicit, we consider a system of three quantum coupled oscillators placed at the vertices of an equilateral triangle with disparate pairwise couplings. We analyze the entanglement between one oscillator and the other two with equal (symmetric) and unequal (asymmetric) coupling strengths. As a physical illustration, we apply the results for these two different configurations to address some basic issues in macroscopic quantum phenomena from the quantum entanglement perspective.

Electrical control of transient formation of electron-hole coexisting system at silicon metal-oxide-semiconductor interfaces

Recent observations of macroscopic quantum condensation using electron-hole (e-h) bilayers have activated the research of its application to electronics. However, to the best of our knowledge, no attempts have been made to observe the condensation in silicon, the major material in electronics, due to the lack of technology to form closely-packed and uniform bilayers. Here, we propose a method to meet such requirements. Our method uses the transient response of carriers to a rapid gate-voltage change, permitting the self-organized bilayer formation at the metal-oxide-semiconductor interface with an e-h distance as small as the exciton Bohr radius. Recombination lifetime measurements show that the fast process is followed by a slow process, strongly suggesting that the e-h system changes its configuration depending on carrier density. This method could thus enable controlling the phase of the e-h system, paving the way for condensation and, ultimately, for low-power cryogenic silicon metal-oxide-semiconductor devices.

Exploring plasmonic effect on exciton transport: A theoretical insight from macroscopic quantum electrodynamics.

Exciton transport in extended molecular systems and how to manipulate such transport in a complex environment are essential to many energy and optical-related applications. We investigate the mechanism of plasmon-coupled exciton transport by using the Pauli master equation approach, combined with kinetic rates derived from macroscopic quantum electrodynamics. Through our theoretical framework, we demonstrate that the presence of a silver nanorod induces significant frequency dependence in the ability of transporting exciton through a molecule chain, indicated by the exciton diffusion coefficient, due to the dispersive nature of the silver dielectric response. Compared with the same system in vacuum, great enhancement (up to a factor of 103) in the diffusion coefficient can be achieved by coupling the resonance energy transfer process to localized surface plasmon polariton modes of the nanorod. Furthermore, our analysis reveals that the diffusion coefficients with the nearest-neighbor coupling approximation are ∼10 times smaller than the results obtained beyond this approximation, emphasizing the significance of long-range coupling in exciton transport influenced by plasmonic nanostructures. This study not only paves the way for exploring practical approaches to study plasmon-coupled exciton transport but also provides crucial insights for the design of innovative plasmon-assisted photovoltaic applications.

Current fluctuations and domain depinning in quasi-two-dimensional charge-density-wave 1T-TaS2 thin films

We investigated the temperature dependence of the current fluctuations in thin films of the quasi-two-dimensional 1T-TaS2 van der Waals material. The current fluctuations, determined from the derivative current–voltage characteristics of two-terminal 1T-TaS2 devices, appear prominently at the electric fields that correspond to the transitions between various charge-density-wave macroscopic quantum condensate phases and at the onset of the depinning of the charge density wave domains. The depinning threshold field, ED, monotonically increases with decreasing temperature within the nearly commensurate charge-density-wave phase. The ED value increases with the decreasing 1T-TaS2 film thickness, revealing the surface pinning of the charge density waves. Our analysis suggests that the domain depinning is pronounced in the nearly commensurate phase. It is induced by the electric field but facilitated by local heating. The measured trends for ED of the domain depinning are important for understanding the physics of charge density waves in quasi-two-dimensional crystals and for developing electronic devices based on this type of quantum materials.

Signature of spin-phonon coupling driven charge density wave in a kagome magnet

The intertwining between spin, charge, and lattice degrees of freedom can give rise to unusual macroscopic quantum states, including high-temperature superconductivity and quantum anomalous Hall effects. Recently, a charge density wave (CDW) has been observed in the kagome antiferromagnet FeGe, indicative of possible intertwining physics. An outstanding question is that whether magnetic correlation is fundamental for the spontaneous spatial symmetry breaking orders. Here, utilizing elastic and high-resolution inelastic x-ray scattering, we observe a c-axis superlattice vector that coexists with the 2times2times1 CDW vectors in the kagome plane. Most interestingly, between the magnetic and CDW transition temperatures, the phonon dynamical structure factor shows a giant phonon-energy hardening and a substantial phonon linewidth broadening near the c-axis wavevectors, both signaling the spin-phonon coupling. By first principles and model calculations, we show that both the static spin polarization and dynamic spin excitations intertwine with the phonon to drive the spatial symmetry breaking in FeGe.

