最优实数态克隆作为标准BB84方案的最优个体窃听攻击

我们给出最优ARSC是对标准BB84方案的最优个体窃听分析.基于量子克隆的个体窃听,说明在由Csiszár和Korner定理的密钥产生率的两个充分条件中,其中一个可以作为最好的充分条件.     

相位协变量子克隆的腔-超导量子干涉仪实现

在腔-超导量子干涉仪(SQUID)体系中提出了两个实现1→2最优相位协变量子克隆的方案.在这两个方案中,三能级SQUID通过拉曼转换与量子化腔场和微波脉冲相作用.在大失谐的条件下,激发态被绝热消去.腔场始终处于真空态,在腔和SQUID之间没有信息转移,腔的衰退得到很好的抑制.用这种方法,相位协变量子克隆可以通过四步来实现.     

利用离子阱技术实现1→2和1→3的最优非对称经济型相位协变克隆的方案

我们提出利用离子阱技术来实现1→2和1→3的最优非对称经济型相位协变克隆的实验可行性方案.在这两个方案中集体振动模开始处于真空态.在第一个方案中,我们先用激光驱动第一个离子,然后把振动模的态映射到第二个离子上.在第二个方案中,先用两束不同的激光驱动两个离子,然后把振动模的态映射到第三个离子上.这两个方案都是以共振边带激发为基础的,因此用现在的离子阱技术是可以实现的.     

Scheme for Implementation of Ancillary-Free 1→3 Optimal Phase-Covariant Quantum Cloning with Trapped Ions

We propose a simple scheme for the implementation of the ancillary-free 1→3 optimal phase-covariant quantum cloning for x-y equatorial qubits in ion-trap system. In the scheme, the vibrational mode is only virtually excited, which is very important in view of decoherence. The present proposal can be realized based on current available technologies.     

腔QED中相位协变量子克隆机的实现及纠错

应用N个二能级原子和单模真空腔场相互作用,提出了一个1→2的相位协变量子克隆机的方案.同时,基于这种克隆机,我们也提出了量子纠错方案,考虑了由相位和比特反转错误所产生的消相干影响,通过对后两个比特位进行Bell测量,并沿着合适的轴旋转第一比特,就可以恢复初始态.     

腔QED技术实现最优非对称经济型1到3的相位协变克隆方案

本文提出一个在腔QED中实现最优非对称经济型1到3相位协变克隆的可行性方案,这种克隆不需要辅助粒子.在这个方案中,三个原子中的两个同时与腔场发生作用,并且受经典场的作用.此方案不受腔场的态和腔衰变的影响,因此,在实验上是可能实现的.     

利用腔QED技术实现最优非对称经济型1到3的相位协变克隆

本文提出一个在腔QED中实验上可行的方案来实现最优非对称经济型1到3相位协变克隆,这种克隆是不需要辅助粒子的。在这个的方案中,三个原子中的两个同时与腔场发生作用,并且它们受经典场的作用。并且此方案不受腔场的态和腔衰变的影响,因此,在实验上是可能实现的。     

在腔QED中实现最优非对称经济型1到3的相位协变克隆方案

本文提出一个在腔QED中实验上可行的方案来实现最优非对称经济型1到3相位协变克隆,这种克隆是不需要辅助粒子的。在这个的方案中,三个原子中的两个同时与腔场发生作用,并且它们受经典场的作用。并且此方案不受腔场的态和腔衰变的影响,因此,在实验上是可能实现的。     

Scheme for the implementation of 1→3 optimal phase-covariant quantum cloning in ion-trap systems

This paper proposes a scheme for the implementation of 1→ 3 optimal phase-covariant quantum cloning with trapped ions. In the present protocol, the required time for the whole procedure is short due to the resonant interaction, which is important in view of decoherence. Furthermore, the scheme is feasible based on current technologies.     

