arXiv subjects

G. L. Long

Publications and source records attributed to G. L. Long.

10 recordsLinked to original sources

arXiv2007

Scalable quantum computer using superconducting charge qubits

We present a scalable scheme for superconducting charge qubits with the assistance of one-dimensional superconducting transmission line resonator (STLR) playing the role of data bus. The coupling between qubit and data bus may be turned on and off by just controlling the gate voltage and externally applied flux of superconducting charge qubit. In our proposal, the entanglement between arbitrary two qubits and $W$ states of three qubits can be generated quickly and easily.

quant-ph↗

arXiv2004

General Scheme for Super Dense Coding between Multi-Parties

Dense coding or super-dense coding in the case of high-dimension quantum states between two parties and multi-parties has been studied in this paper. We construct explicitly the measurement basis and the forms of the single-body unitary operations corresponding to the basis chosen, and the rules for selecting the one-body unitary operations in a multi-party case.

quant-ph↗

arXiv2003

Collective Properties of Low-lying Octupole Excitations in $^{208}_{82}Pb_{126}$, $^{60}_{20}Ca_{40}$ and $^{28}_{8}O_{20}$

The octupole strengths of $β$-stable nucleus $^{208}_{82}Pb_{126}$, a neutron skin nucleus $^{60}_{20}Ca_{40}$ and a neutron drip line nucleus $^{28}_{8}O_{20}$ are studied by using the self-consistent Hartree-Fock calculation plus the random phase approximation (RPA) with Skyrme interaction. The collective properties of low-lying excitations are analyzed by using particle-vibration coupling. The results show that the lowest isoscalar states above threshold in $^{60}_{20}Ca_{40}$ and $^{28}_{8}O_{20}$ are the superpositions of collective excitations and unperturbed transitions from bound state to nonresonance states. For these three nuclei, both the low-lying isoscalar states and giant isoscalar resonance carry isovector strength. The ratio B(IV)/B(IS) is checked. It is found that, for $^{208}_{82}Pb_{126}$, the ratios are equal to $(\frac{N-Z}{A})^2$ in good accuracy, while for $^{60}_{20}Ca_{40}$ and $^{28}_{8}O_{20}$, the ratios are much larger than $(\frac{N-Z}{A})^2$. This results from the excess neutrons with small binding energies in $^{60}_{20}Ca_{40}$ and $^{28}_{8}O_{20}$.

nucl-th↗

arXiv2003

Isospin and F-spin structure in low-lying levels of 48,50Cr isotopes

The low-energy level structure and electromagnetic transitions of $^{48,50}$Cr nuclei have been studied by using interacting boson model with isospin (IBM-3). A sequence of isospin excitation bands with isospin $(T= T_{z}$, $T_{z}+1$ and $ T_{z}+2) $ has been assigned, and compared with available data. According to this study, the $2^{+}_{3} $ and $2^{+}_{2} $ states are the lowest mixed symmetry states in $^{48,50}$Cr respectively. In particular, the present calculations suggest that a combination of isospin and F-spin excitation can explain the structure in these nuclei. The transition probabilities between the levels are analyzed in terms of isoscalar and isovector decomposition which reveal the detailed nature of the energy levels. The results obtained are found in good agreement with recent experimental data.

nucl-th↗

arXiv2002

Experimental Realization of Brüschweiler's exponentially fast search algorithm in a homo-nuclear system

Compared with classical search algorithms, Grover quantum algorithm [ Phys. Rev. Lett., 79, 325(1997)] achieves quadratic speedup and Bruschweiler hybrid quantum algorithm [Phys. Rev. Lett., 85, 4815(2000)] achieves an exponential speedup. In this paper, we report the experimental realization of the Bruschweiler$ algorithm in a 3-qubit NMR ensemble system. The pulse sequences are used for the algorithms and the measurement method used here is improved on that used by Bruschweiler, namely, instead of quantitatively measuring the spin projection of the ancilla bit, we utilize the shape of the ancilla bit spectrum. By simply judging the downwardness or upwardness of the corresponding peaks in an ancilla bit spectrum, the bit value of the marked state can be read out, especially, the geometric nature of this read-out can make the results more robust against errors.

quant-ph↗

arXiv2001

Analysis of Density Matrix reconstruction in NMR Quantum Computing

Reconstruction of density matrices is important in NMR quantum computing. An analysis is made for a 2-qubit system by using the error matrix method. It is found that the state tomography method determines well the parameters that are necessary for reconstructing the density matrix in NMR quantum computations. Analysis is also made for a simplified state tomography procedure that uses fewer read-outs. The result of this analysis with the error matrix method demonstrates that a satisfactory accuracy in density matrix reconstruction can be achieved even in a measurement with the number of read-outs being largely reduced.

quant-ph↗

arXiv2001

Fetching marked items from an unsorted database in NMR ensemble computing

Searching a marked item or several marked items from an unsorted database is a very difficult mathematical problem. Using classical computer, it requires $O(N=2^n)$ steps to find the target. Using a quantum computer, Grover's algorithm uses $O(\sqrt{N=2^n})$ steps. In NMR ensemble computing, Brushweiler's algorithm uses $\log N$ steps. In this Letter, we propose an algorithm that fetches marked items in an unsorted database directly. It requires only a single query. It can find a single marked item or multiple number of items.

quant-ph↗

arXiv2001

Experimental NMR Realization of A Generalized Quantum Search Algorithm

A generalized quantum search algorithm, where phase inversions for the marked state and the prepared state are replaced by $π/2$ phase rotations, is realized in a 2-qubit NMR heteronuclear system. The quantum algorithm searches a marked state with a smaller step compared to standard Grover algorithm. Phase matching requirement in quantum searching is demonstrated by comparing it with another generalized algorithm where the two phase rotations are $π/2$ and $3π/2$ respectively. Pulse sequences which include non 90 degree pulses are given.

quant-ph↗

arXiv2001

Grover Algorithm with zero theoretical failure rate

In standard Grover's algorithm for quantum searching, the probability of finding the marked item is not exactly 1. In this Letter we present a modified version of Grover's algorithm that searches a marked state with full successful rate. The modification is done by replacing the phase inversion by two phase rotation through angle $ϕ$. The rotation angle is given analytically to be $ϕ=2 \arcsin(\sin{π\over (4J+6)}\over \sinβ)$, where $\sinβ={1\over \sqrt{N}}$, $N$ the number of items in the database, and $J$ an integer equal to or greater than the integer part of $({π\over 2}-β)/(2β)$. Upon measurement at $(J+1)$-th iteration, the marked state is obtained with certainty.

quant-ph↗

arXiv1999

Comprehensive evidences of octupole vibration in $^{158}$Gd

Comprehensive evidences of the SU(3) limit in the spdf interacting boson model, a dynamical symmetry describing octupole vibration in rotational nucleus, are found in the spectrum, E2 and E1 transition rates, and relative intensities in $^{158}$Gd. This gives a good example of rotational nucleus with octupole vibration in rare-earth region.

nucl-ex↗