Optical quantum cloning

D. Bouwmreiter

Rui Zhang, Yanbo Lou, Xiaolan Liu +3 more

An unknown quantum state is prohibited from perfect cloning due to the principles of quantum mechanics, while approximate cloning of an unknown quantum state can be achieved by constructing quantum cloning machines. In the continuous variable regime, to effectively improve the cloning fidelity, an N + N ′ → M + M ′ phase-conjugate inputs (PCI) quantum cloning scheme is proposed based on an optical parametric amplifier and beam splitter network. However, due to the difficulties in constructing an optical parametric amplifier approaching the quantum noise limit, such quantum cloning scheme has not been experimentally realized. In this work, we present all-optical N + N ′ → M + M ′ PCI quantum cloning of coherent states by utilizing a phase-sensitive amplifier based on a four-wave mixing process. In particular, we experimentally realize deterministic all-optical 1+1→ M + M ′ ( M = M ′ =2, 4) and 2+2→ M + M ′ ( M = M ′ =3, 4, 6, 8) PCI quantum cloning. The maximum cloning fidelities experimentally achieved are 96.76 % ±0.57 % and 96.80 % ±0.58 % in the 2+2→3+3 case, which are the maximum cloning fidelities in deterministic continuous variable quantum cloning, to our knowledge. Our results provide an effective scheme for enhancing cloning fidelity and can find applications in achieving high-fidelity quantum information protocols.

V. Buž Ek, Mark S. Hillery

Shengshuai Liu, Yanbo Lou, Yingxuan Chen +1 more

The laws of quantum mechanics forbid the perfect copying of an unknown quantum state, known as the no-cloning theorem. In spite of this, approximate cloning with imperfect fidelity is possible, which opens up the field of quantum cloning. In general, quantum cloning can be divided into discrete variable and continuous variable (CV) categories. In the CV regime, all-optical implementation of the optimal N→M quantum cloning has been proposed in two original parallel works, which involves a parametric amplifier and a set of beam splitters and thus avoids the optic-electro and electro-optic conversions in the current CV quantum cloning technologies. However, such original proposal of all-optical CV optimal N→M quantum cloning scheme has never been experimentally implemented. Here, we show that optimal N→M quantum cloning of coherent states can be realized by utilizing a parametric amplifier based on four-wave mixing process in a hot atomic vapor and a set of beam splitters. In particular, we realize 1→M, 2→M, and 4→M quantum cloning. We find that the fidelity of N→M quantum cloning increases with the decrease of clone number M and the increase of original replica number N. The best cloning fidelity achieved in our experiment is about 93.3% ±1.0% in the 4→5 case. Our results may find potential applications in realizing all-optical high-fidelity quantum state transfer and all-optical high-compatibility eavesdropping attack in quantum communication networks.

Jaromı́r Fiurášek

We propose an optical implementation of the Gaussian continuous-variable quantum cloning machines. We construct a symmetric N-->M cloner which optimally clones coherent states, and we also provide an explicit design of a class of asymmetric 1-->2 cloning machines. All proposed cloning devices can be built from just a single nondegenerate optical parametric amplifier and several beam splitters.

Sadegh Raeisi, Wolfgang Tittel, Christoph Simon