Searcharxiv⌕ Search

arXiv subjects

Gui Lu Long

Publications and source records attributed to Gui Lu Long.

At least 37 records · Page 2Linked to original sources
arXiv2010

Realization of Quantum State Privacy Amplification in a Nuclear Magnetic Resonance Quantum System

Quantum state privacy amplification (QSPA) is the quantum analogue of classical privacy amplification. If the state information of a series of single particle states has some leakage, QSPA reduces this leakage by condensing the state information of two particles into the state of one particle. Recursive applications of the operations will eliminate the quantum state information leakage to a required minimum level. In this paper, we report the experimental implementation of a quantum state privacy amplification protocol in a nuclear magnetic resonance system. The density matrices of the states are constructed in the experiment, and the experimental results agree with theory well.

quant-ph↗
arXiv2010

The minimal time of dynamic evolution to an arbitrary state

Two bounds on the minimal time of dynamic rotating an initial state by arbitrary angle have been obtained. These bounds have been applied to study the evolutions in the Hadamard-Walsch gate, the Control-NOT quantum gate, and the Grover algorithm.

quant-ph↗
arXiv2009

Non-Adiabatic Fluctuation in Measured Geometric Phase

We study how the non-adiabatic effect causes the observable fluctuation in the "geometric phase" for a two-level system, which is defined as the experimentally measurable quantity in the adiabatic limit. From the Rabi's exact solution to this model, we give a reasonable explanation to the experimental discovery of phase fluctuation in the superconducting circuit system [P. J. Leek, \textit{et al}., Science \textbf{318}, 1889 (2007)], which seemed to be regarded as the conventional experimental error.

quant-ph↗
arXiv2008

Modified entanglement purification scheme with doubly entangled photon state

Recently Xiao et al. proposed a scheme for entanglement purification based on doubly entangled photon states (Phys. Rev. A 77(2008) 042315). We modify their scheme for improving the efficiency of entanglement purification. This modified scheme contains two steps, i.e., the bit-flip error correction and the entanglement purification of phase-flip errors. All the photon pairs in the first step can be kept as all the bit-flip errors are corrected. For purifying the phase-flip errors, a wavelength conversion process is needed. This scheme has the advantage of high efficiency and it requires the original fidelity of the entangled state wanted fay lower than other schemes, which makes it more feasible in a practical application.

quant-ph↗
arXiv2008

Negative-Parity States and beta-decays in odd Ho and Dy Nuclei with A=151,153

We have investigated the negative-parity states and electromagnetic transitions in $^{151,153}$Ho and $^{151,153}$Dy within the framework of the interacting boson fermion model 2 (IBFM-2). Spin assignments for some states with uncertain spin are made based on this calculation. Calculated excitation energies, electromagnetic transitions and branching ratios are compared with available experimental data and a good agreement is obtained. The model wave functions have been used to study $β$-decays from Ho to Dy isotones, and the calculated $\log ft$ values are close to the experimental data.

nucl-th↗
arXiv2007

Reusable Vernam Cipher with Quantum Media

A revised version will be uploaded later. In this Letter, it is shown that the one-time-pad key in the Vernam cipher can be repeatedly used with unconditional security using quantum media. The security proof is given with two explicit protocols, and the error rate threshold is analyzed.

quant-ph↗
arXiv2007

Deleting a marked item from an unsorted database with a single query

In this Letter we present a quantum deletion algorithm that deletes a marked state from an unsorted database of $N$ items with only a single query. This algorithm achieves exponential speedup compared with classical algorithm where O(N) number of query is required. General property of this deleting algorithm is also studied.

quant-ph↗
arXiv2007

Analytic Constructions of General n-Qubit Controlled Gates

In this Letter, we present two analytic expressions that most generally simulate $n$-qubit controlled-$U$ gates with standard one-qubit gates and CNOT gates using exponential and polynomial complexity respectively. Explicit circuits and general expressions of decomposition are derived. The exact numbers of basic operations in these two schemes are given using gate counting technique.

quant-ph↗
arXiv2007

Duality and Recycling Computing in Quantum Computers

Quantum computer possesses quantum parallelism and offers great computing power over classical computer \cite{er1,er2}. As is well-know, a moving quantum object passing through a double-slit exhibits particle wave duality. A quantum computer is static and lacks this duality property. The recently proposed duality computer has exploited this particle wave duality property, and it may offer additional computing power \cite{r1}. Simply put it, a duality computer is a moving quantum computer passing through a double-slit. A duality computer offers the capability to perform separate operations on the sub-waves coming out of the different slits, in the so-called duality parallelism. Here we show that an $n$-dubit duality computer can be modeled by an $(n+1)$-qubit quantum computer. In a duality mode, computing operations are not necessarily unitary. A $n$-qubit quantum computer can be used as an $n$-bit reversible classical computer and is energy efficient. Our result further enables a $(n+1)$-qubit quantum computer to run classical algorithms in a $O(2^n)$-bit classical computer. The duality mode provides a natural link between classical computing and quantum computing. Here we also propose a recycling computing mode in which a quantum computer will continue to compute until the result is obtained. These two modes provide new tool for algorithm design. A search algorithm for the unsorted database search problem is designed.

