49 research outputs found
Speedup of quantum state transfer by three- qubit interactions: Implementation by nuclear magnetic resonance
Universal quantum information processing requires single-qubit rotations and
two-qubit interactions as minimal resources. A possible step beyond this
minimal scheme is the use of three-qubit interactions. We consider such
three-qubit interactions and show how they can reduce the time required for a
quantum state transfer in an XY spin chain. For the experimental
implementation, we use liquid-state nuclear magnetic resonance (NMR), where
three-qubit interactions can be implemented by sequences of radio-frequency
pulses.Comment: Comments are welcome to [email protected] or
[email protected]. More experimental results are adde
Realization of generalized quantum searching using nuclear magnetic resonance
According to the theoretical results, the quantum searching algorithm can be
generalized by replacing the Walsh-Hadamard(W-H) transform by almost any
quantum mechanical operation. We have implemented the generalized algorithm
using nuclear magnetic resonance techniques with a solution of chloroform
molecules. Experimental results show the good agreement between theory and
experiment.Comment: 11 pages,3 figure. Accepted by Phys. Rev. A. Scheduled Issue: 01 Mar
200
Simulation of a Heisenberg XY- chain and realization of a perfect state transfer algorithm using liquid nuclear magnetic resonance
The three- spin chain with Heisenberg XY- interaction is simulated in a
three- qubit nuclear magnetic resonance (NMR) quantum computer. The evolution
caused by the XY- interaction is decomposed into a series of single- spin
rotations and the - coupling evolutions between the neighboring spins. The
perfect state transfer (PST) algorithm proposed by M. Christandl et al [Phys.
Rev. Lett, 92, 187902(2004)] is realized in the XY- chain
Direct observation of quantum criticality in Ising spin chains
We use NMR quantum simulators to study antiferromagnetic Ising spin chains
undergoing quantum phase transitions. Taking advantage of the sensitivity of
the systems near criticality, we detect the critical points of the transitions
using a direct measurement of the Loschmidt echo. We test our simulators for
spin chains of even and odd numbers of spins, and compare the experimental
results to theoretical predictions
Modularization of multi-qubit controlled phase gate and its NMR implementation
Quantum circuit network is a set of circuits that implements a certain
computation task. Being at the center of the quantum circuit network, the
multi-qubit controlled phase shift is one of the most important quantum gates.
In this paper, we apply the method of modular structuring in classical computer
architecture to quantum computer and give a recursive realization of the
multi-qubit phase gate. This realization of the controlled phase shift gate is
convenient in realizing certain quantum algorithms. We have experimentally
implemented this modularized multi-qubit controlled phase gate in a three qubit
nuclear magnetic resonance quantum system. The network is demonstrated
experimentally using line selective pulses in nuclear magnetic resonance
technique. The procedure has the advantage of being simple and easy to
implement.Comment: to appear in Journal of Optics B: Quantum and Semiclassical Optic
Optimal photon energies for initialization of hybrid spin quantum registers of NV centers in diamond
Initializing quantum registers with high fidelity is a fundamental precondition for many applications like quantum information processing and sensing. The electronic and nuclear spins of a Nitrogen-Vacancy (NV) center in diamond form an interesting hybrid quantum register that can be initialized by a combination of laser, microwave, and radio-frequency pulses. However, the laser illumination, which is necessary for achieving electron spin polarization, also has the unwanted sideeffect of depolarizing the nuclear spin. Here, we study how the depolarization dynamics of the 14N nuclear spin depends on the laser wavelength. We show experimentally that excitation with an orange laser (594 nm) causes signifficantly less nuclear spin depolarization compared to the green laser (532 nm) typically used for excitation and hence leads to higher nuclear spin polarization. This could be because orange light excitation inhibits ionization of NV^0 into NV^_ and therefore suppresses one source of noise acting on the nuclear spin