Application prospect and preparation method of nanomaterials

Nanoparticles are atomic or molecular groups composed of a very small number of atoms or molecules. The particles have a shell structure. Nanomaterials are made up of a long-range ordered arrangement of atoms in grains and a disordered interface composition. The nanomaterial has a large number of interfaces. These unique volume effects, surface effects, and macroscopic quantum tunnelling effects enable nanomaterials to have unusual mechanical, electrical, magnetic, thermal, optical, catalysis, and superconducting properties. Such characteristics make nanomaterials have significant application value in the fields of national defense, electronics, chemical industry, metallurgy, light industry, aviation, ceramics, catalysts, medicine, etc. The development of nanomaterial technology will have a profound impact on the productivity and may solve a series of problems such as food, health, energy and environmental protection fundamentally. This article analyzes the application prospect of nanomaterial and different preparation method. At the same time, the advantages and disadvantages of preparation are shown in the article which provides a literature review for researchers to refer.

Nonreciprocal genuine steering of three macroscopic samples in a spinning microwave magnonical system

Here, we propose to generate the nonreciprocal macroscopic entanglement and steering of magnon modes from three yttrium iron garnet spheres, which are placed in a spinning microwave resonator damped by a squeezed reservoir. Strikingly, the genuine entanglement and steering among three magnons can be achieved due to the correlation transfer from squeezed microwave to three magnons and the steady-state entanglement and steering show strong robustness against temperature. Furthermore, the nonreciprocal tripartite entanglement and steering are simultaneously existent based on Fizeau light-dragging effect by spinning the resonator at the steady state, which provides an alternative way to manipulate nonreciprocal effects in a cavity magnonical system and may have potential applications in manipulating the macroscopic quantum states of the multipartite system.

Controlling magnon-magnon entanglement and steering by atomic coherence.

Here we show that it is possible to control magnon-magnon entanglement in a hybrid magnon-atom-cavity system based on atomic coherence. In a four-level V-type atomic system, two strong fields are applied to drive two dipole-allowed transitions and two microwave cavity modes are coupled with two dipole forbidden transitions as well as two magnon modes simultaneously. It is found that the stable magnon-magnon entanglement, one-way steering and two-way EPR steering can be generated and controlled by atomic coherence according to the following two points: (i) the coherent coupling between magnon and atoms is established via exchange of virtual photons; (ii) the dissipation of magnon mode is dominant over amplification since one of the atomic states mediated one-channel interaction always keeps empty. The coherent control of magnon-magnon correlations provides an effective approach to modify macroscopic quantum effects using the laser-driven atomic systems.

Full‐Landscape Condensation Phases for Long‐Lived Excitons in 2D Tellurium: Crystal‐Field Splitting and Finite‐Momentum Excitons

AbstractThe realization of high‐temperature exciton macroscopic quantum phases in materials still remains challenging due to strict constraints in thermal stabilities and excitonic lifetimes. In this work, by using first‐principles calculations, the exciton dispersions and macroscopic quantum phase transitions of 2D α‐ and β‐Te are investigated. The excitons with lowest eigen energy for both α‐ and β‐Te are dark restricted by the crystal‐field symmetries. The Bose–Einstein condensation (BEC) transition for α‐ and β‐Te can be realized at 165.4 and 32.8 K with low excitation power densities of 0.42 × 1012 and 1.0 × 1012 cm−2, respectively. Furthermore, the phase transitions from insulating free exciton (FE) gas to conducting electron–hole plasma (EHP) and electron–hole liquid (EHL), as well as that from BEC to superfluidity phases are also predicted. Finally, the authors investigate the microscopic dynamics for bright excitons of 2D tellurium and find that they reach thermal equilibrium at 1–50 fs and excitonic lifetimes can reach 1–40 ns, beneficial for experimental observation of quantum condensate states. The findings in this work not only demonstrate the excellent optoelectronic properties of 2D tellurium allotropes, but also provide a promising platform for experimental realization of high‐temperature excitonic macroscopic quantum condensates.