quant-ph↗
arXiv2007

Secure Reusable Base-String in Quantum Key Distribution

Protecting secure random key from eavesdropping in quantum key distribution protocols has been well developed. In this letter, we further study how to detect and eliminate eavesdropping on the random base string in such protocols. The correlation between the base string and the key enables Alice and Bob to use specific privacy amplification to distill and reuse the previously shared base string with unconditional security and high efficiency. The analysis of the unconditional secure reusable base string brings about new concept and protocol design technique.

quant-ph↗
arXiv2007

Multiple Entropy Measures for Multipartite Quantum Entanglement

A new entanglement measure, the multiple entropy measures (MEMS), is proposed to quantify quantum entanglement of multi-partite quantum state. The MEMS is vector-like with $m=[N/2]$, the integer part of $N/2$, components: $[S_1, S_2,..., S_m]$, and the $i$-th component $S_i$ is the geometric mean of $i$-body partial entropy of the system. The $S_i$ measures how strong an arbitrary $i$ bodies from the system are entangled with the rest of the system. The MEMS is not only transparent in physical picture, but also simple to calculate. It satisfies the conditions for a good entanglement measure. We have analyzed the entanglement properties of the GHZ-state, the W-states and cluster-states under MEMS. The cluster-state is more entangled than the GHZ-state and W-state under MEMS.

quant-ph↗
arXiv2007

Generating Squeezed States of Nanomechanical Resonator

We propose a scheme for generating squeezed states in solid state circuits consisting of a nanomechanical resonator (NMR), a superconducting Cooper-pair box (CPB) and a superconducting transmission line resonator (STLR). The nonlinear interaction between the NMR and the STLR can be implemented by setting the external biased flux of the CPB at certain values. The interaction Hamiltonian between the NMR and the STLR is derived by performing Fr$\rm\ddot o$hlich transformation on the total Hamiltonian of the combined system. Just by adiabatically keeping the CPB at the ground state, we get the standard parametric down-conversion Hamiltonian. The CPB plays the role of ``nonlinear media", and the squeezed states of the NMR can be easily generated in a manner similar to the three-wave mixing in quantum optics. This is the three-wave mixing in a solid-state circuit.

quant-ph↗
arXiv2007

Simulation of four-body interaction in a nuclear magnetic resonance quantum information processor

Four-body interaction plays an important role in many-body systems, and it can exhibit interesting phase transition behaviors. Historically it was the need to efficiently simulate quantum systems that lead the idea of a quantum computer. In this Letter, we report the experimental demonstration of a four-body interaction in a four- qubit nuclear magnetic resonance quantum information processor. The strongly modulating pulse is used to implement spin selective excitation. The results show a good agreement between theory and experiment.

quant-ph↗
arXiv2007

Effects of Imperfect Gate Operations in Shor's Prime Factorization Algorithm

The effects of imperfect gate operations in implementation of Shor's prime factorization algorithm are investigated. The gate imperfections may be classified into three categories: the systematic error, the random error, and the one with combined errors. It is found that Shor's algorithm is robust against the systematic errors but is vulnerable to the random errors. Error threshold is given to the algorithm for a given number $N$ to be factorized.

quant-ph↗
arXiv2007

One-party Quantum Error Correcting Codes for Unbalanced Errors: Principles and Application to Quantum Dense Coding and Quantum Secure Direct Communications

In this article, we present the unbalanced quantum error correcting codes(one-party-QECC), a novel idea for correcting unbalanced quantum errors. In some quantum communication tasks using entangled pairs, the error distributions between two parts of the pairs are unbalanced, and. one party holds the whole entangled pairs at the final stage, and he or she is able to perform joint measurements on the pairs. In this situation the proposed one-party-QECC can improve error correction by allowing a higher tolerated error rate. We have established the general correspondence between linear classical codes and the one-party-QECC, and we have given the general definition for this type quantum error correcting codes.It has been shown that the one-party-QECC can correct errors as long as the error threshold is not larger than 0.5. The one-party-QECC works even for fidelity less than 0.5 as long as it is larger than 0.25. We give several concrete examples of the one-party-QECC. We provide the applications of one-party-QECC in quantum dense coding so that it can function in noisy channels. As a result, a large number of quantum secure direct communication protocols based on dense coding is also able to be protected by this new type of one-party-QECC.

quant-ph↗