Note on Implementation of Three-Qubit SWAP Gate

In this paper, the synthesis and implementation of three-qubit SWAP gate is discussed. The three-qubit SWAP gate can be decomposed into product of 2 two-qubit SWAP gates, and it can be realized by 6 CNOT gates. Research illustrated that although the result is very simple, the current methods of matrix decomposition for multi-qubit gate can not get that. Then the implementation of three-qubit SWAP gate in the three spin system with Ising interaction is investigated and the sequence of control pulse and drift process to implement the gate is given. It needs 23 control pulses and 12 drift processes. Since the interaction can not be switched on and off at will, the realization of three-qubit SWAP gate in specific quantum system also can not simply come down to 2 two-qubit SWAP gates.     

飞秒激光直写光量子逻辑门

量子比特在同一时刻可处于所有可能状态上的叠加特性使得量子计算机具有天然的并行计算能力,在处理某些特定问题时具有超越经典计算机的明显优势.飞秒激光直写技术因其具有单步骤高效加工真三维光波导回路的能力,在制备通用型集成光量子计算机的基本单元—量子逻辑门中发挥着越来越重要的作用.本文综述了飞秒激光直写由定向耦合器构成的光量子比特逻辑门的进展.主要包括定向耦合器的功能、构成、直写和性能表征,集成波片、哈达玛门和泡利交换门等单量子比特逻辑门、受控非门和受控相位门等两量子比特逻辑门的直写加工,并对飞秒激光加工三量子比特逻辑门进行了展望.     

Toffoli gate made from a single resonant interaction with a trapped ion system

We propose a simple but practical scheme to implement a three-qubit Toffoli gate by a single resonant interaction in a trapped ion system. The scheme does not require two-qubit controlled-NOT gates but uses a three-qubit phase gate and two Hadamard gates, where the phase gate can be implemented by only a single resonant interaction of the trapped ions with the first lower vibrational sideband mode. Both the situations, with and without spontaneous ionic emission, are investigated. Discussions are made for the advantages and the experimental feasibility of our scheme.     

基于二维囚禁离子实现受控非门、交换门和相位门

研究了二维囚禁离子与光场相互作用系统中几种基本量子逻辑门的实现方案.通过适当选取激光场与离子内部跃迁频率的失谐量,简化了系统的哈密顿量,并进一步推导出受控非门(C-NOT门)、交换门与相位门的实现方法.在此过程中,系统需满足Lamb-Dicke极限,并要求光场的Rabi振荡频率远远小于离子的振动频率. 关键词： 囚禁离子 受控非门(C-NOT门) 交换门 相位门     

Quantum Circuit Synthesis using a New Quantum Logic Gate Library of NCV Quantum Gates

Since Controlled-Square-Root-of-NOT (CV, CV^?) gates are not permutative quantum gates, many existing methods cannot effectively synthesize optimal 3-qubit circuits directly using the NOT, CNOT, Controlled-Square-Root-of-NOT quantum gate library (NCV), and the key of effective methods is the mapping of NCV gates to four-valued quantum gates. Firstly, we use NCV gates to create the new quantum logic gate library, which can be directly used to get the solutions with smaller quantum costs efficiently. Further, we present a novel generic method which quickly and directly constructs this new optimal quantum logic gate library using CNOT and Controlled-Square-Root-of-NOT gates. Finally, we present several encouraging experiments using these new permutative gates, and give a careful analysis of the method, which introduces a new idea to quantum circuit synthesis.     

高维辅助的普适量子线路优化

受到Lanyon等(Lanyon B P et al 2008 Nature Physics. 5 134)利用高维Hilbert空间成功简化Toffoli门的启发, 本文将辅助维度应用到普适量子线路中, 结合Cosine-Sine Decomposition(CSD), Quantum Shannon Decomposition(QSD)等矩阵分解方法, 优化了两比特和三比特普适幺正量子线路, 给出了计算n比特普适量子线路复杂度的公式, 并利用线性光学和腔QED系统设计了实验方案. 结果表明, 两比特和三比特量子线路的复杂度已分别接近和优于目前最优结果, 且随着比特数的增加, 本方案的优势愈加明显.     

Silicon photonic crystal all-optical logic gates

All-optical logic gates, including OR, XOR, NOT, XNOR, and NAND gates, are realized theoretically in a two-dimensional silicon photonic crystal using the light beam interference effect. The ingenious photonic crystal waveguide component design, the precisely controlled optical path difference, and the elaborate device configuration ensure the simultaneous realization of five types of logic gate with low-power and a contrast ratio between the logic states of “1” and “0” as high as 20 dB. High power is not necessary for operation of these logic gate devices. This offers a simple and effective approach for the realization of integrated all-optical logic devices.     