相位阻尼下非X态的量子失协和几何失协

研究了在相位阻尼作用下非X态的量子失协与几何失协,用图像诠释了Bloch矢量以及相位阻尼系数p对失协的影响。通过讨论我们发现量子失协和几何失协都能在一段有限时间间隔内保持一定值,并且具有相同的突变点。量子失协和几何失协不会出现量子纠缠的突然死亡和重生现象,所以研究失协比纠缠更具有实际应用意义。     

Scheme to Implement Optimal Asymmetric Economical Phase-Covariant Quantum Cloning in Cavity QED

We propose an experimentally feasible scheme to implement the optimal asymmetric economical 1→2 phase-covariant quantum cloning in two dimensions based on the cavity QED technique. The protocol is very simple and only two atoms are required. Our scheme is insensitive to the cavity field states and cavity decay. During the processes, the cavity is only virtually excited and it thus greatly prolongs the efficient decoherent time. Therefore, it may be realized in experiment.     

Approximate Disentanglement

We construct a quantum machine which, by using an asymmetric cloner, disentangles an entangled state and nearly retains it. The attainable maximum value of the scaling parameter for disentangling is identical to that obtained in previous works. The fidelity of the output residual entangled state with respect to the input entangled state is state-dependent. The result shows that it is possible to deal with disentanglement and broadcasting entanglement in a single unitary evolution.     

Scheme for Implementation of Optimal Cloning of Arbitrary Single Particle Atomic State into Two Photonic States

We present a feasible scheme to implement the 1→2 optimal cloning of arbitrary single particle atomic state into two photonic states, which is important for applications in long distance quantum communication. Our scheme also realizes the tele-NOT gate of one atom to the distant atom trapped in another cavity. The scheme is based on the adiabatic passage and the polarization measurement. It is robust against a number of practical noises such as the violation of the Lamb Dicke condition, spontaneous emission, and detection inefficiency.     

Optimal 1 → M phase-covariant cloning in three dimensions

In this paper, we derive the explicit transformations of the optimal 1 → 3, 4, 5 phase-covariant cloning in three dimensions, and then generalize them to the cases of 1 → M = 3n, 3n + 1, 3n + 2(n ≥ 1 integer) cloning. The clone fidelities are coincident with the theoretical bounds found.     

Implementing ancilla-free phase covariant quantum cloning with atoms trapped in cavities

We propose a scheme to implement ancilla-free 1 to 2 optimal phase covariant quantum cloning with atoms trapped in cavities.In the scheme the W-class state of three atoms,which are individually trapped in three spatially separated cavities,is deterministically generated.Then by the use of this W-class state and detection of the atomic state,an optimal ancilla-free 1 to 2 phase-covariant quantum cloning between two spatially separated trapped atoms can be realized.The scheme is robust for atomic spontaneous ...     

Optimal Phase-Covariant Cloning in 3 Dimensions

In this paper, we present the explicit transformations of the optimal 1 → 3, 4, 5 phase-covariant cloning in 3 dimensions. The cloning fidelities are covered by the theoretical bounds of the optimal 1 → 3k, 3k + 1, 3k + 2 phase-covariant cloning of qutrits, where k ≥ 1 is the integral [Phys. Rev. A 67 (2003) 042306].     

Probabilistic quantum cloning of real states

We construct the explicit formulation of the probabilistically perfect quantum cloning machine that perfectly duplicates the input states chosen from the special set consisting of the linearly independent and nonorthogonal quantum states with 〈φ_i ∣φ_j〉 = r ∈ (0, 1)(i ≠ j). The success probabilities of cloning the input states are equal and maximal. As two examples, we present the explicit transformations of the optimal 1 → 2 probabilistically perfect quantum cloning of the real states in 2 and 3 dimensions. The success probabilities of each of two cloning machines are equal and maximal.     

Economical phase-covariant cloning with multiclones

This paper presents a very simple method to derive the explicit transformations of the optimal economical 1 to M phase-covariant cloning. The fidelity of clones reaches the theoretic bound [D'Ariano G M and Macchiavello C 2003 Phys. Rev. A 67 042306]. The derived transformations cover the previous contributions [Delgado Y, Lamata L et al, 2007 Phys. Rev. Lett.98 150502] in which M must be odd.