Significantly enhanced superconductivity in monolayer FeSe films on SrTiO3(001) via metallic δ-doping.

Superconductivity transition temperature (Tc) marks the inception of a macroscopic quantum phase-coherent paired state in fermionic systems. For 2D superconductivity, the paired electrons condense into a coherent superfluid state at Tc, which is usually lower than the pairing temperature, between which intrinsic physics including Berezinskii-Kosterlitz-Thouless transition and pseudogap state are hotly debated. In the case of monolayer FeSe superconducting films on SrTiO3(001), although the pairing temperature (Tp) is revealed to be 65-83K by using spectroscopy characterization, the measured zero-resistance temperature ([Formula: see text]) is limited to 20K. Here, we report significantly enhanced superconductivity in monolayer FeSe films by δ-doping of Eu or Al on SrTiO3(001) surface, in which [Formula: see text] is enhanced by 12K with a narrowed transition width ΔTc ∼ 8K, compared with non-doped samples. Using scanning tunneling microscopy/spectroscopy measurements, we demonstrate lowered work function of the δ-doped SrTiO3(001) surface and enlarged superconducting gaps in the monolayer FeSe with improved morphology/electronic homogeneity. Our work provides a practical route to enhance 2D superconductivity by using interface engineering.

Revealing quantum effects in bosonic Josephson junctions: a multi-configuration atomic coherent state approach

The mean-field approach to two-site Bose–Hubbard systems is well-established and leads to non-linear classical equations of motion for population imbalance and phase difference. It can, for example, be based on the representation of the solution of the time-dependent Schrödinger equation either by a single Glauber state or by a single atomic (SU(2)) coherent state [S. Wimberger et al., Phys. Rev. A 103, 023326 (2021)]. We demonstrate that quantum effects beyond the mean-field approximation are easily uncovered if, instead, a multiconfiguration ansatz with a few time-dependent SU(2) basis functions is used in the variational principle. For the case of plasma oscillations, the use of just two basis states, whose time-dependent parameters are determined variationally, already gives a good qualitative agreement of the phase space dynamics with numerically exact quantum solutions. In order to correctly account for more non-trivial effects, like macroscopic quantum self-trapping, moderately more basis states are needed. For the onset of spontaneous symmetry breaking, however, a multiplicity of 2 gives a significant improvement already. In any case, the number of variational trajectories needed for good agreement with the full quantum results is orders of magnitude smaller than that in the semi-classical case, which is based on multiple mean-field trajectories.

Unraveling the mystery of the cosmological constant: Does spacetime uncertainty hold the key?(a)

In addressing the cosmological constant problem, we propose that the discrepancy between the theoretical and observed values can be ascribed to the inherent uncertainty in the spacetime metric. Mach's principle, which posits that mass shapes spacetime, intersects with quantum mechanics’ description of a particle as a quantum cloud, rendering the precise location of a particle's mass unknowable. Consequently, understanding spacetime structure at the quantum level becomes elusive. This connection between quantum and spacetime uncertainty could hold the key to resolving the cosmological constant problem. Intriguingly, the length scale of spacetime uncertainty, aligns with the macroscopic quantum weirdness observed in recent experiments. The spacetime uncertainty can be quantified by the scale factor in the Friedmann-Lemaître-Robertson-Walker (FLRW) universe.