Scalable quantum computing with Josephson charge-phase qubits inside a cavity

This Letter proposes a theoretical scheme for scalable quantum computing with charge-phase qubits inside a common cavity. Individually addressing the applied gate pulses, we obtain the switchable interqubit couplings mediated by the cavity mode, from which a universal set of logic gates can be constructed. In our scheme the interqubit couplings are completely feasible to perform conditional gates, and the classical microwaves cause negligible leakage errors.     

Realization of Toffoli gate operation using four-level atoms in cavity QED system

This paper proposes a scheme for realization of a three-qubit Toffoli gate operation using three four-level atoms by a selective atom--field interaction in a cavity quantum electrodynamics system. In the proposed protocol, the quantum information is encoded on the stable ground states of atoms, and atomic spontaneous emission is negligible as the large atom--cavity detuning effectively suppresses the spontaneous decay of the atoms. The influence of the dissipation on fidelity and success probability of the three-qubit Toffoli gate is also discussed. The scheme can also be applied to realize an N-qubit Toffoli gate and the interaction time required does not rise with increasing the number of qubits.     

Economic scheme for remote preparation of an arbitrary five-qubit Brown-type state

A scheme for remotely preparingan arbitrary five-qubit Brown state by using three three-qubit GHZ states as the quantum channel is proposed. It is shown that, after the sender performs two different three-qubit projective measurements, the receiver should introduce two auxiliary qubits and employ suitable C-NOT gates, Toffoli gate and unitary operations on his qubits, the original state can be recovered with unit probability. Compared with the previous scheme, the advantage of the present scheme is that the entanglement resource can be reduced.     

Approximate Toffoli Gate Originated from a Single Resonant Interaction of Cavity Dissipation and Atomic Spontaneous Emission

We propose a potentially practical scheme to implement an approximate three-qubit Toffoli gate by a single resonant interaction in dissipative cavity QED in which the cavity mode decay and atomic spontaneous emission are considered. The scheme does not require two-qubit controlled-NOT gates but uses a three-qubit phase gate and two Hadamard gates, where the approximate phase gate can be implemented by only a single dissipative resonant interaction of atoms with the cavity mode. Discussions are made for the advantages and the experimental feasibility of our scheme.     

Two-qubit gate of combined single-spin rotation and interdot spin exchange in a double quantum dot

A crucial requirement for quantum-information processing is the realization of multiple-qubit quantum gates. Here, we demonstrate an electron spin-based all-electrical two-qubit gate consisting of single-spin rotations and interdot spin exchange in a double quantum dot. A partially entangled output state is obtained by the application of the two-qubit gate to an initial, uncorrelated state. We find that the degree of entanglement is controllable by the exchange operation time. The approach represents a key step towards the realization of universal multiple-qubit gates.     

Implementation of a Quantum Conditional Phase Gate for the Quantum Fourier Transform in Circuit QED

It is well known that multiple superconducting charge qubits coupled to a transmission line resonator can be controlled to achieve quantum logic gates between two arbitrary qubits. We propose a scheme to realize a quantum conditional phase gate with a geometric property by circuit electrodynamics, and it is applied naturally to reaJize the quantum Fourier transform with high fidelity. It is also demonstrated that the application is feasible and considerable under the present experimental technology.     

Realization optical signal processing components using SOA

This paper simulated simultaneously AND and NOT logic gate with frequency converter by using semiconductor optical amplifier. These logic gates and frequency converter are obtained with SOA effects like XGM and FWM of signals. Simulative realization of these logic gates and frequency converter will lead revolution in optical signal processing for high speed operation.     

Generation of Perfectly Entangled Two and Three Qubits States by Classical Random Interaction

This study examines the possibility of finding perfect entanglers for a Hamiltonian which corresponds to several quantum information platforms of interest at the present time. However, in this study, a superconducting circuit is used that stands out from other quantum-computing devices, especially because transmon qubits can be coupled via capacitors or microwave cavities, which enables to combine high coherence, fast gates, and high flexibility in its design parameters. There are currently two factors limiting the performance of superconducting processors: timing mismatch and the limitation of entangling gates to two qubits. In this work, a two-qubit SWAP and a three-qubit Fredkin gate is presented, additionally, a perfect adiabatic entanglement generation between two and three programmable superconducting qubits is also demonstrated. Furthermore, the impact of random dephasing, emission, and absorption noises on the quantum gates and entanglement is also demonstrated in this study. It is demonstrated by numerical simulation that CSWAP gate and W-state generation can be achieved perfectly in one step with high reliability under weak coupling conditions. Hence, this scheme could contribute to quantum teleportation, quantum communication, and some other areas of quantum information processing.     

