Quantum Simulation of 2p-πElectronic Hamiltonian in Molecular Ethylene by Using an NMR Quantum Computer

Classical simulation of a quantum system is a hard problem. It’s known that these problems can be solved efficiently by using quantum computers. This study demonstrates the simulation of the molecular Hamiltonian of 2p-π electrons of ethylene in order to calculate the ground state energy. The ground state energy is estimated by an iterative phase estimation algorithm. The ground state is prepared by the adiabatic state preparation and the implementation of the procedure is carried out by numerical simulation of two-qubit NMR quantum simulator. The readout scheme of the simulator is performed by extracting binary bits via NMR interferometer.

Quantum Mechanical Nature in Liquid NMR Quantum Computing

The quantum nature of bulk ensemble NMR quantum computing — the center of recent heated debate, is addressed. Concepts of the mixed state and entanglement are examined, and the data in a two-qubit liquid NMR quantum computation are analyzed. The main points in this paper are: i) Density matrix describes the 'state' of an average particle in an ensemble. It does not describe the state of an individual particle in an ensemble; ii) Entanglement is a property of the wave function of a microscopic particle (such as a molecule in a liquid NMR sample), and separability of the density matrix cannot be used to measure the entanglement of mixed ensemble; iii) The state evolution in bulk-ensemble NMR quantum computation is quantum-mechanical; iv) The coefficient before the effective pure state density matrix, ?, is a measure of the simultaneity of the molecules in an ensemble. It reflects the intensity of the NMR signal and has no significance in quantifying the entanglement in the bulk ensemble NMR system. The decomposition of the density matrix into product states is only an indication that the ensemble can be prepared by an ensemble with the particles unentangled. We conclude that effective-pure-state NMR quantum computation is genuine, not just classical simulations.

Energy Spectrum Symmetry of Heisenberg Model in Fock Space

We extend the BCS paring model with equally spaced energy levels to a general one-dimensional spin-1/2 Heisenberg model The two well-known symmetries of the Heisenberg model, i.e. permutational and spin-inversion symmetries, no longer exist. However, when jointing these two operations together, we find a new symmetry of energy spectrum between its subspace n and subspace L - n of the Fock space. A rigorous proof is presented.

Experimental quantum simulation of Avian Compass in a nuclear magnetic resonance system

Avian magnetoreception is the capacity for avians to sense the direction of the Earth's magnetic field. Discovered more than forty years ago, it has attracted intensive studies over the years. One promising model for describing this capacity in avians is the widely used reference-and-probe model where radical pairs within the eyes of bird combines to form singlet and triplet quantum states.The yield depends on the angle between the Earth's magnetic field and the molecules' axis, hence the relative value of yield of the singlet state or triplet state enables avians to sense the direction. Here we report the experimental demonstration of avian magnetoreception in a nuclear magnetic resonance quantum information processor. It is shown clearly from the experiment that the yield of the singlet state attains maximum when it is normal to the Earth's magnetic field, and the experimental results agree with theory very well.

Experimental cryptographic verification for near-term quantum cloud computing

An important task for quantum cloud computing is to make sure that there is a real quantum computer running,instead of classical simulation.Here we explore the applicability of a cryptographic verification scheme for verifying quantum cloud computing.We provided a theoretical extension and implemented the scheme on a 5-qubit NMR quantum processor in the laboratory and a 5-qubit and 16-qubit processors of the IBM quantum cloud.We found that the experimental results of the NMR processor can be verified by the scheme with about 1.4%error,after noise compensation by standard techniques.However,the fidelity of the IBM quantum cloud is currently too low to pass the test(about 42%error).This verification scheme shall become practical when servers claim to offer quantum-computing resources that can achieve quantum supremacy.

Structural determination of eleven new preschisanartane-type schinortriterpenoids from two Schisandra species and structural revision of preschisanartanin J using NMR computation method

Nineteen preschisanartane-type schinortriterpenoids(SNTs),among which eleven ones were previously undescribed,were isolated from two Schisandra species,S.sphaerandra and S.rubriflora.Their structures were determined using 1 D and 2 D NMR spectroscopic analyses,NMR data comparison,quantum chemical calculation of NMR parameters,electronic circular dichroism(ECD),X-ray single crystal diffraction,and chemical derivation.Furthermore,structural re-examination of a few previously reported preschisanartane-type SNTs led to the structural revision of preschisanartanin J.Besides,it is suggested that the reported structures of arisanlactone D and schilancidilactone W should be re-checked.Finally,a few isolated SNTs were found to possess neurite outgrowthpromoting activities,and protective activities against neural injuries.