The synthesis of Cr2O3 nanocrystal has been done by chemical precipitation method using ammonia as a precipitating agent. The hexagonal crystal structure and single crystalline nature of Cr2O3 powder were verified by X-ray diffraction (XRD) analysis. Debye-Scherrer formula was utilized to ascertain the average size of crystallites. The structure, shape, size, and composition of Cr2O3 nanoparticles were probed by SEM (Scanning Electron Microscopy) and EDX (Energy Dispersive X-ray Spectrometry). Optical band gap energy was estimated by UV-Vis spectroscopy. The various functional groups in Cr2O3 nanoparticles were reckoned by FTIR (Fourier transform infrared spectroscopy) findings. Inductance, Capacitance, and Resistance (LCR) meter was used to ascertain the electrical behavior of Cr2O3 nanoparticles. These finding suggests that the synthesized nanocrystal may be used in development of the electrical and optoelectronic devices.
Quantum computers generally need to operate under more regulated physical condition than classical computer because of quantum mechanics. Classical computer uses bits and quantum computer use qubits. According to IBM, “Groups of quits in superposition can create complex, multidimensional computational spaces” that enable more complex calculations. Quantum algorithms like Shor’s and Grover’s run significantly faster than various algorithms for classical computer. Quantum entanglement offers fascinating opportunities for enhancing AI algorithms through improved computational efficiency. But practical implementation remains challenging due to technical limitations and the need for further research in the field of quantum machine learning. This article provides a brief overview of different quantum computing methods.
Recent discovery of various magnetism in Tsai-type quasicrystalline approximants, in whose alloys rare-earth ions located on icosahedral apices are coupled with each other via the Ruderman--Kittel--Kasuya--Yosida interaction, opens an avenue to find novel magnetism originating from the icosahedral symmetry. Here we investigate classical and quantum magnetic states on an icosahedral cluster within the Heisenberg interactions of all bonds. Simulated annealing and numerical diagonalization are performed to obtain the classical and quantum ground states. We obtain qualitative correspondence of classical and quantum phase diagrams. Our study gives a good starting point to understand the various magnetism in not only quasicrystalline approximants but also quasicrystals.
Şebnem Güneş Söyler, Mikhail Kiselev, Nikolay V. Prokof'ev
et al.
We establish the full groundstate phase diagram of disordered Bose-Hubbard model in two-dimensions at unity filling factor via quantum Monte Carlo simulations. Similarly to the three-dimensional case we observe extended superfluid regions persisting up to extremely large values of disorder and interaction strength which, however, have small superfluid fractions and thus low transition temperatures. In the vicinity of the superfluid--insulator transition of the pure system, we observe an unexpectedly weak---almost not resolvable---sensitivity of the critical interaction to the strength of (weak) disorder.
Parameters of the nonorthogonal tight-binding model for hydrocarbons are derived based on a criterion of the best agreement between the calculated and experimental values of bond lengths and binding energies for different molecules CnHm. The results obtained can be used, e. g., to study the kinetics of hydrogen absorption by carbon nanostructures, to simulate the dynamics of hydrocarbon clusters like cubane C8H8, etc.
Measurements of the effect of a magnetic field on the light output and current through an organic light emitting diode made with deuterated aluminium tris(8-hydroxyquinoline) have shown that hyperfine coupling with protons is not the cause of the intrinsic organic magnetoresistance. We suggest that interactions with unpaired electrons in the device may be responsible.
We calculate ground state properties (energy, magnetization, susceptibility) and one-particle spectra for the $S = 1$ Heisenberg antiferromagnet with easy-axis or easy-plane single site anisotropy, on the square lattice. Series expansions are used, in each of three phases of the system, to obtain systematic and accurate results. The location of the quantum phase transition in the easy-plane sector is determined. The results are compared with spin-wave theory.
Very diluted Bose gas placed into a disordered environment falls into a fragmented localized state. At some critical density the repulsion between particles overcomes the disorder. The gas transits into a coherent superfluid state. In this article the geometrical and energetic characteristics of the localized state at zero temperature and the critical density at which the quantum phase transition from the localized to the superfluid state proceeds are found.
We investigate numerically the Multiple Quantum (MQ) NMR dynamics in systems of nuclear spins 1/2 coupled by the dipole-dipole interactions in the case of the pseudopure initial state. Simulations of the MQ NMR with the real molecular structures such as six dipolar-coupled proton spins of a benzene, hydroxyl proton chains in calcium hydroxyapatite and fluorine chains in calcium fluorapatite open the way to experimental NMR testing of the obtained results. It was found that multiple-spin correlations are created faster in such experiments than in the usual MQ NMR experiments and can be used for the investigation of many-spin dynamics of nuclear spins in solids
We study chemical reaction between a single hydrogen atom and a graphene, which is the elemental reaction between hydrogen and graphitic carbon materials. In the present work, classical molecular dynamics simulation is used with modified Brenner's empirical bond order potential. The three reactions, that is, absorption reaction, reflection reaction and penetration reaction, are observed in our simulation. Reaction rates depend on the incident energy of the hydrogen atom and the graphene temperature. The dependence can be explained by the following mechanisms: (1) The hydrogen atom receives repulsive force by pi-electrons in addition to nuclear repulsion. (2) Absorbing the hydrogen atom, the graphene transforms its structure to the ``overhang'' configuration such as sp-3 state. (3) The hexagonal hole of the graphene is expanded during the penetration of the hydrogen atom.
