2,226 research outputs found
Entanglement in nuclear quadrupole resonance
Entangled quantum states are an important element of quantum information
techniques. We determine the requirements for states of quadrupolar nuclei with
spins >1/2 to be entangled. It was shown that entanglement is achieved at low
temperature by applying a magnetic field to a quadrupolar nuclei possess
quadrupole moments, which interacts with the electricfield gradient produced by
the charge distribution in their surroundings.Comment: 9 pages, 5 figure
Quantum information processing by NMR using a 5-qubit system formed by dipolar coupled spins in an oriented molecule
Quantum Information processing by NMR with small number of qubits is well
established. Scaling to higher number of qubits is hindered by two major
requirements (i) mutual coupling among qubits and (ii) qubit addressability. It
has been demonstrated that mutual coupling can be increased by using residual
dipolar couplings among spins by orienting the spin system in a liquid
crystalline matrix. In such a case, the heteronuclear spins are weakly coupled
but the homonuclear spins become strongly coupled. In such circumstances, the
strongly coupled spins can no longer be treated as qubits. However, it has been
demonstrated elsewhere, that the energy levels of a strongly coupled N
spin-1/2 system can be treated as an N-qubit system. For this purpose the
various transitions have to be identified to well defined energy levels. This
paper consists of two parts. In the first part, the energy level diagram of a
heteronuclear 5-spin system is obtained by using a newly developed
heteronuclear z-cosy (HET-Z-COSY) experiment. In the second part,
implementation of logic gates, preparation of pseudopure states, creation of
entanglement and entanglement transfer is demonstrated, validating the use of
such systems for quantum information processing.Comment: 23 pages, 8 figure
Evolution of spin entanglement and an entanglement witness in multiple-quantum NMR experiments
We investigate the evolution of entanglement in multiple-quantum (MQ) NMR
experiments in crystals with pairs of close nuclear spins-1/2. The initial
thermodynamic equilibrium state of the system in a strong external magnetic
field evolves under the non-secular part of the dipolar Hamiltonian. As a
result, MQ coherences of the zeroth and plus/minus second orders appear. A
simple condition for the emergence of entanglement is obtained. We show that
the measure of the spin pair entanglement, concurrence, coincides qualitatively
with the intensity of MQ coherences of the plus/minus second order and hence
the entanglement can be studied with MQ NMR methods. We introduce an
Entanglement Witness using MQ NMR coherences of the plus/minus second order.Comment: 5 pages, 2 figure
Multiple Quantum NMR and Entanglement Dynamics in Dipolar Coupling Spin
We investigate numerically the time dependence of the multiple quantum
coherences and entanglement in linear chains up to nine nuclear spins of 1/2
coupled by the dipole-dipole interactions. Two models are considered: (1) a
spin chain with nearest-neighbor dipole -dipole interactions; (2) a more
realistic model with interactions between all spins. It is shown that the
entangled states appear between remote particles which do not interact directly
(model 1), while the interaction between all spins (model 2) not always results
in entanglement between remote spins.Comment: 14 pages, 3 figures. accepted for publication in Physical Review
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