Power Dependent Resonant Frequency of a Microwave Cavity Due to Magnetic Levitation

The fact that a magnet levitates above a superconductor is a fascinating consequence of the interaction between electromagnetic fields and the macroscopic quantum state of the superconductor. Such field-matter interactions, which include the Meissner and Josephson effects, combined with superconducting devices, such as low-loss superconducting microwave cavities, are emerging as key elements used in quantum computers. One technique that can be used to monitor the levitation of a magnet is to place the magnet within a superconducting microwave cavity and monitor the microwave resonance of that cavity. Here, we report measurements of the change in resonance frequency of the microwave cavity with the Meissner-levitated permanent magnet. The cavity resonance changes because the magnet perturbs the radio-frequency field inside the microwave cavity. The changes in resonant frequency and quality factor were measured as functions of input power and temperature. The observed power-dependent variations are explained in terms of the power dependence of the London penetration depth.

Incandescent temporal metamaterials

Regarded as a promising alternative to spatially shaping matter, time-varying media can be seized to control and manipulate wave phenomena, including thermal radiation. Here, based upon the framework of macroscopic quantum electrodynamics, we elaborate a comprehensive quantum theoretical formulation that lies the basis for investigating thermal emission effects in time-modulated media. Our theory unveils unique physical features brought about by time-varying media: nontrivial correlations between fluctuating electromagnetic currents at different frequencies and positions, thermal radiation overcoming the black-body spectrum, and quantum vacuum amplification effects at finite temperature. We illustrate how these features lead to striking phenomena and innovative thermal emitters, specifically, showing that the time-modulation releases strong field fluctuations confined within epsilon-near-zero (ENZ) bodies, and that, in turn, it enables a narrowband (partially coherent) emission spanning the whole range of wavevectors, from near to far-field regimes.

Effects of quantum fluctuations on macroscopic quantum tunneling and self-trapping of a BEC in a double-well trap

In this paper, we study the influence of quantum fluctuations (QFs) on the macroscopic quantum tunneling and self-trapping (ST) of a two-component Bose–Einstein condensate in a double-well trap. QFs are described by the Lee–Huang–Yang (LHY) term in the modified Gross–Pitaevskii (GP) equation. Employing the modified GP equation in a scalar approximation, we derive a dimer model using a two-mode approximation. The frequencies of Josephson oscillations and ST conditions under QFs are found analytically and proven by numerical simulations of the modified GP equation. The tunneling and localization phenomena are also investigated for the case of the LHY fluid loaded in a double-well potential.

Vortex-lattice structures in rotating Bose-Fermi superfluid mixtures

The system of Bose-Fermi superfluid mixture offers a playground to explore rich macroscopic quantum phenomena. In a recent experiment of Yao et al. (2016) [35], 41K-6Li superfluid mixture is implemented. Coupled quantized vortices are generated via rotating the superfluid mixture, and a few unconventional behaviors on the formations of vortex numbers are observed, which can be traced to boson-fermion interactions. Here we provide a theoretical insight into the unconventional behaviors observed in the experiment. To this end, the orbital-free density functional theory is hired, and its utility is validated by making comparison of the numerical results and a microscopic theory for vortex lattices in strongly interacting Fermi superfluids alone. We also predict interesting phenomena which can be readily explored experimentally, including the novel structures of bosonic-fermionic vortices, and attractive interactions between the bosonic and fermionic vortices.

Investigation of near-field optical tweezers based on the edge effect of extraordinary optical transmission in thin microcavity

Optical tweezers are powerful tools capable to trap and manipulate particles directly. However, using conventional optical tweezers for nanosized objects remains a formidable challenge due to the optical diffraction limits and high-power levels required for nanoscale trapping, which usually causes irreversible damage to the captured particles. In this paper, we investigate the near-field edge effect of thin microcavity due to macroscopic quantum effect, and the highly enhanced electric field can reach 2.4 times. Thus, a dual near-field optical trap potential well is generated at the edge of the thin microcavity. We theoretically show that this near-field potential well can stably capture nanoparticles smaller than 10 nm while keeping the incident optical power level below 100 mW. Besides, the relationship between size of the microcavity and optical gradient force has also been carefully studied. Finally, the theoretical model of near-field optical tweezers with double thin microcavity is established, and the electric field magnitude of the double microcavity model is enhanced by 4.5 times compared with single microcavity model, in which the coupling effect of double hole makes smaller particles be stably trapped. Our research presents a huge potential for optical trapping and separation of nanoparticles and biomolecules.