We calculated the binding energy of a polaron bound to a hydrogenic donor impurity located in a spherical quantum dot by means of a variational and numerical technique for finite potential models. The polaronic effect has been considered taking into account the ion-phonon coupling under the Lee Low Pines approach. The results show that the binding energies are drastically affected by the dot radius, the potential barrier height and the polaronic effects.
It is well known that the convection of liquid solution or melt liquid is inhibited by the magnetic field experimentally, and so that we can make the larger and better crystals at the cost of slow growth rate. We shall show here another two effects due to the magnetic field. First, when the ionised molecule diffuses on the surface of crystal under the magnetic field applied normal to the surface,its diffusion constant decreases due to the magnetic effect. Second, even if the molecule has no electric charge, if it has electric dipole moment, the kinetic energy decreases by different mechanism.
We present diffusion Monte Carlo (DMC) results on a new metastable, superfluid phase above the crystal ground state in two-dimensional 4He at densities > 0.065 1/A^2. The state is anisotropic with hexatic orbital order. This implies that the liquid--solid phase transition has two stages: A second order phase transition from the isotropic superfluid to the hexatic superfluid, followed by a first order transition that localizes atoms into the triangular crystal order. This metastable hexatic phase has finite condensate fraction and it provides a natural explanation for the superflow in the supersolid grain boundaries.
A simple yet highly reproducible method to suppress contamination of graphene at low temperature inside the cryostat is presented. The method consists of applying a current of several mA through the graphene device, which is here typically a few $μ$m wide. This ultra-high current density is shown to remove contamination adsorbed on the surface. This method is well suited for quantum electron transport studies of undoped graphene devices, and its utility is demonstrated here by measuring the anomalous quantum Hall effect.
Khan W. Mahmud, Mary Ann Leung, William P. Reinhardt
We provide a scheme for the generation of controlled entangled number states of Bose-Einstein condensates in multiple wells, and also provide a novel method for the creation of squeezed states without severe adiabatic constraints on barrier heights. The condensate in a multiple well trap can be evolved, starting with a specific initial phase difference between the neighboring wells, to a tunable entangled state or a squeezed state. We propose a general formula for the initial phase difference between the neighboring wells that is valid for any number of wells, even and odd.
We study polar molecules in a stack of strongly confined pancake traps. When dipolar moments point perpendicular to the planes of the traps and are sufficiently strong, the system is stable against collapse but attractive interaction between molecules in different layers leads to the formation of extended chains of molecules, analogously to the chaining phenomenon in classical rheological electro- and magnetofluids. We analyze properties of the resulting quantum liquid of dipolar chains and show that only the longest chains undergo Bose-Einstein condensation with a strongly reduced condensation temperature. We discuss several experimental methods for studying chains of dipolar molecules.
Relaxation and decoherence of a qubit coupled to environment and driven by a resonant ac field are investigated by analytically solving Bloch equation of the qubit. It is found that the decoherence of a driven qubit can be decomposed into intrinsic and field-dependent ones. The intrinsic decoherence time equals to the decoherence time of the qubit in free decay while the field-dependent decoherence time is identical with the relaxation time of the qubit in driven oscillation. Analytical expressions of the relaxation and decoherence times are derived and applied to study a microwave-driven SQUID flux qubit. The results are in excellent agreement with those obtained by numerically solving the master equation. The relations between the relaxation and decoherence times of a qubit in free decay and driven oscillation can be used to extract the decoherence and thus dephasing times of the qubit by measuring its population evolution in free decay and resonantly driven oscillation.
It is argued that Majorana zero modes in a system of quantum fermions can mediate a teleportation-like process with the actual transfer of electronic material between well separated points. The problem is formulated in the context of a quasi-realistic and exactly solvable model of a quantum wire embedded in a bulk p-wave superconductor. An explicit computation of the tunneling amplitude is given.
We report our studies of zero-frequency shot noise in tunneling through a parallel-coupled quantum dot interferometer by employing number-resolved quantum rate equations. We show that the combination of quantum interference effect between two pathways and strong Coulomb repulsion could result in a giant Fano factor, which is controllable by tuning the enclosed magnetic flux.
We propose that the inversion symmetry of the graphene honeycomb lattice is spontaneously broken via a magnetic field dependent Peierls distortion. This leads to valley splitting of the $n=0$ Landau level but not of the other Landau levels. Compared to quantum Hall valley ferromagnetism recently discussed in the literature, lattice distortion provides an alternative explanation to all the currently observed quantum Hall plateaus in graphene.