Realization of XNOR logic function with all-optical high contrast XOR and NOT gates

In this article, we propose the realization of XNOR logic function by using all-optical XOR and NOT logic gates. Initially, both XOR and NOT gates are designed, simulated and optimized for high contrast outputs. T-shaped waveguides are created on the photonic crystal platform to realize these logic gates. An extra input is used to perform the inversion operation in the NOT gate. Inputs in both the gates are applied with out of phase so as to have a destructive interference between them and produce negligible intensity for logic ‘0'. The XOR and NOT gates are simulated using Finite Difference Time Domain method which results with a high contrast ratio of 55.23?dB and 54.83?dB, respectively at a response time of 0.136?ps and 0.1256?ps. Later, both the gates are cascaded by superimposing the output branch of the waveguide of XOR gate with the input branch of the waveguide of NOT gate so that it can be resulted with compact size for XNOR logic function. The resultant structure of XNOR logic came out with the contrast ratio of 12.27?dB at a response time of 0.1588?ps. Finally, it can be concluded that the proposed structures with fair output performance can suitably be applied in the design of photonic integrated circuits for high speed computing and telecommunication systems.     

利用暗本征态的绝热演化实现非几何条件相位移动:一种实现量子计算的新方法

利用绝热演化，文章提出一种新的方法以实现量子相位门，这种相位移动既非源于动力学过程，也非源于几何操纵，它来源于暗态本身的演化，基于绝热演化的优点，这种量子逻辑门对实验参量的起伏不敏感，与几何相位门相比，这种相位门更简单，并且保真度可得到进一步提高。文章对这种相位门做一简述。     

Optimization Approaches for Designing a Novel 4-Bit Reversible Comparator

Reversible logic is a new rapidly developed research field in recent years, which has been receiving much attention for calculating with minimizing the energy consumption. This paper constructs a 4×4 new reversible gate called ZRQ gate to build quantum adder and subtraction. Meanwhile, a novel 1-bit reversible comparator by using the proposed ZRQC module on the basis of ZRQ gate is proposed as the minimum number of reversible gates and quantum costs. In addition, this paper presents a novel 4-bit reversible comparator based on the 1-bit reversible comparator. One of the vital important for optimizing reversible logic is to design reversible logic circuits with the minimum number of parameters. The proposed reversible comparators in this paper can obtain superiority in terms of the number of reversible gates, input constants, garbage outputs, unit delays and quantum costs compared with the existed circuits. Finally, MATLAB simulation software is used to test and verify the correctness of the proposed 4-bit reversible comparator.     

Experimental Realization of Arbitrary Accuracy Iterative Phase Estimation Algorithms on Ensemble Quantum Computers

We report the first experimental demonstration of a nuclear phase estimation algorithms. Using feedback and iterations, magnetic resonance （NMR） realization of iterative we experimentally obtain the phase with 6 bits of precision on a two-qubit NMR quantum computer. Furthermore, we experimentally demonstrate the effect of gate noise on the iterative phase estimation algorithm. Our experimental results show that errors of measurements of the phase depend strongly on the precision of coupling gates. This experiment can be used as a benchmark for multi-qubit realizations of quantum information processing and precision measurements.     

State-Independent Geometric Quantum Gates via Nonadiabatic and Noncyclic Evolution

Geometric phases are robust to local noises and the nonadiabatic ones can reduce the evolution time, thus nonadiabatic geometric gates have strong robustness and can approach high fidelity. However, the advantage of geometric phase has not been fully explored in previous investigations. Here,a scheme is proposed for universal quantum gates with pure nonadiabatic and noncyclic geometric phases from smooth evolution paths. In the scheme, only geometric phase can be accumulated in a fast way, and thus it not only fully utilizes the local noise resistant property of geometric phase but also reduces the difficulty in experimental realization. Numerical results show that the implemented geometric gates have stronger robustness than dynamical gates and the geometric scheme with cyclic path. Furthermore, it proposes to construct universal quantum gate on superconducting circuits, with the fidelities of single-qubit gate and nontrivial two-qubit gate can achieve 99.97% and 99.87%, respectively. Therefore, these high-fidelity quantum gates are promising for large-scale fault-tolerant quantum computation.