A symmetric 1 to 2 quantum cloning machine (QCM) is presented that provides high-fidelity copies with $0.90 \le F \le 0.95$ for all pure (single-qubit) input states from a given meridian of the Bloch sphere. \cor{Emphasize is placed especially on the states of the (so-called) Eastern meridian, that includes the computational basis states $\ketm{0}, \ketm{1}$ together with the diagonal state $\ketm{+} = \frac{1}{\sqrt{2}} (\ketm{0} + \ketm{1})$, for which suggested cloning transformation is shown to be optimal.} In addition, we also show how this QCM can be utilized for eavesdropping in Bennett's B92 protocol for quantum key distribution with a substantial higher success rate than obtained for universal or equatorial quantum copying.A symmetric 1 to 2 quantum cloning machine (QCM) is presented that provides high-fidelity copies with $0.90 \le F \le 0.95$ for all pure (single-qubit) input states from a given meridian of the Bloch sphere. \cor{Emphasize is placed especially on the states of the (so-called) Eastern meridian, that includes the computational basis states $\ketm{0}, \ketm{1}$ together with the diagonal state $\ketm{+} = \frac{1}{\sqrt{2}} (\ketm{0} + \ketm{1})$, for which suggested cloning transformation is shown to be optimal.} In addition, we also show how this QCM can be utilized for eavesdropping in Bennett's B92 protocol for quantum key distribution with a substantial higher success rate than obtained for universal or equatorial quantum copying.

arXiv:0906.1453Jun 8, 20090 citations

Generators for Symmetric Universal Quantum Cloning Machines

姜明明, 郁司夏

Chinese Physics LettersJan 1, 20100 citations

Distribution of quantum Fisher information in asymmetric cloning machines

Xing Mao Xiao, Yao Yao, Lei‐Ming Zhou +1 more

An unknown quantum state cannot be copied and broadcast freely due to the no-cloning theorem. Approximate cloning schemes have been proposed to achieve the optimal cloning characterized by the maximal fidelity between the original and its copies. Here, from the perspective of quantum Fisher information (QFI), we investigate the distribution of QFI in asymmetric cloning machines which produce two nonidentical copies. As one might expect, improving the QFI of one copy results in decreasing the QFI of the other copy. It is perhaps also unsurprising that asymmetric phase-covariant cloning outperforms universal cloning in distributing QFI since a priori information of the input state has been utilized. However, interesting results appear when we compare the distributabilities of fidelity (which quantifies the full information of quantum states), and QFI (which only captures the information of relevant parameters) in asymmetric cloning machines. Unlike the results of fidelity, where the distributability of symmetric cloning is always optimal for any d-dimensional cloning, we find that any asymmetric cloning outperforms symmetric cloning on the distribution of QFI for d ≤ 18, whereas some but not all asymmetric cloning strategies could be worse than symmetric ones when d > 18.An unknown quantum state cannot be copied and broadcast freely due to the no-cloning theorem. Approximate cloning schemes have been proposed to achieve the optimal cloning characterized by the maximal fidelity between the original and its copies. Here, from the perspective of quantum Fisher information (QFI), we investigate the distribution of QFI in asymmetric cloning machines which produce two nonidentical copies. As one might expect, improving the QFI of one copy results in decreasing the QFI of the other copy. It is perhaps also unsurprising that asymmetric phase-covariant cloning outperforms universal cloning in distributing QFI since a priori information of the input state has been utilized. However, interesting results appear when we compare the distributabilities of fidelity (which quantifies the full information of quantum states), and QFI (which only captures the information of relevant parameters) in asymmetric cloning machines. Unlike the results of fidelity, where the distributability of symmetric cloning is always optimal for any d-dimensional cloning, we find that any asymmetric cloning outperforms symmetric cloning on the distribution of QFI for d ≤ 18, whereas some but not all asymmetric cloning strategies could be worse than symmetric ones when d > 18.

arXiv:1409.2199Scientific ReportsDec 8, 201415 citations

The asymmetric quantum cloning region

Ion Nechita, Clément Pellegrini, Denis Rochette

arXiv:2209.11999Letters in Mathematical PhysicsJun 26, 20235 citations

High-fidelity quantum cloning of two nonorthogonal quantum states via weak measurements

Minghao Wang, Qing-yu Cai

We propose a scheme to enhance the fidelity of a symmetric quantum cloning machine via weak measurements. By adjusting the intensity of the weak measurement parameter $p$ , we obtain copies of initial states with different values of fidelity. Choosing a proper value of $p$ , we can obtain perfect copies. In this paper, we focus on $1\ensuremath{-}2$ quantum cloning for two nonorthogonal states. Sets containing more than two linear independent states are also briefly discussed. Due to the probabilistic nature of weak measurements, we obtain high-fidelity copies probabilistically. If the weak measurement is a success, we do subsequent operations to obtain high-fidelity copies; otherwise, the cloning process fails and we quit. From this perspective, the scheme we propose is economical for saving quantum resources and time. Our scheme may be very useful in quantum information processing.We propose a scheme to enhance the fidelity of a symmetric quantum cloning machine via weak measurements. By adjusting the intensity of the weak measurement parameter $p$, we obtain copies of initial states with different values of fidelity. Choosing a proper value of $p$, we can obtain perfect copies. In this paper, we focus on $1\ensuremath{-}2$ quantum cloning for two nonorthogonal states. Sets containing more than two linear independent states are also briefly discussed. Due to the probabilistic nature of weak measurements, we obtain high-fidelity copies probabilistically. If the weak measurement is a success, we do subsequent operations to obtain high-fidelity copies; otherwise, the cloning process fails and we quit. From this perspective, the scheme we propose is economical for saving quantum resources and time. Our scheme may be very useful in quantum information processing.

arXiv:1806.08112Physical Review AJan 15, 201915 citations

A symmetric 1 to 2 quantum cloning machine (QCM) is presented that provides high-fidelity copies with

0.90 \le F \le 0.95

for all pure (single-qubit) input states from a given meridian of the Bloch sphere. \cor{Emphasize is placed especially on the states of the (so-called) Eastern meridian, that includes the computational basis states $\ketm{0}, \ketm{1}$ together with the diagonal state $\ketm{+} = \frac{1}{\sqrt{2}} (\ketm{0} + \ketm{1})$, for which suggested cloning transformation is shown to be optimal.} In addition, we also show how this QCM can be utilized for eavesdropping in Bennett's B92 protocol for quantum key distribution with a substantial higher success rate than obtained for universal or equatorial quantum copying.

We propose a scheme to enhance the fidelity of a symmetric quantum cloning machine via weak measurements. By adjusting the intensity of the weak measurement parameter

p

, we obtain copies of initial states with different values of fidelity. Choosing a proper value of

p

, we can obtain perfect copies. In this paper, we focus on $1\ensuremath{-}2$ quantum cloning for two nonorthogonal states. Sets containing more than two linear independent states are also briefly discussed. Due to the probabilistic nature of weak measurements, we obtain high-fidelity copies probabilistically. If the weak measurement is a success, we do subsequent operations to obtain high-fidelity copies; otherwise, the cloning process fails and we quit. From this perspective, the scheme we propose is economical for saving quantum resources and time. Our scheme may be very useful in quantum information processing.